The energy process of the cell briefly. The main processes occurring in the cell. Why you need to chew food thoroughly

The energy that must be additionally imparted to a chemical system in order to “start” a reaction is called the activation energy for a given reaction and serves as a kind of energy ridge that must be overcome.

In non-catalyzed reactions, the source of activation energy is collisions between molecules. If the colliding molecules are properly oriented and the collision is strong enough, there is a chance that they will react.

It is clear why chemists heat flasks to speed up reactions: as the temperature rises, the speed of thermal motion and the frequency of collisions increase. But under the conditions of the human body you cannot heat a cell; this is unacceptable for it. And reactions occur, and at speeds that are unattainable when carried out in a test tube. Another invention of nature works here - enzymes , which we mentioned earlier.

As already mentioned, during chemical transformations those reactions can occur spontaneously in which the energy contained in the reaction products is less than in the starting substances. Other reactions require an influx of energy from outside. A spontaneous reaction can be compared to a falling weight. Initially, a load at rest tends to fall down, thereby reducing its potential energy.

Likewise, a reaction, once initiated, tends to proceed towards the formation of substances with less energy. This process, during which work can be done, is called spontaneous.

But if you connect two loads in a certain way, then the heavier one, when falling, will lift the lighter one. And in chemical, especially biochemical, processes a reaction that releases energy can cause an associated reaction to occur that requires an influx of energy from outside. Such reactions are called conjugated.

In living organisms, conjugate reactions are very common, and it is their occurrence that determines all the subtle phenomena accompanying life and consciousness. A falling “heavy load” causes another, lighter one to rise, but by a smaller amount. When we eat, we absorb substances with a high quality of energy due to the Sun, which then disintegrate in the body and are ultimately released from it, but at the same time they manage to release energy in an amount sufficient to support the process called life.

In a cell, the main energy intermediary, that is, the “driving wheel” of life, is adenosine triphosphate (ATP) . Why is this connection interesting? From a biochemical point of view, ATP is a medium-sized molecule capable of attaching or “dropping” terminal phosphate groups in which the phosphorus atom is surrounded by oxygen atoms.

The formation of ATP occurs from adenosine diphosphate (ADP) due to the energy released during the biological oxidation of glucose. On the other hand, breaking the phosphate bond in ATP releases a large amount of energy. Such a bond is called high-energy or high-energy. The ATP molecule contains two such bonds, the hydrolysis of which releases energy equivalent to 12-14 kcal.

It is not known why nature, in the process of evolution, “chose” ATP as the energy currency of the cell, but several reasons can be assumed. Thermodynamically, this molecule is quite unstable, as evidenced by the large amount of energy released during its hydrolysis.

But at the same time, the rate of enzymatic hydrolysis of ATP under normal conditions is very low, that is, the ATP molecule has high chemical stability, providing effective energy storage.

The small size of the ATP molecule allows it to easily diffuse into different parts of the cell where energy is needed to perform any work. Finally, ATP occupies an intermediate position on the scale of high-energy compounds, which gives it versatility, allowing it to transfer energy from higher to lower energy compounds.

Thus, ATP is the main universal form of storing cellular energy, the cell's fuel, available for use at any time. And the main supplier of energy to the cell, as we have already mentioned, is glucose obtained from the breakdown of carbohydrates. “Burning” in the body, glucose forms carbon dioxide and water, and this process provides the reactions of cellular respiration and digestion. The word “burns” in this case is an image; there is no flame inside the body, and energy is extracted through multi-stage chemical methods.

At the first stage, occurring in the cytoplasm without the participation of oxygen, the glucose molecule breaks up into two fragments (two molecules of pyruvic acid), and this stage is called glycolysis . This releases 50 kcal/mol of energy (that is, 7% of the energy contained in glucose), part of which is dissipated as heat, and the other is spent on the formation of two ATP molecules.

The subsequent extraction of energy from glucose occurs mainly in mitochondria - the power stations of the cell, the work of which can be compared to galvanic cells. Here, at each stage, an electron and a hydrogen ion are removed, and eventually glucose is decomposed into carbon dioxide and water.

IN mitochondria electrons and hydrogen ions are introduced into a single chain of redox enzymes (the respiratory chain), passing from mediator to mediator until they combine with oxygen. And at this stage, it is not air oxygen that is used for oxidation, but oxygen from water and acetic acid.

Air oxygen is the last acceptor of hydrogen, completing the entire process of cellular respiration, which is why it is so necessary for life. As is known, the interaction of gaseous oxygen and hydrogen is accompanied by an explosion (instant release of a large amount of energy).

This does not happen in living organisms, since hydrogen gas is not formed, and by the time it binds with oxygen in the air, the supply of free energy decreases so much that the reaction of water formation proceeds completely calmly (see picture 1).

Glucose is the main, but not the only substrate for energy production in the cell. Along with carbohydrates, our body receives fats, proteins and other substances from food, which, after breakdown, can also serve as sources of energy, turning into substances that are included in biochemical reactions occurring in the cell.

Fundamental research in the field of information theory led to the emergence of the concept information energy (or energy of information impact), as the difference between certainty and uncertainty. Here I would like to note that the cell consumes and spends information energy to eliminate uncertainty at every moment of its life cycle. This leads to the implementation of the life cycle without increasing entropy.

Disruption of energy metabolism processes under the influence of various influences leads to failures at individual stages and, as a result of these failures, to disruption of the subsystem of the life activity of the cell and the entire organism as a whole. If the number and prevalence of these disorders exceed the compensatory capabilities of homeostatic mechanisms in the body, then the system goes out of control and the cells stop working synchronously. At the body level, this manifests itself in the form of various pathological conditions.

Thus, a lack of vitamin B1, which is involved in the work of certain enzymes, leads to blocking the oxidation of pyruvic acid, an excess of thyroid hormones disrupts the synthesis of ATP, etc. Fatalities from myocardial infarction, carbon monoxide poisoning, or potassium cyanide poisoning are also associated with blocking the process of cellular respiration by inhibiting or uncoupling sequential reactions. The action of many bacterial toxins is indirect through similar mechanisms.

Thus, the functioning of a cell, tissue, organ, organ system or organism as a system is supported by self-regulatory mechanisms, the optimal course of which, in turn, is ensured by biophysical, biochemical, energy and information processes.

The set of all values of thermodynamic parameters necessary to describe the system is called thermodynamic state .

A physical characteristic of a system, the change in which when the system transitions from one state to another is determined by the values of the parameters of the initial and final states and does not depend on the transition, is called state function (thermodynamic potential).

The state functions are:

· internal energy;

· enthalpy;

· entropy;

· free energy;

· chemical and electrochemical potentials.

The amount of any quantity transferred per unit time through a certain surface is called flow this value.

The phenomenon in which one process energetically ensures the occurrence of a second process is called pairing .

The process that produces energy is called...
conjugating. The process that consumes energy is called conjugate .

The first and second laws of thermodynamics. According to the first law of thermodynamics, which reads as follows: the heat imparted to the system is spent on increasing the internal energy of the system and the system performing work on external forces, different types of energy can transform into each other, but during these transformations the energy does not disappear and does not appear from nothing . This means that for a closed system
∆U = ∆Q –W, where ∆U is the change in the internal energy of the system; ∆Q is the heat absorbed by the system; W is the work done by the system. [Internal energy differs from heat and work in that it always changes the same when transitioning from one state to another, regardless of the path of transition!].

The change in thermal energy ∆Q of an isolated system is proportional to the absolute temperature T, that is, ∆Q = T ∙ ∆S, where ∆S is a proportionality coefficient called the change in entropy.

The second law of thermodynamics exists in two formulations. The first formulation (Clausius's formulation) is as follows: spontaneous transfer of heat from bodies with a lower temperature to bodies with a higher temperature is impossible. The second formulation (Thomson's formulation) says that it is impossible to create a perpetual motion machine of the kind, that is, such a cyclic process as a result of which all the heat absorbed by the system would be spent on doing work. According to the second law of thermodynamics, the entropy of an isolated system increases in an irreversible process, but remains unchanged in a reversible process. Entropy is a function of the state of the system, the differential of which in an infinitesimal reversible process is equal to the ratio of the infinitesimal amount of heat imparted to the system to the absolute temperature of the latter (ΔS=ΔQ:T). The unit of entropy is J/K. Entropy is a measure of the disorder of a system: if entropy increases, this means that the system tends to move into a state with a higher thermodynamic probability, that is, into a less ordered state. The conclusion follows from the second law of thermodynamics: at a constant temperature, thermal energy cannot be converted into mechanical work. Since thermal energy is caused by the chaotic movement of particles, the sum of the velocity vectors of these particles in any direction is zero. Only that energy that represents the unidirectional movement of bodies (the kinetic energy of a flying body, the energy of moving ions or electrons in an electric field) can be converted into mechanical work.

Conclusion based on two laws:

The first law establishes a quantitative relationship between heat, work and the change in internal energy, but does not determine the direction of the thermodynamic process. It is always performed and for any systems. The basic relation of thermodynamics: TΔS ≥ ΔU+W.

The second law is statistical and valid for systems with a large, finite number of particles. It indicates the most likely direction of the process. If it is stated that this process is impossible, then it should be understood that the probability of its occurrence exists, but is negligible.

Table 1. Thermodynamic potentials

Transformation of energy in a living cell. In a living cell, chemical energy, which is stored in organic compounds, is converted into osmotic, electrical and mechanical energy. For example, the chemical energy of glucose is converted during cellular oxidation partly into heat and partly into the energy of macroergic bonds of ATP. Due to the hydrolysis of ATP, the transfer of substances from an area of lower to an area of higher concentration can occur (osmotic work), the transfer of ions to an area of higher electrical potential (electrical work), and in the animal’s body - muscle contraction (mechanical work). In this case, part of the chemical energy of ATP is converted into osmotic, electrical and mechanical energy.

Free energy and electrochemical potential. The electrical, osmotic and chemical energy of the cell is used to perform work, that is, for the directed movement of particles against the forces acting on them. A quantitative measure of the transformation of these types of energy is the change in free energy (∆F). ΔF is the Helmholtz free energy (ΔF =ΔU – TΔS). Since it depends on the conditions of the process, in particular on the concentration of the reacting substances, they began to use the so-called thermodynamic Gibbs potential of 1 mole of a substance ΔG. In chemistry, for uncharged particles it is called the chemical potential - μ, for charged particles - the electrochemical potential - μ.

The occurrence of chemical reactions in the liquid phase does not change the pressure, but can change the volume. Therefore, for such systems, instead of changing the internal energy, they use the change in enthalpy (∆H), which is equal to ∆U+p∆V, where p is pressure, ∆V is the change in volume. [Note: enthalpy is a function of the state of a thermodynamic system with independent parameters of entropy and pressure]. According to the laws of thermodynamics, there is a relationship between the change in internal energy and the change in enthalpy: ∆G = ∆H -T∆S (at t and p = const), where ΔG is the Gibbs thermodynamic potential, ΔH is internal energy, T * ΔS is thermal energy.

In physicochemical systems, a change in free energy is usually described through a change in electrochemical potential (∆μ): ∆G=m∙∆μ, where m is the amount of substance (mole) in the system. The change in the electrochemical potential during the transition of the system from state 1 to state 2 is determined by the change in chemical, osmotic and electrical energies: ∆μ = μ 02 -μ 01 +RT ln (c 2 /c 1) + zF (φ 2 -φ 1). Then ∆G = m μ 02 -μ 01 +RT ln (c 2 /c 1) + zF (φ 2 -φ 1).

The physical meaning of the electrochemical potential is that its change is equal to the work that must be expended in order to:

1. synthesize 1 mole of a substance (state 2) from the starting substances (state 1) and place it in a solvent (command μ 02 -μ 01) - chemical work;

2. concentrate the solution from concentration from 1 to c 2 [term RT ln (c 2 /c 1)] – osmotic work;

3. overcome the electric repulsion forces that arise in the presence of a potential difference (φ 2 -φ 1) between solutions [the term zF (φ 2 -φ 1] – electrical work.

It should be noted that the terms can be both positive and negative.

The second law of thermodynamics and the equilibrium condition. The second law of thermodynamics states that free energy cannot increase in an isolated system. In other words, in a system where ∆H = 0, ∆G = -T∆S ≤0. As long as energy transformations in a given system are accompanied by transitions of different types of energy into each other without their conversion to heat, that is, ∆G=0, all these processes are reversible. But as soon as part of the energy turns into heat, the process becomes irreversible. The concept of process reversibility is associated with the concept of dynamic equilibrium. Equilibrium is a state of the system in which each particle can move from some state 1 to some state 2 and back, but in general the proportion of states 1 and states 2 in the system does not change. In physicochemical systems, processes are in equilibrium in which ∆μ = ∆G/m = 0, that is, μ 02 -μ 01 +RT ln (c 2 /c 1) + zF (φ 2 -φ 1) = 0.

Substrates and products of a biochemical reaction or ions on both sides of the membrane may be in equilibrium. Therefore, there are applications to the equation describing the equilibrium state of the system:

1. equation of the chemical equilibrium constant: ∆μ 0 = -RT lnK, where K is the equilibrium constant;

2. equation of equilibrium membrane potential (Nernst equation): if the cell membrane is permeable to any one ion, then an equilibrium membrane potential is established on the membrane: φ M = φ 1 – φ 2 = RT/zF lnc 1 / c 2, at temperature 37С 0 φ Μ = 60 ln(s 1 / s 2) mV. For a more concise writing, we introduced the concept of dimensionless potential ψ Μ, which is equal to ln(c 1 /c 2), then the Nernst equation will look like this: ψ Μ = ψ 1 – ψ 2 = ln(c 1 /c 2).

3. Boltzmann distribution: if in a molecule there are two energy electronic levels with energies E 1 and E 2, then the population of these levels with electrons in a state of equilibrium can be found: ∆E = E 2 – E 1.

Experimental determination of thermodynamic parameters of biological systems. To determine the thermodynamic parameters of biological systems, two methods are used: determination of heat production (calorimetry) and measurement of equilibrium constants. Since the object located in the calorimeter does not produce work, the change in energy (enthalpy) can be considered equal to the amount of heat released ∆Q. This is how the change in enthalpy ∆H is found during the biophysical process or biochemical reaction being studied. Another method for studying thermodynamic parameters is based on measuring equilibrium constants at different temperatures. But this method is suitable only when the change in enthalpy and change in entropy do not depend on temperature. In this case, the Van't Hoff equation is used: lnK = -∆H/RT + ∆S/R (for one mole of substance).

Organisms as thermodynamic systems. When applying thermodynamics to biological systems, it is necessary to take into account the peculiarities of the organization of living systems:

1) biological systems are open to flows of matter and energy;

2) processes in living systems are irreversible;

3) living systems are far from equilibrium;

4) biological systems are heterophasic, structured, and individual phases may have a small number of molecules.

All this distinguishes biological systems from isolated systems close to equilibrium. Therefore, to more adequately describe the properties of living systems, it is necessary to apply the thermodynamics of irreversible processes. Unlike classical thermodynamics, the thermodynamics of irreversible processes considers the course of processes over time. A fundamental concept in classical thermodynamics is the concept of an equilibrium state. In the thermodynamics of irreversible processes, an important concept is the concept of a stationary state of a system.

Note: It must be taken into account that a living organism is constantly developing and changing and therefore, as a whole, is not a stationary system. In this case, there is an admission: for a short period of time, the state of some of its sections is accepted as stationary.

In contrast to thermodynamic equilibrium, the stationary state is characterized by

· constant influx of substances into the system and removal of metabolic products;

· constant expenditure of free energy, which maintains the constancy of the concentrations of substances in the system;

· constancy of thermodynamic parameters (including internal energy and entropy).

A system in a stationary state can be either closed or open. An open system can only exist due to the influx of energy from outside and the outflow of energy into the environment. In biological systems, the most important flows are the flows of substances and electrical charges.

Flows of substances as a result of diffusion and electrodiffusion. 1. The main driving force in the transport of particles by simple diffusion is the concentration gradient. The flow of a substance as a result of diffusion through the cell membrane is calculated according to Fick’s law for the passive transfer of substances through the membrane: Φ = –DK/l (c in -c in) = –P (c in -c in), where Φ is the flow; D – diffusion coefficient; K is the distribution coefficient of the substance between the membrane and the surrounding aqueous phase; l – membrane thickness; c cc – concentration of particles inside the cell; с in – concentration of particles outside the cell; P – permeability coefficient. If we consider diffusion from the perspective of energy conversion, then the calculation must be carried out using the following equation: Φ = – uc (dG/dx), where u = D/RT is a proportionality coefficient that depends on the rate of diffusion of molecules and is called mobility. Thus, the flow is proportional to the concentration of the substance and the gradient of the thermodynamic potential in the direction of the flow.

2. The main driving force in the transfer of charged particles in the absence of a concentration gradient is the electric field. In this case, the Theorell equation is used: Φ = – cu (dμ/dx), where μ is the electrochemical potential. So, the flux is equal to the product of the carrier concentration by its mobility and the gradient of its electrochemical potential. The “–” sign indicates that the flow is directed in the direction of decreasing μ. In addition, the Nernst–Planck electrodiffusion equation is used: Φ = –uRT (dc/dx) –cuz Fdφ/dx.

The flows and thermodynamic forces that determine the occurrence of vital processes are shown in Table 3.

Table 3. Conjugate flows and forces in nonequilibrium thermodynamics

Thermodynamics of a steady state. Open systems have specific features: the coupling of flows and the emergence of stationary states. These features of open systems are explained by the thermodynamics of linear irreversible processes. It describes the simultaneous occurrence of various interrelated stationary processes. Onsager formulated the theory of thermodynamics of linear irreversible processes. The experimental basis of this theory is phenomenological laws that establish a linear relationship between flows and the forces that cause them (see Table 2). Let us assume that there are two flows in the system - heat flow (Φ 1) and diffusion mass flow (Φ 2) and two generalizing forces - temperature difference X 1 and concentration difference X 2. According to Onsager, in an open system, each flow depends on all the forces present, and vice versa, that is

Φ 1 = L 11 X 1 + L 12 X 2

Φ 2 = L 21 X 1 + L 22 X 2,

where L 12 and others are proportionality coefficients between flow 1 and force 2, etc.

These equations are called phenomenological Onsager equations. They indicate the dependence of input and output flows on both conjugate and non-conjugate forces. As Onsager showed, near equilibrium the proportionality coefficients between the flows are equal to each other (L 12 = L 21). In other words, an equal action causes an equal response. For example, the braking effect that a moving solvent has on a solute is equal to the resistance that the solute exerts on the solvent.

In nature, there is a situation when flows that come with an increase in energy cannot flow independently, but can flow under the action of some forces. This phenomenon is called flow conjugation. The criterion for the possibility of conjugating flows in the system is the positive value of the dissipative function ψ = Τ/V dS/dt ≥ 0, where Τ is the absolute temperature; dS/dt – rate of entropy production; V is the volume of the system.

The dissipative function is a measure of the dissipation of a system's energy into heat. It determines the rate of increase in entropy in a system in which irreversible processes occur. The higher the value of the dissipative function, the faster energy of all types is converted into heat. In addition, the dissipative function determines the possibility of a spontaneous process: for ψ>0 the process is possible, for ψ<0 – нет.

Thermodynamics shows that if the system is nonequilibrium, but close to equilibrium, then ψ can be represented by the sum of the products of generalized forces - Xi and generalized flows - Φi, that is, the sum of the powers of the processes ψ = ∑ΦiXi ≥0. A positive value of the dissipative function ψ means that in any energy converter the input power must exceed the output power. In most biological processes, chemical energy is converted into osmotic, electrical and mechanical energy. In all these processes, part of the chemical energy is dissipated into heat. For biological processes, the coupling efficiency is 80-90%, that is, only 10-20% of the energy turns into heat.

The stationary state of an open system is characterized by Prigogine's theorem: in a stationary state with fixed external parameters, the rate of entropy production in the system is constant in time and minimal in value.

If the criterion for the evolution of a system in classical thermodynamics is that the entropy for irreversible processes in an isolated system tends to a maximum value( Clausius criterion), then in an open system the production of entropy tends to a minimum( Prigogine criterion). Prigogine criterion (Δψ>0) - stability criterion - when deviating from the stable state Δψ<0. Это является доказательством того, что второй закон термодинамики выполняется в живой природе.

From Prigogine's theorem it follows that if a system is taken out of a stationary state, then it will change until the specific rate of entropy production takes on the lowest value. That is, until the dissipative function reaches a minimum.

Pathways of energy conversion in a living cell. The molecular mechanism of coupling the oxidation and phosphorylation reactions was deciphered by Mitchell in 1976. The author developed a chemiosmotic theory of oxidative phosphorylation. The second part of Mitchell's theory is that there is an asymmetric ATPase in the membrane that works reversibly, that is, it can also be an ATP synthetase:

ATP + NON (ATPase) ADP + P + 2H +

The asymmetry in the action of ATPase is that

a) during ATP hydrolysis, proton H+ and hydroxyl OH- are captured on opposite sides of the membrane;

b) during the synthesis of ATP, water dissociates into OH-, which enters the more acidified side of the membrane, and H+, which diffuses in the opposite direction.

In general, the process of ADP phosphorylation is carried out due to a change in free energy during the neutralization of the OH- ion in an acidic environment, and the H+ ion in an alkaline environment.

From the point of view of energy conversion, the process of oxidative phosphorylation consists of two stages:

1. Conversion of the chemical energy of electron transfer into energy associated with the difference in the electrochemical potentials of protons as a result of the coupling of electron transfer along the respiratory chain and proton transfer through the membrane. In this case: Δμ H+ = FΔφ M + RT ln ( 1 / 2), where Δμ H+ is the difference in electrochemical potentials; Δφ M – the difference in electrical potential between the outer and inner sides of the mitochondrial membrane; ( 1 and 2 – proton concentrations in the environment and inside mitochondria.

2. Conversion of the energy determined by the difference in electrical potentials into the chemical energy of the high-energy bond of ATP (coupling the transfer of 2H+ and the synthesis of one ATP molecule from ADP and phosphate). This can be conventionally represented as Δμ H+ → QUOTE ~ ~.

It has now been shown that in the presence of a difference in electrochemical potentials H+, not only chemical work (ATP synthesis), but also osmotic work (during the transport of various compounds through membranes), mechanical work (movement of flagella in bacteria), and heat is also released (heat-regulatory uncoupling of oxidative phosphorylation).

Symbolically, the chemiosmotic theory of coupling the processes of oxidation (i.e., electron transfer - e) and phosphorylation (synthesis of macroergs - QUOTE ~ ~) can be represented in the form of a diagram e QUOTE Δμ H+ QUOTE QUOTE ~ ~. The following main consequences of the chemiosmotic theory follow from this scheme:

1. If Δμ H+ = 0, then ATP synthesis does not occur during electron transfer.

2. When the respiratory chain operates, the membrane potential is generated (e→Δφ M).

3. The creation of a sufficient electric potential on the energy-coupling membrane with a “+” sign on the outside will lead to the synthesis of ATP from ADP and orthophosphate (Δφ M → QUOTE ~) ~).

4. Due to the membrane potential, it is possible to stop and even “reverse” the flow of electrons in the respiratory chain (Δφ M →e).

5. When ATP is hydrolyzed at the coupling membrane, a membrane potential is generated (QUOTE ~ ~ → Δφ M).

So, the main types of work in a living cell - electrical and osmotic - are performed with the direct participation of biological membranes. The central role in the energy of the cell is played by the processes of ATP synthesis and breakdown. In the cell, ATP is the accumulator of chemical energy.

Energy is used for various chemical reactions that occur in the cell. Some organisms use the energy of sunlight for biochemical processes - these are plants, while others use the energy of chemical bonds in substances obtained during nutrition - these are animal organisms. Substances from food are extracted through breakdown or biological oxidation through the process of cellular respiration.

Cellular respiration is a biochemical process in a cell that occurs in the presence of enzymes, as a result of which water and carbon dioxide are released, energy is stored in the form of macroenergetic bonds of ATP molecules. If this process occurs in the presence of oxygen, then it is called “aerobic”. If it occurs without oxygen, then it is called “anaerobic.”

Biological oxidation includes three main stages:

1. Preparatory

2. Oxygen-free (glycolysis),

3. Complete breakdown of organic substances (in the presence of oxygen).

Preparatory stage. Substances received from food are broken down into monomers. This stage begins in the gastrointestinal tract or in the lysosomes of the cell. Polysaccharides break down into monosaccharides, proteins into amino acids, fats into glycerols and fatty acids. The energy released at this stage is dissipated in the form of heat. It should be noted that for energy processes, cells use carbohydrates, or better yet, monosaccharides. And the brain can only use monosaccharide - glucose - for its work.

Glucose during glycolysis breaks down into two three-carbon molecules of pyruvic acid. Their further fate depends on the presence of oxygen in the cell. If oxygen is present in the cell, then pyruvic acid enters the mitochondria for complete oxidation to carbon dioxide and water (aerobic respiration). If there is no oxygen, then in animal tissues pyruvic acid is converted into lactic acid. This stage takes place in the cytoplasm of the cell. As a result of glycolysis, only two ATP molecules are formed.

Oxygen is required for complete oxidation of glucose. At the third stage, complete oxidation of pyruvic acid to carbon dioxide and water occurs in the mitochondria. As a result, another 36 ATP molecules are formed.

In total, the three steps produce 38 ATP molecules from one glucose molecule, taking into account the two ATPs produced during glycolysis.

Thus, we examined the energy processes occurring in cells. The stages of biological oxidation were characterized. This concludes our lesson, all the best to you, goodbye!

The difference between breathing and burning. Respiration occurring in a cell is often compared to the combustion process. Both processes occur in the presence of oxygen, releasing energy and oxidation products. But, unlike combustion, respiration is an ordered process of biochemical reactions that occurs in the presence of enzymes. During respiration, carbon dioxide arises as the end product of biological oxidation, and during combustion, the formation of carbon dioxide occurs through the direct combination of hydrogen with carbon. Also, during respiration, a certain number of ATP molecules are formed. That is, breathing and combustion are fundamentally different processes.

Biomedical significance. For medicine, not only the metabolism of glucose is important, but also fructose and galactose. The ability to form ATP in the absence of oxygen is especially important in medicine. This allows you to maintain intense work of skeletal muscle in conditions of insufficient efficiency of aerobic oxidation. Tissues with increased glycolytic activity are able to remain active during periods of oxygen starvation. In the cardiac muscle, the possibilities for glycolysis are limited. She has a hard time suffering from disruption of the blood supply, which can lead to ischemia. There are several known diseases caused by the lack of enzymes that regulate glycolysis:

- hemolytic anemia (in fast-growing cancer cells, glycolysis occurs at a rate exceeding the capabilities of the citric acid cycle), which contributes to increased synthesis of lactic acid in organs and tissues. High levels of lactic acid in the body can be a symptom of cancer.

Fermentation. Microbes are able to obtain energy during fermentation. Fermentation has been known to people since time immemorial, for example, in the making of wine. Lactic acid fermentation was known even earlier. People consumed dairy products without realizing that these processes were associated with the activity of microorganisms. This was first proven by Louis Pasteur. Moreover, different microorganisms secrete different fermentation products. Now we will talk about alcoholic and lactic acid fermentation. As a result, ethyl alcohol and carbon dioxide are formed and energy is released. Brewers and winemakers have used certain types of yeast to stimulate fermentation, which turns sugars into alcohol. Fermentation is carried out mainly by yeast, as well as some bacteria and fungi. In our country, Saccharomycetes yeast is traditionally used. In America - bacteria of the genus Pseudomonas. And in Mexico, “moving rod” bacteria are used. Our yeast typically ferments hexoses (six-carbon monosaccharides) such as glucose or fructose. The process of alcohol formation can be represented as follows: from one glucose molecule two molecules of alcohol, two molecules of carbon dioxide and two molecules of ATP are formed. This method is less profitable than aerobic processes, but allows you to maintain life in the absence of oxygen. Now let's talk about fermented milk fermentation. One molecule of glucose forms two molecules of lactic acid and at the same time two molecules of ATP are released. Lactic acid fermentation is widely used for the production of dairy products: cheese, curdled milk, yoghurts. Lactic acid is also used in the production of soft drinks.

The ability to photosynthesize is the main characteristic of green plants. Plants, like all living organisms, must eat, breathe, remove unnecessary substances, grow, reproduce, respond to environmental changes. All this is ensured by the work of the relevant organs of the body. Typically, organs form systems of organs that work together to ensure the performance of one or another function of a living organism. Thus, a living organism can be represented as a biosystem. Each organ in a living plant performs a specific job. Root absorbs water with minerals from the soil and strengthens the plant in the soil. The stem carries the leaves towards the light. Water, as well as mineral and organic substances, move along the stem. In leaf chloroplasts, in the light, organic substances are formed from inorganic substances, which they feed on. cells all organs plants. Leaves evaporate water.

If the functioning of any one organ of the body is disrupted, this can cause disruption of the functioning of other organs and the entire body. If, for example, water stops flowing through the root, the entire plant may die. If a plant does not produce enough chlorophyll in its leaves, then it will not be able to synthesize a sufficient amount of organic substances for its vital functions.

Thus, the vital activity of the body is ensured by the interconnected work of all organ systems. Life activity is all the processes that occur in the body.

Thanks to nutrition, the body lives and grows. During nutrition, necessary substances are absorbed from the environment. They are then absorbed in the body. Plants absorb water and minerals from the soil. Aboveground green organs of plants absorb carbon dioxide from the air. Water and carbon dioxide are used by plants to synthesize organic substances, which are used by the plant to renew body cells, grow and develop.

Gas exchange occurs during breathing. Oxygen is absorbed from the environment, and carbon dioxide and water vapor are released from the body. All living cells need oxygen to produce energy.

During the metabolic process, substances that the body does not need are formed and released into the environment.

When a plant reaches a certain size and age required for its species, if it is in sufficiently favorable environmental conditions, then it begins to reproduce. As a result of reproduction, the number of individuals increases.

Unlike the vast majority of animals, plants grow throughout their lives.

The acquisition of new properties by organisms is called development.

Nutrition, respiration, metabolism, growth and development, as well as reproduction are influenced by the plant’s environmental conditions. If they are not favorable enough, then the plant may grow and develop poorly, its vital processes will be suppressed. Thus, the life of plants depends on the environment.

Question 3_Cell membrane, its functions, composition, structure. Primary and secondary shell.

The cell of any organism is an integral living system. It consists of three inextricably linked parts: the membrane, the cytoplasm and the nucleus. The cell membrane directly interacts with the external environment and interacts with neighboring cells (in multicellular organisms). Cell membrane. The cell membrane has a complex structure. It consists of an outer layer and a plasma membrane located underneath it. In plants, as well as in bacteria, blue-green algae and fungi, a dense membrane, or cell wall, is located on the surface of the cells. In most plants it consists of fiber. The cell wall plays an extremely important role: it is an outer frame, a protective shell, and provides turgor for plant cells: water, salts, and molecules of many organic substances pass through the cell wall.

Cell membrane or wall - a rigid cell membrane located outside the cytoplasmic membrane and performing structural, protective and transport functions. Found in most bacteria, archaea, fungi and plants. Animals and many protozoa do not have a cell wall.

Functions of the cell membrane:

1. The transport function provides selective regulation of metabolism between the cell and the external environment, the flow of substances into the cell (due to the semi-permeability of the membrane), as well as regulation of the cell’s water balance

1.1. Transmembrane transport (i.e. across the membrane):
- Diffusion
- Passive transport = facilitated diffusion
- Active = selective transport (involving ATP and enzymes).

1.2. Transport in membrane packaging:
- Exocytosis - release of substances from the cell
- Endocytosis (phago- and pinocytosis) - absorption of substances by the cell

2) Receptor function.
3) Support (“skeleton”)- maintains the shape of the cell, gives strength. This is mainly a function of the cell wall.
4) Cell isolation(its living contents) from the environment.
5) Protective function.
6) Contact with neighboring cells. Combination of cells into tissues.

This video lesson is devoted to the topic “Providing cells with energy.” In this lesson we will look at the energy processes in the cell and study how cells are provided with energy. You will also learn what cellular respiration is and what stages it consists of. Discuss each of these steps in detail.

BIOLOGY 9TH GRADE

Topic: Cellular level

Lesson 13. Providing cells with energy

Stepanova Anna Yurievna

candidate of biological sciences, associate professor MSUIE

Moscow

Today we will talk about providing cells with energy. Energy is used for various chemical reactions that occur in the cell. Some organisms use the energy of sunlight for biochemical processes - these are plants, while others use the energy of chemical bonds in substances obtained during nutrition - these are animal organisms. Substances from food are extracted through breakdown or biological oxidation through the process of cellular respiration.

Biological oxidation includes three main stages:

1. Preparatory,

2. Oxygen-free (glycolysis),

3. Complete breakdown of organic substances (in the presence of oxygen).

In total, the three steps produce 38 ATP molecules from one glucose molecule, taking into account the two ATPs produced during glycolysis.

Thus, we examined the energy processes occurring in cells. The stages of biological oxidation were characterized. This concludes our lesson, all the best to you, goodbye!

Hemolytic anemia (in fast-growing cancer cells, glycolysis occurs at a rate exceeding the capabilities of the citric acid cycle), which contributes to increased synthesis of lactic acid in organs and tissues. High levels of lactic acid in the body can be a symptom of cancer.

Abundant growth of fat trees,
which root on the barren sand
approved, clearly states that
fat sheets fat fat from the air
absorb...
M. V. Lomonosov

How is energy stored in a cell? What is metabolism? What is the essence of the processes of glycolysis, fermentation and cellular respiration? What processes take place during the light and dark phases of photosynthesis? How are the processes of energy and plastic metabolism related? What is chemosynthesis?

Lesson-lecture

The ability to convert one type of energy into another (radiation energy into the energy of chemical bonds, chemical energy into mechanical energy, etc.) is one of the fundamental properties of living things. Here we will take a closer look at how these processes are realized in living organisms.

ATP IS THE MAIN CARRIER OF ENERGY IN THE CELL. To carry out any manifestations of cell activity, energy is required. Autotrophic organisms receive their initial energy from the Sun during photosynthesis reactions, while heterotrophic organisms use organic compounds supplied with food as an energy source. Energy is stored by cells in the chemical bonds of molecules ATP (adenosine triphosphate), which are a nucleotide consisting of three phosphate groups, a sugar residue (ribose) and a nitrogenous base residue (adenine) (Fig. 52).

Rice. 52. ATP molecule

The bond between phosphate residues is called macroergic, since when it breaks, a large amount of energy is released. Typically, the cell extracts energy from ATP by removing only the terminal phosphate group. In this case, ADP (adenosine diphosphate) and phosphoric acid are formed and 40 kJ/mol are released:

ATP molecules play the role of the cell's universal energy bargaining chip. They are delivered to the site of an energy-intensive process, be it the enzymatic synthesis of organic compounds, the work of proteins - molecular motors or membrane transport proteins, etc. The reverse synthesis of ATP molecules is carried out by attaching a phosphate group to ADP with the absorption of energy. The cell stores energy in the form of ATP during reactions energy metabolism. It is closely related to plastic exchange, during which the cell produces the organic compounds necessary for its functioning.

METABOLISM AND ENERGY IN THE CELL (METABOLISM). Metabolism is the totality of all reactions of plastic and energy metabolism, interconnected. The cells constantly synthesize carbohydrates, fats, proteins, and nucleic acids. The synthesis of compounds always occurs with the expenditure of energy, i.e. with the indispensable participation of ATP. Energy sources for the formation of ATP are enzymatic reactions of oxidation of proteins, fats and carbohydrates entering the cell. During this process, energy is released and stored in ATP. Glucose oxidation plays a special role in cellular energy metabolism. Glucose molecules undergo a series of successive transformations.

The first stage, called glycolysis, takes place in the cytoplasm of cells and does not require oxygen. As a result of successive reactions involving enzymes, glucose breaks down into two molecules of pyruvic acid. In this case, two ATP molecules are consumed, and the energy released during oxidation is sufficient to form four ATP molecules. As a result, the energy output of glycolysis is small and amounts to two ATP molecules:

C 6 H1 2 0 6 → 2C 3 H 4 0 3 + 4H + + 2ATP

Under anaerobic conditions (in the absence of oxygen), further transformations can be associated with various types fermentation.

Everybody knows lactic acid fermentation(milk souring), which occurs due to the activity of lactic acid fungi and bacteria. The mechanism is similar to glycolysis, only the final product here is lactic acid. This type of glucose oxidation occurs in cells when there is a lack of oxygen, such as in intensely working muscles. Alcohol fermentation is close in chemistry to lactic acid fermentation. The difference is that the products of alcoholic fermentation are ethyl alcohol and carbon dioxide.

The next stage, during which pyruvic acid is oxidized to carbon dioxide and water, is called cellular respiration. Reactions associated with respiration take place in the mitochondria of plant and animal cells, and only in the presence of oxygen. This is a series of chemical transformations before the formation of the final product - carbon dioxide. At various stages of this process, intermediate products of oxidation of the starting substance are formed with the elimination of hydrogen atoms. In this case, energy is released, which is “conserved” in the chemical bonds of ATP, and water molecules are formed. It becomes clear that it is precisely in order to bind the separated hydrogen atoms that oxygen is required. This series of chemical transformations is quite complex and occurs with the participation of the internal membranes of mitochondria, enzymes, and carrier proteins.

Cellular respiration is very efficient. 30 ATP molecules are synthesized, two more molecules are formed during glycolysis, and six ATP molecules are formed as a result of transformations of glycolysis products on mitochondrial membranes. In total, as a result of the oxidation of one glucose molecule, 38 ATP molecules are formed:

C 6 H 12 O 6 + 6H 2 0 → 6CO 2 + 6H 2 O + 38ATP

The final stages of oxidation of not only sugars, but also proteins and lipids occur in mitochondria. These substances are used by cells, mainly when the supply of carbohydrates comes to an end. First, fat is consumed, the oxidation of which releases significantly more energy than from an equal volume of carbohydrates and proteins. Therefore, fat in animals represents the main “strategic reserve” of energy resources. In plants, starch plays the role of an energy reserve. When stored, it takes up significantly more space than the energy equivalent amount of fat. This is not a hindrance for plants, since they are immobile and do not carry supplies on themselves, like animals. You can extract energy from carbohydrates much faster than from fats. Proteins perform many important functions in the body, and therefore are involved in energy metabolism only when the resources of sugars and fats are depleted, for example, during prolonged fasting.

PHOTOSYNTHESIS. Photosynthesis is a process during which the energy of solar rays is converted into the energy of chemical bonds of organic compounds. In plant cells, processes associated with photosynthesis occur in chloroplasts. Inside this organelle there are membrane systems in which pigments are embedded that capture the radiant energy of the Sun. The main pigment of photosynthesis is chlorophyll, which absorbs predominantly blue and violet, as well as red rays of the spectrum. Green light is reflected, so chlorophyll itself and the parts of plants that contain it appear green.

There are two phases in photosynthesis - light And dark(Fig. 53). The actual capture and conversion of radiant energy occurs during the light phase. When absorbing light quanta, chlorophyll goes into an excited state and becomes an electron donor. Its electrons are transferred from one protein complex to another along the electron transport chain. The proteins of this chain, like pigments, are concentrated on the inner membrane of chloroplasts. When an electron moves along a chain of carriers, it loses energy, which is used for the synthesis of ATP. Some of the electrons excited by light are used to reduce NDP (nicotinamide adenine dinucleotiphosphate), or NADPH.

Rice. 53. Reaction products of the light and dark phases of photosynthesis

Under the influence of sunlight, water molecules are also broken down in chloroplasts - photolysis; in this case, electrons appear that compensate for their losses by chlorophyll; This produces oxygen as a by-product:

Thus, the functional meaning of the light phase is the synthesis of ATP and NADPH by converting light energy into chemical energy.

Light is not needed for the dark phase of photosynthesis to occur. The essence of the processes taking place here is that the ATP and NADPH molecules produced in the light phase are used in a series of chemical reactions that “fix” CO2 in the form of carbohydrates. All dark phase reactions take place inside chloroplasts, and the carbon dioxide ADP and NADP released during “fixation” are again used in light phase reactions for the synthesis of ATP and NADPH.

The overall equation for photosynthesis is as follows:

RELATIONSHIP AND UNITY OF PLASTIC AND ENERGY EXCHANGE PROCESSES. The processes of ATP synthesis occur in the cytoplasm (glycolysis), in mitochondria (cellular respiration) and in chloroplasts (photosynthesis). All reactions occurring during these processes are reactions of energy exchange. The energy stored in the form of ATP is consumed in plastic exchange reactions for the production of proteins, fats, carbohydrates and nucleic acids necessary for the life of the cell. Note that the dark phase of photosynthesis is a chain of reactions, plastic exchange, and the light phase is energy exchange.

The interrelation and unity of the processes of energy and plastic exchange is well illustrated by the following equation:

When reading this equation from left to right, we get the process of oxidation of glucose to carbon dioxide and water during glycolysis and cellular respiration, associated with the synthesis of ATP (energy metabolism). If you read it from right to left, you get a description of the reactions of the dark phase of photosynthesis, when glucose is synthesized from water and carbon dioxide with the participation of ATP (plastic exchange).

CHEMOSYNTHESIS. In addition to photoautotrophs, some bacteria (hydrogen bacteria, nitrifying bacteria, sulfur bacteria, etc.) are also capable of synthesizing organic substances from inorganic ones. They carry out this synthesis due to the energy released during the oxidation of inorganic substances. They are called chemoautotrophs. These chemosynthetic bacteria play an important role in the biosphere. For example, nitrifying bacteria convert ammonium salts that are not available for absorption by plants into nitric acid salts, which are well absorbed by them.

Cellular metabolism consists of reactions of energy and plastic metabolism. During energy metabolism, organic compounds with high-energy chemical bonds - ATP - are formed. The energy required for this comes from the oxidation of organic compounds during anaerobic (glycolysis, fermentation) and aerobic (cellular respiration) reactions; from sunlight, the energy of which is absorbed in the light phase (photosynthesis); from the oxidation of inorganic compounds (chemosynthesis). ATP energy is spent on the synthesis of organic compounds necessary for the cell during plastic exchange reactions, which include reactions of the dark phase of photosynthesis.

What are the differences between plastic and energy metabolism?
How is the energy of sunlight converted into the light phase of photosynthesis? What processes take place during the dark phase of photosynthesis?
Why is photosynthesis called the process of reflecting planetary-cosmic interaction?