Unit 4 - Ch 14 - Gene Regulation

Question 1

Types of Genes (3)

Answer 1

Constitutive

Inducible

Repressible

Question 2

Constitutive genes

Answer 2

genes that are always “on” (being transcribed and translated)

• producing proteins needed for basic life functions => enzymes in glycolysis
• however, not all expressed at the same rate

Question 3

Inducible genes

Answer 3

genes that are normally “off” (not being transcribed or translated)

• may be turned on, usually by a chemical signal
• usually for catabolic functions

Question 4

Repressible Genes

Answer 4

genes that are normally “on”

• may be turned off to save cellular energy, usually by a chemical signal
• usually associated with anabolic activity

Question 5

Operon

Answer 5

Gene complex in prokaryotes consisting of a group of structural genes with related functions plus the closely linked DNA sequences responsible for controlling them.

Question 6

Lac Operon components (in order)

Answer 6

An inducible operon

Components

1. Repressor Gene – produces repressor protein; always “on”
2. Promoter – RNA polymerase binds to the DNA; start transcription
3. Operator – structural gene swithch
4. Structural Gene –series of genes in a metabolic pathway

Question 7

Control of Lac Operon when lactose is present

Answer 7

lactose binds to the repressor protein and inactivates it so it does not bind to the operator and structural genes are transcribed and translated

Question 8

Control of Lac Operon when lactose is absent

Answer 8

repressor binds to the operator and blocks RNA polymerase

- no transcription or translation of structural genes occurs

Question 9

Trp Operon

Answer 9

A repressible operon

- synthesizes tryptophan in prokaryotes

Question 10

Trp Operon components (in order)

Answer 10

1. Repressor Gene – produces repressor protein (constitutive)
2. Promoter – RNA polymerase binds, transcription start
3. Operator – repressor binds here
4. Structural Gene – genes needed to synthesize tryptophan

Question 11

Control of Trp Operon with Tryptophan present

Answer 11

repressor protein is activated; binds to operator

- blocks transcription

Question 12

Control of Trp Operon with Tryptophan absent

Answer 12

repressor protein cannot bind to operator

- RNA polymerase transcribes the structural genes

Question 13

In Eukaryotes gene regulation occurs where?

Answer 13

Nucleus

Cytoplasm

Question 14

Two major types of nuclear gene regulation

Answer 14

Transcriptional Control

Posttranscriptional Control

Question 15

Transcriptional Control. Involves (4)

Answer 15

producing mRNA in the nucleus of eukaryotes. Involves:

a. Chromosome organization
b. DNA methylation
c. Multiple gene copies – more RNA is produced
d. UPEs/Enhancers

Question 16

Posttranscriptional Control. Involves (2)

Answer 16

mRNA has been formed, is still in the nucleus. Involves:

a. mRNA processing
– introns and exons are initially transcribed - introns are removed - exons are retained in mature transcript

b. mRNA transport – rate is controlled via nuclear pores

Question 17

Two major types of Cytoplasmic gene regulation

Answer 17

Translational Control

Posttranslational Control

Question 18

Translational Control

Answer 18

Determines how long / often mRNA is translated.

Often influenced by chemical signals in the cytoplasm.

Question 19

Posttranslational Control. Involves (2)

Answer 19

A protein has been produced. Involves:

a. Polypeptide Modification – often involves phosphorylation of a protein to activate it’s activity (consumes ATP)
b. Polypeptide Degredation – Selective degradation targets specific proteins for destruction by proteasomes - terminal amino group AA often impacts protein longevity

Question 20

Chromosome organization as part of Transcriptional Control

Answer 20

Euchromatin is transcribed while Heterochromatin is not.

heterochromatin: appears dense in micrographs
euchromatin: appears spread out

Question 21

DNA methylation

Answer 21

– of cytosine nucleotides

• methylated DNA is inaccessible to transcription
• inactivates the DNA - basis for barr body inactivation

Question 22

UPE’s / Enhancers

Answer 22

Upstream Promoter Elements

DNA sequences that enhance the amount of mRNA produced