The structure of alpha helix is stabilized by hydrogen bonds between the hydrogen atom attached to the electronegative nitrogen atom of a peptide linkage and the electronegative carbonyl oxygen atom of the fourth amino acid on the amino-terminal side of that peptide bonds. Within the helix, every peptide bond (except those close to each end of the helix) participates in such hydrogen bonding. Each successive turn of the helix is held to adjacent turns by three to four hydrogen bonds, conferring significant stability on the overall structure. Which of the following are correct statements regarding these findings?

A. At the ends of a helical segment, there are always three or four amide carbonyl or amino groups that participate in this stabilised helical pattern of hydrogen bonding.

B. Helix ends are exposed to the surrounding solvent, where they hydrogen-bond with water, or other parts of the protein may cap the helix to provide the needed hydrogen-bonding partners.

C. Helix can form in polypeptides consisting of either L- or D-amino acids but a D-amino acid will disrupt a regular structure consisting of L-amino acids, and vice versa.

D. The most stable form of a helix consisting of L-amino acids is left-handed.

E. 310 helix occupies similar place as turns in Ramachandran plot due to its confirmation

#Question id: 10372

#Unit 6. System Physiology – Plant

Nod genes, which NodD activates, code for nodulation proteins, most of which are involved in the biosynthesis of Nod factors such as;

 a) Nod factors are lipochitin oligosaccharide signal molecules

 b) Nod factor shave a chitin β-1→ 4-linked N-acetyl-D-glucosamine backbone

 c) These N-acetyl-D-glucosamine backbone varying in length from three to six sugar units

 d) A fatty acid chain on the C-2 position of the nonreducing sugar determine the length and degree of saturation of the fatty acyl chain by NodL

 Which of the following is incorrect?

#Question id: 10371

#Unit 6. System Physiology – Plant

There are three essential nod gene for every bacterial species that is−NodA, NodB and NodC, that are required for synthesizing this basic structure such as;

a) NodA is an N-acyltransferase that catalyzes the addition of a fatty acyl chain

b) NodB is a chitin-oligosaccharide synthase that links the acetyl group of the terminal nonreducing sugar

c) NodC is a chitin-oligosaccharide synthase that links N-acetyl-D-glucosamine monomers

d) NodB is a chitin-oligosaccharide deacetylase that removes the acetyl group from the terminal nonreducing sugar

e) NodC is a chitin-oligosaccharide deacetylase that removes links N-acetyl-D-glucosamine monomers

Which of the following statements about NOD Factor is incorrect?

#Question id: 10367

#Unit 6. System Physiology – Plant

Cyanobcteria also fixes nitrogen under anaerobic conditions without  heterocyst where?

#Question id: 10366

#Unit 6. System Physiology – Plant

Cyanobacteria can fixes nitrogen in an anaerobic conditions. Which of the following statements about heterocyst which is specialized cell of blue-green algae is incorrect?

#Question id: 10365

#Unit 6. System Physiology – Plant

Why the nitrogenase enzymes catalyzes the nitrogen fixation reaction only in microanaerobic or anaerobic conditions?

#Question id: 10364

#Unit 6. System Physiology – Plant

Which of the following is the most common type of symbiosis occurs between members of the plant family and soil bacteria?