You have isolated two mutations in the Lac operon that cause constitutive expression of Lac genes. You designate these mutants Lac1– and Lac2–. Making use of an F' that carries the Lac operon with the LacY gene mutated, you construct strains that you test for both ß-galactosidase activity and Lac permease activity with results shown below.

     

Classify each mutation as dominant or recessive and as cis- or trans-acting, giving the experimental result that allows you to arrive at each conclusion. Finally, deduce what type of Lac mutation best fits the properties of Lac 1– and of Lac 2–.

#Question id: 883

#Unit 1. Molecules and their Interaction Relevant to Biology

The “core autophagy machinery” controls the initiation and growth of the autophagosome and has been divided into three main protein groups:

i. A-ATG9, B-TOR, C-PI(3) Complex

ii. A- ATG9, B-PI(3) Complex, C-TOR

iii. The TOR kinase complex acts as a negative regulator of autophagy

iv. The TOR kinase complex acts as a positive regulator of autophagy

#Question id: 884

#Unit 1. Molecules and their Interaction Relevant to Biology

The hydrogen bonds, which are central features of protein structures, then what is the reason behind it makes only minor contributions to protein stability?

#Question id: 885

#Unit 1. Molecules and their Interaction Relevant to Biology

The half-lives of many cytoplasmic proteins vary with the identities of their N-terminal residues via the  N-end rule.

a) Proteins with the “destabilizing” N-terminal residues contain Asp, Arg, Leu, Lys, and Phe with their half-lives > 2 to 3 hours

b) Proteins with the “destabilizing” N-terminal residues with their half-lives of only 2 to 3 minutes contain; Asp, Arg, Leu, Lys, and Phe

c) Proteins contain Ala, Gly, Met, Ser, Thr, and Val have half-lives of >10 hours are stabilizing N-terminal residue in prokaryotes

d) Those with the “stabilizing” N-terminal residues Ala, Gly, Met, Ser, Thr, and Val have half-lives of >20 hours in eukaryotes

Which of the following is correct?

#Question id: 886

#Unit 1. Molecules and their Interaction Relevant to Biology

An experiment of Anfinsen on ribonuclease A (RNase A) showed that proteins can be denatured reversibly by 2-mercaptoethanol and 8 M urea. The protein must therefore renature spontaneously;

a) Remove mercaptoethanol and then removal of the urea

b) Removal of the mercaptoethanol allows the protein to re-form disulfide bonds in the presence of oxygen and then removal of the urea

c) Removal of the denaturant (urea) and reductant (mercaptoethanol) allows the protein to renature and re-form disulfide bonds in the absence of oxygen

d) Adding a small amount of mercaptoethanol to the scrambled protein in the absence of O2 catalyzes its conversion to the active enzyme

Which one of the following steps will leads to regaining of the full activity of ribonuclease A (RNase A)

#Question id: 887

#Unit 1. Molecules and their Interaction Relevant to Biology

Polypeptides fold rapidly by a stepwise process, how does the polypeptide chain arrive at its native conformation?

#Question id: 888

#Unit 1. Molecules and their Interaction Relevant to Biology

Which one of the following statements about the protein folding is incorrect?