Lac Operon

Question 1

In prokaryotic cells what are the groups genes are put in

Answer 1

Operons

Question 2

What is an operon

Answer 2

A group of genes under the same regulatory mechanism and are all transcribed in one single unit

Question 3

Why are operons useful

Answer 3

Genes that code for proteins involved in a specific metabolic pathway can all be switched on or off

Question 4

What do bacteria use as their main respiratory substrate and why

Answer 4

Glucose as it is very easy to metabolise

Question 5

What can bacteria also use as a respiratory substrate

Answer 5

Lactose

Question 6

What has to be done so that lactose can be metabolised

Answer 6

Different proteins must be produced

Question 7

When are proteins required to metabolise lactose produced

Answer 7

When glucose is absent

Question 8

Where are the genes that code for proteins needed for lactose metabolism located

Answer 8

In an operon (the lac operon)

Question 9

What does it mean that all the genes that code for proteins needed for lactose metabolism are in an operon

Answer 9

They can be easily repressed when they are not required

Question 10

Describe the structure of the lac operon

Answer 10

It is a section of DNA that has an operator region, a promoter region and 3 structural genes: lacZ, lacY and lacA (THEY CODE FOR PROTEINS)

Question 11

Describe the structure of the section of DNA located near the lac operon

Answer 11

Contains the regulatory gene lac I

Question 12

What does the gene lacZ code for

Answer 12

The enzyme B-galactosidase

Question 13

What does the enzyme B-galactosidase do

Answer 13

Catalyses the hydrolysis of the disaccharide lactose into glucose and galactose

Question 14

What does the gene lacY code for

Answer 14

The membrane carrier protein lactose permeate which helps transport lactose into the bacterial cell

Question 15

What is the promoter region

Answer 15

The section of DNA where the RNA polymerase binds in order to begin transcription

Question 16

What is lac I

Answer 16

The regulatory gene

Question 17

What does the regulatory gene lac I do

Answer 17

Codes for a protein that prevents transcription for the structural genes - repressor protein

Question 18

What is the operator region

Answer 18

The section of DNA that the repressor protein binds to in order to prevent transcription

Question 19

What occurs in the absence of lactose

Answer 19

Transcription of the lac genes is always repressed (genes are switched off)

Question 20

Why is the transcription of the lac genes repressed in absence of lactose

Answer 20

Regulatory gene lac I is always switched on, resulting in production of repressor protein which binds to the operator region which is next to promoter region. This prevents RNA polymerase from being able to bind and therefore prevents transcription

Question 21

What does the presence of lactose allow

Answer 21

The transcription of the structural genes

Question 22

What is produced as a result of transcription of the structural genes

Answer 22

B-galactosidase and lactose permease

Question 23

How does lactose allow the transcription of the structural genes

Answer 23

It acts as an inducer by binding to the repressor protein and causing it to change shape and prevents it from being able to bind to the operator region

Question 24

What occurs as a result of repressor protein no longer binding to operator region

Answer 24

RNA polymerase is able to bind to the promoter and transcription of the structural lac genes can occur

Question 25

What is the purpose of the lac operon

Answer 25

Conserves resources by only metabolising lactose when required