Uncoupler of Oxidative Phosphorylation

Uncouplers of oxidative phosphorylation in mitochondria inhibit the coupling between the electron transport and phosphorylation reactions and thus inhibit ATP synthesis without affecting the respiratory chain and ATP synthase. Uncouplers inhibit ATP synthesis by preventing this coupling reaction in such a fashion that the energy produced by redox reactions cannot be used for phosphorylation. Uncouplers include DNP, valinomycin, and CCCP. Most of them are hydrophobic weak acids that act by protonophoric action and activities (Zirnrner, 2000).

One example of an ‘uncoupler’ of oxidative phosphorylation is DNP (2,4-dinitrophenol).

2,4-Dinitrophenol (DNP), C6H4N2O5, is a cellular metabolic poison. It uncouples oxidative phosphorylation by carrying protons across the mitochondrial membrane, leading to a rapid consumption of energy without generation of ATP (Chappell, 1963).

In living cells, DNP acts as a proton ionophore, an agent that can shuttle protons (hydrogen ions) across biological membranes. It defeats the proton gradient across mitochondrial membrane, collapsing the proton motive force that the cell uses to produce most of its ATP chemical energy. Instead of producing ATP, the energy of the proton gradient is lost as heat.

DNP is often used in biochemistry research to help explore the bioenergetics of chemiosmotic and other membrane transport processes (Zirnrner, 2000).

The HMP shunt represents an alternative pathway for the breakdown of glucose. Briefly describe the main products produced by this pathway and it’s biological significance.

The main product are Ribose-5-P, NADPH and Intermediates of the glycolytic pathway. HMP shunt represents an alternate degradative pathway for the breakdown of glucose, and it provides a link between glycolysis and nucleotide metabolism and fatty acid.

Biological significance of Ribose-5-P is that serves as the precursor to various nucleotides (ATP, NAD, NADP, coenzyme A) and nucleic acids (DNA) within our cells.

Biological significance of NADPH: represents the major source of reducing power for biosynthetic reactions within cells, particularly the synthesis of fatty acids. It follows that the HMP shunt is active in tissues specialized for the synthesis of fatty acids or steroids.

Biological significance of Intermediates of the glycolytic pathway: the demand for NADPH in the cell is usually far greater than the demand for ribose-5-P, thus the second phase of this pathway is devoted to recycling the 5-carbon skeletons into intermediates of the glycolytic pathway so that the cell can harness the energy that is present in these molecules

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For each of the following statements indicate whether it is true or false. If false, explain why, using formulae and/or equations to support your answer where appropriate.

(a) The regulation of the glycolytic pathway involves allosteric inhibition by ADP.

False.

Because it it’s inhibition by ATP not ADP. The regulation of the glycolytic pathway involves allosteric stimulation by ADP. ADP can be regulated in many ways through a metabolic pathway of glycolysis, such as concentration of enzymes responsible for rate-limiting step，availability of substrate, allosteric regulation of enzymes and covalent modification of enzymes (Klingenberg and others, 1979).

In a eukaryotic cell, the enzymes of glycolysis and the TCA cycle are located in the cytosol and mitochondrial matrix respectively.

True.

Mixing pure O2 into a yeast culture growing on grape juice will cause the yeast to multiply faster and to metabolize the sugars much more rapidly. The effect on the desired final product (wine) would be a nearly alcohol-free beverage.

True.

The energetic efficiency of a family-size car (petrol –> motion) is ~25%. By contrast, the energetic efficiency of aerobic carbohydrate metabolism (glucose –> ATP) in vivo is less than 10%.

False.

Because glucose has delta G = 686 kcal/mol and each ATP is equal to approximately 10 kcal/mol, and 32 ATP = 320 kcal/mol which is almost half of the energy in glucose, not 10%. In addition, aerobic carbohydrate metabolism supplies many O2, and is resting levels of energy expenditure. Most ATP produced until energy-efficient oxidative pathways. Under anaerobic conditions such as those experienced during strenuous physical activity, the production is necessary to achieve the re-oxidisation of NADH back to NAD+ (Bergman, 2002).

Barbiturates disrupt energy metabolism by inhibiting the exit of electrons from complex I of the electron transport chain. This in turn blocks the conversion of NADH to NAD+

True

Adrenaline has the ability to upregulate carbohydrate metabolism via stimulation of a signal transduction cascade involving cAMP and multiple protein phosphorylation reactions.

True

The concentration of glucose in human blood is maintained at ~5mM. Provide a brief overview of the mechanisms employed to accomplish this relatively constant blood glucose level and comment on why it is necessary.

The primary source of energy for many of the body’s cells, and it tightly regulated by pancreatic hormones. Insulin can decreases blood glucoce. While the pancreas is constantly secreting insulin, the amount of insulin is dependent on how much blood glucose is in the blood. In adiition, it increases the cellular rate of glucose make use of as an energy source and it accelerates the formation of glycogen from glucose in skeletal muscle cells and liver.

It is necessary because if the body is not producing insulin, it will cause Type I diabetes. If people have this type of diabetes, they must be injected with synthetic insulin in order to regulate their blood sugar levels.

Glucagon has a major role in maintaining normal concentrations of glucose in blood. However, glucagon has opposite effect of insulin, which is glucagon has the effect of increasing blood glucose levels. When blood levels of glucose begin to fall below the normal range, the glucagon accelerates the breakdown of glycogen to glucose in liver and skeletal muscle cells. Additional, it increases the breakdown of fats to fatty acids and glycerol in adipose tissue, and then release of these substances into the blood. (Messier and Gagnon, 1996)