Genetics 10

Question 0

Retroviruses contain what 3 genes?

Answer 0

Gag: proteolytic cleavage
Pol: reverse polymerase
Env: envelope gene

Question 1

Reverse transcriptase

Answer 1

Allows ssRNA viral genome to be synthesized into a DNA strand that is complementary to viral RNA.
-RNA strand of viral RNA-DNA hybrid is degraded, replaced with DNA, which can be incorporated into the host’s genome.

Question 2

Function of LTRs

Answer 2

• At end of RNA genome, facilitate integration of viral chromosome into host DNA.
• Also contain promoters that drive viral gene expression.

Question 3

src gene

Answer 3

• oncogene
• encodes tyrosine kinase
• c-rsrc= native proto-onocgene in a cell that will cause cancer if mutated.
• v-src gene: oncogene located in a retrovirus. Contributes to unregulated cell division and cancer.
• *not defective: contains genes necessary for replication (unusual)

Question 4

Why are most transducing retroviruses defective? What do they need?

Answer 4

• The insertion of cellular proto-oncogenes may result in deletion of viral structural genes.
• Require helper virus (wild-type retrovirus) to provide gag, pol and/or env, to allow defective virus to replicate.

Question 5

Monomeric G proteins

Answer 5

• Contain GTPase activity.
• slower to activate than trimeric G protein (slower GDP dissociation rate)
• slower to inactivate (slower intrinsic GTPase rate) relative to alpha subunit of trimeric G protein.

Question 6

Ras superfamily

Answer 6

• GTPases, involved in cell signaling and growth.
• regulates cell growth through serine-threonine protein kinases.
• Activating mutations of c-ras accounts for 30% of all cancers.

Question 7

C-ras signaling involves

Answer 7

1) GTP-binding proteins with high affinity
2) Intrinsic GTPase rate that is slow compared to Ga GTPases
3) Spontaneous rate of GDP dissociation is very slow.

Question 8

What accessory proteins regulate Ras?

Answer 8

-GTPase Activating Protein (GAP)
-Guanine nucleotide exchange factor (GEF, aka GNRP, GNEP)
-

Question 9

GAP

Answer 9

• Accelerates intrinsic GTPase activity of c-ras (by activating GTPase, you inhibit Ras)
• Accelerates ras GTPase by 10^4-10^5.
• Built in off mechanism hydrolyzes GTP and turns off Ras.

Question 10

GEF

Answer 10

Accelerates GDP dissociation from c-ras.

-Activates by stimulating rate limiting step of GDP dissociation, turns ras on.

Question 11

Ras is stimulated by:

Answer 11

1) Inhibition of GAP
2) Activation of GEF
3) Inhibition of GDI

Question 12

Rho

Answer 12

• Subfamily of Ras GTPases.
• involved in cytoskeleton organization through serine-threonine protein kinases.
• turned off by GAP
• Activates effector via GEF
• Inactive Rho stabilized by GDI (desensitization)

Question 13

Mitogen

Answer 13

-stimulates growth and cell division

Question 14

What enters the nucleus and phosphorylates TFs?

Answer 14

MAP-kinase, which was activated by MAP-kinase-kinase, which was activated by MAP-kinase-kinase-kinase.

Question 15

Raf

Answer 15

• equivalent of an effector molecule.

- serves as central site for activations by Ras and stimulation of MAP kinase cascades.

Question 16

Immediate early gene

Answer 16

• first genes activated by TFs. Function as primary response genes.
• Low expression in quiescent cells
• Induced transcription within minutes of stimulation
• Turn on independent of protein synthesis
• Shutoff dependent on protein synthesis
• short mRNA half-life 5-15 mins

Question 17

Functions of immediate early gene protein products

Answer 17

1) Bind late response genes to turn them on in a protein-synthesis dependent manner
2) Bind genes or mRNA of immediate early genes to turn them off/degrade them.

Question 18

Late response genes

Answer 18

Function as secondary/delayed response genes.

1) Gene expression occurs after several hours
2) Turn on dependent on protein synthesis.