During alcoholic fermentation, in addition to the main products - alcohol and CO 2, many other so-called secondary fermentation products arise from sugars. From 100 g of C 6 H 12 O 6, 48.4 g of ethyl alcohol, 46.6 g of carbon dioxide, 3.3 g of glycerol, 0.5 g of succinic acid and 1.2 g of a mixture of lactic acid, acetaldehyde, acetoin and others are formed organic compounds.
Along with this, yeast cells, during the period of reproduction and logarithmic growth, consume from grape must the amino acids necessary to build their own proteins. This produces fermentation by-products, mainly higher alcohols.
In the modern scheme of alcoholic fermentation, there are 10-12 phases of biochemical transformations of hexoses under the action of a complex of yeast enzymes. In a simplified form, three stages of alcoholic fermentation can be distinguished.
Istage - phosphorylation and breakdown of hexoses. At this stage, several reactions occur, as a result of which hexose is converted into triose phosphate:
ATP → ADP
The main role in the transfer of energy in biochemical reactions is played by ATP (adenosine triphosphate) and ADP (adenosine diphosphate). They are part of enzymes, accumulate a large amount of energy necessary for the implementation of life processes, and are adenosine - component nucleic acids - with residues phosphoric acid. First, adenylic acid (adenosine monophosphate, or adenosine monophosphate - AMP) is formed:
If we denote adenosine by the letter A, then the structure of ATP can be represented as follows:
A-O-R-O ~ R-O ~ R-OH
The symbol with ~ denotes the so-called high-energy phosphate bonds, which are extremely rich in energy, which is released during the elimination of phosphoric acid residues. The transfer of energy from ATP to ADP can be represented by the following scheme:
The released energy is used by yeast cells to ensure vital functions, in particular their reproduction. The first act of energy release is the formation of phosphorus esters of hexoses - their phosphorylation. The addition of the phosphoric acid residue from ATP to hexoses occurs under the action of the enzyme phosphohexokinase supplied by yeast (we denote the phosphate molecule by the letter P):
Glucose Glucose-6-phosphate Fructose-1,6-phosphate
As can be seen from the diagram above, phosphorylation occurs twice, and the phosphoryl ester of glucose, under the action of the enzyme isomerase, is reversibly converted into the phosphorus ester of fructose, which has a symmetrical furan ring. The symmetrical arrangement of phosphoric acid residues at the ends of the fructose molecule facilitates its subsequent rupture right in the middle. The breakdown of hexose into two trioses is catalyzed by the enzyme aldolase; as a result of decomposition, a nonequilibrium mixture of 3-phosphoglyceraldehyde and phosphodioxyacetone is formed:
Phosphoglyceraldehyde (3.5%) Phosphodioxyacetone (96.5%)
Only 3-phosphoglyceraldehyde participates in further reactions, the content of which is constantly replenished under the action of the isomerase enzyme on phosphodioxyacetone molecules.
II stage of alcoholic fermentation- formation of pyruvic acid. At the second stage, triose phosphate in the form of 3-phosphoglyceraldehyde is oxidized into phosphoglyceric acid under the action of the oxidative enzyme dehydrogenase, which, with the participation of the corresponding enzymes (phosphoglyceromutase and enolase) and the LDP-ATP system, is converted into pyruvic acid:
First, each molecule of 3-phosphoglyceraldehyde attaches to itself another phosphoric acid residue (at the expense of a molecule of inorganic phosphorus) and 1,3-diphosphoglyceraldehyde is formed. Then, under anaerobic conditions, its oxidation into 1,3-diphosphoglyceric acid occurs:
The active group of dehydrogenase is a coenzyme of complex organic structure NAD (nicotinamide adenine dinucleotide), which fixes two hydrogen atoms with its nicotinamide core:
NAD+ + 2H+ + NAD H2
NAD oxidized NAD reduced
By oxidizing the substrate, the coenzyme NAD becomes the owner of free hydrogen ions, which gives it a high reduction potential. Therefore, fermenting wort is always characterized by a high reducing ability, which has a large practical significance in winemaking: the pH of the environment decreases, temporarily oxidized substances are restored, pathogenic microorganisms die.
In the final phase of the second stage of alcoholic fermentation, the phosphotransferase enzyme double catalyzes the transfer of a phosphoric acid residue, and phosphoglyceromutase moves it from the 3rd carbon atom to the 2nd, opening the opportunity for the enzyme enolase to form pyruvic acid:
1,3-Diphosoglyceric acid 2-Phosphogliceric acid Pyruvic acid
Due to the fact that from one molecule of doubly phosphorylated hexose (2 ATP consumed) two molecules of doubly phosphorylated trioses are obtained (4 ATP formed), the net energy balance of the enzymatic breakdown of sugars is the formation of 2 ATP. This energy ensures the vital functions of the yeast and causes an increase in the temperature of the fermenting medium.
All reactions preceding the formation of pyruvic acid are inherent in both the anaerobic fermentation of sugars and the respiration of protozoan organisms and plants. Stage III relates only to alcoholic fermentation.
IIIstage of alcoholic fermentation - the formation of ethyl alcohol. At the final stage of alcoholic fermentation, pyruvic acid is decarboxylated under the action of the enzyme decarboxylase to form acetaldehyde and carbon dioxide, and with the participation of the enzyme alcohol dehydrogenase and coenzyme NAD-H2, acetaldehyde is reduced to ethanol:
Pyruvic acid Acetylaldehyde Ethanol
If there is an excess of free sulfurous acid in the fermenting wort, then part of the acetaldehyde is bound into an aldehyde sulfur compound: in each liter of wort, 100 mg of H2SO3 is bound to 66 mg of CH3SON.
Subsequently, in the presence of oxygen, this unstable compound disintegrates, and free acetaldehyde is found in the wine material, which is especially undesirable for champagne and table wine materials.
IN compressed form The anaerobic conversion of hexose to ethyl alcohol can be represented by the following scheme:
As can be seen from the scheme of alcoholic fermentation, phosphorus esters of hexoses are formed first. In this case, glucose and fructose molecules, under the action of the enzyme hexokenase, add the phosphoric acid residue from adenositol triphosphate (ATP), resulting in the formation of glucose-6-phosphate and adenositol diphosphate (ADP).
Glucose-6-phosphate, under the action of the enzyme isomerase, is converted into fructose-6-phosphate, which adds another phosphoric acid residue from ATP and forms fructose-1,6-diphosphate. This reaction is catalyzed by phosphofructokinase. The formation of this chemical compound ends the first preparatory stage of the anaerobic breakdown of sugars.
As a result of these reactions, the sugar molecule passes into the oxy form, becomes more lable and becomes more capable of enzymatic transformations.
Under the influence of the enzyme aldolase, fructose-1, 6-diphosphate is broken down into glycerinaldehydephosphoric and dihydroxyacetonephosphoric acids, which can be converted one into one under the action of the enzyme triosephosphate isomerase. Phosphoglyceraldehyde undergoes further transformation, of which approximately 3% is formed compared to 97% of phosphodioxyacetone. Phosphodioxyacetone, as phosphoglyceraldehyde is used, is converted by phosphotriose isomerase into 3-phosphoglyceraldehyde.
In the second stage, 3-phosphoglyceraldehyde adds another phosphoric acid residue (at the expense of inorganic phosphorus) to form 1, 3-diphosphoglyceraldehyde, which is dehydrated by triosephosphate dehydrogenase and gives 1, 3-diphosphoglyceric acid. Hydrogen, in this case, is transferred to the oxidized form of the coenzyme NAD. 1, 3-diphosphoglyceric acid, giving up one phosphoric acid residue to ADP (under the action of the enzyme phosphoglycerate kenase), is converted into 3-phosphoglyceric acid, which, under the action of the enzyme phosphoglyceromutase, is converted into 2-phosphoglyceric acid. The latter, under the action of phosphopyruvate hydrotase, is converted into phosphoenolpyruvic acid. Further, with the participation of the enzyme pyruvate kenase, phosphoenolpyruvic acid transfers the phosphoric acid residue to the ADP molecule, as a result of which an ATP molecule is formed and the enolpyruvic acid molecule is converted into pyruvic acid.
The third stage of alcoholic fermentation is characterized by the breakdown of pyruvic acid under the action of the enzyme pyruvate decarboxylase into carbon dioxide and acetaldehyde, which is reduced into ethyl alcohol under the action of the enzyme alcohol dehydrogenase (its coenzyme is NAD).
The overall equation for alcoholic fermentation can be represented as follows::
C6H12O6 + 2H3PO4 + 2ADP → 2C2H5OH + 2CO2 + 2ATP + 2H2O
Thus, during fermentation, one molecule of glucose is converted into two molecules of ethanol and two molecules of carbon dioxide.
But the indicated course of fermentation is not the only one. If, for example, the substrate does not contain the enzyme pyruvate decarboxylase, then pyruvic acid does not split into acetaldehyde and pyruvic acid is directly reduced, turning into lactic acid in the presence of lactate dehydrogenase.
In winemaking, fermentation of glucose and fructose occurs in the presence of sodium bisulfite. Acetaldehyde, formed by decarboxylation of pyruvic acid, is removed by binding with bisulfite. The place of acetaldehyde is taken by dihydroxyacetone phosphate and 3-phosphoglyceraldehyde; they receive hydrogen from reduced chemical compounds, forming glycerophosphate, which is converted by dephosphorylation to glycerol. This is the second form of fermentation according to Neuberg. According to this scheme of alcoholic fermentation, glycerol and acetaldehyde accumulate in the form of a bisulfite derivative.
Substances formed during fermentation.
Currently, about 50 higher alcohols have been found in fermentation products, which have a variety of odors and significantly affect the aroma and bouquet of wine. Isoamyl, isobutyl and N-propyl alcohols are formed in the largest quantities during fermentation. In Muscat sparkling and semi-sweet table wines produced by the so-called biological nitrogen reduction, aromatic higher alcohols β-phenylethanol (FES), tyrosol, terpene alcohol farnesol, which have the aroma of rose, lily of the valley, linden flowers, were found in large quantities (up to 100 mg/dm3) . Their presence in small quantities is desirable. In addition, when aging wine, higher alcohols enter into esterification with volatile acids and form esters, giving the wine favorable ethereal tones of bouquet maturity.
Subsequently, it was proven that the bulk of aliphatic higher alcohols are formed from pyruvic acid by transamination and direct biosynthesis with the participation of amino acids and acetaldehyde. But the most valuable aromatic higher alcohols are formed only from the corresponding amino acids of the aromatic series, for example:
The formation of higher alcohols in wine depends on many factors. IN normal conditions they accumulate on average 250 mg/dm3. With slow, long-term fermentation, the amount of higher alcohols increases, and with an increase in fermentation temperature to 30 ° C, it decreases. Under conditions of continuous flow fermentation, yeast reproduction is very limited and fewer higher alcohols are formed than with batch fermentation.
With a decrease in the number of yeast cells as a result of cooling, settling and rough filtration of fermented wort, a slow accumulation of yeast biomass occurs and at the same time the amount of higher alcohols, primarily of the aromatic series, increases.
An increased amount of higher alcohols is undesirable for dry white table wines, champagne and cognac wine materials, but it gives a variety of shades in the aroma and taste of red table wines, sparkling and strong wines.
Alcoholic fermentation of grape must is also associated with the formation of high-molecular aldehydes and ketones, volatile and fatty acids and their esters, which are important in the formation of the bouquet and taste of wine.
1. Can photo- and chemosynthetic organisms get energy thanks to oxidation of organic matter? Of course they can. Plants and chemosynthetics are characterized by oxidation, because they need energy! However, autotrophs will oxidize those substances that they themselves synthesized.
2. Why do aerobic organisms need oxygen? What is the role of biological oxidation? Oxygen is the final electron acceptor that come from higher energy levels oxidizable substances. During this process electrons release significant amounts of energy, and this is precisely the role of oxidation! Oxidation is the loss of electrons or a hydrogen atom, reduction is their addition.
3. What is the difference between combustion and biological oxidation? As a result of combustion, all energy is completely released in the form heat. But with oxidation, everything is more complicated: only 45 percent of the energy is also released in the form of heat and is used to maintain normal body temperature. But 55 percent - in the form of ATP energy and other biological batteries. Consequently, most of the energy still goes into creating high energy connections.
Stages of energy metabolism
1. Preparatory stage characterized splitting polymers into monomers(polysaccharides are converted into glucose, proteins into amino acids), fats into glycerol and fatty acids. At this stage, some energy is released in the form of heat. The process takes place in the cell lysosomes, at the organism level - in digestive system. This is why once the digestion process begins, the body temperature rises.
2. Glycolysis, or oxygen-free stage- incomplete oxidation of glucose occurs.
3. Oxygen stage- final breakdown of glucose.
Glycolysis
1. Glycolysis goes in the cytoplasm. Glucose C 6 H 12 ABOUT 6 breaks down to PVA (pyruvic acid) C 3 H 4 ABOUT 3 - into two three-carbon PVC molecules. There are 9 different enzymes involved here.
1) At the same time, two molecules of PVK have 4 less hydrogen atoms than glucose C 6 H 12 O 6, C 3 H 4 O 3 - PVK (2 molecules - C 6 H 8 O 6).
2) Where do 4 hydrogen atoms go? Due to 2 atoms 2 NAD+ atoms are reduced to two NADH. Due to the other 2 hydrogen atoms, PVK can turn into lactic acid C 3 H 6 ABOUT 3 .
3) And due to the energy of electrons transferred from high energy levels of glucose to a lower level of NAD+, they are synthesized 2 ATP molecules from ADP and phosphoric acid.
4) Part of the energy is wasted in the form heat.
2. If there is no oxygen in the cell, or there is little of it, then 2 molecules of PVK are reduced by two NADH to lactic acid: 2C 3 H 4 O 3 + 2NADH + 2H+ = 2C 3 H 6 O 3 (lactic acid) + 2NAD+. The presence of lactic acid causes muscle pain during exercise and lack of oxygen. After an active load, the acid is sent to the liver, where hydrogen is split off from it, that is, it again turns into PVC. This PVC can go into the mitochondria for complete breakdown and formation of ATP. Part of the ATP is also used to convert most of the PVC back into glucose by reversing glycolysis. Glucose will go into the muscles in the blood and be stored as glycogen.
3. As a result anoxic oxidation of glucose total is created 2 ATP molecules.
4. If the cell already has, or begins to enter it oxygen, PVK can no longer be reduced to lactic acid, but is sent to mitochondria, where it is completely oxidation to CO 2 AndH 2 ABOUT.
Fermentation
1. Fermentation is the anaerobic (oxygen-free) metabolic breakdown of molecules of various nutrients, such as glucose.
2. Alcoholic, lactic acid, butyric acid, acetic acid fermentation occurs under anaerobic conditions in the cytoplasm. Essentially, as a process, fermentation corresponds to glycolysis.
3. Alcoholic fermentation is specific for yeast, some fungi, plants, bacteria, which switch to fermentation under oxygen-free conditions.
4. To solve problems, it is important to know that in each case, during fermentation, glucose is released 2 ATP, alcohol, or acid- oil, vinegar, milk. During alcoholic (and butyric acid) fermentation, not only alcohol and ATP, but also carbon dioxide are released from glucose.
Oxygen stage of energy metabolism includes two stages.
1. Tricarboxylic acid cycle (Krebs cycle).
2. Oxidative phosphorylation.
Energy exchange (catabolism, dissimilation) - a set of reactions of the breakdown of organic substances, accompanied by the release of energy. The energy released during the breakdown of organic substances is not immediately used by the cell, but is stored in the form of ATP and other high-energy compounds. ATP is a universal source of cell energy. ATP synthesis occurs in the cells of all organisms through the process of phosphorylation - the addition of inorganic phosphate to ADP.
U aerobic organisms (living in an oxygen environment) distinguish three stages of energy metabolism: preparatory, oxygen-free oxidation and oxygen oxidation; at anaerobic organisms (living in an oxygen-free environment) and aerobic with a lack of oxygen - two stages: preparatory, oxygen-free oxidation.
Preparatory stage
It consists of the enzymatic breakdown of complex organic substances into simple ones: protein molecules- to amino acids, fats - to glycerol and carboxylic acids, carbohydrates - to glucose, nucleic acids - to nucleotides. The breakdown of high molecular weight organic compounds is carried out either by enzymes of the gastrointestinal tract or by lysosome enzymes. All the energy released in this case is dissipated in the form of heat. The resulting small organic molecules can be used as " building material» or may undergo further degradation.
Anoxic oxidation, or glycolysis
This stage consists of further breakdown of organic substances formed during the preparatory stage, occurs in the cytoplasm of the cell and does not require the presence of oxygen. The main source of energy in the cell is glucose. The process of oxygen-free incomplete breakdown of glucose - glycolysis.
The loss of electrons is called oxidation, the gain is called reduction, in which the electron donor is oxidized and the acceptor is reduced.
It should be noted that biological oxidation in cells can occur both with the participation of oxygen:
A + O 2 → AO 2,
and without his participation, due to the transfer of hydrogen atoms from one substance to another. For example, substance “A” is oxidized due to substance “B”:
AN 2 + B → A + VN 2
or due to electron transfer, for example, divalent iron is oxidized to ferric:
Fe 2+ → Fe 3+ + e - .
Glycolysis is a complex multi-step process that includes ten reactions. During this process, glucose is dehydrogenated, and the coenzyme NAD + (nicotinamide adenine dinucleotide) serves as a hydrogen acceptor. As a result of a chain of enzymatic reactions, glucose is converted into two molecules of pyruvic acid (PVA), with a total of 2 ATP molecules and a reduced form of the hydrogen carrier NADH 2 being formed:
C 6 H 12 O 6 + 2ADP + 2H 3 PO 4 + 2NAD + → 2C 3 H 4 O 3 + 2ATP + 2H 2 O + 2NAD H 2.
Further fate PVC depends on the presence of oxygen in the cell. If there is no oxygen, alcoholic fermentation occurs in yeast and plants, during which acetaldehyde is first formed, and then ethyl alcohol:
- C 3 H 4 O 3 → CO 2 + CH 3 COH,
- CH 3 SON + NADH 2 → C 2 H 5 OH + NAD +.
In animals and some bacteria, when there is a lack of oxygen, lactic acid fermentation occurs with the formation of lactic acid:
C 3 H 4 O 3 + NADH 2 → C 3 H 6 O 3 + NAD +.
As a result of glycolysis of one glucose molecule, 200 kJ is released, of which 120 kJ is dissipated as heat, and 80% is stored in ATP bonds.
Oxygen oxidation, or respiration
It consists in the complete breakdown of pyruvic acid, occurs in mitochondria and in the obligatory presence of oxygen.
Pyruvic acid is transported to mitochondria (structure and functions of mitochondria - lecture No. 7). Here, dehydrogenation (elimination of hydrogen) and decarboxylation (elimination of carbon dioxide) of PVC occurs with the formation of a two-carbon acetyl group, which enters into a cycle of reactions called Krebs cycle reactions. Further oxidation occurs, associated with dehydrogenation and decarboxylation. As a result, for every PVC molecule destroyed, three CO 2 molecules are removed from the mitochondrion; Five pairs of hydrogen atoms are formed associated with carriers (4NADH 2, FADH 2), as well as one ATP molecule.
The overall reaction of glycolysis and destruction of PVC in mitochondria to hydrogen and carbon dioxide is as follows:
C 6 H 12 O 6 + 6 H 2 O → 6 CO 2 + 4 ATP + 12 H 2.
Two ATP molecules are formed as a result of glycolysis, two - in the Krebs cycle; two pairs of hydrogen atoms (2NADCH2) were formed as a result of glycolysis, ten pairs - in the Krebs cycle.
The last step is the oxidation of pairs of hydrogen atoms with the participation of oxygen to water with simultaneous phosphorylation of ADP to ATP. Hydrogen is transferred to three large enzyme complexes (flavoproteins, coenzymes Q, cytochromes) of the respiratory chain located in the inner membrane of mitochondria. Electrons are taken from hydrogen, which ultimately combine with oxygen in the mitochondrial matrix:
O 2 + e - → O 2 - .
Protons are pumped into the intermembrane space of mitochondria, into the “proton reservoir”. The inner membrane is impermeable to hydrogen ions; on the one hand it is charged negatively (due to O 2 -), on the other - positively (due to H +). When the potential difference across the inner membrane reaches 200 mV, protons pass through the ATP synthetase enzyme channel, ATP is formed, and cytochrome oxidase catalyzes the reduction of oxygen to water. So, as a result of the oxidation of twelve pairs of hydrogen atoms, 34 ATP molecules are formed.
Lesson topic : Non-cellular life forms.Teacher :
School:
Area:
Item: biology
Class: 10
Lesson type: The lesson is a role-playing game using ICT.
The purpose of the lesson:
Deepen students' knowledge about non-cellular life forms;
and infection with the AIDS virus.
Lesson objectives:
Providing opportunities for students to unite according to their interests, ensuring a variety of role activities; expand the ability to work with additional literature and Internet materials; foster a sense of collectivism; formation of supra-subject competence.
Time: 1 hour
Phone: 72-1-16
Equipment: computer, projector, screen, teaching materials.
Preparatory stage:
A week before the lesson, role groups of “biologists,” “historians,” and “infectious disease specialists” are formed from class students and asked to find relevant material about non-cellular life forms for the groups’ report. The teacher offers them the necessary literature and Internet resources.
During the classes:
Organizing time(1 min)
Checking work assignments - multi-level tested work
Test No. 1
1) Glycolysis is the process of breakdownI :
A) proteins into amino acids;
B) lipids to higher carboxylic acids and glycerin;
2) Fermentation is a process:
A) The breakdown of organic substances under anaerobic conditions;
B) Glucose oxidation;
B) ATP synthesis in mitochondria;
D) Conversion of glucose into glycogen.
3) Assimilation is:
A) Formation of substances using energy;
B) The breakdown of substances with the release of energy.
4) Arrange the stages of energy metabolism of carbohydrates in order:
A - cellular respiration;
B- glycolysis;
B-preparatory.
5) What is phosphorylation ?
A) ATP formation;
B) Formation of lactic acid molecules;
B) Breakdown of lactic acid molecules.
Test No. 2
1) Where do the first and second stages of the breakdown of high-molecular compounds occur: A) cytoplasm; B) mitochondria: C) lysosomes D) Golgi complex.
2) In the cells of which organisms does alcoholic fermentation occur?:
A) animals and plants; B) plants and mushrooms.
3)The energetic effect of glycolysis is the formation
2 molecules:
A) lactic acid; B) pyruvic acid; B)ATP;
D) ethyl alcohol.
4) Why is dissimilation called energy exchange?
A) energy is absorbed; B) Energy is released.
5) What is included in ribosomes?
A) DNA; B) lipids; C) RNA; D) proteins.
Test No. 3
1) What is the difference between energy metabolism in aerobes and anaerobes?
A) - lack of a preparatory stage; B) absence of oxygen-free cleavage; c) absence of the cellular stage.
2) Which stage of energy metabolism occurs in mitochondria?
A- preparatory B- glycolysis; B cell respiration
3) what organic matter rarely used to obtain energy in the cell:
A-proteins; B-fats;
4) In which cell organelles does the breakdown of organic substances occur:
A-ribosomes B-lysosomes; B-nucleus.
5) Where does the energy for the synthesis of ATP from ADP come from?
A) - in the process of assimilation; B) - in the process of dissimilation.
Self-control. Slide No. 2
Updating knowledge.
What do we know about life forms on earth?
What do we know about non-cellular life forms?
Why do we need this knowledge?
4. Presentation of the work plan and purpose.
Slide No. 3,4
5. Operational and executive.
Work of primary groups
a) Speech by gr. "historians" with information about the discovery
viruses. Slide No. 5
b) Speech by the group, “biologists” with information about the structure of the viral particle, about the division of viruses into RNA and DNA containing ones, about the structure of the bacteriophage. Slides No. 6,7,13
c) The teacher explains how viruses reproduce; students work with a notebook. Slide No. 11
d) Speech by gr. “infectious diseases” with reports on infectious diseases of humans, animals and plants caused by viruses. Slides No. 8,9,10
e) the teacher’s story about the danger of contracting the AIDS virus. Slide No. 12,14
Work of secondary groups
The guys are forming groups of new composition. And every group
searches for an answer to a question or problematic task proposed to her. For example: Find the difference between viruses and inanimate matter? Find the difference between viruses and living matter?
For what purpose are antibiotics prescribed during a viral disease?
6. Reflective-evaluative.
Checking the work of groups; Slide No. 15
Executing the test;
check yourself
1 Bacterial viruses ____________
2 The enzyme reversetase is present in the virus ________
3Virus envelope ______________
4 Free-living form of the virus _____________
5 Quantity nucleic acids in virus cells _
6 Viruses of which organisms have not been described __________
7 Viral diseases_________________________
Mutual control.
7.Summing up the lesson
8.Creative homework
- making a crossword puzzle;
Drawing up a cluster on this topic.
Information sources
N. V. Chebyshev Biology, the latest reference book. M-2007.
http //schols .keldysh .ru /scyooll 11413/bio /viltgzh /str 2.htm
1. What is the chemical nature of ATP?
Answer. Adenosine triphosphate (ATP) is a nucleotide consisting of the purine base adenine, the monosaccharide ribose and 3 phosphoric acid residues. In all living organisms it acts as a universal battery and energy carrier. Under the action of special enzymes, the terminal phosphate groups are cleaved off, releasing energy that goes into muscle contraction, synthetic and other vital processes.
2. What chemical bonds are called macroergic?
Answer. The bonds between phosphoric acid residues are called macroergic, since when they are broken, a large number of energy (four times more than when breaking other chemical bonds).
3. Which cells have the most ATP?
Answer. The highest ATP content is in cells in which energy expenditure is high. These are liver and striated muscle cells.
Questions after §22
1. In the cells of which organisms does alcoholic fermentation occur?
Answer. In most plant cells, as well as in the cells of some fungi (for example, yeast), instead of glycolysis, alcoholic fermentation occurs: the glucose molecule under anaerobic conditions is converted into ethyl alcohol and CO2:
C6H12O6 + 2H3PO4 + 2ADP → 2C2H5OH + 2CO2 + 2ATP + 2H2O.
2. Where does the energy for the synthesis of ATP from ADP come from?
Answer. ATP synthesis occurs in the following stages. At the stage of glycolysis, a glucose molecule containing six carbon atoms (C6H12O6) is split into two molecules of three-carbon pyruvic acid, or PVA (C3H4O3). Glycolysis reactions are catalyzed by many enzymes and occur in the cytoplasm of cells. During glycolysis, the breakdown of 1 M glucose releases 200 kJ of energy, but 60% of it is dissipated as heat. The remaining 40% of the energy is sufficient to synthesize two ATP molecules from two ADP molecules.
C6H12O6 + 2H3PO4 + 2ADP → 2C3H6O3 + 2ATP + 2H2O
In aerobic organisms, after glycolysis (or alcoholic fermentation), the final stage of energy metabolism follows - complete oxygen breakdown, or cellular respiration. During this third stage, organic substances formed during the second stage during oxygen-free decomposition and containing large reserves of chemical energy are oxidized to final products CO2 and H2O. This process, like glycolysis, is multistage, but occurs not in the cytoplasm, but in mitochondria. As a result of cellular respiration, the breakdown of two lactic acid molecules produces 36 ATP molecules:
2C3H6O3 + 6O2 + 36ADP + 36H3PO4 → 6CO2 + 42H2O + 36ATP.
Thus, the total energy metabolism of a cell in the case of glucose breakdown can be represented as follows:
C6H12O6 + 6O2 + 38ADP + 38H3PO4 → 6CO2 + 44H2O + 38ATP.
3. What stages are distinguished in energy metabolism?
Answer. Stage I, preparatory
Complex organic compounds They break down into simple ones under the action of digestive enzymes, releasing only thermal energy.
Proteins → amino acids
Fats → glycerol and fatty acids
Starch → glucose
Stage II, glycolysis (oxygen-free)
It occurs in the cytoplasm and is not associated with membranes. It involves enzymes; Glucose is broken down. 60% of the energy is dissipated as heat, and 40% is used for ATP synthesis. Oxygen is not involved.
Stage III, cellular respiration (oxygen)
It is carried out in mitochondria and is associated with the mitochondrial matrix and the inner membrane. It involves enzymes and oxygen. Lactic acid is broken down. CO2 is released from mitochondria into environment. The hydrogen atom is included in a chain of reactions, the final result of which is the synthesis of ATP.
Answer. All manifestations of aerobic life require the expenditure of energy, the replenishment of which occurs through cellular respiration - a complex process in which many enzyme systems are involved.
Meanwhile, it can be represented as a series of sequential oxidation-reduction reactions, in which electrons are detached from a molecule of any nutrient and transferred first to the primary acceptor, then to the secondary one, and then to the final one. In this case, the energy of the electron flow accumulates in high-energy chemical bonds(mainly phosphate bonds of the universal energy source - ATP). For most organisms, the final electron acceptor is oxygen, which reacts with electrons and hydrogen ions to form a water molecule. Only anaerobes survive without oxygen and cover their energy needs through fermentation. Anaerobes include many bacteria, ciliated ciliates, some worms and several types of mollusks. These organisms use ethyl or butyl alcohol, glycerol, etc. as the final electron acceptor.
The advantage of the oxygen, that is, aerobic type of energy metabolism over anaerobic is obvious: the amount of energy released during the oxidation of a nutrient with oxygen is several times higher than during its oxidation, for example, with pyruvic acid (occurs in such a common type of fermentation as glycolysis). Thus, due to the high oxidative capacity of oxygen, aerobes use consumed nutrients more efficiently than anaerobes. However, aerobic organisms can only exist in an environment containing free molecular oxygen. Otherwise they die.
