Molecular Genetics

Question 1

No of strands in DNA

Answer 1

Double stranded molecule

Question 2

Nitrogen bases in DNA

Answer 2

Purine bases:

• Adenine (A)
• Guanine (G)

​Pyrimidine bases:

• Cytosine (C)
• Thymine (T)

Question 3

Backbone of DNA

Answer 3

Covalently bonded deoxyribose sugar phosphate residues

Question 4

In DNA, what is the bond between deoxyribose sugar and residues?

Answer 4

Covalent bond

Question 5

In DNA, which nitrogen base pairs with which base?

Answer 5

Purine with pyrimidine:

• A and T: Adenine pairs with Thymine (by 2 H-bonds)​
• C and G: Cytosine pairs with Guanine (by 3 H-bonds)

(A, G are purine bases & C, T are nitrogen bases)

Question 6

In DNA, how are two antiparallel strands held together?

Answer 6

By hydrogen bonds

Question 7

In DNA, how can the hydrogen bonds (bondage between 2 strands) be disrupted & re-formed?

Answer 7

Disrupted by heating

Reformed by cooling

Question 8

Full form fo DNA & RNA

Answer 8

DNA = Deoxyribonucleic acid

RNA = Ribonucleic acid

Question 9

Where does DNA transcription occur?

Answer 9

Nucleus

Question 10

In the nucleus, DNA is transcribed into-?

Answer 10

mRNA (messenger RNA)

Question 11

Where does translation of mRNA occur?

Answer 11

Ribosome of cytoplasm

Question 12

In ribosome of cytoplasm, mRNA is translated into-?

Answer 12

Polypeptide chain

Question 13

Main structural difference between DNA & RNA

Answer 13

Strand: DNA >> double-stranded & RNA >> single-stranded

Nitrogen base: Thymine of DNA is replaced by Uracil in RNA (Rests are same)

Sugar backbone: DNA >> deoxyribose sugar; RNA >> ribose sugar

Question 14

Purpose of PCR (Polymerase Chain Reaction)

Answer 14

From very small samples of DNA >>>>> to generate large amounts of DNA

Question 15

Can PCR be adapted to use with RNA?

Answer 15

Possible, if RNA is first converted to DNA

Question 16

What was the traditional DNA sequencing method & its disadvantages

Answer 16

Traditional method:

Taken DNA of individual axons (length up to approx. 1-2 kilobases, kb) >>> amplified by single PCR reactions >>> sequenced by ‘dideoxy (Sanger) sequencing’

Disadvantages:

Very difficult & expensive to test >>

• mutation in large genes
• heterogenous disorders

Question 17

What is the new DNA sequencing method & its advantage?

Answer 17

Massively parallel sequencing technologies (since mid-2000)

Advantages:

• Single experiment reads millions DNA bases
• Cost fallen dramatically
• Single investigation for heterogenous disorders (HOCM, retinal dystrophy etc.)
• Undiagnosed conditions/phenotype >>>>> offered sequencing of whole exome (all coding genetic material) >>>>> to indentify the responsible mutation

Disadvantage:

• Requires significant infrastructure & bioinformatic expertise

Question 18

How to detect CFTR gene mutation in the delta F508 region of chromosome 7?

Answer 18

Routine molecular testing >> only looks for comonly identified mutations >> so, 15% cases are missed (& so can not exclude cystic fibrosis)

“Sequencing of whole CFTR gene” can demonstrate rare alleles