DNA structure

Question 1

How many H bonds are present in A + T association?

Answer 1

2 H bonds

Question 2

Which base binds to Adenine in DNA?

Answer 2

Thymine

Question 3

Which base bonds to Guanine in DNA?

Answer 3

Cytosine

Question 4

How many H bonds are present in G + C association?

Answer 4

3 H bonds

Question 5

How many carbon rings are in purines? give 2 examples

Answer 5

2 carbon rings
Adenine
Guanine

Question 6

How many carbon rings are in pyrimidines? give 2 examples

Answer 6

1 carbon ring
Thymine
Cytosine

Question 7

Describe Watson and Crick’s model of DNA

Answer 7

-Complementary A-T and G-C H bonded base pairs
- Antiparallel strands (5’-3’ polarity is in different directions)
- Double helical structure
- Major and minor grooves

Question 8

Describe eukaryotic chromosomes

Answer 8

Linear molecules, held in the nucleus of the cell
Often lots of chromosomes per genome
E.g human genome - 22 pairs of chromosomes + 2 sex chromosomes. From 5x10 7 - 2.5x10 9 base pairs

Question 9

Compare the origins of replication in human vs E. coli genomes

Answer 9

A single origin of replication in the E. coli genome Vs 10s of thousands of origins in the human genome
→ Bidirectional replication forks

Question 10

Describe prokaryotic genomes

Answer 10

• Bacteria generally have a single, circular chromosome
• Size typically a few million bp (smaller and more compact than eukaryotes)
• Plasmids are often found - also circular:
• Size typically a few thousand bp
• Can carry a variety of advantageous genes e.g Antibiotic resistance cassettes
• Passed between cells by conjugation

Question 11

What are the roles of DNA binding domains in proteins?

Answer 11

Regulate gene expression
Cut DNA at specific sequences
Protect DNA

Question 12

Give 3 examples of DNA binding domains in proteins.

Answer 12

Transcriptional regulators
Restriction endonucleases
Histones

Question 13

Describe the function of transcriptional regulators

Answer 13

Bind to regulatory sequences near the gene promoters to either stimulate/ block transcription.
They do this by bending into an unfavourable shape
E.g lac operon in E.coli → enzyme for breaking down lactose sugar

Question 14

Describe the function of restriction endonucleases

Answer 14

Cut DNA at specific (normally palindromic) sequences 6-10bp
Originated in bacteria to restrict the action of viruses