Question

1) In a biochemical reaction in which ΔH < 0 and ΔS > 0,

Select one:

a. the reaction is spontaneous

b. the reaction is endothermic

c. the reaction is endergonic

d. ΔG is positive

2) NAD⁺ and FAD are often referred to as

Select one:

a. redox proteins

b. polymers

c. reduced dinucleotides

d. electron-carrying coenzymes

3) What is [P]/[R] when ΔG = ΔG°´?

Select one:

a. –1

b. 0

c. 1

d. 2.3

4) For the binding reaction A + B → AB, the dissociation constant is equal to

Select one:

a. [AB]/([A] + [B])

b. ([A] + [B])/[AB]

c. K_eq

d. a and c

Answer 1

1) In a biochemical reaction, in which ∆H<0 and ∆S>0, the reaction is spontaneous.

• ie, the answer is (a). The reaction is spontaneous.
• Spontaneous reaction is a reaction which occurs spontaneously or on its own without any external influence.
• Spontaneous reaction occurs when change in enthalpy decreases or is negative and change in entropy increases or is positive with gibbs free energy or ∆G <0.
• ∆G depends on both change in enthalpy and entropy.
• ∆G=∆H-T∆S
• Thus when ∆G and ∆H are negative and ∆S>0 the reaction is spontaneous at all temperatures.

(2) The answer is (d). Electron carrying coenzymes.

• First of all , coenzymes are non protein molecules which are necessary for the better functioning of enzymes and helps to carry out various biochemical processess along with enzymes.
• NAD stands for Nicotinamide Adenine Dinucleotide and NAD+ is the oxidized form of NAD.
• It is one of the most important electron carriers during cellular respiration.
• Nad molecules can exist in both oxidised and reduced form by either donating or accepting electronsduring cellular respiration.
• FAD stands for Flavin Adenine Dinucleotide.
• FAD in its oxidised form accepts 2 hydrogen atoms and forms FADH2.
• Similarly it donates hydrogen atoms and electrons during respiration to produce energy.
• Thus NAD+ and FAD are both electron carrying coenzymes as they are involved in redox reactions of cellular respiration.

(3) The answer is 0.

• ∆G° is the standard free energy change when all the reactants and products are in their standard state or it is the gibbs energy change for a system under standard conditions. ie, when pressure equals 1atm and temperature equals 298.15 K.
• According to the reaction, ∆G= ∆G°+RTlnK
• If ∆G=∆G°, RTlnK should be zero. ie, RTlnK=0
• According to the Ideal gas equation , PV=nRT
• P/R will be 0.

(4)The answer is (b).

• Dissociation constant is defined as the extent to which a substance in a solution is dissociated into its constituent ions.
• For the binding reaction A+B=AB
• Kd or dissociation constant can be determined by the equation Kd=(A+B)/AB.