Organisation and Control of Prokaryotic Genome

Question 1

Describe the structure and organisation of prokaryotic genomes (including DNA/RNA, single-/double-stranded, number of nucleotides, packing of DNA, linearity/circularity and presence/absence of introns)

Answer 1

• DNA found in the bacteria nucleoid, which is not membrane-bound
• DNA form looped domains which are anchored by DNA binding proteins, followed by negative supercoiling
• Chromosome is double stranded and circular
• Number of nucleotides is more than viral genome but fewer than eukaryotic genome
• Absence of introns

Question 2

Suggest the advantages to bacteria of arranging some genes in operons

Answer 2

• Operon arranges genes coding for enzymes in the same metabolic pathway together for more efficient control of gene expression, allowing bacteria to respond rapidly and appropriately to the environment
• Since bacteria do not have a nuclear envelope, transcription and translation occurs simultaneously, thus the regulation of gene expression usually occurs at transcriptional level so that bacterium only produces enzymes when required and does not waste of energy and resources

Question 3

What is a structural gene?

Answer 3

• A region of DNA that codes for a protein or RNA molecule that forms part of a structure or has an enzymatic function

Question 4

What is a regulatory gene?

Answer 4

A gene that codes for a specific protein product that inhibits the expression of the structural genes

Question 5

Explain the role of the F plasmid (structure -> function)

Answer 5

• Small circular double stranded DNA
• The F factor consists of several F factor genes, most required for the production of sex pili
• The F factor allow bacteria to mate with each other via conjugation whereby there is a transfer of genetic material from donor bacterium to recipient bacterium and through the process, leading to genetic variation in bacteria