Ch. 23 Cancer

Question 1

RNAi

Answer 1

RNA interference (gene silencing)

Question 2

what are some examples of post-transcriptional RNAi?

Answer 2

miRNA
siRNA
piRNA

Question 3

miRNA

Answer 3

imperfectly matched to their target RNA sequence

• inhibit translation
• target RNA for degradation
• regulate endogenous genes*

-requires a dicer and an argonaute

Question 4

siRNA

Answer 4

perfectly matched to their target

• target RNA for degradation
• target DNA for chromatin remodeling
• defend against genomic invaders (viruses)*

-requires a dicer and an argonaute

Question 5

dicer

Answer 5

(aka RNase)

cleaves dsRNA (double stranded RNA virus)

Question 6

argonaute

Answer 6

Argonaute proteins bind different classes of small non-coding RNAs (miRNAs, siRNAs, and piRNAs).

Small RNAs guide Argonaute proteins to their specific targets through complementary base pairing, which then leads to mRNA cleavage or translation inhibition

Question 7

RISC

Answer 7

example of an argonaute

• RNA induced silencing complex
• uses siRNA to target mRNA for cleavage and destruction
• uses miRNA for translation inhibition

Question 8

RITS

Answer 8

RNA induced transcriptional silencing
-uses siRNA to target DNA for chromatin remodeling or DNA methylation/histone methylation (make DNA not accessible, cant be transcribed)

Question 9

name the phases of the cell cycle

Answer 9

G1/G0 - cell grows, cell enters into non dividing stage 
G1/S checkpoint
S - DNA replicates 
G2 - cell prepares for M phase 
G2/M checkpoint 
M phase - mitosis and cytokinesis

Question 10

what happens at the G1/S checkpoint?

Answer 10

check for cell size, correct nutrients for DNA replication, growth factors, DNA damage, prep for DNA replication
-after this, cell is committed to dividing

Question 11

what happens at the G2/M checkpoint?

Answer 11

check for cell size, make sure DNA replication occurred correctly

Question 12

what happens at the spindle assembly checkpoint?

Answer 12

make sure all chromosomes have properly attached to their spindle fibers (during metaphase of the M phase)

Question 13

kinase

Answer 13

an enzyme that adds a phosphate to a protein

Question 14

cyclin dependent kinases (CDKs)

Answer 14

kinases that control key events of the cell cycle

• only functional when associated with a cyclin (another protein type) cyclins appear at different points in the cell cycle
• specific cyclins determine which proteins the kinases phosphorylate

Question 15

retinoblastoma protein

Answer 15

RB is a tumor suppressor! helps control progression through the G1/S checkpoint

• RB protein binds to E2F and keeps it inactive
• cyclin D and cyclin E CDKs phosphorylate RB
• RB releases E2F
• E2F binds DNA and initiates transcription

if RB proteins are non functional, E2F will always initiate transcription = uncontrolled cell division = tumor = cancer

Question 16

what are some external factors that regulate cell cycle progression?

Answer 16

hormones and growth factors (but these can’t pass through the cell membrane)

SO they have to use the signal transduction pathway!

Question 17

RAS signal transduction pathway

Answer 17

inactive - RAS binds to GDP

active - RAS binds to GTP

Question 18

what happens when MAP kinase is activated?

Answer 18

activates transcription factors that stimulate transcription of cell cycle genes

Question 19

characteristics of cancer cells

Answer 19

1. cells do not respond to normal controls of cell division
2. cells divide rapidly and constantly (tumor growth)
3. metastasis (tumors shed cells which invade other body regions)

Question 20

benign tumor

Answer 20

cells remain localized

Question 21

malignant tumor

Answer 21

cells invade other body regions

Question 22

unilateral sporadic model of cancer

Answer 22

less effect

Question 23

bilateral familial

Answer 23

more effect

Question 24

protooncogene

Answer 24

gene with the potential to cause cancer