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Carbon and nitrogen metabolism


Academic year: 2023

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Part of the energy released from oxidation of food and from light is stored in a molecule known as adenosine triphosphate (ATP). This can be explained by the structures of both ATP and its hydrolysis products, ADP and Pi. ATP has a very high phosphoryl transfer potential, i.e. the ability to transfer its phosphate group. ATP in most respiration is formed as a result of the activity of an electron transport chain.

A detailed pathway showing the structures of intermediate compounds, enzymes involved in various reactions is shown in the figure. Glyceraldehyde 3-phosphate can then be oxidized to pyruvate by enzymes of the EMP pathway. Most catabolic pathways generate NADH as a reducing agent (electron source).

Pyruvate is a product of three pathways of glucose catabolism – EMP, ED and the pentose phosphate pathway. E2 molecules are present in the center of the complex, while E1 and E3 molecules are bound to the outside. That is, they accept electrons from an electron donor and transfer them to an electron acceptor. ii) They store some of the energy released during electron transfer for ATP synthesis.

This energy is calculated in terms of the free energy change, ∆G0'. n = number of electrons transferred from one carrier to another. This hypothesis proposes that electron transport by the carriers causes the pumping of protons (H+ ions) from the inner mitochondrial matrix to the other side of the membrane. These bacteria are differentiated from each other on the basis of the inorganic compounds they oxidize, e.g.

The reducing power in some of the chemolithotrophs is obtained directly from the inorganic compound. In the majority of chemolithotrophs, however, this is not possible, as these compounds have more positive reduction potentials than NAD+ / NADP+. Some of the proton motive force is also used to force electrons to flow up the reduction potential gradient from nitrite to NAD+ (left branch).

This part of the cycle is almost similar to the pentose phosphate pathway and involves the transketolase and trnsaldolase reactions. Some of the bacteria use CO2 as their only source of carbon and are called photolithotrophic autotrophs (or photoautotrophs). Since most of the reactions of TCA cycle are reversible, the reductive TCA cycle is almost its reversal (Fig. 19a).

There is no ETC in fermentation. iv) During fermentation, one organic compound (i.e. substrate) serves as an electron donor and another organic compound (product) is an electron acceptor. v) The electron donor and acceptor are neutral in the redox state, i.e. they are neither strongly oxidized nor strongly reduced. you).

Fig. 1: The structure of adenosine triphosphate (ATP). ATP is a typical nucleotide  consisting of an adenine ring, a ribose, and three phosphate groups
Fig. 1: The structure of adenosine triphosphate (ATP). ATP is a typical nucleotide consisting of an adenine ring, a ribose, and three phosphate groups

In addition to these sugars, bacteria can also ferment amino acids and organic acids such as acetic acid, lactic acid, citric acid, etc. Figure 22b: Formation of CO2, lactate and ethanol from glucose via the heterofermentative pathway, 1-Hexokinase; 2-glucose-6-phosphate dehydrogenase; 3-6-phosphogluconate dehydrogenase; 4-ribulose-5-phosphate-3-epimerase; 5-Phosphoketolase. It is produced during the last step of the anaerobic food chain through a process called methanogenesis or methane fermentation.

Fig. 22 a: Formation of lactate from glucose by the homofermentative pathway. 1- Enzymes of  the Embden-Meyerhof-Parnas pathway; 2- lactate dehydrogenase
Fig. 22 a: Formation of lactate from glucose by the homofermentative pathway. 1- Enzymes of the Embden-Meyerhof-Parnas pathway; 2- lactate dehydrogenase

They live in anaerobic environments which are rich in organic matter, e.g. marshes, digesters, animal rumen and intestinal system, freshwater and marine sediments, etc. Through this thread, bacteria move, divide and infect cells around the thread of infection. v) Inside the root cells, most bacteria take irregular shape and are called bacteroids. In the anaerobic environment, nitrate acts as the final electron acceptor at the end of the electron transport chain and is reduced to products such as NO2--, N2, etc.

This is because the nitrogen atom in ammonia is at the same oxidation level as that of the organic nitrogen. The amino group of glutamate and alanine is then transferred to other carbon compounds by transamination reactions. In addition, the activity of these enzymes must be controlled depending on the needs (energy or cellular components) of the organism.

The trp operon five structural genes which code for five proteins in the tryptophan biosynthesis pathway. However, when tryptophan is deficient, synthesis of the leader peptide is blocked and transcription of the rest of the operon continues. Let's see how translation of the leader peptide regulates the transcription of the tryptophan genes.

Attenuation occurs because part of the newly formed mRNA folds into a structure called a stem loop. Transcription is thus stopped before the RNA polymerase reaches the first structural gene of the operon. The presence of stalled ribosome at this position allows for alternative attachment of the stem loop.

Two regions of the growing mRNA chain can form double-stranded loops, shown as. An allosteric enzyme has two major binding sites: a) the active site where the substrate binds. When an inhibitor binds at the allosteric site, the attachment of the enzyme molecule changes (Fig. 32).

When the concentration of inhibitor drops, equilibrium favors dissociation of the inhibitor from the allosteric site, returning the enzyme molecule to its original attachment. When the effector combines with the allosteric site, the conformation of the enzyme is changed to the. substrate can no longer bind.

Fig. 23: Structure of novel coenzymes present in methanogens
Fig. 23: Structure of novel coenzymes present in methanogens


Fig. 3: Glycolysis/Embden – Meyerhof Pathway for the conversion of glucose and other  sugars to pyruvate
Fig. 5: The Pentose Phosphate Pathway
Fig. 6: Reactions catalyzed by the pyruvate dehydrogenase complex. E 1 , pyruvate  dehydrogenase; E 2 , dihydrolipoate transacetylase; E 3 , dihydrolipoate dehydrogenase;
Fig. 7: The Tricarboxylic Acid Cycle


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