Chapter 8 Part 2

Question 1

Genes that are always expressed are called

Answer 1

constitutively expressed
“housekeeping genes” that encode proteins that are always needed for a cell to remain alive and functional

Question 2

Why are constitutively expressed genes important?

Answer 2

“housekeeping genes” that encode proteins that are always needed for a cell to remain alive and functional

Question 3

Most expression of genes can be regulated. Why?

Answer 3

It allows the cell to produce proteins that are needed in a given environment/situation and not waste energy or resources by expressing proteins that aren’t needed
- not all genes are expressed at the same time

Question 4

Induce =

Answer 4

increase expression

Question 5

Repress

Answer 5

decrease expression

Question 6

Repression is always expressed until

Answer 6

it gets turned off

Question 7

Define Operon

Answer 7

1. a group of adjacent genes that are transcribed together and controlled by a single promoter
2. genes within an operon encode proteins that function together in the same cellular process
3. ensures that all genes are expressed at the same time and level
4. common in bacterial not Eukaryotes

Question 8

Describe the structure of the operon (left to right)

Answer 8

Dna - regulatory gene (I )
Promoter (p) and Operator (O) called the control region
Structural genes of Z, Y, and A
Operon consists of everything after the regulatory gene

Question 9

Define promoter

Answer 9

a region upstream of the gene(s) where the RNA polymerase binds
- specifically to the sigma factor (one of the RNA polymerase subunits)

Question 10

Define operator

Answer 10

region upstream of the gene(s) where a repressor binds
- by binding the operator, repressors influence the ability of the RNA polymerase (sigma factor) to bind to the promoter

Question 11

Define regulatory gene

Answer 11

gene that encodes a regulatory protein (the repressor)
- repressors are DNA-binding proteins that bind to the operator and turn off transcription of the structural genes

Question 12

Define inducible operons

Answer 12

The default state of this operon is OFF
- the repressor is bound to the operator preventing transcription of the structural genes

Question 13

What does an inducer do?

Answer 13

an inducer binds to the repressor leading to transcription of the structural genes (turns it ON)
- RNA polymerase can now bind to the promoter

Question 14

Give an example of an inducible operon

Answer 14

Lac operon

Question 15

Describe Lac operon

Answer 15

LacI is the regulatory gene that encodes the LacI repressor
- Allolactose is the inducer that when present pulls off the lacI repressor off the operator resulting in the expression of LacZYA (the structural genes)

Question 16

Define lac Z and lac Y

Answer 16

beta galactosidase (breaksdowns lactose) and lactose permease (transports lactose in the cell) are proteins that enable the breakdown of lactose

Question 17

What is the logic behind the Lac operon?

Answer 17

if lactose is present at significant levels, the cell should produce proteins capable of breaking it down to extract energy
- if lactose is around, lac Z and Y will turn on and use of the energy (sugar = energy)

Question 18

Define repressible operons

Answer 18

the default state is ON
- the repressor is unable to bind to the operator so transcription of the structural genes proceeds

Question 19

What does a co-repressor do?

Answer 19

A co-repressor binds to the repressor and prevents transcription of the structural genes

Question 20

What is an example or a repressible operon?

Answer 20

Trp operon
Tryptophan

Question 21

What does the trp operon do?

Answer 21

its a copressor that when present binds to the Trp repressor and enables it to bind to the operator and prevents transcription of the trp structural genes

Question 22

What are trpA-E genes involved in?

Answer 22

the synthesis of tryptophan

Question 23

What is the logic of tryptophan?

Answer 23

if Tryptophan is already present at significant levels, the cell doesn’t want to waste energy synthesizing more trytophan

Question 24

Why is trytophan important?

Answer 24

it makes 1 of the 20 essential amino acids

Question 25

Tryptophan in huge amounts?

Answer 25

stop transcription bc there is some readily available

Question 26

tryptohan in low amounts?

Answer 26

no co pressor present - need to make more tryptophan