Recombination in bacteria and bacteriophages

Question 1

Describe the structure of a bacterial chromosome

Answer 1

• Bacterial chromosomes contain all the necessary genetic information for a functional cell
• It is a single molecule containing double stranded DNA
• the nucleus is NOT surrounded by a membrane

Question 2

What are plasmids?

Answer 2

Plasmids are autonomously replication dsDNA which encode for accessory functions that are advantageous to the cell e.g. the production of toxins

Question 3

What experiment explains bacterial conjugation?

Answer 3

• 2 strains of e. coli that need different nutrients to grow.
• Both strains mixed together and added to minimal nutrient medium (on which neither strains could grow)
• colonies still observed so it means that they somehow found a way to grow without extra nutrients being added
• Suggests that recombination of genes took place
• Physical contact needed and this process is now called conjugation

Question 4

Describe the process of bacterial conjugation.

Answer 4

Conjugating bacteria do not act equally. One cell is the donor and one is the recipient.
F plasmid from the donor directs the synthesis of pili, which contacts the recipient cell and draws it in closer.
F plasmid in the donor makes a ss copy of itself and it enters the recipient through a pore, where it makes the other strand, forming a double helix.

Question 5

What is an F’ plasmid?

Answer 5

A plasmid carrying bacterial genomic DNA, possibly from the result of an unclean exit from a chromosome.

Question 6

What are R plasmids?

Answer 6

vectors capable of carrying multiple antibiotic resistance genes. This is important in designing strains or use in genetic engineering.

Question 7

What is transduction?

Answer 7

Transduction is the ability of phages to acquire bacterial genes and transduce (transfer) them from one bacterial cell to another.

Question 8

How is transduction different to transformation and conjugation?

Answer 8

Transformation is when one cell turns into another cell (mice experiment)
Conjugation is when one cell shares DNA with another cell, but it involves physical contact and the use of F plasmids
Even though transduction is the transfer of DNA from one bacterial cell to another, there is no contact needed. To prove this, the “U tube” experiment was done where two strains were placed on seperate sides of a U shaped tube with a fine filter in between to prevent contact.

Question 9

What are the two different types of transduction?

Answer 9

Generalised transduction - phages can carry any part of the bacterial chromosome
Specialised transduction - phages only carry specific parts of the bacterial chromosome