Question

define nucleotide?
1)define nucleotide
2)summarize the structure of a nucleotide,including the following:
a)the three molecules that are bonded together to form a nucleotide.
b)show how the carbons of deoxyribose are numbered.
c)state which number carbon is bonded to the phosphate
d)state which number carbon is bonded to the nitrogenous base

3,define nucleotide,DNA strand,Double stranded DNA,DNA helix

4)state which type of bond connects nucleotides together to form a strand of DNA, and state where that bond is located.

5)state which nitrogenous bases are able to hydrogen bond to eachother.

6)define antiparallel and summarize why we say that one strand of DNA runs from 5' to 3' and the other runs from 3' to 5'.
7)State the differences between the structure of DNA and the structure of RNA

Answer 1

1. Nucleotides are the monomers or building blocks of DNA and RNA.

2. a) Each nucleotide consists of 3 molecules:

i) Pentose sugar: Ribose (RNA) and Deoxyribose (DNA).

ii) Phosphate group: It is a chemical derivative of phosphoric acid. (PO₄^2-).

iii) Nitrogenous bases: These are nitrogen containing planar, hydrophobic, weak bases.
There are two basic types of nitrogenous bases i.e. Pyrimidines ( Cytosine, Thymine/Uracil) and Purines (Adenine and Guanine).

b) Deoxyribose  sugar has total 5 carbons (Pentose) the Carbon of aldehyde group is considered as the first Carbon and the Carbon attached to the phosphate is labelled 5.

c) Carbon 5 of deoxyribose sugar is attached to phosphate group.

d) The Carbon bonded to nitrogenous bases is Carbon one of deoxyribose.

3) Nucleotide is a building block of Nucleic acids, DNA strand is chain of nucleotides connected with each other through phosphodiester bonds, Two polynucleotide chains coiled around each other in an anti parallel direction form double stranded DNA, DNA helix describes the appearance of double stranded DNA composed of two anti parallel chains of nucleotides twisted around each other in a clockwise direction.

4) Two stranded of DNA in a helix are attached to each other with the help of hydrogen bonds formed between the nucleotides of opposite strands.

5) Adenine form two hydrogen bonds with thymine and Guanine form 3 three hydrogen bonds with Cytosine. Hydrogen bonds are formed between Nitrogen or Oxygen and Hydrogen of the opposite strand.

6) Two strands of DNA are anti parallel to each other because the orientation of deoxyribose sugar is opposite in the two strands. 5’ and 3’ represents the carbon number of the pentose sugar. Each strand of a linear DNA has a free 5’ end and a 3’ end. So anti parallel strands have opposite orientations of 5’ and 3 ‘ ends.

7)

DNA	RNA
Deoxyribose sugar	Ribose sugar
Double stranded	Single stranded
Thymine instead of uracil	Uracil instead of thymine