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1.1 Getting started > Cell Growth and Cell Death > Flashcards

Cell Growth and Cell Death Flashcards

1
Q

What are some examples of cells that frequently?

A

skin, small intestine

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2
Q

What are some examples of cells that never divide

A

neurons, skeletal and cardiac muscle cells

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3
Q

What is an example of cells that divide only if they need to?

A

liver cells

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4
Q

What is the proliferative activity of labile tissues?

A

continuously dividing

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5
Q

What is the proliferative activity of stable tissue?

A

can divide in response to stimulus

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6
Q

What is the proliferative activity of permanent tissues?

A

non dividing

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7
Q

What are some examples of labile cells?

A
  • surface epithelia of the skin
  • the columnar epithelium of the GI tract
  • cells of the bone marrow
  • hematopoietic tissues
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8
Q

What are some examples of stable cells?

A
  • fibroblasts
  • endothelial cells
  • smooth muscle cells
  • chondrocytes
  • osteoblasts
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9
Q

What are some examples of permanent cells?

A
  • neurons
  • skeletal and cardiac muscle (injury to brain/heart is irreversible)
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10
Q

What are the 4 main phases of the cell cycle?

A

G1 - S - G2 - M

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11
Q

M phase

A

Mitotic phase (or cell division) which consists of telophase, anaphase, metaphase and prophase

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12
Q

G1 phase

A

cell prepares for DNA synthesis (S phase); makes proteins needed for DNA replication

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13
Q

S phase

A

DNA replication

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14
Q

G2 phase

A

cell prepares for mitosis; cell grows in size, replicates organelles etc

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15
Q

When do cells enter the G0 phase?

A

when the cell isn’t dividing

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16
Q

What phase do cells enter the G0 phase from?

A

G1 phase

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17
Q

What is temporary G0?

A

some cells can be placed in G0 temporarily “called back” to the cycle by external signal

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18
Q

What is an example of temporary G0 occurring?

A

liver cells are mostly non dividing but in response to signal (e.g injury) they can start to divide again known as quiescence

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19
Q

What is permanent G0?

A

cells that are differentiated/highly specialised enter a permanent G0 arrest and can never divide again

20
Q

What is an example of permanent G0?

A

nerve and muscle cells - known as terminally differentiated

21
Q

What are mitogens?

A

a class of growth factors that stimulate cells to grow and divide

22
Q

What phase are cells responsive to mitogens in?

A

G1 (which is considered the start of the cell cycle)

23
Q

What happens in the absence/withdrawal of mitogenic growth factors?

A

cells are pushed from G1 to G0 (quiescence)

24
Q

What are some examples of mitogens?

A
  • platelet derived growth factor (PDGF)
  • insulin growth factor (IGF)
  • epidermal growth factor (EGF)
25
Q

How do mitogens work?

A
  • mitogens function by binding to growth factor receptors which trigger a biological response in the cell to drive the cell cycle out of G1
  • mitogens activate what are known as ‘signalling cascade reactions’ involving numerous proteins
26
Q

Progression through the cell cycle is mediated via what two classes of proteins?

A

cyclins and cyclin dependent kinases (CDKs)

27
Q

Summary of mitogen activation off cyclins/CDKs

A
  • mitogen interacts with receptor
  • stimulates synthesis of cyclin D
  • cyclin D complexes with CDK - 4 - 6
  • active cyclin D/CDK 4&6 enzyme complex is formed
  • enzyme complex causes activation of target proteins
28
Q

What protein mediates the G1 DNA damage checkpoint?

A

p53 protein

29
Q

What protein mediates the G1 restriction checkpoint?

A

pRb

30
Q

What are the steps of the DNA damage checkpoint

A
  1. DNA damage/mutation is recognised by the cell through a series of ‘sensor’ proteins
  2. sensor proteins trigger the activation of p53 protein
  3. activated p53 triggers either a cell cycle arrest or cell death
31
Q

What is senescence?

A
  • senescence is an intrinsically programmed limit to cell proliferation
  • most cells have a replicative potential; this means after a period of cell division, most somatic cells will undergo a permanent growth arrest termed replicative senescence or cellular senescence
32
Q

What makes senescence different than G0?

A

senescence cannot be reversed by growth factor stimulation

33
Q

What are telomeres?

A
  • specialized DNA structures termed telomeres are important regulators of senescence
  • telomeres are complexes of DNA and protein that ‘cap’ linear chromosomes
34
Q

Describe the structure of telomeres

A

telomeres are non coding DNA sequences and are made up of multiple repeats of the sequence TTAGGG. The ends of chromosomes have hundreds/thousands of these TTAGGG repeats, most of the telomere is double stranded, the end is single stranded

35
Q

How do telomeres regulate cell division?

A

with each cell division, the end of the chromosomes, telomeres is shortened; this loss of telomere DNA will continue with each round of division until the telomeres become very short and this triggers the cell to stop dividing and enter senescence

36
Q

Why do telomeres shorten?

A

this is due to the ‘end replication problem’ in DNA replication.
In DNA replication, one strand replicates to the end the other strand however has a small (8-12bp) gap at the 5’ end, this ‘gap’ arises with each round of cell division meaning the telomere gets progressively shorter

37
Q

What are some examples of immortal cells?

A

cancer cells, stem cells and germ cells

38
Q

What are immortal cells?

A

cells that can maintain telomere lengths throughout cell division and hence the signal to enter senescence is bypassed and these cells can divide indefinitely

39
Q

How is immortality is cells achieved?

A

immortality is achieved by expression of an enzyme called telomerase that can synthesise telomere DNA back onto the end of the chromosome, so whilst the end replication looses DNA, telomerase resynthesises telomere DNA

40
Q

What happens to telomere length as you age?

A

it shortens

41
Q

What are the 3 main cell death pathways?

A
  • apoptosis
  • necrosis
  • autophagy
42
Q

Apoptosis is a normal physiological process required for…

A

homeostasis and animal development

43
Q

What are caspases?

A

a class of enzymes that are important in apoptosis and activate nucleases (cleaves DNA) and proteases (cleave proteins) and bring about the morphological changes in apoptotic cells

44
Q

What is the process of apoptosis?

A
  1. chromatin condenses; DNA fragments resulting in regular size fragments of DNA produced
  2. cytoplasm shrinks and membrane ‘blebs’
  3. cell contents are packaged into membrane bound apoptotic bodies
  4. phospholipid phosphatidylserine is exposed on the surface
  5. receptors on phagocytic cells (macrophages) recognize exposed phospholipid and engulf the fragments
45
Q

What are some factors that can result in necrosis?

A
  • oxygen deprivation
  • physical agents - mechanical trauma, extreme heat, electric shock, radiation
  • chemical agents/drugs
  • viral/bacterial infections
46
Q

What is the process of necrosis?

A
  1. chromatin clumps together
  2. organelles and cell swell, plasma membrane ruptures
  3. cell undergoes lysis; disintegrates
  4. cell contents are ‘spilled’ out in the surrounding
  5. immune response

1.1 Getting started (31 decks)

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