Question

11. Which of the following is NOT a non-covalent bond that gives form to proteins ?

(A) H-bond     (B) ionic bond (C) disulfide bridge      (D) van der Waals interactions

12. Which of the following would prevent transcription of the lactose operon?

(A) lactose       (B) allolactose (C) tryptophan             (D) glucose

13. Which of the following would prevent transcription of the tryptophan operon?

(A) lactose       (B) allolactose             (C) tryptophan             (D) glucose

Answer 1

11.  the following is NOT a non-covalent bond that gives form to proteins :

(B) ionic bond

Explanation = Ionic bond is not a type of noncovalent bond , because ionic bonds are formed by donating an electron to the other atom participating in the bond.

while covalent bonds are formed by sharing of electrons equally between atoms.

therefore ionic bond is NOT a non-covalent bond that gives form to proteins.

INCORRECT OPTIONS =

(A) H-bond (C) disulfide bridge      (D) van der Waals interactions

These 3 are the noncovalent types of interactions that gives to form proteins.

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12. The following would prevent transcription of the lactose operon

(D) glucose

Explanation = when glucose levels are high, no cAMP is made, Catabolite activator protein(CAP) can not bind DNA without cAMP, so transcription occurs only at a low level. or transcription is prevented by glucose therefore it acts to prevent transcription of the lactose operon.

INCORRECT OPTIONS=

(A) lactose       (B) allolactose (C) tryptophan   

LACTOSE and allolactose acts as inducer of lac operon.

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13. the following would prevent transcription of the tryptophan operon

  (C) tryptophan

Explanation = When there is high level of tryptophan , then tryptophan binds to the trp repressor and causes it to change shape, converting into its active form.The trp repressor with the bound tryptophan attaches to the operator , blocking RNA polymerase from binding to the promoter and preventing transcription of the operon.