Bacteria

Question 1

Binary Fission

Answer 1

• DNA replication begins at the origin of replication where DNA is unzipped by breaking hydrogen bonds between bases of the 2 strands to form a replication bubble
• DNA replicates by semi-conservative replication where each original strand serves as a template for synthesis of daughter strand by complementary base pairing
• 2 newly formed ori move to opposite poles of the cell and attach to plasma membrane
• cell elongates to prepare for division
• DNA is circular with no free ends, and the daughter DNA molecules will be interlocked with the completion of replication
• enzyme topoisomerase cut, separate and reseal the two DNA molecules
• invagination of the plasma membrane and the deposition of new cell wall eventually divide the parent cell into two daughter cells

Question 2

Transformation

Answer 2

• uptake of foreign naked DNA from the surrounding, resulting in a change of the bacterial cells’ genotype and phenotype

1. fragments of foreign naked DNA in the surrounding. medium are taken up by naturally competent bacterial cells via cell surface proteins
2. foreign DNA is incorporated into host cell chromosome through crossing over at homologous regions on the bacterial chromosome. resulting in a recombinant cell
3. if different alleles of a gene were exchanged and the new allele is expressed, this results in a permanent change in genotype and phenotype and the cell is said to be transformed

Question 3

conjugation

Answer 3

• direct transfer of genetic material from one bacterial cell to another through a mating bridge between the two cells via the transfer of F plasmic from an F+ donor to a F- recipient cell

1. sex pilus of F+ bacterial makes contact with a F- cell and retracts to bring the 2 cells closer
2. the hollow pilus then acts as a cytoplasmic mating bridge between the 2 cells
3. one of the two strands of the plasmid DNA is nicked and transferred from the F+ cell to the F- cell through the mating bridge. the other strand is used as a template for synthesis of a complementary strand thus forming ds plasmid in donor cell
4. ss F plasmid DNA circularises in F- cell and is used as a template to synthesise a complementary strand in order to form a ds plasmid DNA. F- recipient cell is now F+ cell
5. Replication of plasmid via rolling circle DNA replication occurs

Question 4

Transduction

Answer 4

• process by which bacterial DNA from one host cell is introduced into a bacterial host cell by a bacteriophage due to abberations in the phage reproductive cycle