bacterial genetics

Question 2

Describe the bacterial genome

Answer 2

Haploid
Circular chromosome
dsDNA
some episomal elements - plasmids
Transferable DNA
Bacteriophages/viruses

Question 3

What is a plasmid?

Answer 3

Independent small DNA molecule that replicates independently
Contains suicide genes - if plasmid lost, bacteria dies

Question 4

What is the nucleoid of bacteria?

Answer 4

Tightly packed genome - supercoiled by DNA gyrase
- DNA binding proteins
- RNA polymerase
- RNA
- bound regulatory proteins

Question 5

What is different between the transcription of bacteria and eukaryotes?

Answer 5

Eukaryote transcription requires splicing to remove introns
Bacteria - no introns so transcription is direct

Question 6

What genes are found on a plasmid?

Answer 6

Replication and partition genes - required for replication and partition between cells when bacteria divide
Transfer genes - allow transfer between bacteria
Undefined bacteria

Question 7

Describe replication of the bacterial genome

Answer 7

Via binary fission
=> clones of bacteria

Question 8

How do bacteria vary their genome to evolve?

Answer 8

Mutation of genes
Transfer of genes
Rearrange their DNA
Delete genes
New genes inserted

Question 9

What are the possible effects of mutation of bacterial genome?

Answer 9

Silent mutation => same amino acid
Nonsense mutation => stop codon => gene knocked out
Missense mutation => new amino acid => alters protein sequence, may affect function

Question 10

What types of bacterial genome mutation are there?

Answer 10

Nonsense
Missense
Silent
Frame shift

Question 11

What is phase variation

Answer 11

gene switching
Some bacteria exploit mutation to generate increased phase variation

Question 12

what are the mechanisms of introduction of new DNA into and between bacteria?

Answer 12

Transformation
Conjugation
Transduction recombination

Question 13

What are the mechanisms of movement of DNA already in bacteria

Answer 13

Transposition
Recombination

Question 14

Describe transformation of DNA in bacteria

Answer 14

Uptake of naked DNA:
- degraded by nucleus
- or is recombined into genome

Question 15

Describe conjugation of bacterial DNA

Answer 15

transfer of genetic material between bacteria through direct cell-to-cell contact
Horizontal gene transfer
similar bacteria attached by protein filament (pilus) to allow transfer
Single strand is transferred and both bacteria then produce a 2nd strand to have 2 ‘identical’ plasmids

Question 16

Describe the clinical relevance of conjugation of bacterial DNA

Answer 16

Transfer of plasmids can move whole blocks of properties
e.g., antibiotic resistance, toxins, virulence properties

Question 17

Describe transduction of bacterial DNA

Answer 17

Viruses that infect bacteria = bacteriophage
Virus binds to specific receptor and inject their genome to infect the bacteria
Route to transfer bacterial DNA

Question 18

what are the types of transduction of bacterial DNA?

Answer 18

Lytic and generalised transduction
Temperate phage and specialised transduction

Question 19

Describe generalised transduction - lytic bacteriophage

Answer 19

Bacteriophage attaches
Infection/injection of nucleic acid
Lag phase as things replicate
Lysis
=> randomly packed bacterial DNA

Question 20

Describe specialised transduction - lysogenic phage

Answer 20

Lysogen formed
Bacterial replication with integrated prophage
Induction
Transduction
Infection with phage with bacterial DNA
Integration of new DNA
Packaged DNA related to where prophage inserted

Question 21

What happens to DNA that enters bacteria?

Answer 21

non-specific degradation by general nucleases
Specific degradation via specific restriction endonucleases (DNA restriction)
It manages to integrate with genome (DNA recombination)

Question 22

Describe homologous recombination

Answer 22

2 DNA sequences are the same so can intercalate their strands
Can get spliced during replication

Question 23

What is directed insertion?

Answer 23

insertion elements have repeats which leads to homologous/directed insertions in specific sites or enzymes that direct integration at set sites

Question 24

what is the role of restriction endonucleases in bacteria?

Answer 24

degrade DNA not made in their own cells (act on specific sites)

Question 25

Describe transposition of DNA

Answer 25

Transposon = sequence of DNA that can move around to different positions within the genome
Encode transposases => cut out and re-insert DNA
carry accessory genes

Question 26

What is the difference between gene island and gene cassettes?

Answer 26

Both are regions of DNA with genes conferring properties on the bacteria.
Gene island - refers to well established genes which are now part the bacteria though evolution (i.e. permanent).
Gene cassettes - elements which are more mobile and could be considered to be circulating within or between bacterial population.

Question 27

What are insertion sequences?

Answer 27

type of transposon
Short DNA sequence that acts as a transposable element

Question 28

what is the clinical relevance of bacterial mutations?

Answer 28

Alteration of antibiotic binding sites
Avoidance of vaccines
Alteration of metabolism

Question 29

what is genetic drift?

Answer 29

changes over time by mutations of genomes