!!!! Organisation of Genomes

Question 1

[structure] Compare LOCATION of prokaryotic, eukaryotic and viral genomes

Answer 1

Prokaryotic - nucleoid
Eukaryotic - membrane-bound nucleus
Viral - enclosed in capsid

Question 2

[structure] Compare GENOME SIZE of prokaryotic, eukaryotic and viral genomes

Answer 2

• Eukaryotic > Prokaryotic

Viral - DNA viruses > RNA viruses

Question 3

[structure] Compare APPEARANCE of prokaryotic, eukaryotic and viral genomes

Answer 3

Prokaryotic - single, cicular dsDNA
Eukaryotic - multiple, linear dsDNA
Viral - either RNA/DNA; single/segmented; ds/ss; circular/linear

Question 4

[structure] Compare ASSOCIATION WITH PROTEINS of prokaryotic, eukaryotic and viral genomes

Answer 4

Prokaryotic - associated with non-histone proteins to form loop domains which subsequently supercoil to form condensed DNA
Eukaryotic - associated with proteins e.g histone proteins, scaffold proteins
Viral - not associated with any, but enclosed by protein coat called capsid

Question 5

[structure] Compare LEVEL OF DNA PACKING of prokaryotic, eukaryotic and viral genomes

Answer 5

Prokaryotic - relatively low
Eukaryotic - high
Viral -

Question 6

[structure] Compare PRESENCE OF EXTRA-CHROMOSOMAL DNA in prokaryotic, eukaryotic and viral genomes

Answer 6

Prokaryotic - Plasmids (small, autonomously replicating DNA molecules), in some
Eukaryotic - none within nucleus, except mtDNA and chloroplast DNA
Viral - None

Question 7

[organisation] Compare NUMBER OF GENES in prokaryotic, eukaryotic and viral genomes

Answer 7

Eukaryotic > Prokaryotic > Viral

Some viral genomes have overlapping genes to enable genome to be extensively utilised (mRNA undergoes alternative splicing)

Question 8

[organisation] Compare PRESENCE OF NON-CODING REGIONS in prokaryotic, eukaryotic and viral genomes

Answer 8

Prokaryotic - Not common
Eukaryotic - Common
Viral - Not common

Question 9

[organisation] Compare PRESENCE OF INTRONS in prokaryotic, eukaryotic and viral genomes

Answer 9

Prokaryotic - None
Eukaryotic - Many
Viral - Some viruses

Question 10

[organisation] Compare PRESENCE OF PROMOTERS in prokaryotic, eukaryotic and viral genomes

Answer 10

Prokaryotic - Yes, Pribnow box
Eukaryotic - Yes, TATA box
Viral - Yes

Question 11

[organisation] Compare PRESENCE OF ENHANCERS/SILENCERS in prokaryotic, eukaryotic and viral genomes

Answer 11

Prokaryotic - None
Eukaryotic - Common
Viral - Some viruses

Question 12

[organisation] Compare PRESENCE OF REPEAT SEQUENCES in prokaryotic, eukaryotic and viral genomes

Answer 12

Prokaryotic - Few
Eukaryotic - Many
Viral - Few

Question 13

[organisation] Compare PRESENCE OF OPERONS in prokaryotic, eukaryotic and viral genomes

Answer 13

Prokaryotic - Many
Eukaryotic - Few e.g Yeast
Viral - None

Question 14

[organisation] Compare NUMBER OF ORIGINS OF REPLICATION in prokaryotic, eukaryotic and viral genomes

Answer 14

Prokaryotic - 1
Eukaryotic - Many
Viral - 1

Question 15

Function of Promoter (PROXIMAL control element)

Answer 15

• DNA sequence located upstream of gene

- mediates binding of basal transcription factors and RNA polymerase, thereby allowing transcription to begin

Question 16

Function of Enhancer (DISTAL control element)

Answer 16

• DNA sequence located upstream of gene / far from promoter
• mediate binding of activators (specific TFs) and thus help to from transcription initiation complex
• increase rate of transcription

Question 17

Function of Silencer (DISTAL control element)

Answer 17

• DNA sequence located upstream of gene / far from promoter
• mediate binding of repressors (specific TFs) and thus help to from transcription initiation complex
• decrease rate of transcription