DNA

Question 1

Why does the double helix have a major and minor groove?

Answer 1

Uneven spacing between the bases

Question 2

Why is RNA less stable than DNA?

Answer 2

RNA has an OH instead of H making it susceptible to hydrolysis

Question 3

What is the difference between purines and pyrimidines?

Answer 3

Purine = 2 rings, 9 members
Pyrimidine = 1 ring, 6 members

Question 4

What are the purine bases?

Answer 4

Adenine and guanine

Question 5

What are the pyrimidine bases?

Answer 5

Cytosine, Guanine and Uracil

Question 6

What is Chargaff’s rule?

Answer 6

Ratio of A and T= 1:1 and C and G = 1:1

Question 7

Why is some DNA stronger than others?

Answer 7

Higher proportion of C-G base pairs (3 H bonds)

Question 8

What is the distance of H bonds in the C-G pair?
What about A-T?

Answer 8

3Å
2.8Å

Question 9

Describe the A form of DNA

Answer 9

Short and wide (diameter 2.2nm)
Deep major groove and wide minor groove
11 base pairs per right hand turn
A form is only seen in low humidity conditions

Question 10

Describe the B-form of DNA

Answer 10

Longer and narrower than A form
Diameter of 2nm
10 base pairs per right-hand turn
Found in high humidity conditions
Closest to dna found in cells

Question 11

Describe the Z form of DNA

Answer 11

Long and thin
Deep minor groove
Alternating purine and pyrimidine bases
Can exist as left or right handed turn
Diameter of 1.8nm
Left handed helix has a zig zag orientation

Question 12

Practice reading DNA sections u mong

Question 13

How many genes on the X and Y chromosomes in humans?

Answer 13

X chromosomes = 900 genes
Y chromosomes = 55 genes

Question 14

Give an example of a pseudoautosomal region

Answer 14

SRY on Y chromosome: initiates male sex determination, starts seminiferous tubule development

Question 15

What is the difference between euchromatin and heterochromatin?

Answer 15

Euchromatin: less condensed
Heterochromatin: heavily condensed

Question 16

Describe the state of heterochromatin

Answer 16

Solenoid 30nm fibre
Genes not expressed

Question 17

Describe the state of euchromatin

Answer 17

Beads on a string
Genes expressed

Question 18

What is a nucleosome?

Answer 18

Histone core with DNA wrapped around it
Basic repeating subunit of chromatin inside the nucleus

Question 19

Describe an octamer of histones

Answer 19

Core : H2A, H2B, H3 and H4 proteins (2 of each)
Core wrapped with DNA
H1 protein on outside of DNA
Octamers bind about 147 bp DNA, held together by linker sequence, which are 38-53 bp long

Question 20

What is the purpose of solenoids?

Answer 20

Condense the DNA and create DNA loops to do this further
Solenoids are supercoiled

Question 21

When in the cell cycle is DNA replicated?

Answer 21

S phase