Block A - Microbial Genomes and Evolution

Question 1

What type of microbe is this describing and fill in the gaps.
The Chromosome need to be ______ packed to fit inside the cell. It needs to be ________ by more than 1,000 times. (3 marks)

Answer 1

Bacteria. tightly. compacted

Question 2

Bacterial DNA needs to be organised in a way to make it compatible with what process? Give 3 examples (3 marks)

Answer 2

Replication, transcription, repair

Question 3

How do we get from a relaxed nicked circular DNA to a supercoiled circular DNA. (1 mark)

Answer 3

break one strand and rotate one end of broken strand around helix and seal

Question 4

What are 2 characteristics of positive supercoiling? (2 marks)

Answer 4

-increases chromosomal DNA interactions and tightens interaction with histone
-can hinder transcription and gene expression

Question 5

What is a characteristic of negative supercoiling? (1 mark)

Answer 5

-favours local unwinding of the DNA, enhancing processes such as transcription DNA replication and recombination

Question 6

What’s the role of Topoisomerase I in terms of supercoiling? (1 marks)

Answer 6

relaxes negatively supercoiled DNA

Question 7

What’s the role of DNA gyrase in terms of supercoiling? (1 marks)

Answer 7

compacts DNA by introducing supercoils

Question 8

Which enzyme relaxes supercoiled DNA?

Answer 8

Topoisomerase I

Question 9

Which enzyme compacts DNA into supercoils?

Answer 9

DNA gyrase

Question 10

Bacteria divide through a process called ____ _____

Answer 10

binary fission

Question 11

Cell division and replication need to be ______

Answer 11

synchronised

Question 12

What’s terminus segregation? (2 marks)

Answer 12

a process by which the terminus region of a bacterial chromosome moves to the centre of a cell during replication

Question 13

In E.coli which protein plays the biggest role in chromosome segregation

Answer 13

FtsK

Question 14

What is chromosome segregation? (2 marks)

Answer 14

the process by which chromosomes are separated and distributed equally between daughter cells

Question 15

What’s the role of Topoisomerase IV?

Answer 15

Its also involved in cell division

Question 16

Describe the process of bacterial cell division (5 marks)

Answer 16

-FtsZ positions SLmA and MatP on the nucleoid and MinC-MinD-MinE oscilating between the cell poles, to
keep FtsZ from assembling into a Z ring
-replicated daughter nucleoids seperate, a Z ring assembles at midcell (FtsZ protein), MinCDE moves to poles
-Z ring recruits other septum-synthesis proteins which result in the formation of the division septum
-septum synthesis
-nutrient depletion induces a quiescent state in which FtsZ localises to punative biomolecular condensates that can revert back to polymer forms after growth restart

Question 17

Describe the process of transformation in horizontal gene transfer. (1 mark)

Answer 17

where a bacterium absorbs genetic material or naked DNA from a dead bacterium from its environment or from another bacterium.

Question 18

For transformation, the bacterium must be in a state of ______.

Answer 18

competance

Question 19

Describe how we can chemically induce competance of a bacteria in lab? (3 marks)

Answer 19

we can treat the cells with a divalent cation, such as calcium chloride or lithium chloride to increase the efficiency of DNA entering the bacterium through pores in the cell wall

Question 20

Aside from chemically induction, how else would we induce competence into bacteria? (2 marks)

Answer 20

We can use electroporation, which uses electricity or we can expose the cells to a heat shock treatment at 42C for 2 mins

Question 21

Describe natural transformation? (1 mark)

Answer 21

naturally competant bacteria actively pull DNA fragments from their environment into their cells

Question 22

What is transfection? (1 mark)

Answer 22

It is a laboratory technique that introduces foreign nucleic acid from a bacterial virus into eukaryotic cells

Question 23

What is Transduction?

Answer 23

it involves the transfer of a DNA fragment from one bacterium to another by a bacteriophage

Question 24

What is a bacteriophage

Answer 24

a bacterial virus

Question 25

what is phage conversion

Answer 25

phage alters the phenotype of a bacterial host after infecting it

Question 26

what is the difference between generalized transduction and specialized transduction?

Answer 26

the difference is that a bacteriophage can package any part of the bacterial DNA while specialized can only package specific parts of the bacterial DNA

Question 27

What is conjuction/ bacterial sex

Answer 27

when DNA is transferred from a donor to a reciepient bacterium by direct contact

Question 28

What is essential in conjuction?

Answer 28

that the donor cell has a sex pilus

Question 29

In conjugation, what is a F+ cell

Answer 29

cells that have a nonintegrated F plasmid and act as donors during conjugation

Question 30

In conjugation, what is a F- cell

Answer 30

cells that lack the F plasmid and act a recIepient during conjugation

Question 31

What is the importance of conjugation in the field today?

Answer 31

its a major way bacteria exchange antibiotic resistance genes

Question 32

What are the 2 key factors that determine the dynamics of conjugation

Answer 32

the rate of gene transfer and the growth rate

Question 33

Define silent mutation?

Answer 33

does not affect amino acid sequence

Question 34

Define missense mutation?

Answer 34

amino acid changed, polypepetide altered

Question 35

Define nonsense mutation?

Answer 35

codon becomes stop codon: polypeptide is incomplete

Question 36

Define frameshift mutation?

Answer 36

deletion/ insertion resulting in a shift in the reading frame. usually results in complete loss of gene function

Question 37

Name 3 factors that can induce mutations more rapidly?

Answer 37

-chemical mutagens
-ionising radiation (uv radiation, x-rays)
-biological mutagens

Question 38

Describe 3 ways DNA repair itself from mutations

Answer 38

-direct reversal: where the mutated base is still recognisable and can be repaired without
-repair of single strand damage: where damaged DNA is removed and repaired using opposite strand as template
-repair of double strand damage: a break in the DNA requires more error prone repair mechanisms

Question 39

Whats an ames test

Answer 39

makes practical use of bacterial mutations to detect for potentially hazardous chemicals