Please help with all parts A) Some antibiotics form rings that stack and create
ID: 717673 • Letter: P
Question
Please help with all parts
A) Some antibiotics form rings that stack and create a pore through the membrane. Consider a cyclic polypeptide antibiotic in which each of four rings (shown as doughnuts) is composed of one instance of each of the four amino acids: serine, glycine, threonine, and alanine. If the atoms of the backbone are approximated by touching spheres of about 0.2 nanometers in diameter,estimate the circumference of the pore (presume it to be a circle) and the diameter of the largest molecule that could fit through it. Approximate the circumference ( pie diameter) to be 3-diameter. (Show work, draw a picture of the atoms of a ring and calculate.
B) Lactate dehydrogenase (the last enzyme in human anaerobic glycolysis) is a soluble, multimeric protein. If you were to try to fold a single linear polypeptide chain of lactate dehydrogenase, you would find it impossible to do so without leaving a large number of hydrophobic amino acids exposed to water. Create and describe a picture that illustrates why this should be?
Explanation / Answer
A.Peptides are conformatioally flexibilt,selectivity but have poor stability and inefficiency crossing cell membran so peptide cyclization can be perform to improve peptide selectivity, metabolic stability, and bioavailability. One of the most attractive approach it to screen a focused library to screen in which all backbone cyclic peptides have the same primary sequence ,such as ring size and position. the tubular struture of 7 -8 A inrtnal diamter and ring shaped cyclic peptides holds corriderable promise
B.
Pyruvate + NADH + H+ <----> Lactate + NAD+
LDH follows an ordered sequence. lactate oxidized NAD+ must bind to the enzyme first followed by lactate , hydride ion then happens quickly in either direction giving a mixture of the two teranary complexes( enzyme-NAD+-lactate and enzyme-NADH-pyruvate). Pyruvate dissociates from the enzyme followed by NADH. The reverse reaction that the coenzyme, NADH, must bind first before the substrate, pyruvate, can bind which is the rate limiting step . The conversion of pyruvate to lactate with the subsequent regeneration of NAD+ is a very favorable reaction.
At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. It also catalyzes the dehydrogenation of 2-Hydroxybutyrate, but it is a much poorer substrate than lactate.
The Gibbs Free energy value for thisreaction is -200kJ/mol. However, 93% of the original amount of energy still remains in lactate. This is why the reverse of this reaction, lactate to pyruvate, is so important.
The lactate dehydrogenase(LDH) catalyzes is as follows:Pyruvate + NADH + H+ <----> Lactate + NAD+
LDH follows an ordered sequence. lactate oxidized NAD+ must bind to the enzyme first followed by lactate , hydride ion then happens quickly in either direction giving a mixture of the two teranary complexes( enzyme-NAD+-lactate and enzyme-NADH-pyruvate). Pyruvate dissociates from the enzyme followed by NADH. The reverse reaction that the coenzyme, NADH, must bind first before the substrate, pyruvate, can bind which is the rate limiting step . The conversion of pyruvate to lactate with the subsequent regeneration of NAD+ is a very favorable reaction.
At high concentrations of lactate, the enzyme exhibits feedback inhibition, and the rate of conversion of pyruvate to lactate is decreased. It also catalyzes the dehydrogenation of 2-Hydroxybutyrate, but it is a much poorer substrate than lactate.
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