TLS Online TPP Program

#Question id: 3830


Why is DNA damage in skin cells from exposure to excessive UV light not completely reversed by photoreactivation?

#Unit 3. Fundamental Processes
  1. DNA photolyase in humans is activated only under conditions of heat shock.

  2. Humans lack a photoreactivation repair mechanism.

  3. The presence of histones greatly slows photoreactivation, thus humans depend primarily on other forms of DNA repair.

  4. Photoreactivation is specific for the removal of thymine dimers. Thymine dimers do not form in human DNA.

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TLS Online TPP Program

#Question id: 71

#Unit 1. Structure and Function of Biomolecules

Which of the following is not the priority rule for R, S Configuration?

TLS Online TPP Program

#Question id: 72

#Unit 1. Structure and Function of Biomolecules

For the reaction catalyzed by the enzyme hexokinase: Glucose + ATP → glucose 6-phosphate + ADP the equilibrium constant, Keq, is 7.8 × 102. In living E. coli cells, [ATP] = 5 mM, [ADP] = 0.5 mM, [glucose] = 2 mM, and [glucose 6-phosphate] = 1 mM. Which of the following conclusions made on the basis of the above calculations is incorrect?

TLS Online TPP Program

#Question id: 73

#Unit 1. Structure and Function of Biomolecules

Match the Variation of Reaction Spontaneity (Sign of ΔG) given in Column I with the Signs of ΔH and ΔS given in column II.

COLUMN I

COLUMN II

 

 

 

  ΔH

ΔS

ΔG = ΔH – TΔS

1.

+

a. The reaction is both enthalpically and entropically opposed. It is nonspontaneous (endergonic) at all temperatures.

2.

 −

− 

b. The reaction is enthalpically opposed (endothermic) but entropically favored. It is spontaneous only at temperatures above T = ΔH/ΔS.

3.

+

+

c. The reaction is enthalpically favored but entropically opposed. It is spontaneous only at temperatures below T = ΔH/ΔS.

4.

+

d. The reaction is both enthalpically favored (exothermic) and entropically favored. It is spontaneous (exergonic) at all temperatures.

TLS Online TPP Program

#Question id: 73

#Unit 1. Structure and Function of Biomolecules

Match the Variation of Reaction Spontaneity (Sign of ΔG) given in Column I with the Signs of ΔH and ΔS given in column II.

COLUMN I

COLUMN II

 

 

 

  ΔH

ΔS

ΔG = ΔH – TΔS

1.

+

a. The reaction is both enthalpically and entropically opposed. It is nonspontaneous (endergonic) at all temperatures.

2.

 −

− 

b. The reaction is enthalpically opposed (endothermic) but entropically favored. It is spontaneous only at temperatures above T = ΔH/ΔS.

3.

+

+

c. The reaction is enthalpically favored but entropically opposed. It is spontaneous only at temperatures below T = ΔH/ΔS.

4.

+

d. The reaction is both enthalpically favored (exothermic) and entropically favored. It is spontaneous (exergonic) at all temperatures.

TLS Online TPP Program

#Question id: 74

#Unit 1. Structure and Function of Biomolecules

The enthalpy and entropy of the initial and final states of a reacting system are shown in the table. Calculate the change in free energy for the reaction when the temperature is 4°C.

TLS Online TPP Program

#Question id: 75

#Unit 1. Structure and Function of Biomolecules

The experimental approach taken in current biological investigations presumes that ________.