Regulation of Gene Expression

Question 1

Why regulate gene expression?

Answer 1

Waste of energy + no cell differentiation.

Question 2

Proks and unicellular euks

Answer 2

Have to be able to respond to environmental cues:
-pH
-gases
-cell communication
-Presence or absence of food
-Temperature

Question 3

Multicellular Euks Regulation

Answer 3

Have more ways of gene regulation than proks, and even unicellular euks.
-Same environmental cues
-Developmental changes: Fetal hemoglobin vs adult hemoglobin
-Cell specialization/differentiation: Pepsinogen - gene is in toes/liver, but only stomach expresses.

Question 4

Sites of Gene regulation

Answer 4

-Transcription
-Post-transcriptional regulation
-Post-translational regulation

Question 5

Transcription Regulation

Answer 5

DNA PHOSPHORYLATION ???Most modification occurs here, beginning of gene production.
-Chromatin modification (Epigenetic regulation?): DNA methylation (tighter) and Histone (protein) acetylation (looser).
-Transcription initiation: A key control point.

Question 6

Post-transcriptional Regulation

Answer 6

-Alternative RNA splicing: 2 types of mRNA from a single hnRNA strand.
-mRNA degradation: Destroying mRNA depending on if you need it or not.
-mRNA location/availability: In Nucleus = can’t be translated

Question 7

Post Translational Regulation

Answer 7

Regulation of protein activity

Question 8

Constitutive Enzymes

Answer 8

Always there, i.e. glycolysis
-Most of bacterial enzymes, varies by cell type for multicellular euks.
-Might not last forever, but need them, so they make new ones.

Question 9

Regulated Enzymes

Answer 9

On or off as needed.
-Digestive or Biosynthetic pathways:
-Fewer of bacterial enzymes, varies by cell type for multicellular euks.
-Some proteins during mitosis/meiosis, i.e. cyclins.

Question 10

Operon

Answer 10

An operon is a collection of several genes for ONE biosynthetic pathway. Plus its regulatory regions.

Question 11

Regulatory Regions

Answer 11

-Promoter: Site for RNA Polymerase.
-Operator: Controls access of RNA polymerase to genes. Repressor protein binding site.
-Activator Binding sites: Doesn’t have a cool name like promoter or operon.

Question 12

Negative control vs. Positive control operons

Answer 12

Negative control: Use a repressor protein
Positive control: Use an activator protein.

Question 13

Negative control operon

Answer 13

Use a repressor protein.
1. Repressible: Normally turned on (active). Corepressor binds to repressor, changes shape, and binds to operator. Blocking access of RNA Pol.
2. Inducible: Normally turned off. Inducer binds to repressor, repressor releases operator. Allowing access of RNA Pol.

Question 14

Positive Control Operons

Answer 14

Use an activator protein.
1. Inducible: If [glucose] is low, then cAMP goes up, cAMP binds to CRP (cAMP Receptor Protein). CRP binds to DNA, increasing the transcription of lac operon (only possible if lactose has already bonded to receptor protein and removed it).

Question 15

Proto-Oncogenes

Answer 15

Genes for normal cell growth and division.

Question 16

Oncogenes

Answer 16

Cancer causing genes

Question 17

What causes a proto-oncogene to become an oncogene?

Answer 17

1. Epigenetic changes: DNA Methylation and acetylation (Phosphorylation?)
2. Translocation or transposition: Gene used to be under control of normal promoter, mutates, moved under a promoter that causes too many copies
3. Gene amplification: Duplication of a region of a chromosome
4. Point mutation: substitution, deletion/insertion.

Question 18

Tumor-Suppressor genes

Answer 18

1. Normally prevent uncontrolled mitosis & growth
2. Mutation here removes control, leads to cancer.

Question 19

Cell signaling pathway problems.

Answer 19

1. Cell cycle-stimulating pathway:
   a. A protein stimulates cell cycle
   b. Cell cycle repeated too much -> cancer
2. Cell cycle-inhibiting pathway defective:
   a. The protein that inhibits cell cycle not produced
   b. Uncontrolled cell cycle -> Cancer