GENETICS - Bacteria

Question 1

In very general terms, how do bacteria evolve?

Answer 1

Bacteria evolve through mutations and gene exchange

Question 2

Describe the structure of the bacterial chromosome

Answer 2

Usually a closed circle of double stranded DNA

Question 3

Which species of bacteria has a linear chromosome rather than a circular one?

Answer 3

Spirochetes

Question 4

What are operons?

Answer 4

Operons are genes with related functions linked together in the bacterial genome

Question 5

Describe the two different bacterial gene pools

Answer 5

Core gene pool: genes required for life
Flexible gene pool: genes that allow bacteria to evolve and cause disease

Question 6

List some of the things that allow bacteria to have a flexible gene pool

Answer 6

• Genomic islands
• Genomic islets
• Phages (bacteriophages)
• Plasmids
• Integrons
• Transposons

Question 7

Describe two types of mutation seen in bacteria

Answer 7

• Spontaneous mutation (occur due to natural replication errors)
• Mutagenic mutation (mutations induced in a lab setting through the use of chemicals, radiation and insertion of transposons or bacteriophages)

Question 8

What are transposons?

Answer 8

Transposons are genes that can move from one genomic location to another - also known as ‘jumping genes’

Question 9

What are the two forms of transposons?

Answer 9

• Insertion elements (IS) where the transponase gene has only one phenotype
• Composite transposons where the transponase gene has several phenotypes

Question 10

What often happens when transposons undergo transposition (removal and insertion into a new genomic location) to operons?

Answer 10

The removal and insertion of transposons often causes polar mutations of the DNA. If a transposon is inserted in the first gene of an operon, the whole operon will be mutated

Question 11

Describe the two mechanisms of transposition

Answer 11

• Conservative transposition: the existing transposon is inserted into the new genomic location
• Replicative transposition: the replication of the existing copy of the transposon which is inserted into the new genomic location

Question 12

What are plasmids?

Answer 12

Plasmids are autonomously replicating closed circles of double stranded DNA which often encode for antibiotic resilience genes and virulence factors

Question 13

What are bacteriophages?

Answer 13

Bacterial viruses

Question 14

How do bacteriophages infect bacteria?

Answer 14

Bacteriophages bind to and insert their genetic material into the cytoplasm of the bacterium in order to use the bacterial machinery to produce new phage particles

Question 15

What is a lytic bacteriophage?

Answer 15

Lytic phages take over the machinery of the cell to make phage components. They then lyse the bacterium, releasing new phage particles

Question 16

What is a lysogenic bacteriophage?

Answer 16

A lysogenic bacteriophage is a virus that infects bacteria, but incorporates its DNA into the host cell’s DNA to become a non-infectious phage, called a prophage. When conditions become unfavourable, the prophage enter the lytic lifecycle, producing new phage particles and lysing the bacterium

Question 17

(T/F) Bacteriophages can be used as antibacterial therapy

Answer 17

TRUE

Question 18

How can bacteriophages enhance bacterial pathogenicity?

Answer 18

Bacteriohages can enhance bacterial pathogenicity by several ways including transferring gene encoding toxins, duplicating the virulence factors, or changing the regulatory sequences controlling bacterial virulence genes

Question 19

What are pathogenicity islands?

Answer 19

Pathogenicity islands are blocks of DNA containing virulence genes which are inserted into the chromosome

Question 20

Where do pathogenicity islands come from?

Answer 20

Pathogenicity islands come from other organisms such as bacteriophages or via transposons

Question 21

What indicates that pathogenicity islands come from other organisms?

Answer 21

Pathogenicity islands have a lower guanine and cytosine (G+C) content than the rest of the bacterial chromosome

Question 22

Why is the transfer of genes between bacteria so important?

Answer 22

The transfer of genes between bacteria is what allows the movement of antibiotic resistance genes and virulence factors between bacteria as well as to change the antigen makeup to allow for immune evasion

Question 23

What is bacterial transformation?

Answer 23

Transformation is the uptake of ‘naked’ DNA i.e. when bacteria in the immediate environment uptake DNA from lysed bacteria into their genome and express this DNA

Question 24

What is bacterial transduction?

Answer 24

Transduction is the transfer of DNA from one bacterium to another via a bacteriophage

Question 25

What are the two methods of bacterial transduction?

Answer 25

1. Generalised transduction: transduction via a lytic bacteriophage which can package any of the DNA fragments from the host bacterium
2. Specialised transduction: transduction via a lysogenic bacteriophage which can only package specific DNA fragments from the host bacterium

Question 26

What is bacterial conjugation?

Answer 26

Conjugation is when a plasmid is transferred to a recipient bacterium via pili

Question 27

What is conjugation important for?

Answer 27

Conjugation is important for the transfer of antibiotic resilience genes between bacterium