8 The Developing Cell

Question 1

how is the cell cycle controlled?

Answer 1

by cyclins

which activate cyclin-dependent kinases

which catalyse the addition of a phosphate group onto a protein, changing its tertiary structure

Question 2

what happens if errors in DNA are detected?

Answer 2

p21 binds to CDKs to halt the cell cycle at G1 ∴ DNA can be replaced

Question 3

outline the interphase stage of the cell cycle

Answer 3

G1: cells grow in size and mass; organelles replaced

S: semi-conservative replication of DNA

G2: energy stores increased; chloroplast and mitochondria increase

Question 4

what is required to pass the G1 checkpoint?

Answer 4

chemicals for S-C replication present

cell is sufficiently large and has enough nutrients

Question 5

what is required to pass the G2 checkpoint?

Answer 5

DNA has been replicated without damage

cell is sufficiently large

Question 6

prophase (I)

Answer 6

DNA condenses into visible chromosomes

centrioles move to poles and produce spindle fibres

nucleolus breaks down

(crossing over between non-sister chromatids)

Question 7

metaphase (I)

Answer 7

chromosomes (bivalents) line up on equator

spindle fibres attach to centromere

Question 8

anaphase (I)

Answer 8

spindle fibres contract and centromeres split (do not)

daughter chromosomes pulled to opposite poles

(whole chromosomes pulled to opposite poles, forming 2 haploid sets)

Question 9

telophase (I)

Answer 9

(daughter) chromosomes reach poles

chromosomes uncoil

spindle fibres disintegrate and nuclear envelope reforms

Question 10

prophase II

remember this is meiosis only (this should be in the next chapter)

Answer 10

chromosomes shorten and thicken

2 sister chromatids joined by centromere

centrioles move to poles and microtubules form

nuclear envelope and nucleolus disintegrate

Question 11

metaphase II

remember this is meiosis only (this should be in the next chapter)

Answer 11

chromosomes line up on equator

spindle fibres attach to centromeres

Question 12

anaphase II

remember this is meiosis only (this should be in the next chapter)

Answer 12

spindle fibres contract and centromeres split

sister chromatids form daughter chromosomes

Question 13

telophase II

remember this is meiosis only (this should be in the next chapter)

Answer 13

chromosomes reach pole, uncoil and lengthen

spindle fibres disintegrate

nucleolus reforms

Question 14

how do we analyse the cell cycle?

Answer 14

flow cytometry:

• DNA stained with fluorescent dye
• passed through flow cytometer
• fluorescent intensity recorded

more DNA = more fluorescence ∴ increases G1 -> S -> G2

Question 15

what is apoptosis?

Answer 15

programmed cell death

Question 16

how is apoptosis initiated?

Answer 16

p53 (a tumour supressor protein)

Question 17

outline the process of apoptosis

Answer 17

pyknosis (cell shrinks and nucleus condenses)

enzymes break down the cytoskeleton

CSM forms blebs

karyorhrhexis (nucleus breaks down)

cell splits into apoptotic bodies

phosphatidylserine found on outside of apoptotic bodies; binds to receptors on macrophages

macrophages engulf cell fragments

Question 18

outline the differences between mitosis in animal and plant cells

Answer 18

a: occurs in most tissues; p: only in meristematic tissues
a: cells become rounded; p: no change
a: use centriole; p: do not
a: spindles disappear completely before cytokinesis; P: some remain
a: microfilaments involved; p: do not play a major role

Question 19

what is the importance of apoptosis?

Answer 19

growth

development

cell proliferation