L11- genetics of bacteria

Question 1

what is a nutrient broth

Answer 1

rich culture media

C source and all nutrients & AA’s needed for growth

Question 2

what can a nutrient broth be derived from

Answer 2

yeast extract

caesin

Question 3

what is a minimal media

Answer 3

mixture of salts
C source (glucose)
buffer
no AA’s - bacteria have to make all of their own AAs

Question 4

define prototroph

Answer 4

a bacteria that can grow on minimal media and synthesise all own AAs

Question 5

define autotroph

Answer 5

bacteria that will only grow if extra ingredient(s) are added to minimal media eg AAs

Question 6

what happens in lag phase of bacterial growth

Answer 6

initial adaptation period

Question 7

what happens in log phase of bacterial growth

Answer 7

exponential growth

dividing in fixed intervals (doubling time)

Question 8

what happens in stationary phase of bacterial growth

Answer 8

limited division due to limited nutrients

Question 9

when will a colony be visible?

Answer 9

when 10^7 progeny obtained from single cell

Question 10

describe prokaryote DNA

Answer 10

• single chromosome (usually circle of double stranded DNA)
• some bacteria contain plasmids of DNA
• little ‘non coding’ DNA regions

Question 11

what is an operon?

Answer 11

how functionally related genes are grouped in prokaryotes

Question 12

is a mutation more likely to appear in the phenotype of an E or P and why

Answer 12

P - because they are haploid

Question 13

describe E.coli

Answer 13

• circular double stranded genome
• 4600 kb pairs
• 4288 genes

Question 14

what media can E.coli wildtype grow on?

Answer 14

minimal media

Question 15

define conjugation

Answer 15

transfer of plasmids between bacteria

Question 16

what is horizontal gene transfer and what are the 3 methods

Answer 16

transfer of genetic material in bacteria (donor cell to recipient cell, not an exchange)

1. conjugation
2. transduction
3. transformation

Question 17

what is transduction

Answer 17

bacteriophage used to transfer gDNA fragment from one cell to another

Question 18

what is transformation

Answer 18

uptake of DNA fragments by bacteria from environment

Question 19

describe process of transformation

Answer 19

1. double stranded donor DNA (from environment) binds to receptor on recipient cell
2. one strand is degraded as it enters bacterial cell
3. if single strand isn’t degraded it may integrate into host chrom by homologous recombination (2x)

Question 20

what is homologous recombination

Answer 20

swapping over of identical sequences

Question 21

define competency

Answer 21

ability of bacterial cell to take up DNA by transformation

Question 22

how does competency vary?

Answer 22

depending on growth phase of bacteria

Question 23

how can competency be increased

Answer 23

1. grow in rich liquid culture
2. harvest in log phase
3. treat with salt solution

Question 24

what is copy number

Answer 24

the amount of times a plasmid can divide

Question 25

describe bacteriophage structure

Answer 25

• icosahedral head containing single chromosome
• hollow protein sheath
• sometimes tail fibres

Question 26

describe lytic phage (virulent) life cycle

Answer 26

1. phage attaches to host cell and injects its chromosome
2. host C degraded, phage DNA circularises and is replicated using host enzymes
3. T & T of phage genes producing heads sheaths etc
4. replicated phage C injected into heads
5. lysis of host cell and release of phage progeny

Question 27

describe T4 lytic life cycle

Answer 27

1. adsorption, penetration and arrest of host gene expression (immediate)
2. enzyme synthesis (5 min)
3. DNA replication of phage DNA (10 min)
4. formation of new phages (12 min)
5. cell lysed

Question 28

how long is the T4 lytic life cycle

Answer 28

30 min at 37 degrees

Question 29

what pathways can bacteriophage λ follow once entering cell

Answer 29

1. lytic cycle
2. lysogenic cycle
3. lysogenic cycle, then can excise and follow lytic cycle

Question 30

describe lysogenic cycle

Answer 30

1. circularised DNA recombines into host genome

becomes silent prophage that is copied with every cell division

Question 31

what is generalised transduction

Answer 31

when a bacteriophage inserts a piece of bacterial DNA into a new head instead of its own because it cant distinguish between its DNA and bacterial DNA

Question 32

example of temperate phage

Answer 32

bacteriophage λ

Question 33

define temperate phage?

Answer 33

a bacteriophage that is able to undergo lysogenic cycle

Question 34

what bacteriophages can carry out specialised transduction

Answer 34

can only be carried out by temperate phage’s that integrate into host genome

Question 35

what is specialised transduction

Answer 35

when a temperate phage eg (λ) integrates into host genome, then brings part of the host genome (either side of integration site) with it when it separates and transports it to another cell

for λ this can only be bio/gal

Question 36

describe specialised transduction of λ in Ecoli

Answer 36

• λ inserts between bio and gal genes of E.coli

- when it separates EITHER of these can separate with it

Question 37

define aberrant induction

Answer 37

when part of the bio/gal operon is packaged into the phage genome when it excises from host chromosome