Cell Cycle and Apoptosis

Question 1

4 major phases of the cell cycle

Answer 1

G1, S, G2: Interphase

M

Question 2

G0 phase

Answer 2

Cell is no longer dividing
Quiescent (dormant)
Can re-enter cell cycle

Question 3

M phase

Answer 3

Cell division

2 parts: mitosis (nuclear division) and cytokinesis (cytoplasmic division)

Question 4

Prophase/Prometaphase

Answer 4

Chromosomes condense
Nuclear envelope breaks down
Mitotic spindle (microtubules) forms
Kinetochore (protein structure at centromere) connects chromosomes to microtubules
Centrosomes (organizing centers) form at opposite sides of cells

Question 5

Metaphase

Answer 5

Centromeres line up at metaphase plate

Question 6

Anaphase

Answer 6

Sister chromatids separate

Kinetochores pull chromosomes along microtubules

Question 7

Telophase

Answer 7

Two daughter nuclei form

Question 8

G1 phase

Answer 8

Cell grows and makes more macromolecules and organelles

Question 9

S phase

Answer 9

DNA is replicated

Question 10

G2 phase

Answer 10

Cell grows and makes more materials as in G1

Question 11

3 major checkpoints in the cell cycle

Answer 11

End of G1
End of G2
Partway through M
Cell machinery is always surveying the state of the cell

Question 12

G1 checkpoint

Answer 12

Make sure that there is enough material to replicate DNA

Look for DNA damage

Question 13

G2 checkpoint

Answer 13

Make sure that DNA has been duplicated completely and correctly

Question 14

M checkpoint

Answer 14

Make sure that mitotic spindles are attached properly and that there is enough material to make daughter cells

Question 15

2 major proteins involved in checkpoints

Answer 15

Cyclins

Cyclin-dependent kinases (Cdks)

Question 16

Cyclin-Cdk complex

Answer 16

Cyclin binds to Cdk -> Cdk changes shape -> kinase ability is activated (Cdk can phosphorylate key proteins that initiate the next step in the cell cycle)
More cyclin present- greater Cdk activity

Question 17

Specificity of cyclin-Cdk

Answer 17

Specific cyclin-Cdk complexes exist for each checkpoint

Different targets are phosphorylated to activate next step

Question 18

Cdc6 and cyclin-Cdk complex

Answer 18

G1: Cdc6 (protein) is bound to origin recognition complex (ORC), which is bound to origin of replication
Cdc6 + ORC + origin of replication = pre-replicative complex
S: S-Cdk triggers S phase -> Cdc6 is phosphorylated and then degraded -> replication fork assembled -> DNA replication
Cdc6 phosphorylation: beginning of transcription
Once Cdc6 is phosphorylated, origin of replication can’t be used again

Question 19

Regulation of cyclin-Cdk complex

Answer 19

Cdk is phosphorylated and then dephosphorylated to turn on
Cyclin is degraded to turn off
Cdk inhibitor proteins can hold back or turn off completely
Extracellular cues

Question 20

Phosphorylation of cyclin-Cdk complex

Answer 20

Cdk is phosphorylated and de-phosphorylated according to cellular cues
Cyclin binds to Cdk -> protein kinases phosphorylate Cdk -> activating protein phosphatase removes inhibitory phosphate, leaving activating phosphate -> active cyclin-Cdk complex

Question 21

Ubiquitylation of cyclin-Cdk complex

Answer 21

Allows for Cdk to be deactivated
Ub-ligase attaches ubiquitin to cyclin, tagging it for proteosome
Proteosome degrades cyclin

Question 22

Inhibitor proteins

Answer 22

Proteins inhibit formation of cyclin-Cdk or cyclin-Cdk activity
DNA damage activates protein kinases that activate p53 protein -> active p53 binds to regulatory region of p21 gene -> transcription and then translation of p21 gene -> p21 protein binds to cyclin-Cdk complex, inhibiting it

Question 23

Survival factors

Answer 23

Inhibit apoptosis

Question 24

Mitogens

Answer 24

Stimulate cell division by activating corresponding cell cycle cascade
Mitogen binds to mitogen receptor in cell membrane -> mitogen-activated protein (MAP) kinase cascade -> activation of Cdk -> Rb protein is phosphorylated -> Rb lets go of transcription factor -> cell proliferation

Question 25

Growth factors

Answer 25

Stimulate cell growth | Activate signaling cascade -> increased production of macromolecules

Question 26

Components of cytoskeleton that aid in cell division

Answer 26

Mitotic spindle | Contractile ring

Question 27

Contractile ring

Answer 27

Actin and myosin assemble on cytoplasmic face of plasma membrane Slide like muscle contraction, pulling membrane in

Question 28

Phragmoblasts

Answer 28

Found in plants Construct cell wall as final step in cell division Phragmoblast microtubules position Golgi-derived membrane to form new cell wall

Question 29

3 classes of microtubules

Answer 29

Kinetochore microtubules Aster microtubules Interpolar microtubules All 3 types array from centrosome

Question 30

Kinetochore microtubules

Answer 30

Attach to centromere and pull chromosomes apart as they (MTs) shorten

Question 31

Aster microtubules

Answer 31

Pull centrosomes apart

Question 32

Interpolar microtubules

Answer 32

Push poles apart using sliding force

Question 33

Timing of assembly of mitotic spindle

Answer 33

Centrosomes replicate during interphase and migrate during M phase

Question 34

Dead cells

Answer 34

Loss of integrity of plasma membrane Cell, including nucleus, has undergone complete fragmentation into discrete apoptotic bodies and/or its corpse or fragments has been engulfed by an adjacent cell

Question 35

Causes of cell death

Answer 35

Damage to cell (DNA, ER, oxidative stress, etc.) Cell is no longer working efficiently Development ("webbing" between fingers disappears in embryo)

Question 36

2 types of cell death

Answer 36

Necrosis | Apoptosis

Question 37

Necrosis

Answer 37

"Messy" death Acute injury causes cell to lyse and dump its components Compromising of cell membrane

Question 38

Apoptosis

Answer 38

``` "Neat" death Cell is engulfed by phagocytic cell and cellular components are recycled Compartmentalized No damage to neighboring cells Complex signaling cascade ```

Question 39

Vacuoles in apoptosis

Answer 39

Vacuoles become enlarged: cell partitions itself off

Question 40

What happens to cell during apoptosis

Answer 40

1. Blebbing of cell: cytoskeleton uncouples from membrane and ball-like structures (blebs-contain cell components) form 2. Cell shrinks 3. Nucleus fragments 4. Chromatin condenses 5. DNA fragments

Question 41

2 major pro-aptotic pathways

Answer 41

Extrinsic: extracellular cues induce Intrinsic: cellular damage induces (causes activation through mitochondria)

Question 42

Intrinsic apoptotic pathway

Answer 42

1. Cell stress activates BAX 2. BAX causes permeabilization of mitochondria 3. Cytochrome C leaks out (cytochrome C: electron transport chain- end of energy production, committed step) 4. Apoptosome forms 5. Apoptotic processes activated by caspases

Question 43

Extrinsic apoptotic pathway

Answer 43

1. 1st messenger binds to death receptor 2. Caspases activate BAX 3. BAX causes permeabilization of mitochondria 4. Cytochrome C leaks out 5. Apoptosome forms 6. Apoptosis by caspases OR Caspases that activate BAX also activate caspases that cause apoptosis

Question 44

Bcl2 protein

Answer 44

Anti-aptotic: inhibits BAX

Question 45

Caspases

Answer 45

Proteases (cleave proteins) Activated by cleavage To activate: cleave procaspase Regulate apoptosis using irreversible method (cleavage is permanent): cell is damaged- don't want to go back 1 molecule of this can cleave many molecules of this, which in turn cleave more molecules of this

Question 46

Ways to measure apoptosis

Answer 46

Cleaved caspase 3 (Western blot: Ab on cleaved caspase) TUNEL stain: label ends of chopped-up DNA and look at it under microscope Phosphoserine exposure: phospholipids are flipped to outer side of membrane during apoptosis (usually on inner)

Question 47

Phosphoserine exposure

Answer 47

Annexin 5 binds to phosphoserine Use Ab to Annexin 5 to label apoptotic cells Measure Ab binding by flow cytometry (control graph: no shoulder; experimental graph: shoulder)