METABOLISM METABOLIC PROCESSES ALL INVOLVE OXIDATION AND REDUCTION WHICH

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METABOLISM:

Metabolic processes all involve oxidation and reduction which are opposites.

For every oxidation there is also a reduction occurring somewhere else.

Oxidation Reduction

1. Add oxygen 1. remove oxygen

2. Remove hydrogen 2. Add hydrogen

3. Remove electrons 3. Add electrons

Exchange of electrons always occurs!!!

Two major types of metabolic process (opposites) S P

Catabolism - oxidation, degradation, breaking of covalent bonds, release of energy (Exergonic) . Energy is released to produce ATP from ADP by Phosphorylation.

Anabolism – reduction, biosynthesis of new macromolecules by forming covalent bonds, requires energy input (Endergonic) . Energy is from ATP ADP (dephosphorylation).

ATP provided by catabolism therefore reactions coupled. Coupling Agent is ATP.

Catabolic reactions are theoretically Spontaneous because of Energy Gradient in Substrate relative to end products. Anabolic reaction not.

Catabolic reactions are not spontaneous however, because energy in molecular motion not sufficient to overcome covalent bond energy. Need an input of energy or the removal of the energy difference. This energy is referred to as Activation Energy.

Regulation of catabolic reaction is accomplished by removing the activation Energy using Enzymes.

Enzymes:

Protein
Specific
Have an Active site to attach to substrate and reduce activation energy
are unchanged during the course of a reaction (thus can reuse)
Lower activation energies of reaction to make them Spontaneous

Catabolic Reactions (Energy Generating)

Respiration : 1. aerobic – requires molecular oxygen

2. anaerobic – requires a bound form of oxygen

Both of the above are the complete oxidation of glucose (remove all the hydrogen)

And thus produce the maximum amount of ATP

Fermentation: occurs in the presence or absence of oxygen because not required.

Incomplete oxidation of glucose ( not all hydrogen removed) and therefore very little ATP produced.

Three biochemical processes are potentially involved with Respiration and fermentation

1. Glycolysis (removal of hydrogen with a coenzyme NADNADH)

2. Tricarboxylic Acid cycle {TCA, Citric Acid or Kreb’s cycles} (removal of hydroden with NADNADH and FAD—FADH)

3. Oxidative phosphorylation (using cytochromes to transfer hydrogen from NADH and FADH to a form of oxygen (molecular or bound).

Glycolysis:

Glucose  pyruvic acid + ATP + NADH

Three major steps:

1. Glucose Fructose Diphosphate Activation using ATP

2. Fructose Diphosphate Glyceraldehyde Phosphate splitting glucose with

Aldolase

3. Glyceraldehyde Phosphate  pyruvic acid + ATP + NADH oxidation by

removal of hydrogen – no oxygen required , and phosphorylation. No carbon dioxide given off.

TCA cycle:

Pyruvic Acid  Carbon Dioxide + ATP + FADH + NADH

Oxidation by removal of hydrogen – no oxygen required, and phosphorylation.

By definition decarboxylation occurs. Carbon dioxide is given off in the TCA cycle

There is actually a transition step between Glycolysis and The TCA cycle proper.

Pyruvic Acid Acetic acid + Carbon dioxide + NADH

Oxidative Phosphorylation:

Oxidation of coenzymes and phosphorylation occurs.

NADH + FADH + Oxygen (molecular or bound) NAD + FAD + reduced Oxygen

+ATP

Hydrogen transferred from NADH and FADH to cytochromes

Cytochromes transfer hydrogen to a form of oxygen to reduce it.

Electrons flow through the cytochromes in a membrane in this process and Protons back and forth across the membrane using ATPase which also produces ATP

For each NADH NAD 3 ATP’s produced

FADHFAD 2 ATP’s produced

All three processes described above occur in respiration

Only glycolysis in Fermentation

Fermentation is

Glucose acid/alcohol + ATP

It is therefore Gylcolysis plus one additional step to convert NADHNAD

That step is:-

Pyruvic Acid +NADH  acid/alcohol +NAD

The hydrogen is transferred from the NADH to the pyruvic acid to produce the acid/alcohol

Glycolysis and the TCA cycle occur in the cytoplasm of Prokaryotes. Oxidative Phosphorylation in the Cell membrane

Glycolysis occurs in the cytoplasm of Eukaryotes. The TCA cycle and Oxidative phosphorylation in the mitochondria.

PHOTOSYNTHESIS: is the reduction of carbon dioxide to glucose using solar radiation.

6CO₂ + 6H₂O  C₆H₁₂O₆ + 6O₂

There are two major types of reaction involved in the above process

Light Dependant
Light Independent

In the light dependant reactions chlorophyll absorbs light as a source of energy. There are two types of chlorophyll molecules and associated reactions termed photosystems I and II.

Photosystem II occurs first.

On the absorption of a photon of light energy the chlorophyll becomes oxidized by the loss of an electron. The electron passes through a cytochrome chain while protons move back and forth across the membrane in which the cytochromes are located resulting in the production of ATP. The electrons lost from chlorophyll on oxidation and the protons moving across the membrane are derived from water when it is photolysed as follows:-

H₂0  O + 2H 2H  2H⁺ + 2e^-

In Photosystem I absorption of light also causes oxidation of chlorophyll by loss of an electron which the enters a second cytochrome chain. The electron flows through the chain just as in PSII however protons do not pass across the membrane and therefore ATP is not produced. The electron lost from chlorophyll is replaced by electrons from the cytochrome chain of PS II.

When electrons come out of the cytochrome chain associated with PSI they recombine with protons from water and attach to NADP (a coenzyme) reducing it to NADPH.

In summary:

PSII generates ATP energy

PSI generates reducing power (H from water) in the form of NADPH

Light Independent Reactions: require

1. Carbon Dioxide from air

2. ATP from PS II

3. H in the form of NADPH from PSI

4. An enzyme Ribulose Biphosphate carboxylase (Rubisco)

5. Sugar – Ribulose biphosphate to attach Carbon dioxide to.

There are three major reactions:

1 Ribulose Biphosphate + carbon dioxide  Phosphoglyceraldehyde {PGA}

(catalyzed by Rubisco)

2. Some PGA is converted to Glucose by the reverse of glycolysis. This requires

ATP and H from NADPH (reduction) both generated in the Light dependant

reactions.

3. . Some PGA is used to regenerate Ribulose biphosphate. This also requires

ATP and H from NADPH (reduction) both generated in the Light dependant

Reactions. This particular series of reactions is referred to as the Calvin

Benson cycle.

Light dependant reactions occur in the thylakoid membranes and the light independent reactions in the stroma of the chloroplasts.

A SOCIACIÓN ARGENTINA DE OSTEOLOGÍA Y METABOLISMO MINERAL P
AMERICAN DIETETIC ASSOCIATION DISORDERS OF LIPID METABOLISM TOOLKIT DISORDERS
AMINO ACID METABOLISM NITROGEN BALANCE D IETARY PROTEIN

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