Question

1. The citric acid cycle is a set of sequential reactions where 2 carbon atoms from Acetyl CoA (that derives from a glucose molecule) are coupled to a 4 carbon molecule. The carbon atoms from Acetyl CoA are released as CO2. Redox reactions and phosphorylation reactions are used to harvest energy in the form of ATP, NADH and FADH2. The product of these reactions is again a 4 carbon molecule that can be coupled with 2 carbon atoms from another Acetyl CoA to repeat the whole process

A. False, the citric acid cycle employs only redox reactions.

B. True, this is a correct description of the citric acid cycle.

C. False, the citric acid cycle starts with pyruvate as a substrate.

D. False, the citric acid cycle does not yield NADH.

2. In the absence of oxygen, cellular respiration switches to fermentation. Fermentation is a set of alternative reactions to complete glycolysis and produce 2 ATP for a glucose molecule, by making sure that the following reagent is available.

A. NAD (oxidized electron carrier)

B. EtOH (alcohol)

C. Acetyl CoA (substrate for citric acid cycle)

D. NADH (reduced electron carrier)

Answer 1

Ans.

1). Citric acid cycle ;

Citric acid cycle is also known as tricarboxilic acid (TCA) cycle or the Krebs cycle.

It is a key reaction to drive the cellular respiration.

Mitochndrial matrix is the site of this cycle in eukaryotes whereas in prokaryotes this cycle takes place in cytoplasm.

In this cycle, Acetyl CoA (the starting material), is converted to NADH, FADH2 and ATP through a series of redox reactions.

Oxaloacetate, a 4 carbon acceptor molecule, combines with Acetyl CoA in the first step of TCA cycle resulting in the production of citrate (a six carbon molecule).

A pair of NADH molecule is produced after a rearrengement of citrate molecules and also two of it's carbon are released in the form of carbon dioxide.

Other 4 molecules of carbon go additional reaction series and generate ATP and FADH2 .

So, it can be said that above given statement is a correct description of the citric acid cycle.

2). Fermentation ;

• Any metabolic process which uses enzymes and changes the chemical properties of a substrate is called as fermentation.
• Although, the above statement is more then sufficient to explain the process of fermentation, but it's definition can vary depending upon the context it is being used.
• It has many industrial applications such as production of alcohol and preservation of pickles.
• In microbes it produces ATP by degrading organic nutrients.
• Fermentation is a set of alternative reactions to complete glycolysis and produce 2 ATP for a glucose molecule, by making sure that NADH (reduced electron carrier) is available.
• During the process of fermentation, NADH reacts with an endogenous oxidized electron acceptor such as pyruvate resulting in production of NAD+ and organic molecules such as ethanol, lactic acid, carbon dioxide... etc.