Horizontal gene transfer

Question 1

What is horizontal gene transfer (HGT)?

Answer 1

Transfer of genetic material between organisms without being parent-to-offspring.

Question 2

How is horizontal gene transfer different from vertical gene transfer?

Answer 2

HGT occurs between organisms of the same generation, vertical is parent to offspring.

Question 3

What are the three main mechanisms of HGT?

Answer 3

Transduction, transformation, and conjugation.

Question 4

What is transduction?

Answer 4

DNA transfer via bacteriophages that infect bacteria.

Question 5

What is the difference between generalised and specialised transduction?

Answer 5

Generalised: random DNA; Specialised: specific DNA regions transferred.

Question 6

What is a bacteriophage?

Answer 6

A virus that infects prokaryotic cells.

Question 7

What is transformation in bacteria?

Answer 7

Uptake and integration of external DNA by a bacterial cell.

Question 8

What is natural competence?

Answer 8

A bacterium’s natural ability to take up DNA from its environment.

Question 9

What are the steps involved in natural transformation?

Answer 9

1. DNA capture via pilus, 2. ssDNA transport into cytoplasm, 3. RecA recombination.

Question 10

What is conjugation?

Answer 10

Transfer of ssDNA from donor to recipient cell through direct contact.

Question 11

What is the F factor?

Answer 11

A plasmid responsible for conjugation, first discovered in E. coli.

Question 12

What are the steps of bacterial conjugation?

Answer 12

1. Nick at oriT, 2. DNA transfer via T4SS, 3. Circularization and replication.

Question 13

What is a transconjugant?

Answer 13

The recipient cell after receiving DNA via conjugation.

Question 14

What is RecA and what does it do?

Answer 14

A protein that facilitates homologous recombination by searching for DNA homology.

Question 15

What is homologous recombination?

Answer 15

Recombination based on sequence similarity, integrating foreign DNA.

Question 16

What is transposition?

Answer 16

Movement of DNA segments within the genome using transposases.

Question 17

What is an IS element?

Answer 17

A short mobile element with only a transposase and flanking repeats.

Question 18

What is a transposon?

Answer 18

A mobile genetic element with transposase and other ‘cargo’ genes.

Question 19

How do transposons differ from IS elements?

Answer 19

Transposons carry additional genes; IS elements are simpler.

Question 20

What is a plasmid?

Answer 20

Circular, double-stranded DNA separate from chromosomal DNA.

Question 21

What are the types of plasmids based on mobility?

Answer 21

Conjugative, mobilizable, and nonmobilizable plasmids.

Question 22

What is a conjugative plasmid?

Answer 22

Has genes for pilus formation and transfer machinery.

Question 23

What is a mobilizable plasmid?

Answer 23

Lacks pilus genes but uses another element’s transfer system.

Question 24

What is a nonmobilizable plasmid?

Answer 24

Cannot self-transfer and lacks mobility genes.

Question 25

What are ICEs?

Answer 25

Mobile DNA that integrates into chromosome and transfers via conjugation.

Question 26

How do ICEs integrate and excise?

Answer 26

1. Integrated in genome, 2. Excised, 3. Transferred, 4. Integrated into new host.

Question 27

Why is HGT important in bacterial evolution?

Answer 27

Drives adaptation and spreads traits like antibiotic resistance.

Question 28

What is a mutation?

Answer 28

A permanent change in the DNA sequence.

Question 29

What is the difference between spontaneous and induced mutations?

Answer 29

Spontaneous: replication errors; Induced: from mutagens like UV or chemicals.

Question 30

What are the three types of point mutations?

Answer 30

Silent, missense, and nonsense mutations.

Question 31

What is the role of the relaxosome in conjugation?

Answer 31

Nicks DNA at oriT and aids in DNA transfer.

Question 32

What is oriT?

Answer 32

The origin site for DNA transfer during conjugation.

Question 33

How do mobile genetic elements spread antibiotic resistance?

Answer 33

By carrying genes that confer resistance traits.

Question 34

What are examples of cargo genes in transposons?

Answer 34

Antibiotic resistance genes, toxin production genes, or metabolic genes.

Question 35

What is site-specific recombination?

Answer 35

Recombination at specific DNA sequences.

Question 36

What is the role of integrases and transposases?

Answer 36

Enzymes that mediate specific integration or movement of DNA.

Question 37

What is the significance of RecA-independent recombination?

Answer 37

Allows mobile elements to integrate without homologous recombination.

Question 38

What is the typical size of composite transposons?

Answer 38

Typically 2–10 kb in size.

Question 39

What is the oriC and oriT in plasmids?

Answer 39

oriC: replication origin; oriT: transfer origin.

Question 40

How do plasmids replicate independently?

Answer 40

Using their own replication origin independent of chromosomal replication.

Question 41

What are some natural examples of ICEs?

Answer 41

ICESXT in Vibrio cholerae.

Question 42

What triggers ICE excision?

Answer 42

DNA damage like antibiotics or mutagens.

Question 43

What is an att site in ICE integration?

Answer 43

Specific attachment sites on chromosome and ICE.

Question 44

What is meant by a ‘cargo gene’?

Answer 44

A gene carried by MGEs that can add new traits to the host.

Question 45

How can HGT affect bacterial virulence?

Answer 45

By inserting into or modifying virulence-associated genes.

Question 46

How does mutation contribute to genetic diversity?

Answer 46

It introduces changes that can lead to beneficial traits.

Question 47

Why do transposons contribute to genome plasticity?

Answer 47

They enable reshuffling of genetic material within the genome.

Question 48

What are the health implications of HGT?

Answer 48

They contribute to antibiotic resistance, making infections harder to treat.