1.5 Cells and Proteins: Protein control/cell division

Question 1

what is the cytoskeleton?

Answer 1

a fibrous framework that gives mechanical support and shape to cells

Question 2

what are microtubules?

Answer 2

*hallow cylinders composed of molecules of the protein tubulin
*they radiate from the microtubule organising centre (MTOC) or centrosome

Question 3

what do microtubules control?

Answer 3

the movement of membrane-bound organelles that are attached to them and the movements of chromosomes during cell division

Question 4

cell division involves remodelling of the cytoskeleton, how are microtubules formed during remodelling?

Answer 4

polymerisation of tubulin by adding more units

Question 5

what happens to tubulin during the breakdown of microtubules?

Answer 5

depolymerisation

Question 6

what else do microtubules form?

Answer 6

spindle fibres that are active during cell division

Question 7

what are the two phases in the cell cyle?

Answer 7

interphase
mitotic phase

Question 8

what three phases are included within the interphase?

Answer 8

G1 phase
S phase
G2 phase

Question 9

what occurs during the G1 phase?

Answer 9

cell growth

Question 10

what occurs during the S phase?

Answer 10

DNA replication

Question 11

what occurs during the G2 phase?

Answer 11

preparation for mitosis

Question 12

what are the two parts that make up the mitotic phase?

Answer 12

mitosis
cytokinesis

Question 13

summarise the two phases:

Answer 13

mitosis is the separation of chromosomal material by spindle microtubules, cytokinesis is the separation of the cytoplasm into two daughter cells

Question 14

what are the four phases within mitosis?

Answer 14

(PMAT)
prophase
metaphase
anaphase
telophase

Question 15

what occurs in the prophase?

Answer 15

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

Question 16

what occurs in the metaphase?

Answer 16

chromosomes are aligned at the metaphase plate or equator of the spindle

Question 17

what occurs at the anaphase?

Answer 17

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

Question 18

what occurs at the telophase?

Answer 18

chromosomes start to decondense and new nuclear membranes are formed around them

Question 19

what is meant by checkpoints in mitosis?

Answer 19

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

Question 20

what happens if the go-ahead signal is not reached at the G1 checkpoint?

Answer 20

the cell may switch to a non-dividing or resting state

Question 21

what is the non-dividing/resting state called?

Answer 21

G0

Question 22

what factors does the G1 checkpoint assess?

Answer 22

cell size
DNA damage

Question 23

what factors does the G2 checkpoint assess?

Answer 23

DNA replication
DNA damage

Question 24

what does the metaphase checkpoint assess?

Answer 24

chromosome spindle attachment
chromosome alignment

Question 25

what are the proteins called that can accumulate during cell growth and regulate the cell cycle?

Answer 25

cyclins

Question 26

how do cyclins work?

Answer 26

they can combine with cyclin dependent kinases (CDKs) to from active cyclin-CDKs complexes

Question 27

what do cyclin-CDK complexes do?

Answer 27

they phosphorylate the proteins that regulate progression through the cycle

Question 28

how/when does progression occur?

Answer 28

when sufficient phosphorylation occurs

Question 29

describe the events that allow go-ahead at G1 and take the cell into the cell into the S phase of the cell cycle:

Answer 29

cyclin-CDKs phosphorylate Rb protein, the phosphorylated Rb protein is inhibited allowing transcription of genes that code for proteins needed for DNA replication

Question 30

DNA damage is also monitored at G1, what does DNA damage trigger?

Answer 30

the activation of several proteins including p53

Question 31

what is the role of the protein p53?

Answer 31

stimulates DNA repair, arrest the cell cycle or cause cell death

Question 32

what happens at the metaphase checkpoint?

Answer 32

controls progression from metaphase to anaphase, progression is halted until the chromosomes are aligned correctly on the metaphase plate and securely attached to the spindle microtubules

Question 33

what may result in tumour formation?

Answer 33

an uncontrolled increase in the rate of the cell cycle

Question 34

what is the name of the normal gene which can mutate into a tumour -promoting oncogene?

Answer 34

proto-oncogene

Question 35

explain why a tumour may be formed:

Answer 35

a proto-oncogene can mutate to form a tumour promoting oncogene

Question 36

what is apoptosis?

Answer 36

programmed cell death

Question 37

what can apoptosis be used for?

Answer 37

to remove cells that are old, damaged or starting to divide an an uncontrolled rate during tumour formation

Question 38

what triggers apoptosis?

Answer 38

cell death signals

Question 39

what are the two different types of death signals?

Answer 39

internal external

Question 40

what are external death signals?

Answer 40

bind to a surface receptor protein and trigger a protein cascade within the cytoplasm e.g. lymphocytes

Question 41

what are internal death signals?

Answer 41

results in DNA damage and causes activation of p53 tumour-suppressor or protein

Question 42

what protein is activated by both types of death signal?

Answer 42

protease enzymes called caspases

Question 43

what is the role of caspases?

Answer 43

act in cascades and cause the destruction of the cell

Question 44

in what situation may cells initiate apoptosis?

Answer 44

in the absence of growth factors

Question 45

explain how apoptosis can be triggered:

Answer 45

by external death signals (lymphocytes), internal death signals (DNA damage) activation of p53, absence of growth factors

Question 46

explain the significance of apoptosis for the whole organism:

Answer 46

allows for metamorphosis in some species and can lead to tumour suppression and desruction