1 - Nucleic acids and chromosomes

Question 1

What is the difference between a nucleoside and a nucleotide?

Answer 1

A nucleotide has a phosphate group.

A nucleoside does not.

Question 2

Which bases are ‘purines’ and which are ‘pyrimidines’?

Answer 2

• adenine and guanine (AG)=purine (double ring)

- thymine, cytosine and uracil (CUT)=pyrimidine (single ring)

Question 3

What type of bind joins adjacent nucleotides?

Answer 3

Phosphodiester

Question 4

How many base pairs are there in one helical turn of DNA?

Answer 4

Around 10

Question 5

How is melting and re annealing of complementary strands of DNA done?

Answer 5

• melting/denaturing=heat/low salt

- reannealing/hybridisation=cooling/high salt

Question 6

How many H bonds to the complementary base pairs form?

Answer 6

• A and T=2

- G and C=3

Question 7

Compare:
1) the number of base pairs
2) the structure
3) the length of the genomes
In Homo sapiens and E.coli

Answer 7

1) E.coli=4.6x10^6 H.sapiens=3x10^9 (I.e. Many more)
2) E.c= single circular double stranded molecule
H.s= chromosomes that contain linear DNA
3) E.c.= 1.4mm length H.s=2m long

Question 8

What is chromatin?

Answer 8

When DNA is tightly wrapped around proteins

Question 9

What is a nucleosome?

Answer 9

2 turns of DNA tightly wrapped with proteins
8 histones
causes 7 fold condensing
histones are positively charged, so interacts closely with the negatively charged sugar-phosphate background