Gene Expression

Question 1

Inducible operon

Answer 1

Operon that is usually turned off but can be turned on (induced)

• lac operon

Question 2

Repressible operon

Answer 2

Operon that is usually turned on but can be turned off (repressed)

Question 3

Glucose present in lac operon

Answer 3

Operon is OFF

repressor protein is bound to operator and is not removed

No cAMP present ; no CAP protein production

Question 4

Lactose Present in lac operon

Answer 4

Operon is turned ON

• cAMP is make and helps form CAP protein to bind to CAP site
• allolactose (inducer) is created and binds to repressor and inactivates it

Question 5

Glucose and Lactose present in lac operon

Answer 5

Lac operon is turned OFF
(might do very small amounts of transcription)

• no cAMP production so no CAP protein formation (no transcription)
• allolactose is generated inactivating repressor

Question 6

Regulatory mechanisms of transcription

Answer 6

Cis-acting

Trans-acting

Question 7

Cis-acting elements

Answer 7

Core promotor, TATA box and regulatory proteins

• can be proximal (closer to promotor)
• can be distal (further from promotor)
• are physically parts of the DNA

Question 8

Trans-acting elements

Answer 8

Transcription factors

General: initiate transcription

Specific: regulate how much is transcribed

• not physically part of the DNA

Question 9

Regulatory mechanisms of post-transcriptional regulation

Answer 9

Alternative splicing

Alternative polyadenilation

MRNA editing

MRNA stability

Question 10

Alternative splicing

Answer 10

Different splicing sites can be removed or not removed depending on splicesome and snRNA activity

• produces shorter functional proteins called isoforms in addition to normal protiens.
• ex: tropomyosin

Question 11

Alternative polyadenylation

Answer 11

MRNA with different 3’ ends

• produces structural differences (hydrophobic vs hydrophilic)

Ex: antibodies

Question 12

MRNA editing

Answer 12

Altering 1 base in the mRNA via polyadenylation splicing.

Usually results in shorter protein production with different functions

Ex: small intestine apoB proteins

Question 13

MRNA stability

Answer 13

Additional degradation protections

Examples: TfR protein receptors and IRE-BP complexes

Question 14

RNA interference

Answer 14

Reduces gene expression by repressing translation or increasing degradation of mRNA

• can be done endogenously or exogenously

Question 15

Endogenous RNA interference

Answer 15

Conducted via MiRNA

Induces degradation of mRNA or block the translation.

• use RISC protein to do the functions

Question 16

Exogenous RNA interference

Answer 16

Conducted by siRNA’s

Question 17

Epigenetic regulation

Answer 17

Changes in histones and chromatin that affect transcription and translation

Question 18

Direct transposition

Answer 18

Transposase cuts out Tn segment and inserts it into the new site

Question 19

Replicative transposition

Answer 19

Tn is copied and the copy is inserted somewhere via transposase. (Original copy is still there).

Question 20

Acetylation of histones

Answer 20

Type of epigenetic regulation

Uses histone acetyltransferases to transfer acetyl groups to histone tails.

-unwinds DNA and allows for MORE transcription/gene expression

Question 21

Methylation of DNA

Answer 21

Epigenetic regulation

Binds methyl groups to cytosine residues

• allows for LESS gene expression/transcription