Question

BIOCHEMISTRY

1) consider the following 2 scenarios and answer:

a) When you isolated a hot thermal vents of the ocean floor and another soil bacteria that lives in cold dark place. which one will have the higher GC content and why?

b) In a double stranded RNA containing 40% cytosine, spontaneous deamination occurs and 20% of the cytosine is converted to uracil. A repair enzyme comes and fills the correct complement for the Uracil. what will be the melting point of the coded RNA?

2) The enzyme succinate dehydrogenase acts on succinate and convert it to fumarate tn the TCA cycle. In the presence of malonate the apparent km reduced but the vmax remains unaltered. What can you conclude about the type of inhibition by malonate and the structure of malonate?

3) A short fragment of a double -stranded DNA is heated to 60 degress celsius and the student monitirs the reaction by UV spectroscopy. What will happen to the absorbance when th temperature increased and why?

Answer 1

A. The bacteria isolated from thermal went will have higher GC content because this bacteria lives under high temperature and therefore the DNA is prone to melting. So to avoid melting, more amount of GC content will be found in this bacteria. This is because there are three hydrogen bonds between guanine and cytosine which are difficult to break as compared to to hydrogen bonds present between adenine and thymine.

B.

As per chargaff rules,

For double stranded nucleic acid,

A = T or U

G = C

Initially,

C = 40%, so, G = 40%

A = U = 10%

After mutation,

C = 20%

U = 10 + 20 = 30

So, G = 20%

A = 30%

Melting temperature = 2 (A + U) + 4 (G + C) = 2 (60) + 4 (40) = 120 + 160 = 280

2. In the question it is given that when the malonate inhibitor is present, Km is decreased and maximum velocity is an altered. This happens when ever there is a type of competitive inhibition.

Competitive inhibition is the mechanism of presence of a competitive inhibitor which is structurally similar to the substrate molecule and binds to the active site of enzyme and therefore prevents the binding of substrate to the enzyme. However this type of inhibition is reversible because if the concentration of substrate molecules is increased, normal catalytic activity of the enzyme is restored.

3. At 60 degree Celsius, double-stranded DNA molecule will be denatured to single-stranded molecules. This will result in the exposure of nitrogenous bases which are present in between the sugar phosphate backbone. Because of this, the number of species absorbing light will also be increased and therefore the overall absorption of the DNA molecule increases when it is denatured at high temperature.

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