Bacterial Plasmids

Question 1

Describe the genetic prokaryotic DNA

Answer 1

• Consists of a single chromosome consisting of a circular DNA molecule = genophore
• DNA is naked = not associated with proteins
• may contain additional circular DNA molecules called plasmids

Question 2

What is a replicon ?

Answer 2

• a stretch of DNA present in plasmids that acts as an origin of replication

Question 3

Describe a typical bacterial replicon

Answer 3

• may consist of a number of elements
• the gene for plasmid-specific relplication initiation protein
• repeating units called iterons
• DnaA boxes
• adjacent AT-rich region

Question 4

What are the 2 classifications of plasmids ?

Answer 4

• conjugative plasmids
• non-conjugative plasmids

Question 5

Define Conjugative plasmids

Answer 5

contain a set of transfer genes with promote sexual conjugation between different cells

Question 6

Define non-conjugative plasmids

Answer 6

• incapable of initiating conjugation, so they can only be transferred with the assistance of conjugative plasmids

Question 7

How else can plasmids be classified ?

Answer 7

into incompatibility groups or by function

Question 8

What happens if 2 plasmids aren’t compatible ?

Answer 8

• a microbe can harbour different types of plasmids, but different plasmids can only exist in a single bacterial cell if theyre compatible
• one or the other will be rapidly lost from the cell

Question 9

What are the 5 main functional classes of plasmids ?

Answer 9

1. Fertility F-plasmids
2. Resistance plasmids
3. Col plasmids
4. Degradative plasmids
5. Virulence plasmids

Question 10

Define Fertility F-plasmids

Answer 10

• contain tra genes
• capable of conjugation & result in the expression of sex pili

Question 11

Define Resistance (R) Plasmids

Answer 11

• contain genes that provide resistance against antibiotics or antibacterial agents

Question 12

Define Degradative plasmids

Answer 12

• enables the digestion of unusual substances
• eg. toluene

Question 12

Define Col Plasmids

Answer 12

• contain genes that code for bacteriocins = proteins than can kill other bacteria

Question 13

Define virulence plasmids

Answer 13

• turns the bacterium into a pathogen

Question 14

Describe the role of Plasmids in cloning

Answer 14

• most commonly used bacterial cloning vectors
• cloning vectors contain a site than allows DNA fragments to be inserted
• after gene of interest is inserted plasmids are introduced to bacteria via transformation
• plasmids contain a selectable marker typically antibiotic resistance

Question 15

Describe plasmid use in protein expression

Answer 15

• grow bacteria containing a plasmid harbouring the gene of interest
• just as the bacterium produces proteins to confer its antibiotic resistance, can also be induced to produce large amounts of proteins from the inserted gene
• cheap and easy way of mass producing the protein
• example = insulin