1.5 Protein Control of Cell Division

Question 1

what does the cytoskeleton do

Answer 1

gives mechanical support and shape to cells

Question 2

what does the cytoskeleton consist of

Answer 2

different protein structures including microtubules, which are found in all eukaryotic cells

Question 3

what are microtubules

Answer 3

hollow cylinders composed of the protein tubulin

Question 4

where are the microtubules found

Answer 4

they radiate from the microtubule organising centre (MTOC) or centrosome

Question 5

what do microtubules do

Answer 5

control the movement of membrane-bound organelles and chromosomes

Question 6

what does cell division require

Answer 6

remodelling of the cytoskeleton

Question 7

what does formation and breakdown of microtubules involve

Answer 7

polymerisation and depolymerisation of tubulin

Question 8

what do microtubiles form

Answer 8

the spindle fibres that are active during cell division

Question 9

what does the cell cycle consist of

Answer 9

interphase and mitotic (M) phase

Question 10

what does the interphase involve

Answer 10

growth and DNA synthesis including:
G1, a growth phase,
S phase, during which the DNA is replicated,
and G2, a further growth phase

Question 11

what does the mitotic phase involve

Answer 11

mitosis and cytokinesis

Question 12

what happens in mitosis

Answer 12

the chromosomal material is separated by the spindle microtubules
this is followed by cytokinesis

Question 13

what happens in cytokinesis

Answer 13

the cytoplasm is separated into two daughter cells

Question 14

what does mitosis consist of

Answer 14

prophase
metaphase
anaphase
telophase

Question 15

what is prophase

Answer 15

DNA condenses into chromosomes each consisting of two sister chromatids.
nuclear membrane breaks down.
spindle microtubules extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region

(think pro means before)

Question 16

what is metaphase

Answer 16

chromosomes are alligned at the metaphase plate (equator of the spindle)

(think middle)

Question 17

what is anaphase

Answer 17

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

(think away)

Question 18

what is telophase

Answer 18

the chromosomes decondense and nuclear membranes are formed around them

(think two)

Question 19

what is progression in the cell cycle controlled by

Answer 19

checkpoints

Question 20

what are checkpoints

Answer 20

mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met

Question 21

what is involved in regulating the cell cycle

Answer 21

cyclin proteins that accumulare during cell growth

Question 22

what do cyclins combine with

Answer 22

they combine with and activate cyclin-dependent kinases (CDKs)

Question 23

active cyclin-CDK complexes phosphorylate

Answer 23

proteins that regulate progression through the cycle

if sufficient phosphorylation is reached, progression occurs

Question 24

what happens at the G1 checkpoint

Answer 24

retinalblastoma proteins (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication

Question 25

what does phosphorylation by G1 cyclin-CDK inhibit

Answer 25

the retinalblastoma protein (Rb)

Question 26

what does the inhibation of Rb allow

Answer 26

transcription of the genes that code for proteins needed for DNA replication.
cells progress from G1 to S phase

Question 27

what happens at G2 checkpoint

Answer 27

the success of DNA replication and any damage to DNA is assessed

Question 28

what does DNA damage trigger

Answer 28

the activation of several proteins including p53

Question 29

what is p53

Answer 29

it can stimulate DNA repair,
arrest the cell cycle,
or cause cell death (apoptosis)

Question 30

what does a metaphase checkpoint control

Answer 30

the progression from metaphase to anaphase

Question 31

what happens at the metaphase checkpoint

Answer 31

progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules

Question 32

what can an uncontrolled reduction in the rate of the cell cycle result in

Answer 32

degenerative disease

Question 33

what can an increase in the rate of the cell cycle result in

Answer 33

tumour formation

Question 34

what is a proto-oncongene

Answer 34

a normal gene, usually involved in the control of cell growth or division, which c an mutate to form a tumour-promoting oncogene

Question 35

what triggers apoptosis

Answer 35

apoptosis is triggered by cell signals that can be external or internal

Question 36

what is an example of an external death signal

Answer 36

the production of death signal molecule from lymphocytes

Question 37

what is an example of internal death signal

Answer 37

DNA damage

Question 38

what do external death signal molecules bind to

Answer 38

a surface receptor protein and trigger a protein cascade within the cytoplasm

Question 39

what does an internal death signal resulting from DNA damage cause

Answer 39

activation of p53 tumour-suppressor protein

Question 40

what do both internal and external death signal result in

Answer 40

the activation of caspases that cause the destruction of the cell

Question 41

what is caspases

Answer 41

types of protease enzyme

Question 42

why is apoptosis essential during development of an organism

Answer 42

to remove cells no longer required as development progresses or during metamorphosis

Question 43

what can happen in the absence of growth factors

Answer 43

cells may initiate apoptosis