Chromosomes and Genomes

Question 1

Give examples of:

• Double-stranded DNA
• Single-stranded DNA
• Double-stranded RNA
• Single-stranded RNA

Answer 1

1. Human
2. M13 Bacteriophage
3. Bluetongue virus
4. Retrovirus

Question 2

Give examples of:

• Circular ds DNA
• Linear ds DNA
• Linear ss DNA
• Circular ss DNA

Answer 2

1. E. coli
2. Human
3. Parvovirus
4. M13 Bacteriophage

Question 3

Explain the sequence of a retrovirus ?

Answer 3

R - Repeat region for insertion into host genome - they also enhance expression
P - Packaging signal for assembly of new virus particles
gag - capsid protein
pol - Reverse Transcriptase
env - Envelope protein

Question 4

Rank genome the size variation of viruses, bacteria and eukaryotes ?

Answer 4

1. Viruses
2. Bacteria
3. Eukaryotes

Question 5

What is the smallest free-living genome ?

Answer 5

Pelagibacter ubique

Question 6

What are the special features of Pelagibacter ubique ?

Answer 6

• No pseudogenes, phage genes, or recent gene duplications – no junk!
• Very few regulatory genes
• Very small intergenic regions

Question 7

Polyomavirus genomic organisation is designed to pack ?

Answer 7

Maximal information (6 genes) into minimal space (5kbp). This paradox is achieved by the use of both strands of the genome DNA and overlapping genes

Question 8

The origin of replication is surrounded by ?

Answer 8

By non-coding regions which control transcription.

Question 9

What kind of chromosome does a bacteria contain ?

Answer 9

Most bacteria contain a single chromosome (and often plasmids as well)

Question 10

Some bacteria contain an additional ?

Answer 10

Replicons which can be considered either megaplasmids or mini chromosomes

Question 11

How many origin of replication do bacterial chromosomes have ?

Answer 11

Bacterial chromosomes have single origin of replication

Question 12

What happens to genes that are closer to the origin ?

Answer 12

Genes closer to origin can have higher copy number (up to 4 copies) in dividing cells due to multiple initiations

Question 13

How are genes often orientated ?

Answer 13

Genes are often oriented in direction of replication

Question 14

What does this orientation prevent ?

Answer 14

This may prevent head-on collision between replication fork and transcription machinery

Question 15

What is the minimal genome?

Answer 15

The theoretical minimal set of genes required to sustain cellular life

Question 16

What can the organism’s genes be divided into ?

Answer 16

• Essential genes required for a core set of functions required for basic cellular processes (e.g. DNA replication, protein synthesis, basic transcription machinery)
• Genes that are non-essential but that confer a selective advantage within the specific environmental niche it occupies

Question 17

What is life ?

Answer 17

The state characterised by the ability to get and use energy, reproduce, grow, and respond to change