Question

Please answer these 3 qs and I will rate. Thank you!
The glyosidic linkage in a nucleoside forms from the C-1 carbon of the sugar to the a. N-1 nitrogen of pyrimidines b. N-2 nitrogen of purines c. N-9 nitrogen of pyrimidines d. N-6 nitrogen of purines

Answer 1

Ans)

1) a. N-1 nitrogen of pyrimidines

The glycosidic linkage in a nucleoside forms from the C-1' carbon of the sugar to the "N-1 nitrogen of pyrimidines"

Glycosidic bonds :

O-glycosidic bonds

S-glycosidic bonds

N-glycosidic bonds

C-glycosidic bonds

N-glycosidic bonds:

  N-glycosidic bonds are also called as Glycosylamines - glycosyl group attached to amine group, -NR_2.

• Glycosylamines are nucleoside that can be thought of as nucleotides without a phosphate group.
• A nucleoside consists of nucleobase(nitrogenous base) and five-carbon sugar (ribose or 2-deoxy ribose)
• A nucleotide is composed of nucleobase, ribose sugar and one or more phosphate groups.
• In nucleosides, the anomeric carbon is linked through a glycosidic bond to the N-9 of purine or N-1 of pyrimidine.
• examples:- (Cytidine, Uridine) N-1 of pyrimidine (Adenosine, Guanosine) N-9 of purine
• 
  NH2 [N1 of pyrimidine NH Но. HO OH òH OH OH cytidine oridine [N-9 of purine NH2 NH HO. -NH2 က် HO. OF OH olt Adenosine OH Guanosine
  

2) a. 3'-hydroxyl :

The last nucleotide added to a growing DNA chain has a 3'-hydroxyl on the sugar.

DNA and RNA are composed of nucleotides that are linked to one another in a chain by chemical bonds called ester bonds, between the sugar base of one nucleotide and the phosphate group of the adjacent nucleotide.

The sugar is the 3' end, and the phosphate is the 5' end of each nucleotide. The phosphate group attached to the 5' carbon of the sugar on one nucleotide forms an ester bond with the free hydroxyl on the 3' carbon of the next nucleotide.

3) b. DNA gyrase :

DNA gyrase is composed of two identical subunits. Hydrolysis of ATP by gyrase's inherent ATPase activity powers the conformational changes that are critical to the enzyme's operation.

The enzyme functions to introduce negative supercoils into closed circular DNA template;

DNA can initiate replication only on a negatively supercoiled template.