Bacterial DNA replication

Question 1

1. What is the genome, genotype and phenotype of an organism ?

Answer 1

Genome= All of the DNA present in a cell
Genotype= Specific set of genes that an organism possesses
Phenotype= The observable characteristics of an expressed genotype

Question 2

2. What is meant by semiconservative replication?

Answer 2

Daughter cells will possess one newly formed strand of DNA and one original strand.

Question 3

3. What is meant by bidirectional replication in bacterial cells?

Answer 3

DNA in bacteria (and archaea) is circular. Therefore replication will occur in both directions from an origin point.

Question 4

4. How does DNA polymerase work and what does it require?

Answer 4

It catalyzes the synthesis of a complementary strand of DNA in a 5’ to 3’ direction. It requires a template strand to direct complimentary synthesis, a primer (short length) and dNTPs (deoxynucleotide triphosphates). Forms phosphodiester bonds between bases.

Question 5

5. Name 2 other enzymes in =volved in replication and their functions

Answer 5

DNA gyrase: topoisomerase enzyme (undercoiling and overcoiling of DNA), also can negatively supercoil
Primase: synthesises short complimentary strands of RNA to act as primers needed for DNA polymerase.

Question 6

6. What are catenanes and how are they resolved?

Answer 6

When two circular dna strands are linked after replication. Topoisomerases decatenate the strands by temporarily breaking them.

Question 7

7. What is the function of a template strand?

Answer 7

Acts as a template for the formation of RNA in transcription. (complimentary is called the coding strand as rna will be a replica of this)

Question 8

8. What is meant when it is said that bacterial mRNA is Polycistronic ?

Answer 8

Each mRNA molecule codes for more than one polypeptide.

Question 9

9. What are the functions of 16s and 23s rna in translation ?

Answer 9

Initiation

16s: binds to the dalgarno sequence on mRNA for protein synthesis
23s: this ribozyme catalyses the peptide bond formation.

Question 10

10. What molecule initiates translation ?

Answer 10

N-fromylmethionine = initiator tRNA

Question 11

11. What are the three phases of elongation in translation ?

Answer 11

1. Aminoacyl- tRNA binding
2. Transpeptidation reaction
3. Translocation

Question 12

12. What are the three sites involved in elongation ?

Answer 12

Peptidyl (donor;p), Aminoacyl (acceptor A) and Exit site (E)

Question 13

13. What are stop codons and give the three possible examples?

Answer 13

Stop codons are where termination is initiated in translation. UAA UAG UGA

Question 14

14. What is the function of release factors (RF’s) and how many are there in bacteria ?

Answer 14

They recognise the presence of stop codons. There are 3 in bacteria.

Question 15

15. What are chaperone and secretory systems used for in protein maturation ?

Answer 15

Chaperone molecules assist in the folding of proteins. Secretory systems are used if the protein needs to be exported outside of the cell.