L2 Introduction to Bacterial Genetics

Question 1

DNA is arranged in a double helix structure, with the two strands ? to one another.

Answer 1

Antiparallel (parallel, but going in opposite directions)

Question 2

Define: Wildtype

Answer 2

An unmodified natural isolate of a species (e.g. that which is used for comparative experimental purposes)

Question 3

Define: Mutant

Answer 3

A variant from the wild type as a result of a specific change in the DNA sequence (see Mutation)

Question 4

Define: Mutation

Answer 4

A specific change in the DNA sequence of an organism (such that the sequence differs from the wildtype)

Question 5

Define: Allele

Answer 5

One copy of a gene

Question 6

Define: Phenotype

Answer 6

An observable trait that may be altered by genetic mutation

Question 7

Define: Genotype

Answer 7

The defined nucleotide sequence of an organism, usually expressed in terms of alleles of its genes

Question 8

Define: Haploid

Answer 8

Possessing a single copy of each gene

Question 9

Define: Diploid

Answer 9

Possessing two copies of each gene

Question 10

Define: Polyploid

Answer 10

Possessing multiple (more than 2) copies of each gene

Question 11

When a cell is ‘competent’, this means ? is able to occur

Answer 11

Transformation (genetic alteration of a cell resulting from uptake of exogenous genetic material)

Question 12

The transfer of genes by direct cell-to-cell contact is known as…

Answer 12

Conjugation

Question 13

Conjugation involves a donor and a recipient. It is usually mediated by…

Answer 13

Conjugative plasmids

Question 14

In the lab, the Hfr strain allows conjugation to transfer part of the…

Answer 14

Chromosome itself (not just the plasmid)

Question 15

Non-conjugative plasmids lack which gene?

Answer 15

mob gene

Question 16

Transduction involves the use of a ? to introduce exogenous DNA

Answer 16

Bacteriophage (phage)

Question 17

Describe the polarity of dsDNA and the group present at each end

Answer 17

5’ and 3’ ends are reversed between strands. PO4 at 5’, OH at 3’

Question 18

The ‘Central Dogma’ of genetics states that…

Answer 18

Information, once encoded in a protein, cannot be decoded back into RNA or DNA ⏮

Question 19

Transcription can be described in 3 stages…

Answer 19

1. Initiation
2. Elongation
3. Termination

Question 20

DNA synthesis is…

Answer 20

Semi-Conservative ½

Question 21

DNA synthesis in bacteria requires an…

Answer 21

RNA (or DNA) primer

Question 22

dNTP is the DNA precursor, more specifically the 4 types (corresponding to the different bases) are…

Answer 22

1. dATP (adenine)
2. dGTP (guanine)
3. dCTP (cytosine)
4. dTTP (thymine)

Question 23

Bacterial chromosomes are ? shaped

Answer 23

Circle ⃝

Question 24

When DNA is synthesised from the bacterial chromosome, there are two…

Answer 24

Replication forks

Question 25

When DNA synthesis occurs, there are key differences between the two strands, which are known as the...

Answer 25

Leading and lagging strands

Question 26

Mutations are sometimes detectable by phenotype. If not, we can use...

Answer 26

Sequence analysis

Question 27

A transition mutation results in a change from one type of base...

Answer 27

to another base of the same type (e.g. Pyrimidine to Pyrimidine ( C  ⃡ T ) / Purine to Purine ( A  ⃡ G )

Question 28

A transversion mutation results in a change from one type of base...

Answer 28

to another base of a different type (e.g. Pyrimidine (C or T) to Purine (A or G) and vice versa)

Question 29

Mutations can be (4 types)...

Answer 29

1. Silent 2. Missense 3. Nonsense 4. Frameshift

Question 30

A change in the base on position 3 often causes a ? mutation

Answer 30

Silent

Question 31

The more genes are required for a particular phenotype...

Answer 31

The more likely a mutation is to occur (and to have an observable effect)

Question 32

Spontaneous mutations are very rare, partly due to the...

Answer 32

Powerful repair systems in cells

Question 33

Mutagens can be used to artificially overload cell repair mechanisms. This is known as...

Answer 33

Induced Mutation

Question 34

Selection of mutations from cultures is either...

Answer 34

General or specific

Question 35

Describe 3 ways of selecting mutant bacteria...

Answer 35

1. ❌ Negative selection (select for mutants which have lost certain capabilities, uses the velvet pad) 2. 💊Enrichment (prevent growth of mutants, eliminate growing wildtypes with antibiotics) 3. ✅ Positive selection (provide conditions where only the mutants will grow)