Lecture 10

Question 1

Advantages of using bacteria for genetic studies

Answer 1

• Easily cultured
• Short generation time
• Haploid
• E.coli regulary used

Question 2

E.coli DNA

Answer 2

• Most bactiera have a singular circular chromosome
• E.Chromosome is a single double-stranded circular DNA molecule
• Stored in the nuceloid
• 4.6 million bp
• 4500 genes

Question 3

Bacteriophages

Answer 3

• Viruses that infect bacteria
• Structural and functionally diverse

Question 4

Lytic life cycle

Answer 4

1. Phage uses tail fibers to stick to outer surface of host
2. The tail shealth contracts, thrusting a hollow core into the cell. The pahfe injects DNA into the host
3. The emtpty capsid of the phage is left as a “ghost” outside the cell. The cells DNA is hydrolyses
4. The cells directed by phage DNa produce phage products. ITs degraded DNA is used to make a phage genome. The phage products come together to form phages
5. Lysozyme digests bacterias cell wall, with osmosis further damaging the cell, it bursts releasing 100-200 phages

Question 5

Temperate/lysogenic Life cycle

Answer 5

1. Phage uses tail fibres to stick to outer surface of host
2. Phage DNA intergrates into the bacterial chromosome, becoming a prophage
3. The host reproduces normally, copying the prophage and transmitting it to daughter cells
4. Many cell divisions can create a bacteria colony, all infected
5. Occasionally, a prophase exits the host chromosome, initating a lytic cycle

Question 6

Gene transfer in bacteria?

Answer 6

• Uptake - uptake of naked DNA
• Transduction - transfer of bacterial genes from one bacteria to another by a phage
• Conjugation - ability to form sex pili and to transfer DNA by conjugation is determined by a plasmid called f (fertility) factor

Question 7

Generalised Transduction

Answer 7

1. Phage infects host cell
2. Host DNA is hydrolyses into pieces and phage, DNA and proteins are made (lytic)
3. Occasionally, a host chromosome is packed in a plasmid capsid
4. The phage infects new bacteria adding the old host DNa to the new

Question 8

Specialised Transduction

Answer 8

1. Bactiera cell has prophage between genes a and b (lysogenic)
2. Ocassionally, prohphage DNA exits incorrectly taking host genes A and B with it
3. Phage bacteria carry bacteria DNA
4. The phage infects new bacteria, adding the old host DNA to the new

Question 9

Bacteria gene expression

Answer 9

• Controlled at the level of initiation of transcription
• Transcription begins when the RNA polymerase binds to a promotor
• Binding of repressor to operator blocks transcription (Trytophan)
• Binding of a molecule to operator turns on gene expression (cAMP receptor protein)