Chapter 6: 6.7 Introduction to Regulation of Gene Expression

Question 1

Why are not all genes expressed at the same time?

Answer 1

Organisms regulate gene expression in order to:
* Conserve energy and resources when certain gene products are not required

Question 2

What levels can gene expression be regulated?

Answer 2

1. Epigenetic
2. Transcriptional
3. Post-Transcriptional
4. Translational
5. Post-Translational

Question 3

What do epigenetic and transcriptional regulation involve?

Answer 3

Whether a gene (DNA) gets to be transcribed into RNA

Question 4

List:

Examples of epigenetic and transcriptional regulation

Answer 4

• Whether the gene is physically accessible (epigenetic)
• Presence of special molecules called transcription factors to recruit RNA polymerase (transcriptional)
• RNA splicing and control of RNA stability (transcriptional)

Question 5

What does translational regulation involve?

Answer 5

Involves controlling mRNA translation into proteins

Question 6

What does post-translational regulation involve?

Answer 6

Involves modification of the expressed protein, modulating its activity

Question 7

Define:

Constitutively expressed genes

Answer 7

Genes that are expressed continuously

Question 8

True or False:

Constitutively expressed genes are not regulated

Answer 8

False

Question 9

How can expression levels of constitutively expressed genes be regulated?

Answer 9

1. Promoter strength (transcriptional regulation)
2. mRNA half-life (translational regulation)

Question 10

How is a promoter determined to be “stronger”?

Answer 10

Has a sequence closest to the consensus sequence
* Bounds more often and more strongly by RNA polymerase
* Leads to more transcripts

Question 11

True or False:

Only eukaryotes can have all 3 levels of gene regulation

Answer 11

False, eukaryotes and prokaryotes can both have all 3 levels of gene regulation

Question 12

Unlike eukaryotes, bacteria can have - ——- —- between a promoter and a terminator or ——– —– – ——

Answer 12

• A single gene
• Multiple genes in tandem

Question 13

What is an operon?

Answer 13

In prokaryotes, multiple genes in tandem

Question 14

Describe:

Single Protein Genes in Prokaryotes

Answer 14

• One promoter, coding region and terminator
• Encodes for one protein

(2 points)

Question 15

Describe:

Operons (Multi-Protein Gene) in Prokaryotes

(3 points)

Answer 15

• One promoter, several protein coding regions, on terminator
• Encodes for multiple proteins
• Several start and stop codons to define the beginning/end of each protein

Question 16

Where is an operator located?

Answer 16

Directly upstream or downstream of the promoter

Question 17

1. What binds to the operator?
2. What does it do?

Answer 17

1. Regulatory proteins
2. Controls when RNA polymerase binds to promoter to activate transcription

Question 18

What is responsible for transcriptional regulation?

Answer 18

Operator and Regulatory Proteins

Question 19

What is translational regulation?

Answer 19

Means affecting mRNA before it gets translated into proteins

Question 20

What are some methods of translational regulation?

Answer 20

• mRNA is degraded before it gets translated
• mRNA have short RNAs bind to prevent ribosome from binding

Question 21

When does post-translation regulation occur?

Answer 21

Occurs after translation of mRNA into proteins

Question 22

What are some methods of post-translational regulation?

Answer 22

• Degradation of produced proteins to directly control their levels in the cell

Question 23

What is a degron?

Answer 23

A sequence on the protein that designates it for degradation

Question 24

How does degradation of produced proteins in post-translation regulation work?

Answer 24

• Recognin binds to the degron sequence of a protein
• Brings protein to a proteosome

Question 25

What is a proteosome?

Answer 25

A group of proteins that degrade other proteins

Question 26

Why can transcription and translation occur simultaneously in prokaryotes?

Answer 26

They do not have a separate compartment for the nucleus

Question 27

What are the regulatory proteins that control gene expression in many common prokaryotic systems called?

Answer 27

**Activators** and **Repressors**

Question 28

What is the basic structure of a regulatory protein? | (3 points)

Answer 28

* Contains a DNA binding region * Binds to the operator next to the promoter * Can also have a allosteric site that controls the DNA binding site

Question 29

# True or False: Some regulatory proteins have an allosteric site that is controlled by the DNA binding site

Answer 29

False, the allosteric site CONTROLS the DNA binding site

Question 30

# Define: Activators

Answer 30

Promotes binding of RNA polymerase to the promoter to **activate** transcription * Involved in positive regulation

Question 31

# Define: Repressors

Answer 31

Prevents RNA polymerase from binding to the promoter to **inhibit** transcription * Involved in negative regulation

Question 32

What can activators and repressors be influenced by?

Answer 32

Small molecules: * Inducers * Inhibitors * Co-repressors

Question 33

# Define: Inducers

Answer 33

Promote gene expression by inactivating repressors or activating activators

Question 34

# Define: Inhibitors

Answer 34

Prevent gene expression by inhibiting activators

Question 35

# Define: Co-repressors

Answer 35

Prevent gene expression by activators repressors

Question 36

# True or False: Activators are involved in negative regulation

Answer 36

False, they are involved in positive regulation

Question 37

# True or False: Repressors are involved in positive regulation

Answer 37

False, they are involved in negative regulation

Question 38

How do inducers promote gene expression?

Answer 38

By inactivating repressors OR activating activators

Question 39

How do inhibitors prevent gene expression?

Answer 39

By inhibiting activators

Question 40

How do co-repressors prevent gene expression?

Answer 40

By activating repressors

Question 41

# Describe: Positive regulation

Answer 41

Activators may be always bound to DNA promoting transcription * In other cases, activators are not bound and they require an **inducer** to bind to DNA

Question 42

# Describe: Negative regulation

Answer 42

Repressors may be always bound to DNA inhibiting transcription * In other cases, repressors are not bound and they require a **co-repressor** to bind

Question 43

What would be required to stop positive regulation?

Answer 43

An inhibitor

Question 44

What would be required to stop negative regulation?

Answer 44

An inducer