1.5

Question 1

What is the cytoskeleton?

Answer 1

a network of proteins extending through the cytosol, it is anchored to proteins in the plasma membrane and is dynamic in nature, constantly breaking down and reforming.

Question 2

What are the functions of the cytoskeleton?

Answer 2

• gives mechanical support and shape to cells
• anchorage for many organelles and some enzymes
• enables whole cell to move
• enables organelles to move

Question 3

What are microtubules?

Answer 3

hollow straight cylinders composed of globular proteins called tubulins

Question 4

What are microtubules made up of?

Answer 4

alternative dimers of beta tubulin

Question 5

What is the role of microtubules?

Answer 5

they control the movement of membrane-bound organelles and chromosomes

Question 6

Where do microtubules originate?

Answer 6

from the microtubule organising centre (MTOC), contains centrioles

Question 7

Where is the MTOC in the cell?

Answer 7

found near the nucleus

Question 8

What does formation and breakdown of microtubules involve?

Answer 8

involves polymerisation and depolymerisation of tubulin

Question 9

What are spindle fibres?

Answer 9

microtubules that form during cell division

Question 10

What is the result of an uncontrolled reduction in the cell cycle rate?

Answer 10

May result in a degenerative disease, alteration in normal cell cycle control thought to lead to certain proteins being expressed in association with Alzheimer’s disease, resulting in neuronal cell death.

Question 11

What is the result of an uncontrolled increase in the cell cycle rate?

Answer 11

May result in tumour formation, proto-oncogene is a normal gene that can mutate to form tumour-promoting oncogene.

Question 12

What are the two stages of the cell cycle?

Answer 12

Interphase and the mitotic phase

Question 13

Describe interphase…

Answer 13

it lasts much longer than mitotic phase; cannot see interphase through microscope; active period of growth; protein synthesis takes place, cytoplasmic organelles synthesised and cell grows/ replicates it chromosomes

Question 14

What are the three sub-phases of interphase?

Answer 14

G1, S phase and G2

Question 15

Describe G1…

Answer 15

a growth period where proteins and organelles are synthesised

Question 16

Describe S phase…

Answer 16

cell continues to grow and DNA is replicated in preparation for mitosis

Question 17

Describe G2…

Answer 17

second growth period during which proteins and organelles are synthesised

Question 18

What are the two stages of the mitotic phase?

Answer 18

Mitosis - chromosomal material separated by spindle microtubules and nucleus separates contents to divide
cytokinesis - separation of cytoplasm into daughter cells

Question 19

Describe the first stage of mitosis…

Answer 19

prophase - chromatin condense into discrete chromosomes; each chromosome is 2 identical chromatids joined at centromere; nuclear membrane breaks down; spindle microtubules extend from MTOC and attach to kinetochores in centromere region

Question 20

Describe the second stage of mitosis…

Answer 20

metaphase - microtubule bundles line up chromosomes on metaphase plate in euqator and cells then enter anaphase

Question 21

Describe the third stage of mitosis…

Answer 21

anaphase - spindle microtubules shorten, sister chromatids are separated to opposite poles

Question 22

Describe the fourth stage of mitosis…

Answer 22

the chromosomes decondense and nuclear membrane forms around them

Question 23

Describe cytokinesis…

Answer 23

cytosol separates into identical daughter cells with identical genetic material

Question 24

What are checkpoints?

Answer 24

mechanisms in the cell that assess the condition of cell during the cell cycle and halt progression until certain requirements are met

Question 25

What is required for a cell to commit to the next stage in cycle?

Answer 25

Sufficient nutrients and growth factors must be present

Question 26

What is the G1 checkpoint?

Answer 26

Appears the most important in mammalian cells; if cell passes this checkpoint then is usually completes cycle; if not it exits the cycle and goes into a non-dividing state (G0); most somatic cell are in G0 phase as cell is not dividing or is preparing to

Question 27

What are cyclins?

Answer 27

proteins that accumulate during cell growth involved in regulation of cell cycle

Question 28

What do cyclins combine with?

Answer 28

They combine with and activate cyclin-dependent kinases (CDK)

Question 29

What does the active cyclin-CDK complex do?

Answer 29

They phosphorylate proteins that regulate progression through the cell cycle. If sufficient phosphorylation is reached then the cell progresses.

Question 30

What is retinoblastoma (Rb)?

Answer 30

a cell cycle regulatory protein, it's non-phosphorylated form restricts progression from G1 to S phase, tumour suppressor protein

Question 31

How is Rb a tumour suppressor?

Answer 31

It inhibits the transcription of genes that code for proteins needed for DNA replication; It acts by binding to a transcription factor, therefore preventing transcription of certain genes required for S phase

Question 32

How Rb released?

Answer 32

when the cell enters S phase the G1 CDKs phosphorylate the Rb plasma; this inhibits Rb activity so no longer binds to transcription factors; this brings about the transcription of genes needed to initiate DNA replication, allowing S phase

Question 33

What do checkpoints also check for?

Answer 33

They asses DNA damage and prevent it from continuing the cell cycle

Question 34

What does DNA damage trigger?

Answer 34

It triggers the activation of several proteins that can stimulate DNA repair, arrest the cell cycle or cause apoptosis

Question 35

Name a protein activated by DNA damage...

Answer 35

p53

Question 36

What are majority of human cancers linked to?

Answer 36

They are linked to mutations in the p53 gene

Question 37

What is the G2 checkpoint?

Answer 37

It assesses success of DNA replication and DNA damage

Question 38

What is the G2 checkpoint?

Answer 38

It assesses success of DNA replication and DNA damage

Question 39

Describe the responses of p53...

Answer 39

-activate DNA repair proteins to repair damaged cell - arrest cell cycle at G1 checkpoint so cell cycle halts to allow repair proteins time to recognise DNA damage so cell can restart cell cycle - initiate apoptosis if DNA damage is severe

Question 40

What is the metaphase checkpoint?

Answer 40

during metaphase, it controls anaphase entry by checking chromosome alignment and microtubule attachment. ensures each daughter cell receives the correct number of chromosomes

Question 41

What is apoptosis?

Answer 41

The controlled destruction of cells in a multicellular organism, important throughout growth and development of an organism.

Question 42

What signals does apoptosis trigger?

Answer 42

It triggers both external or internal cell death signals

Question 43

Give an example of an external death signal...

Answer 43

production of cell death signal molecules from lymphocytes

Question 44

Give an example of an internal death signal...

Answer 44

DNA damage is an internal death signal

Question 45

What is the importance of apoptosis?

Answer 45

It is essential during development of an organism to remove cells no longer required as development progresses or during metamorphosis.

Question 46

Give an example of apoptosis and organ sculpting...

Answer 46

during embryonic development of an organism to remove cells between fingers/toes allows individual digits

Question 46

Give an example of apoptosis and organ sculpting...

Answer 46

during embryonic development of an organism to remove cells between fingers/toes allows individual digits

Question 47

How do external death signals work?

Answer 47

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

Question 48

What do internal death signals do?

Answer 48

Results from DNA damage causing p53 activation

Question 49

What do both external and internal cell death signals result in?

Answer 49

both result in caspase activation (types of protease enzyme) which cause cell destruction

Question 50

What else may initiate apoptosis?

Answer 50

in the absence of cell growth factors, cells may also initiate apoptosis