DNA structure

Question 1

classes of Nucleobases

Answer 1

pyrimidines, longer name shorter molecule = C, T,U
pyrine, shorter name longer molecule = A, G
G –> C = 3 H bonds
A –> T = 2 H bonds

Question 2

Ribose

Answer 2

OH on each corner = allow for more further possible bonding patterns

Question 3

Deoxyribose

Answer 3

OH missing on 2nd C = leaves bonding for phosphates (carbons 3 and 5) and nucleobases (carbon 1)

Question 4

phosphates

Answer 4

links 5’ to 3’ asymmetrically = gives direction to curl
provides back bone

Question 5

Anti parallel duplex

Answer 5

more G -C pairs = more stable
to get a complimentary strand:
1. split into triplets
2. correct complimentary bases
3. reverse the order to get in the 5’ to 3’ direction

Question 6

why is the double helix formed?

Answer 6

1. base pair H bonds
2. pi stacking of nucleotides compacts vertically
3. -ve charged phosphates repel each other

Question 7

why is the double helix advantageous?

Answer 7

close packing so no water can get inside the helix
keeps the phosphates separated

Question 8

alternative forms of DNA

Answer 8

B- DNA: right handed
A-DNA: right handed but looser in structure
Z-DNA: left handed = undergone methylation