Bacterial Genetics

Question 1

what are the advantages of alterations in the bacterial genome?

Answer 1

microbial diversity, habitat adaptation and driving the evolutionary process

Question 2

what is horizontal gene transfer?

Answer 2

exchange of genetic material between bacterial cells that are not directly related

Question 3

what is a wild type strain?

Answer 3

an organism isolated from the environment

Question 4

what is a mutation?

Answer 4

a permanent change in the nucleotide base sequence of a genome

Question 5

what is a mutant?

Answer 5

a cell derived from the wild type that carries a change in the nucleotide sequence

Question 6

what are spontaneous mutations?

Answer 6

result from occasional errors during DNA replication

Question 7

what are induced mutations?

Answer 7

caused by agents of the environment such as radiation and exposure to chemicals

Question 8

what are the effects of a mutation of a gene?

Answer 8

alter the product of the gene, prevent the gene working correctly, entirely prevent gene function and have no effect on gene function

Question 9

what are the types of mutations?

Answer 9

point, frameshift and deletions

Question 10

what is a silent mutation?

Answer 10

single base pair substitution that leads to no change in polypeptide sequence

Question 11

what is a missense mutation?

Answer 11

the DNA and polypeptide sequence changes so protein inactive or have reduced activity

Question 12

what is a nonsense mutation?

Answer 12

formation of a stop codon that causes premature termination of translation

Question 13

what is a plasmid?

Answer 13

circular piece of DNA that carries extra genes such as antibiotic resistance

Question 14

what is a transposon?

Answer 14

small pieces of DNA that ‘jump’ around the chromosome or transfer from bacterium to bacterium

Question 15

how does genetic transfer occur in bacteria?

Answer 15

recipient cell receives the DNA which is then incorporated into the recipient cell chromosome by recombination

Question 16

what cell is formed from genetic transfer?

Answer 16

a recombinant cell

Question 17

what are the mechanisms of horizontal gene transfer?

Answer 17

transformation, transduction and conjugation

Question 18

what is the general description of transformation?

Answer 18

transfer of naked DNA

Question 19

what is the general description of transduction?

Answer 19

DNA transfer mediated by a bacteriophage

Question 20

what is a general description of conjugation?

Answer 20

requires the attachment of two related species via a bridge that can transport DNA

Question 21

what is a competent cell?

Answer 21

a cell that is able to take up DNA

Question 22

how does transformation occur?

Answer 22

competent bacteria bind DNA to their surface via a DNA binding protein which drags the DNA through the cell wall, the DNA enters the cell and binds to donor DNA. it is then integrated into the recipients chromosome via recombination

Question 23

how might cells become artificially competent?

Answer 23

chemically or via temperature

Question 24

what is the difference between generalised or specialised transduction?

Answer 24

specialised transduction is the selective transfer of small, specific sections of the chromosome

Question 25

how does trandsduction occur?

Answer 25

phage injects its DNA into donor cell and its enzymes degrade the host DNA, new phages are synthesised and some host DNA is incorporated into the new phages, which then inject donor DNA into recipient host cell which is then incorporated into the recipients chromosome

Question 26

does conjugation occur in G+ or G- cells?

Answer 26

both

Question 27

what is the F plasmid of E. coli?

Answer 27

a conjugative plasmid, with the F standing for fertility

Question 28

what are the different regions of the F plasmid?

Answer 28

the tra region that contains genes needed for transfer and the omit region which is the origin of transfer

Question 29

what is the process of conjugation?

Answer 29

donor cell attaches to recipient cell with pilius which may draw the cells together, one strand of the F plasmid is transferred and the recipient synthesises a complementary strand to therefore become F+ and the donor cell recompletes its plasmid

Question 30

by which method does the recipient cell synthesise a new strand in conjugation?

Answer 30

by a rolling circle method of replication

Question 31

what is a high frequency recombination cell?

Answer 31

bacterium with an F plasmid integrated into its bacterial chromosome

Question 32

what occurs in conjugation of Hfr cells?

Answer 32

pilus forms with Hfr cell and an F- cell, but the pilus breaks before the whole part of the F plasmid has been transferred so the recombinant cell remains F-

Question 33

how long are transposons?

Answer 33

between 700 and 40,000 bp

Question 34

where does transposition occur?

Answer 34

between plasmids and chromosomes, within chromosomes and between bacteria via plasmids

Question 35

what are jumping transposons?

Answer 35

move around within a DNA molecule

Question 36

what are replicating transposons?

Answer 36

replicate whilst moving around

Question 37

what is the structure of a transposon?

Answer 37

have a palindromic sequence at both ends and a transposase enzyme in the middle

Question 38

what are complex transposons?

Answer 38

carry other genes not connected with transposition

Question 39

what genes does gene transfer have an important role in?

Answer 39

antibiotic resistance genes, metabolism genes and virulence genes