Cell Cycle and Nucleus

Question 1

Stages of the cell cycle

Answer 1

G1 (growth)–> S (DNA replication)–> G2 (growth)–> M (mitosis)

Question 2

Two main checkpoints in cell cycle

Answer 2

G1/S
G2/M

also have a mitotic spindle checkpoint

Question 3

Questions for G1/ S checkpoint

Answer 3

is the cell big enough?
is the environment good?
is there DNA damage?

Question 4

G1 / S transition is sensitive to the a) and is b) independent

Answer 4

a) extracellular environment
b) growth factor

Question 5

What is the irreversible commitment to go through the cell cycle?

Answer 5

G1/ S transition

Question 6

How does Rb inhibit the G1/ S transition?

Answer 6

Rb can inactivate E2F

(E2F is a transcription factor that increases S-phase gene transcription)

Question 7

How is Rb inactivated ( thus no longer blocking cell division through the G1/S transition)?

Answer 7

Cyclin/CDK adding phosphate to Rb

Question 8

Cyclin Kinase Dependent inhibitors (CKIs)

Answer 8

make cyclin/CDK inactive (inhibit cell division)

Question 9

How does a growth factor act as an extracellular control to affect S phase entry?

Answer 9

growth factor turns on E3 for CKI–> increases CKI degradation–> G1/ S CDK cyclin is then ACTIVE–> adds a phosphate to Rb to make it INACTIVE–> S phase entry

Question 10

At what point in the cycle is the DNA damage checkpoint? and how does it work?

Answer 10

before S (G1/S transition)

DNA damage tells p53 to become active –> acts a TF to increase expression of CKI –> CKI makes S cyclin/ CDK INACTIVE so there is no phosphorylation of Rb and thus decrease cell cycle/ NO S

Question 11

Before S what do you use to degrade cyclin?

Answer 11

ubiquination

Question 12

What questions do you ask at G2 checkpoint?

Answer 12

DNA replicated?
cell big enough?

Question 13

G2/ M transition

Answer 13

PHOSPHORYLATION is very important (and can turn other proteins on OR off)

If you have active M cyclin/ CDK –> Drives towards mitosis

Question 14

Describe how MPF (cyclin/ CDK) becomes active

Answer 14

first cyclin binds CDK which makes an inactive MPF, then it gets phosphorylated TWICE by 1) an activating kinase known as CAK) and 2) an inhibitory kinase known as Wee1–> then an ACTIVATING phosphatase known as CDC 25 removes the inhibitory phosphate –> thus the MPF is now active

Question 15

How does MPF increase its activity so quickly (aka increasing CDK activity all of a sudden)?

Answer 15

positive feedback on the CDC 25
negative feedback on Wee1

Question 16

What is the point of the mitotic spindle checkpoint?

Answer 16

to tell the cell if it is ready to go from metaphase to anaphase

Question 17

What do separase, securin and APC do? How do they work in the mitotic spindle checkpoint?

Answer 17

separase–> cleaves cohesion in between sister chromatids (pushes anaphase)
securin–> inhibits separase (keeps it in metaphase)
APC –> is an E3 for cyclin, and turns OFF securin… pushes anaphase

Question 18

Explain the process of degradation with ubiquination

Answer 18

E1 carries U tag –> E1 E2 E3 form complex –> E1 leaves and passes tag to E2 –> E3 recognizes target protein that needs to be degraded –> E2 passes U to protein and protein gets long U tag that proteasome can come degrade it

Question 19

What is G0

Answer 19

State of differentiation (NOT dividing), shunted here off G1–> S transition

CKIs upregulated in G0 to keep cyclin/ CDK from being active

Question 20

Features of nucleus

Answer 20

double membrane (outer is continuous with the ER)

nuclear pore complex

chromatin

nucleolus (make rRNA)

Question 21

Nuclear lamina

Answer 21

provides structural support inside nucleus (right on edge of inner membrane)

intermediate filaments

A,B, C types

Question 22

What links nuclear lamina to the cytoskeleton?

Answer 22

Sun/KASH complexes (they span the membrane)

could be microfilaments, microtubules, and intermediate filaments

diff complexes in diff cell types

Question 23

Nuclear pore complex

Answer 23

traffic IN and OUT of nucleus

BASKET shape

can expand to transport large cargo

Question 24

What does the long red line point to? The short? where is the view from?

Answer 24

View from cytoplasm.

long line- ribosome

short line- NPCs

Question 25

Ran GTP and nuclear pore traffic

Answer 25

Directionality of protein movement controlled by Ran gradient

In cytoplasm: Ran- GDP

In nucleus: Ran-GTP

theres a nuclear localization signal that binds to a protein and alpha and beta subunits at the pore, brought into the nucleus when Ran GDP –> GTP , then Ran helps take out subunits while signal stays in nucleus, and Ran GTP –> GDP

Question 26

Heterochromatin vs. Euchromatin

Answer 26

Heterochromatin: high condensed = LOW expression

Euchromatin: less condensed = HIGH expression

Question 27

Histone deactylase

Answer 27

removes acetyl groups = condensed chromatin = LESS transcription

Question 28

histone deacetylase inhibitors

Answer 28

inhibits histone deacteylase

which means acetyl groups stay= open chromatin = more transcription

–> ie. more transcription of CKIs to stop diving cells like in cancer (most cancers have high HDAC activity)

Question 29

Laminopathies

Answer 29

nuclear lamin diseases… mutations in the lamens (could just be 1 point mutation typically in A/C genes)

Question 30

Examples of laminopathy

Answer 30

ie. muscular dystrophy, Hutchinson-Gilford Progeria Syndrome (point mutation in Lamin A near C -terminus called progerin)

Question 31

Generally, how do laminopathies cause disease?

Answer 31

Lamin a/c and other inner Nuclear envelope (NE) proteins interact with chromatin, chromatin modifying proteins, and transcription factor. NE proteins may influence gene expression through organization of chromatin structure -> mutations could lead to altered gene expression