1.5 protein control of cell division

Question 1

what is the cytoskeleton?

Answer 1

a network of proteins extending throughout the cytoplasm, anchored to proteins in the PM

Question 2

what is the function of the cytoskeleton?

Answer 2

• provide mechanical support so that the cell maintains its shape
• provide anchorage for many organelles

Question 3

what is the cytoskeleton made of?

Answer 3

several types of protein, including microtubules

Question 4

what are microtubules?

Answer 4

hollow cylinders made of a protein called tubulin

Question 5

where are microtubules formed and radiated from?

Answer 5

a centrosome or MTOC (microtubule organising centre)

Question 6

what is the role of microtubules?

Answer 6

• govern the location and movement of the membrane-bound organelles and other cell components
• form the spindle fibres that are active during cell division

Question 7

how are spindle fibres formed then broken down?

Answer 7

by polymerisation and then depolymerisation of tubulin

Question 8

what does cell division allow?

Answer 8

organisms to grow and develop, by regulating the growth and replacement of genetically identical cells

Question 9

name the two parts into which the cell cycle can be divided

Answer 9

interphase
the mitotic phase

Question 10

describe interphase

Answer 10

an active period of growth

Question 11

name the three sub-phases that interphase can be divided into

Answer 11

G1, G2, S

Question 12

describe G1

Answer 12

a growth period where proteins and organelles are synthesised

Question 13

what happens during S phase

Answer 13

the cell continues to grow and DNA replication takes place

Question 14

describe G2

Answer 14

another growth period

Question 15

what happens after G2

Answer 15

the cell enters the mitotic phase

Question 16

what happens during the mitotic phase?

Answer 16

mitosis and cytokinesis

Question 17

what is mitosis?

Answer 17

when the nucleus and contents divide

Question 18

what is cytokinesis?

Answer 18

the separation of the cytoplasm into daughter cells

Question 19

what could an uncontrolled reduction in the rate of the cell cycle result in?

Answer 19

degenerative diseases

Question 20

what could an uncontrolled increase in the rate of the cell cycle result in?

Answer 20

tumour formation

Question 21

name the 4 stages of mitosis in order

Answer 21

prophase, metaphase, anaphase, telophase

Question 22

describe the first event of prophase

Answer 22

• DNA condenses into discrete chromosomes with each chromosome consisting of 2 sister chromatids

Question 23

describe the second event of prophase

Answer 23

• the nuclear membrane breaks down and spindle fibres extend from the centromere via polymerisation

Question 24

describe the final event of prophase

Answer 24

the fibres then attach to the chromosomes’ centromere at a region called the kinetochore

Question 25

what happens during metaphase?

Answer 25

the chromosomes line up at the metaphase plate at the centre of the cell

Question 26

what happens during anaphase?

Answer 26

as spindle microtubules shorten by depolymerisation, sister chromatids are separated, and the chromosomes are pulled to opposite poles

Question 27

what happens during telophase?

Answer 27

the chromosomes decondense and nuclear membranes are formed around them. cytokinesis also occurs

Question 28

why must the cell cycle be controlled?

Answer 28

to ensure that events in the cycle proceed in the correct order and that each event is completed before the next starts

Question 29

how is the cell cycle controlled?

Answer 29

by checkpoints at various stages within the cell cycle

Question 30

what do checkpoints do?

Answer 30

they asses the condition of the cell and halt the progression onto the next phase until certain that all conditions have been met

Question 31

what is cyclin?

Answer 31

a protein involved in the regulation of the cell cycle by checkpoints

Question 32

what do cyclins do?

Answer 32

they combine with active and inactive cyclin-dependent kinases (CDKs) that phosphorylate other proteins which regulate the cycle

Question 33

what happens when sufficient phosphorylation is reached by CDKs?

Answer 33

progression occurs

Question 34

what does the G1 checkpoint check before the cell enters S phase?

Answer 34

that cell growth has occurred

Question 35

what happens if the G1 checkpoint finds that cell growth has not occurred?

Answer 35

the cell switches to G0 phase

Question 36

what does the G2 checkpoint check for?

Answer 36

that DNA replication has been completed and damage assessed

Question 37

what does the M checkpoint check before the cell enters anaphase?

Answer 37

that chromosomes are aligned correctly on the metaphase plate and attached to spindle fibres

Question 38

name the tumour suppressor protein at G1 checkpoint

Answer 38

retinoblastoma (Rb)

Question 39

what does the Rb protein do?

Answer 39

inhibits transcription of genes that code for proteins needed for DNA replication

Question 40

what happens at the G1 checkpoint that allows the cell to progress to S phase?

Answer 40

CDKs inhibit the Rb protein via phosphorylation, allowing transcription of the genes that code for proteins needed for DNA replication

Question 41

what is a photo-oncogene?

Answer 41

a normal gene involved in controlling cell division

Question 42

what happens when a photo-oncogene mutates?

Answer 42

it becomes a tumour-promoting oncogene, contributing to the development of cancer

Question 43

apoptosis can be triggered by ... signals

Answer 43

internal or external

Question 44

what is an example of an external signal?

Answer 44

lymphocytes producing death signal molecules

Question 45

what is an example of an internal signal?

Answer 45

DNA damage

Question 46

how do external death signal molecules initiate their reaction?

Answer 46

by biding to a surface receptor protein and triggering a protein cascade inside the cytoplasm

Question 47

how does an internal death signal from DNA damage initiate its reaction?

Answer 47

activates a protein called p53

Question 48

what do both internal and external death signals result in?

Answer 48

activation of caspases (a type of protease) that cause destruction in the cell

Question 49

why is apoptosis essential during development?

Answer 49

to remove cells that are no longer required

Question 50

give an example of when apoptosis might be initiated

Answer 50

in the absence of growth factors