Question

Consider a single murine hepatocyte at homeostasis with its surrounding environment, which includes other neighboring hepatocytes and extra-hepatic tissues. Due to changes in the organism’s activity, this hepatocyte receives signals that trigger the need to synthesize exactly 20 copies of a protein required for altered amino acid metabolism.

PLEASE GIVE EXPLANATIONS FOR YOUR ANSWERS. THANK YOU!

1. How many equivalents of ATP are required to synthesize these 20 protein molecules?

2. Under aerobic conditions, how many molecules of glucose must be consumed in order to generate the ATP necessary to complete synthesis of these 20 protein molecules?

3. Under anaerobic conditions, how many molecules of glucose will be needed?

4. In the absence of glucose and under aerobic conditions, how many molecules of a triacylglyceride containing three palmitic acid groups would be needed to supply sufficient ATP?

5. In the absence of glucose and under anaerobic conditions, how many molecules of a triacylglyceride containing three palmitic acid groups would be needed?

Use the following assumptions/constraints when determining your answers:

a. All of the necessary catalytic complexes have already been synthesized within the cell

b. Nucleotides used for transcription must be accounted for

c. A single transcript is sufficient for translation of all 20 polypeptides

d. The primary transcript contains 400 nucleotides that are not translated. This includes the stop codon and a single intron that must be removed by the spliceosome prior to translation

e. The poly-A tail contains an additional 210 nucleotides

f. Amino acids and tRNA’s are readily available, energy required for their synthesis/replacement does not need to be accounted for

g. Each of the 20 protein molecules to be synthesized are identical, and contains 613 amino acids

h. Once translated, no further processing of the 20 molecules occurs, they fold spontaneously and do not require other post-translational modifications

i. Do not account for waste products

Answer 1

Proteins = 613, translated regions = 613X3 = 1839 nucleotides

Poly A aa = 210, untranslated nucleotides = 400

Total nucleotides transcribed = 1839+210+400 = 2449 Nucleotides

5 ATPs/ nucleotides = 2449X5 = 12245 ATPs

1. Net consumption of ATP/amino acid is 9 thus, 613X9X20 = 110340

Total no of ATP = 110340+12245 = 122595

2. 36 molecules of ATPs are produced thus the moleceule of glucose needed = 122585/36 = 3405 molecules of glucose

3. 2 molecules of ATPs are produced in anaerobic conditions = 122585/2 = 61292 glucose

4. ATP produced by palmitic acid in presence of glucose is 106

106X3 = 318 ATPs

Thus, 122585/318 = 385 Approx.

5. ATP produced by palmitic acid in absence of glucose is 2

2X3 = 6 ATPs

Thus, 122585/6 = 20430 Approx.