U3A1: 2E gene regulation

Question 1

gene regulation

Answer 1

conservation of energy in a cell by inhibiting and activating gene expression.

Question 2

what is an operon

Answer 2

multiple structural genes that share a common purpose can be arranged so that their expression is controlled by a single promoter and operator.

Question 3

4 things an operon contains

Answer 3

• regulatory gene
• promoter
• operator
• structural genes.

Question 4

what does the trp operon contain?

Answer 4

series of genes that are involved in the production of the amino acid tryptophan.

Question 5

2 mechanisms of gene regulation

Answer 5

repression and attenuation

Question 6

repression

Answer 6

regulates genes by responding to the concentration of intracellular tryptophan.

Question 7

attenuation

Answer 7

regulates genes by responding to the amount of tRNA-bound tryptophan.

Question 8

explain the mechanism of repression when tryptophan levels are high.

Answer 8

• regulatory gene is expressed, therefore the repressor protein is produced.
• tryptophan binds to repressor protein, causing conformational change and activating the repressor.
• the repressor binds to the operator region, blocking the path of RNA polymerase.
• transcription of structural genes is prevented.

Question 9

explain the mechanism of repression when tryptophan levels are low.

Answer 9

• not enough tryptophan is present to bind to the repressor protein.
• repressor protein detatches from operator.
• RNA polymerase transcribes structural genes.

Question 10

explain the mechanism of attenuation when tryptophan levels are high.

Answer 10

• simultaneous transcription and translation of the trp operon begins.
• ribosome involved in translation arrives at the attenuator sequence.
• tRNA-bound tryptophan travels to ribosome and is added to the protein being made.
• the mRNA molecule being read folds, forming a terminator hairpin loop.
• folding causes the mRNA molecule to seperate from the template DNA at the attenuator sequence.
• RNA polymerase detacthes from DNA, causing transcription to stop.

Question 11

explain the mechanism of attenuation when tryptophan levels are low.

Answer 11

• simulataneous transcription and translation of the trp operon begins.
• ribosome involved in transcription arrives at the attenuator sequence.
• there is no tRNA-bound tryptophan present, so the ribosome pauses. RNA polymerase continues along the DNA.
• mRNA folds to form antiterminator hairpin loop.
• mRNA does not seperate from the template strand at the attenuator sequence.