Cell Division & Differentiation

Question 1

Why do cells grow and divide

Answer 1

• to generate tissues
• to make those tissues grow
• to make up for ‘wear and tear” on those tissues

Question 2

How do cells grow and divide

Answer 2

• cell division - making a new cell

- hypetrophy - a cell getting physically bigger

Question 3

Halting cell division causes ___

Answer 3

death

Question 4

Define ‘cell division’

Answer 4

the process by which cells double their content, then divide to produce 2 daughter cells

Question 5

State the 3 cycles of the cell cycle

Answer 5

1) chromosome cycle
2) cytoplasmic cycle
3) centrosome cycle

Question 6

Outline each of the 3 cycles

Answer 6

chromosome cycle
- DNA replication & segregation (mitosis)

cytoplasmic cycle
- organelle replication & physical division (cytokinesis)

centrosome cycle
- replication of the mitotic spindle

Question 7

State the 3 phases of interphase

Answer 7

1) G1 phase
2) S phase
3) G2 phase

Question 8

Outline phase 1 of interphase (4)

Answer 8

G1 phase

• start point of the cycle
• G = gap
• normal cell activity
• often the longest phase

Question 9

Outline phase 2 of interphase (3)

Answer 9

S phase

• S = synthesis
• cell contents double (DNA & cytoplasm)
• chromosomes duplicate to form sister chromatids

Question 10

Outline phase 3 of interphase (3)

Answer 10

G2 phase

• second gap phase
• normal biosynthesis
• only occurs when all DNA is replicated

Question 11

State the potential 5th phase (3)

Answer 11

G0

• the cell exits the cell cycle
• normal cellular role, but unlikely to ever divide

Question 12

State what protein is involved in cell cycle checkpoints

Answer 12

cyclin

Question 13

State the function of the protein in the cell cycle (2)

Answer 13

• maintain integrity of the replicating genetic material

- if a flaw is found at any single stage, the cell does not progress into the next phase

Question 14

State 2 diff. cytoskeletal machines involved in mitosis

Answer 14

• mitotic spindle –> microtubules

- contractile ring –> actin & myosin

Question 15

Describe the 2 cytoskeletal machines

Answer 15

mitotic spindle

• microtubles grow out like points of a star
• formed via duplication of the centrosome during S phase

contractile ring

• consists of both actin & myosin filaments
• forms under plasma membrane at equator of cell
• contracts to divide cell in 2

Question 16

State the 2 proteins involved in the contractile ring

Answer 16

• actin

- myosin

Question 17

State the 6 stages of M phase

Answer 17

stages 1-5 = mitosis

1) prophase
2) prometaphase
3) metaphase
4) anaphase
5) telophase

stage 6 = cytokinesis

Question 18

Outline step 1 of the M phase (2)

Answer 18

prophase

• chromosomes begin to condense
• outside nucleus, mitotic spindles begin to assemble

Question 19

Outline step 2 of the M phase (4)

Answer 19

prometaphase

• nuclear membrane breaks down
• spindle & chromosomes meet
• attachment via kinetochore
• spindle begins to move to the poles of the cell

Question 20

Outline step 3 of the M phase (2)

Answer 20

metaphase

• sister chromatids align on cell equator
• metaphase plate forms

Question 21

Outline step 4 of the M phase (4)

Answer 21

anaphase

• sister chromatids separated by separase (enzyme) (produced in early part of anaphase)
• spindle poles move outwards
• microtubules shorten
• chromosome slides along microtubule

Question 22

Outline step 5 of the M phase (4)

Answer 22

telophase

• chromosomes arrive at poles
• chromosomes decondense
• nuclear envelope forms
• cells split into 2

Question 23

Outline step 6 of the M phase (4)

Answer 23

cytokinesis

• starts in anaphase, ends in telophase
• actinomyosin ring assembles under cell membrane
• contraction of the ring pinches cell into 2
• each cell has one full set of chromosoms, a centrosome, & half the cytoplasm

Question 24

State what phase differentiated cells are in

Answer 24

G0

Question 25

State what triggers a cell to undergo differentiation (3)

Answer 25

• diffusable factors (signals)
• proteins in ECM
• hormones

Question 26

Define ‘acetylated tubulin’

Answer 26

a protein that neurons express

Question 27

State the 2 steps in cell differentiation

Answer 27

• specification

- determination

Question 28

Outline the 2 steps in cell differentiation (5)

Answer 28

specification

• capable of autonomous differentiation in isolation (if in test tube/dish)
• can be reversed
• not “fate committed”

determination

• cell differentiates into a specific cell type, even when it is placed amongst cells of a diff. type
• irreversible
• “fate committed”

Question 29

Define ‘terminal differentiation’

Answer 29

when division must cease for differentiation to occur

Question 30

State examples of cell types which require terminal differentation (2)

Answer 30

• nerves

- skeletal muscle

Question 31

State what cells which do not require ‘terminal differentiation’ do during division to differentiate

Answer 31

other cell types significantly slow division to differentiate

Question 32

When can cells de-differentiate? (3)

Answer 32

during regeneration

• some animals can regenerate body parts after injury
• cells at injured site de-differentiate