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1.5 Flashcards

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1
Q

What is the cytoskeleton?

A

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.

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2
Q

What are the functions of the cytoskeleton?

A
  • gives mechanical support and shape to cells
  • anchorage for many organelles and some enzymes
  • enables whole cell to move
  • enables organelles to move
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3
Q

What are microtubules?

A

hollow straight cylinders composed of globular proteins called tubulins

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4
Q

What are microtubules made up of?

A

alternative dimers of beta tubulin

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5
Q

What is the role of microtubules?

A

they control the movement of membrane-bound organelles and chromosomes

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6
Q

Where do microtubules originate?

A

from the microtubule organising centre (MTOC), contains centrioles

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7
Q

Where is the MTOC in the cell?

A

found near the nucleus

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8
Q

What does formation and breakdown of microtubules involve?

A

involves polymerisation and depolymerisation of tubulin

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9
Q

What are spindle fibres?

A

microtubules that form during cell division

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10
Q

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

A

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.

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11
Q

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

A

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

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12
Q

What are the two stages of the cell cycle?

A

Interphase and the mitotic phase

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13
Q

Describe interphase…

A

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

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14
Q

What are the three sub-phases of interphase?

A

G1, S phase and G2

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15
Q

Describe G1…

A

a growth period where proteins and organelles are synthesised

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16
Q

Describe S phase…

A

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

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17
Q

Describe G2…

A

second growth period during which proteins and organelles are synthesised

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18
Q

What are the two stages of the mitotic phase?

A

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

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19
Q

Describe the first stage of mitosis…

A

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

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20
Q

Describe the second stage of mitosis…

A

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

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21
Q

Describe the third stage of mitosis…

A

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

22
Q

Describe the fourth stage of mitosis…

A

the chromosomes decondense and nuclear membrane forms around them

23
Q

Describe cytokinesis…

A

cytosol separates into identical daughter cells with identical genetic material

24
Q

What are checkpoints?

A

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

25
Q

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

A

Sufficient nutrients and growth factors must be present

26
Q

What is the G1 checkpoint?

A

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

27
Q

What are cyclins?

A

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

28
Q

What do cyclins combine with?

A

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

29
Q

What does the active cyclin-CDK complex do?

A

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

30
Q

What is retinoblastoma (Rb)?

A

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

31
Q

How is Rb a tumour suppressor?

A

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

32
Q

How Rb released?

A

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

33
Q

What do checkpoints also check for?

A

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

34
Q

What does DNA damage trigger?

A

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

35
Q

Name a protein activated by DNA damage…

A

p53

36
Q

What are majority of human cancers linked to?

A

They are linked to mutations in the p53 gene

37
Q

What is the G2 checkpoint?

A

It assesses success of DNA replication and DNA damage

38
Q

What is the G2 checkpoint?

A

It assesses success of DNA replication and DNA damage

39
Q

Describe the responses of p53…

A

-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

40
Q

What is the metaphase checkpoint?

A

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

41
Q

What is apoptosis?

A

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

42
Q

What signals does apoptosis trigger?

A

It triggers both external or internal cell death signals

43
Q

Give an example of an external death signal…

A

production of cell death signal molecules from lymphocytes

44
Q

Give an example of an internal death signal…

A

DNA damage is an internal death signal

45
Q

What is the importance of apoptosis?

A

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

46
Q

Give an example of apoptosis and organ sculpting…

A

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

46
Q

Give an example of apoptosis and organ sculpting…

A

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

47
Q

How do external death signals work?

A

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

48
Q

What do internal death signals do?

A

Results from DNA damage causing p53 activation

49
Q

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

A

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

50
Q

What else may initiate apoptosis?

A

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

advanced higher biology (17 decks)

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