Cellular Control

Question 1

what happens when lactose is absent in E.coli?

Answer 1

regulatory gene (lacI) produces a protein called lac repressor

Lac repressor is a transcription factor which binds to the operator region

This blocks RNA polymerase from binding to promoter region

structural genes are not transcribed

Question 2

what happens when lactose is present in E.coli?

Answer 2

lactose binds to repressor and changes its shape

repressor can no longer bind to operator

RNA polymerase can bind to promoter region

RNA polymerase transcribes the structural genes - lacZ, lacY and lacA

Question 3

What do the structural genes do in E.Coli?

Answer 3

Code for proteins that allow E.coli to respire lactose

lacZ codes for enzyme beta-galactosidase which breaks glycosidic bonds in lactose

lacY codes for protein lactose permease which transports lactose into cell

Question 4

What are transcription factors?

Answer 4

Proteins that activate and deactivate genes

Activators activate genes
Binds to promoter region and helps RNA polymerase bind

repressors deactivate genes
Binds to the gene and blocks RNA polymerase

Question 5

What are operons?

Answer 5

A section of DNA that contains a cluster of genes which are controlled by a promoter

Operons contain:

Structural genes - code for useful proteins

Control elements - contains promoter region and operator region

Regulatory gene - code for transcription factors

Question 6

What is splicing?

Answer 6

only a proportion of DNA contains the instructions for making proteins

Genes are made of Introns and Exons

Introns dont code for amino acids

Exons