BGM1004/L03 Bacterial Genetics II

Question 1

What is the Central Dogma of Biology?

Answer 1

DNA-RNA-Protein

Question 2

What is different about transcription and translation in bacteria?

Answer 2

They are coupled

Question 3

Describe what coupled transcription and translation means in bacteria.

Answer 3

Ribosomes bind to RNA as it is transcribed

Question 4

Why can’t transcription and translation be coupled in higher organisms?

Answer 4

Transcription and translation occur in different cellular compartments

Question 5

Approximately how proportion of base pairs are organised into genes that code for proteins or (less often) RNA in bacteria?

Answer 5

95%

Question 6

Approximately what proportion of DNA is involved in gene expression and structural organisation in bacteria?

Answer 6

5%

Question 7

Give the 3 phases of transcription.

Answer 7

Initiation
Elongation
Termination

Question 8

Describe initiation.

Answer 8

RNA polymerase binds to promoter sequence and starts transcription

Question 9

Describe elongation.

Answer 9

RNA polymerase uses DNA as a template to synthesise RNA from ribonucleotide triphosphates

Question 10

Describe termination.

Answer 10

RNA polymerase recognises sequences in RNA that stops RNA synthesis

Question 11

Give the 3 most common types of RNA.

Answer 11

Messenger RNA
Ribosomal RNA
Transfer RNA

Question 12

What base differs between DNA and RNA?

Answer 12

Thymine - Uracil

Question 13

How many bases make a codon?

Answer 13

3

Question 14

How many stop codons are there?

Answer 14

3

Question 15

How many reading frames does each piece of duplex DNA have?

Answer 15

6

Question 16

Where does mRNA bind on the ribosome to begin transcription?

Answer 16

End of 16S ribosomal RNA

Question 17

What form does most bacterial DNA take?

Answer 17

Circular chromosome (plasmid)

Question 18

What enzymes are responsible for DNA synthesis?

Answer 18

DNA-dependent DNA polymerases

Question 19

Why is DNA replication described at semi-conservative? (2)

Answer 19

One strand consists of original DNA and one newly synthesised DNA
Old strand used to correct errors in new strand

Question 20

What is required to initiate DNA synthesis?

Answer 20

Pre-existing RNA or DNA primer

Question 21

What bonds do DNA polymerases form and where?

Answer 21

Phosphodiester bonds
Between 3’OH of DNA and 5’PO4 on incoming dNTP

Question 22

What is the unique site of bacterial replication called?

Answer 22

Origin of replication (OriC)

Question 23

How does plasmid replication proceed?

Answer 23

Bi-directionally from origin to terminus (terC)

Question 24

What are the 2 sites of RNA synthesis called?

Answer 24

Replication forks

Question 25

How are mutations detectable? (2)

Answer 25

Sequence analysis or change in phenotype

Question 26

Give 4 examples of types of mutations.

Answer 26

Base-pair changes Frameshifts Deletions Insertions Inversions Duplications

Question 27

What is a transition mutation?

Answer 27

A swap between two purines OR two pyramidines

Question 28

What is a transversion mutation?

Answer 28

A swap between a purine and a pyramidine

Question 29

Give 3 potential consequences of base-change mutations.

Answer 29

No change One amino acid change Premature stop codon

Question 30

What is a silent mutation?

Answer 30

A mutation having no change on amino acid sequence

Question 31

What is a nonsense mutation?

Answer 31

A mutation resulting in a premature stop codon

Question 32

What is a missense mutation?

Answer 32

A mutation having an impact on one amino acid in sequence

Question 33

What is a frameshift mutation?

Answer 33

A mutation resulting in a shift in the reading frame

Question 34

What types of mutation can cause a frameshift?

Answer 34

Insertion or deletion of several bases not divisible by 3

Question 35

What is the probability that a randomly generated codon will be a stop codon?

Answer 35

1/20

Question 36

What is the equation for mutation frequency?

Answer 36

MF = m/N Where m= no. mutants N = total no. bacteria

Question 37

Why do mutations occur spontaneously at low frequencies?

Answer 37

Powerful repair mechanisms

Question 38

What needs to occur to increase mutation frequency?

Answer 38

Overloading of repair systems

Question 39

How can bacterial repair systems be overloaded?

Answer 39

Treatment with chemicals/radiation to damage DNA

Question 40

Describe general selection of mutants.

Answer 40

Isolate randomly distributed mutants Screen for desired mutant

Question 41

Describe specific selection of mutants.

Answer 41

Every mutant isolated is of interest Requires knowledge of system

Question 42

Describe negative selection of mutants.

Answer 42

Select against mutant growing

Question 43

Describe enrichment selection of mutants.

Answer 43

Inhibit growth of mutants and kill wildtype using antibiotics

Question 44

Describe positive selection of mutants.

Answer 44

Selective conditions where only mutants grow