KA 1.5 - Protein Control of Cell division

Question 1

define cytoskeleton:

Answer 1

a fibrous framework which provides mechanical support and shape to cells

Question 2

describe the structure of the cytoskeleton:

Answer 2

consists of different proteins including microtubules which are found in all eukaryote cells

Question 3

describe the structure of a microtubule protein:

Answer 3

a hollow cylinder composed of subunits of molecules of the protein tubulin

Question 4

overall, the cell cycle consists of two phases, what are they?

Answer 4

the interphase and mitotic phase

Question 5

what does the interphase consist of?

Answer 5

G1 phase (cell growth), S phase (DNA replication) and G2 phase (preparation for mitosis)

Question 6

what does the mitotic phase consist of?

Answer 6

mitosis and cytokinesis

Question 7

what are the four phases in mitosis?

Answer 7

Prophase, Metaphase, Anaphase and Telophase

Question 8

describe prophase:

Answer 8

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

Question 9

describe metaphase:

Answer 9

chromosomes are aligned at metaphase plate

Question 10

describe anaphase:

Answer 10

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

Question 11

describe telophase:

Answer 11

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

Question 12

what occurs during the formation of microtubules?

Answer 12

polymerisation of tubulin

Question 13

what occurs during the break down of microtubules?

Answer 13

depolymerisation of tubulin

Question 14

what three phases are checkpoints in the cell cycle?

Answer 14

G1,G2 and Metaphase

Question 15

what is meant by a checkpoint?

Answer 15

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

Question 16

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

Answer 16

the cell may switch to a non-dividing or resting state called G0

Question 17

what factors are checked at G1 checkpoint?

Answer 17

cell size
DNA damage

Question 18

what are cyclins?

Answer 18

proteins that accumulate during the cell growth and are involved in regulating the cell cycle

Question 19

what are CDK’s?

Answer 19

cyclin dependent kinases - they are combined with and activated by cyclin

Question 20

what is the role of active cyclin-CDK complexes?

Answer 20

they phosphorylate proteins that regulate the progression through the cycle.

Question 21

when will progression of the cell cycle occur?

Answer 21

when sufficient phosphorylation is reached

Question 22

why is cell size checked at the G1 checkpoint?

Answer 22

to confirm that there is sufficient mass for daughter cells to be produced

Question 23

what is retinoblastoma (Rb) ?

Answer 23

a protein which acts as a tumour suppressor

Question 24

how does Rb work?

Answer 24

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

Question 25

when can the cell progress from G1 to the S phase?

Answer 25

when phosphorylation by cyclin-CDK inhibits Rb, which allows for the transcription of the genes that code for proteins such as enzymes needed for DNA replication

Question 26

what will happen if damage is detected at the G1 checkpoint?

Answer 26

damage triggers the activation of several proteins including p53

Question 27

what is the role of the protein p53?

Answer 27

*can stimulate DNA repair *arrest the cycle *cell death

Question 28

what is assessed at the G2 checkpoint?

Answer 28

the success of DNA replication and any damage to the DNA

Question 29

what does the metaphase checkpoint control?

Answer 29

controls the entry to anaphase

Question 30

what occurs at the metaphase checkpoint?

Answer 30

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

Question 31

what may result in tumour formation?

Answer 31

an uncontrolled increase in the rate of the cell cycle

Question 32

what is a 'normal' gene involved in the control of cell growth/division called?

Answer 32

proto-oncogene

Question 33

how may the cell cycle become uncontrolled leading to tumour formation?

Answer 33

the mutation in proto-oncogene to form a tumour-promoting oncogene

Question 34

what is the term associated with tumour-promoting?

Answer 34

oncogene

Question 35

define apoptosis:

Answer 35

programmed cell death triggered by cell death signals that can be external or internal

Question 36

what is an example of an external death signal?

Answer 36

death signal molecules from lymphocytes

Question 37

how do external death signals work?

Answer 37

they bind to a surface receptor protein and trigger a protein cascade within the cytoplasm

Question 38

what is an example of an internal death signal?

Answer 38

DNA damage

Question 39

what protein is activated as a result of DNA damage?

Answer 39

p53 tumour suppressor protein

Question 40

what do both signals activate?

Answer 40

caspase cascade

Question 41

what are caspase cascades?

Answer 41

protease enzymes involved in a series of reactions (a cascade) that will destroy the cell

Question 42

in what other circumstance might cells initiate apoptosis?

Answer 42

in the absence of growth factors

Question 43

how may a tumour be formed?

Answer 43

a proto-oncogene mutates to form a tumour-promoting oncogene