1. Describe the role of the citric acid cycle as a central metabolic mechanism. Explain what...

1. Describe the role of the citric acid cycle as a central metabolic mechanism. Explain what happens to the cells' abilities to oxidize acetyl CoA when intermediates of the cycle are drained off for amino acid biosynthesis.

2. Describe the three steps in photosynthesis, detailing the interrelationships among them. (c.f. the discussion in the online classroom).

Expert Solution

(1):Citric acid cycle acts as a central metabolic system because it oxidises the acetyl co-A that is derived from each of carbohydrate, protein and fat. It oxidises acetyl co-A to CO2 and energy in form of ATP.

Hence citric acid cycle acts as a central metabolic mechanism by acting as a common mechanism for the oxidation of carbohydrate, protein and fat.

In the first step the pyruvate(3-C) derived from glycolysis and metabolism of fat and protein is converted to caetyl co-A (2-C) in presence of enzyme pyruvate dehydrogenase. One CO2 mlecue is released along with the conversion of NAD+ to NADH.

Now acetyl Co-A enters into citric acid cycle and converts into a series of organic compounds in cyclic form generating NADH, FADH2 and GTP. NADH and FADH2 enters into oxidative phosphorylation generating ATP.

At the end of the cycle acetyl co-A is regenerated so that the process contineous with out any interruption.

However if the intermediates of the cycle are drained off for amino acid biosynthesis, the efficiency of citric acid cycle decreases as the acetyl co-A is not generated as efficiently as it is needed. However the biosynthesis of aminoacids is also necessary.

2. Photosynthesis is completed in the following three steps that are very closely inter-related to each other.

1. Capturing of light energy from sunlight in form of quanta to be utilised in light-dependent reaction.

2. The light energy ontained in the first process is used to generate ATP and NADPH in light dependent reaction that store energy.

2 H₂O + 2 NADP⁺ + 3 ADP + 3 P_i + light → 2 NADPH + 2 H⁺ + 3 ATP + O₂

During this process H2O is photolysed to generate O2 and H+

2. The energy in form of ATP and NADPH is used in Calvin cycle to convert carbon dioxide and H+ into glucose.

3 CO₂ + 9 ATP + 6 NADPH + 6 H⁺ → C₃H₆O₃-phosphate + 9 ADP + 8 P_i + 6 NADP⁺ + 3 H₂O

queen_honey_blossom answered 11 hours ago

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