Chapter 18: Gene Regulation

Question 1

What does bacteria must do in the environment?

Answer 1

they must respond quickly to changes in the environment

Question 2

Why must bacteria need to stop production if they have enough of a product,

Answer 2

Waste of energy to produce more

Question 3

How must bacteria need to stop production if they have enough of a product?

Answer 3

stop production of enzymes for synthesis

Question 4

Why must bacteria need to utilize the new food/energy source, quickly if they find it?

Answer 4

metabolism, growth, reproduction

Question 5

How must bacteria need to utilize the new food/energy source, quickly if they find it?

Answer 5

start production of enzymes for digestion

Question 6

Feedback Inhibition

Answer 6

products acts as an allosteric inhibitor of 1st enzyme of in tryptophan pathway

Question 7

What is the drawback of feedback inhibition?

Answer 7

Its a wasteful production of enzymes

Question 8

Gene Regulation

Answer 8

blocks the transcription of genes for all enzymes in tryptophan pathways

Question 9

What is the benefit of gene regulation?

Answer 9

Saves energy by not wasting it on unnecessary protein synthesis

Question 10

How do cells vary the amount of specific enzymes ?

Answer 10

regulating gene transcription

Question 11

Operon

Answer 11

genes grouped together w/ related functions
ex: all enzymes in a metabolic pathway

Question 12

Promoter

Answer 12

RNA polymerase binding site, single promoter controls transcription of all genes in operon

Question 13

Operator

Answer 13

DNA binding site of repressor proteins

Question 14

How can genes be turned off?

Answer 14

the repressor protein can bind to DNA at operator site, blocking RNA polymerase, blocks transcription

Question 15

Repressible Operon: Tryptophan

Answer 15

Synthesis pathway model
When excess tryptophan is present, it binds to tryp repressor protein & triggers repressor protein & triggers repressor to bind DNA
- blocks (represses) transcription

Question 16

What happens when excess tryptophan is present

Answer 16

an active repressor protein will bind with the operator to stop the transcription of trytophan.

Question 17

Inducible Operon: lactose

Answer 17

Digestive pathway model when lactose is present, binds to lac repressor protein & triggers repressor to release DNA
- induces transcription

Question 18

What happens when lactose is present?

Answer 18

The inhibitor that blocks the lactase enzyme from being produced is unblocked allowing the production of lactase

Question 19

Jacob & Monod

Answer 19

1st to describe operon system coined the phrase “operon”

Question 20

How does E coli sense the glucose concentration is low?

Answer 20

Cyclic AMP (cAMP) concentration is high.

If glucose is low and lactose is present then lac operon is turned on

Question 21

Repressible operon

Answer 21

usually functions in anabolic pathways
-synthesizing end products
when end product is present in excess,
cell allocates resources to other uses

Question 22

Inducible operon

Answer 22

usually functions in catabolic pathways
-digesting nutrients to simpler molecules
produce enzymes only when nutrient is available
- cell avoids making proteins that have nothing to do, cell allocates resources to other uses

Question 23

points of control

Answer 23

The control of gene expression can occur at any step in the pathway from gene to functional protein

Question 24

What are the points of control?

Answer 24

1. packing/unpacking DNA
2. transcription
3. mRNA processing
4. mRNA transport
5. translation
6. protein processing
7. protein degradation

Question 25

How do you fit all that DNA into nucleus?

Answer 25

DNA coiling & folding -double helix -nucleosomes -chromatin fiber -looped domains -chromosome

Question 26

Nucleosome

Answer 26

"Beads on String" 1st level of DNA packing histone proteins - 8 protein molecules - positively charged amino acid -bind tightly to negatively charged DNA

Question 27

What happens when DNA is tightly wrapped the histone?

Answer 27

no transcription, genes are turned off

Question 28

Missense Mutation

Answer 28

a point mutation, switch between bases, that causes the wrong protein to be

Question 29

Nonsense Mutation

Answer 29

a point mutation because it codes for a stop codon in the middle of the sequence causing the rest of the amino acids to not be coded

Question 30

Silent Mutation

Answer 30

point mutation that has no effect on the amino acid sequence.

Question 31

Methylation of DNA blocks transcription factors

Answer 31

no transcription → genes turned off attachment of methyl groups (–CH3) to cytosine C = cytosine nearly permanent inactivation of genes ex. inactivated mammalian X chromosome = Barr body

Question 32

DNA Phosphorylation

Answer 32

addition of a phosphate group to an amino acid (phosphorylation) will prevent the chromatin from condensing

Question 33

Acetylation of histones

Answer 33

unwinds the DNA -loosely wrapped around histones, which enables transcription and turns on genes attachment of acetyl groups (–COCH3) to histones conformational change in histone proteins transcription factors have easier access to genes

Question 34

Epigenetics Inheritance

Answer 34

Mutations in the DNA are permanent changes….but modifications to the chromatin CAN BE reversed.

Question 35

What is the 1st control of gene expression?

Answer 35

chromatin modifying enzymes by just making the area of DNA more or less accessible to the process of transcription

Question 36

Promoter

Answer 36

nearby control sequence on DNA binding of RNA polymerase & transcription factors "base" rate of transcription binds transcription factors that controls the initiation of transcription

Question 37

Enhancer

Answer 37

distant control sequences on DNA binding of activator proteins...brings it closer to promoter "enhanced" (high level

Question 38

Activator proteins

Answer 38

bind to enhancer sequence & stimulates transcription

Question 39

Silencer proteins

Answer 39

bind to enhancer sequence & block gene transcription

Question 40

Post Transactional Control

Answer 40

Alternative RNA splicing -variable processing of exons creates a family of proteins