Bacterial Genetics

Question 1

Why bacteria?

Answer 1

Easy to maintain in lab in solid or liquid nutrient media

Question 2

Characteristics of bacteria?

Answer 2

• Haploid
• Doesn’t form gametes
• Genes can be transferred between them
• “Crosses” can be made between strains

Question 3

Which bacteria is on the forefront of bacterial molecular genetics?

Answer 3

E. coli

Question 4

Why E. coli?

Answer 4

• Non-pathogenic
• Rapid growth rate
• Grows in simple liquor and on solid media

Question 5

What are the components of minimal medium?

Answer 5

Sugar, various salts, water

Question 6

What type of bacteria grow on minimal medium?

Answer 6

Wild-type bacteria because they can synthesise all the other materials needed

Question 7

What do the wild type bacteria synthesise on minimal medium?

Answer 7

• Amino acids
• Vitamins
• Nucleotides
• Carbohydrates

Question 8

What does complete medium consist of?

Answer 8

Same as minimal medium but also amino acids, vitamins and nucleotides usually produced by biosynthetic pathways in wild type bacteria

Question 9

What type of bacteria will grow on complete medium?

Answer 9

Bacteria with a mutation inactivating their biosynthetic pathways

Question 10

Define auxotroph

Answer 10

Mutant bacteria that cannot synthesise essential nutrients

Question 11

Define prototroph

Answer 11

Bacterial strains that are wild-type

Question 12

Which genes are in the Trp operon?

Answer 12

TrpA, TrpB, TrpC, TrpD, TrpE

Question 13

Which amino acid is associated with the Trp operon?

Answer 13

Tryptophan

Question 14

Bacterial conjugation requires…

Answer 14

Cell-cell contact

Question 15

Lac operon in E. coli

Answer 15

Encodes enzymes that enable lactose –> galactose and glucose

Question 16

What are the parts of the lac operon?

Answer 16

Promoter, operator, lacZ, lacY, lacA

Question 17

What does lacZ code for?

Answer 17

ß-galactosidase

Question 18

What does ß-galactosidase do?

Answer 18

Lactose hydrolysis –> galactose and glucose

Question 19

What does lacY code for?

Answer 19

Lactose permease

Question 20

What does lactose permease do?

Answer 20

Increases the permeability of cells to lactose

Question 21

What does lacA code for?

Answer 21

Transacetylase

Question 22

What happens in the absence of lactose?

Answer 22

The lac repressor binds to the operator region
RNA polymerase binds to the promoter region but cannot transcribe the following structural genes as it is blocked by the lac repressor

Question 23

What happens when lactose is present?

Answer 23

Lactose binds to the lac repressor and induces a conformational change
Lac repressor can’t bind to the operator region
RNA polymerase binds to the promoter region and transcribes the structural genes so that lactose can be used as an energy source

Question 24

Is genetic exchange between bacteria bidirectional?

Answer 24

No, it’s unidirectional

Question 25

Transfer of F plasmid in bacteria

Answer 25

DNA is transferred across a physical bridge from donor to recipient
Donor strain contains a fertility factor, F+
Copy of F plasmas is transferred across F-pilus bridge to recipient

Question 26

What is the bridge between the donor and recipient bacteria during bacterial conjugation called?

Answer 26

F-pilus bridge

Question 27

What is F+?

Answer 27

Plasmid that renders carriers able to conjugate with F- recipient cells

Question 28

What causes the transfer of host chromosomal genes from high frequency recombination (Hfr) strains into F- strains?

Answer 28

The F factor