Final Exam - Regulation of Gene Expression

Question 1

4 levels of regulation in gene expression (eukaryotes)

Answer 1

1. Transcriptional regulation: long and short term
2. Post-transcriptional reg
3. Translational reg
4. Post-translational reg

Question 2

1. transcriptional regulation - long and short term

Answer 2

long term
- methylate the DNA - prevents those regions from being transcribed; also, helps DNA polymerase distinguish old strand from new strand

short term:
Different transcription factors bind to different DNA sequences
- helix-turn-helix proteins
- zinc finger proteins
- leucine zippers

Question 3

coordinated gene regulation:

Answer 3

multiple genes encoding many proteins are turned on simultaneously

Question 4

gene amplification:

Answer 4

sometimes genes are duplicated several times to amplify their # so that enough copies of mRNA can be produced. E.g. the genes for herbicide resistance may be amplified to survive the chemical.

Question 5

2. post-transcriptional regulation

Answer 5

1. alternate splicing - during mRNA processing when introns are removed & exons are spliced some mRNAs are processed differently to yield different proteins (e.g. exons 1,2,3 may form one protein, but exons 1,3 joined make a different one)
2. mRNA stability - may get tagged for degradation or get degraded by RNA binding proteins

Question 6

3. translational regulation

Answer 6

1. timing / mRNA storage - many processed mRNAs are stored in the nucleus of an egg prior to fertilization & are translated after & during embryonic development
2. hormonal regulation - casein mRNA is translated more efficiently when the hormone prolactin is present, which is released when an animal is ready for lactation
3. cofactor influence - when heme molecules accumulate, they increase the translational efficiency of globin mRNAs (make hemoglobin)

Question 7

4. Post-Translational regulation:

Answer 7

last stage of controlling gene expression @ protein level. At this point, most proteins become functional. Situations where it’s a regulatory mechanism:

1. zymogen activation: (zymogen = inactive enzyme precursor) some proteins made in inactive form & are later converted to active form. E.g. insulin
2. selective targeting: proteins targeted for specific locations need to be in the right place. If protein doesn’t reach target, it’s often b/c it’s defective, so remains in the cytoplasm & is degraded.
3. chemical modification: phosphorylation can make proteins active or inactive. E.g. Na+/K+ pump
4. glycoslylation: many membrane proteins are glycosylated (have sugar added to coat) after translation in the Golgi apparatus or rough ER. This reduces degradation by proteases & facilitates signal transduction.

Question 8

Inducible operons

Answer 8

e.g. lac operon - mostly turned off; turned on only when necessary; used in catabolic pathways

Question 9

Repressible operons

Answer 9

e.g. trp operon - stays on; turned off when not needed

Question 10

organization of prokaryotic genes

Answer 10

operons, which include operator (controls the access of RNA polymerase to the genes), promoter & genes they control; they are inducible OR repressible