ii. Bacterial Genetics

Question 1

What is bacterial genetics?

Answer 1

Bacterial genetics is the study of the mechanism of heritable information in bacteria.

Question 2

What are the sources of genetic information?

Answer 2

• Bacterial DNA/Genome: Chromosome
• Extrachromosomal Genetic Material

Question 3

• Bacterial DNA/Genome: Chromosome

Features: (4)

Answer 3

o Single copy per cell
o Circular, double stranded DNA
o 1 origin of replication
o Few million base pairs

Question 4

• Extrachromosomal Genetic Material

Features: (2)

Answer 4

o Plasmids
o Transposons

Question 5

What are plasmids? (5)

Answer 5

• Circular, double stranded DNA within the cytoplasm
• Not essential for life
• Carry advantageous genes which code for toxins or resistance or enhanced pathogenicity
• Number varies: 1-20 copies per cell
• Can be passed on to other bacteria within the same or different species

Question 6

What are Transposons? (3)

Answer 6

• Jumping genes (can change their position within a bacterial genome)
• Pieces of DNA may ‘jump’ from one place in the chromosome/plasmid to another altering
  the cell’s genetic identity and even genome size = Transposition
• May carry advantageous genes that encode for antibiotic resistance, toxins or enhanced
  pathogenicity.

Question 7

Genetic variation occurs in bacteria through Genetic Transfer:

What are the 2 types?

Answer 7

• Vertical Genetic transfer
• Horizontal genetic transfer

Question 8

What is Vertical Genetic transfer? (2)

Answer 8

o Genetic information passed on from parent to offspring
o Mutations

Question 9

What is horizontal genetic transfer? (3)

Answer 9

o Genetic information passed on between bacterial cells

o Results in genetic variations

o These genetic variation are needed for evolution and sometimes for survival

Question 10

o There are three ways in which bacteria transfer genomic information via horizontal gene transfer:(3)

Answer 10

▪ Transformation
▪ Conjugation
▪ Transduction

Question 11

What is transformation in bacteria transfer? (8)

Answer 11

Question 12

What is conjugation in bacteria transfer? (5)

Answer 12

Question 13

What is transduction in bacteria transfer? (4)

Answer 13

Question 14

• Following are the stages of transduction involving a lytic phage: (7)

Answer 14

1. A lytic bacteriophage attaches to a susceptible bacterium
2. The bacteriophage injects its DNA into the bacterial cell. The phage DNA directs the bacteria’s metabolic machinery to manufacture bacteriophage components and enzymes.
3. Occasionally during maturation, a bacteriophage capsid incorporates a fragment of
   the bacteria’s chromosome or a plasmid instead of a phage genome by mistake
4. The bacteriophages are released with the lysis of bacterium
5. The bacteriophage carrying bacterial DNA attaches to another recipient bacterium
6. The bacteriophage injects the bacteria’s DNA it is carrying into the new recipient bacterium
7. The bacteria DNA from the phage is exchanged by recombination for some of the recipient’s DNA

Question 15

What are mutations? (2)

Answer 15

• Heritable variations
• Random or induced

Question 16

MUTATIONS:
- Caused by alterations in the nucleotide sequence due to: (3)

Answer 16

o Substitution
o Addition/Insertion
o Deletion

Question 17

Types of Mutation: (4)

Answer 17

• Missense Mutations
• Nonsense Mutations
• Silent Mutations
• Frame Shift Mutations

Question 18

• Missense Mutations: (3)

Answer 18

o Lead to changes in Amino Acid sequence - Changes protein products
o Point mutation
o Series of mutations

Question 19

• Nonsense Mutations: (2)

Answer 19

o Lead to formation of Stop codon
o Terminates protein synthesis - Incomplete protein product

Question 20

• Silent Mutations: (2)

Answer 20

o Single substitution in DNA sequence
o Results in the same amino acid = same protein product

Question 21

• Frame Shift Mutations: (3)

Answer 21

o Addition or deletion of nucleotide
o Shifts the reading frame of the gene
o Wrong codon Amino acid protein

Question 22

What are the outcomes of mutations?

Answer 22

• Deleterious
• Beneficial
• Random/Spontaneous:

Question 23

• Deleterious: (3)

Answer 23

o Block or disrupts a gene
o Affect the vital function of the cell
o Lead to cell death

Question 24

• Beneficial: (2)

Answer 24

o Added advantage for the cell
o Antibiotic Resistance

Question 25

• Random/Spontaneous: (2)

Answer 25

o No obvious effect on the phenotype
o Silent mutations

Question 26

Genetic basis of Antibiotic Resistance:

What is antimicrobial resistance?

Answer 26

• Antimicrobial resistance is the ability of a microbe to resist the effects of an antibiotic that was once effective in killing that particular microbe.

Question 27

What is intrinsic resistance? (3)

Answer 27

Question 27

• There are two types of Resistance:

Answer 27

o Intrinsic resistance
o Acquired resistance

▪ Mutations
▪ Genetic transfer
▪ Biochemical mechanisms e g decrease permeability of the drug or produce enzymes to inactive drug

Question 28

What is acquired resistance?

Answer 28

Question 29

The Frequency of acquired resistance is affected by: (3)

Answer 29

• The amount of antibiotic being used
• The frequency with which the bacteria can undergoes spontaneous mutations and become
  resistant
• The prevalence of plasmids able to transfer resistance from one bacterium to another

Question 30

Causes of spread of genes conferring antibiotic resistance: (3)

Answer 30

• Selection pressure by increased and inappropriate antibiotic use in humans and animals
• General Practitioners prescribing antibiotics for “common cold”
• Antibiotics used for growth promotion in farm animals drug resistance in gut flora of animals

→ spread to human gut flora → genes transferred to human pathogens!