Organisation And Control Of Prokaryotic Genome

Question 1

What does the prokaryotic genome consist of?

Answer 1

Bacterial Chromosome
Plasmid

Question 2

Structure of bacterial chromosome.

Answer 2

Single circular DNA molecule, associated with non-histone proteins
Single origin of replication
Genes organised into operons
Not interrupted by introns

Question 3

Organisation of bacterial chromosome

Answer 3

Chromosome associated with non histone proteins
Folded into 50 loops called loop domains
Loop domains:
* bound to a central protein scaffold, attached to cell membrane
* supercoil independently, complexed with DNA binding proteins

Question 4

Structure of plasmids

Answer 4

Smaller, double stranded, circular, extrachromosomal DNA
Single origin of replication
Genes present not essential for survival but beneficial under stressful conditions

Question 5

Process of binary fission

Question 6

Vertical transmission

Answer 6

Mutation

Question 7

List the types of horizontal transmission.

Answer 7

Transformation, Transduction, Conjugation

Question 8

Outline the process of transformation.

Answer 8

Uptake of foreign naked DNA into competent cell
Incorporated into recipient chromosome via genetic recombination
Bacteria is haploid, thus express phenotype in foreign DNA

Question 9

Outline the process of generalised transduction.

Question 10

Outline the process of specialised transduction.

Question 11

What is conjugation?

Answer 11

Conjugation involves the direct transfer of DNA between 2 bacterial cells that are in contact with each other.

Question 12

What are the requirements for conjugation to occur?

Answer 12

• One of the bacteria needs to contain the F or R plasmid
• Both bacterial cells need to be in direct contact

Question 13

Outline the process of conjugation.

Answer 13

F factor in segment of DNA or F plasmid codes for the production of a sex pili –> acts as a grappling hook, draws 2 bacteria together, forming a cytoplasmic bridge to allow for DNA transfer. DNA of F factor is nicked, separation of 1 DNA strand –> exported to the recipient via cytoplasmic bridge –> acts as a template to synthesise complementary strand –> becomes an F+ plasmid donor

Question 14

State the components of an operon.

Answer 14

Most upstream
* Promoter for regulatory gene
* Gene coding for repressor
* Promoter
* Operator
* Structural genes

Most downstream

Note that promoter for regulatory gene and gene coding for repressor are not included in an operon, just for extra info

Question 15

State the names of the structural genes in lac operon and what enzyme it codes for with its respective enzyme function.

Answer 15

• lac Z: beta-galactosidase –> enzyme breaks down lactose into glucose and galactose
• lac Y: lactose permease –> enzyme transports lactose into bacterial cell
• lac A: galactoside transacetylase –> enzyme needed for lactose metabolism

Question 16

Low tryptophan concentration.

Answer 16

• Repressor protein inactive, not bound to operator region
• Promoter remains available to RNA polymerase for transcription
• E coli can synthesise tryptophan by expressing 5 structural genes involved

Question 17

High tryptophan concentration.

Answer 17

• Tryptophan acts as a co-repressor to turn off transcription,
• Binds and activates repressor, forming repressor-tryptophan complex –> binds to operator and block transcription
• RNA polymerase cannot bind to promoter