DNA

Question 1

How many rings do purine and pyrimidine have

Answer 1

Purine is 9 membered and pyrimidine is 6 membered

Question 2

What are the chemical name of all the nitrogenous bases

Answer 2

Adenine - 6 aminopurine
Guanine - 6 oxy 2 aminopurine
Cytosine - 2 oxy 4 aminopyrimidine
Thymine - 5 methyl 2,4-dioxypyrimidine

Question 3

Characteristics of nitrogenous bases

Answer 3

They are heterocyclic structure, planer, aromatic and insoluble in water.

Question 4

What kind of sugar pucker found in DNA

Answer 4

A DNA - C3
B DNA - C2
Z DNA - C2 & C3

Question 5

Sugar and nitrogenous bases are joined by which carbon atom and nitrogen atom

Answer 5

Carbon 1
Pyrimidine N1
Purine N9

Question 6

Nucleoside joined to phosphate group by which carbon atom

Answer 6

C5

Question 7

Chargaff’s Rule

Answer 7

%A = %T, %G = %C
Molar ratio A to T and G to C equals 1
Sum of purine equals to sum of pyrimidine
Percentage of C plus G isn’t equal to A plus T

Question 8

Who gave DNA double helix model and x ray diffraction data of DNA fibres

Answer 8

Double helix - Watson and Crick
X Ray - Franklin and Wilkins

Question 9

What is at the core and periphery of B DNA

Answer 9

Core - bases
Periphery - sugar phosphate chain

Question 10

Diameter of A, B and Z DNA and their sugars

Answer 10

A DNA - 23 Å, C3 endo
B DNA - 20 Å C2 endo
Z DNA - 18 Å C2 and C3 endo

Question 11

Where is the major groove and minor groove formed in B DNA

Answer 11

Major Groove - N7 Purine
Minor - N3 Purine

Question 12

Helical turn of all the DNA

Answer 12

A DNA - 11
B DNA - 10
Z DNA - 12

Question 13

Pitch/ axial height and confirmation of all the DNA

Answer 13

A DNA - 24.6 Å, anti
B DNA - 34 Å, anti
Z DNA - 45.6 Å, anti and syn

Question 14

Major and minor groove of all DNA

Answer 14

A DNA - Major - Narrow and deep,
Minor - Wide and shallow
B DNA - Major - Wide and deep
Minor - Narrow and deep
Z DNA - Major - Flat
Minor - Narrow and deep

Question 15

Where is A DNA found?

Answer 15

DNA RNA Hybrid

Question 16

Which sequence is favoured by Z DNA

Answer 16

G and C

Question 17

How is Z DNA formed from B DNA

Answer 17

Negative supercoiling (topoisomerase), 5 methylated cytosine, high salt conc.

Question 18

Who described the triple helical nucleic acid

Answer 18

Falsenfeld and Rich

Question 19

Who described the triple helical nucleic acid

Answer 19

Falsenfeld and Rich

Question 20

What kind of strand form a triple helix. Name circumstances for forming triple DNA

Answer 20

A dsDNA having homopurine and homopyrimidine sequence strand.
Low pH forms triple stranded DNA

Question 21

Name the orientation and hoogsteen hydrogen bonding in the case of
A. Pyrimidine rich on homopurine rich strand
B. Purine rich on homopurine rich strand

Answer 21

A. Orientation is parallel and hoogsteen hydrogen bonding
B. Orientation is antiparallel and reverse hoogsteen hydrogen bonding

Question 22

What is H DNA

Answer 22

When a triple DNA formed that is intramolecular triplex

Question 23

Building blocks of G Quadruplex

Answer 23

G quartets or G tetrads

Question 24

G Quadruplex formed by which bond?

Answer 24

Cyclic hoogsteen hydrogen bonding

Question 25

G Quadruplex stability dependent on?

Answer 25

Monovalent cations, K and Na. And with coordination of positively charged cations with electronegative O6 atom

Question 26

What does intramolecular and intermolecular folding requires in G Quadruplex

Answer 26

Intramolecular needs four or more G rich sequences Intermolecular needs two or four strands that give rise to parallel or antiparallel strands.

Question 27

What stabilises DNA

Answer 27

Base stacking interaction and hydrogen bond

Question 28

Factors that affect melting temperature of DNA

Answer 28

Hydrogen bonds, more H bonds more melting point Presence of Mg and Na, they neutralize the repulsion between phosphate group