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USMLE Biochemistry > Cell Cycle > Flashcards

Cell Cycle Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the 4 main stages of the cell cycle?

A
  • G1
  • S
  • G2
  • M
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2
Q

The cell cycle can also be divided into 2 phases what are these 2 phases?

A
  • Interphase (cell not dividing, G1, G0, S, G2)
  • M phase (mitosis)
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3
Q

The cell can go into a resting phase out of G1 what is this phase called?

A

G0

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4
Q

What are mitogens?

A
  • Extracellular signalling molecules, usually proteins
  • Stimulate cell division
  • Function via cyclin dependent kinases (Cdks)
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5
Q

What is the difference between a mitogen and a growth factor?

Some molecules are both mitogens and GFs. Terms sometimes used interchangeably

A

Mitogen
- Stimulates growth via cell division

Growth factors
- Stimulates growth in size

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6
Q

What phase are most cells in our body?

A

G0

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7
Q

Give examples of cells in a permanent G0 state?

A
  • Neurons
  • Skeletal muscle cells
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8
Q

Give an example of cells which are often in G0 but may divide if stimulated?

A

Liver cells

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9
Q

Give examples of cells which may enter and exit G0 many times in their lifespan?

A
  • Fibroblasts
  • Lymphocytes
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10
Q

What cells are known as labile cells and rarely/never enter G0?

A
  • Bone marrow
  • GI epithelial cells
  • Hair follicles

Most effected by many forms of chemotherapy

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11
Q

What are the 5 major phases of mitosis?

A
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
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12
Q

What is the shortest (most rapid) portion of the cell cycle?

A

M phase
- Mitosis

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13
Q

What occurs in prophase?

A
  • Chromosomes condense
  • Spindle fiber forms
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14
Q

What occurs in prometaphase?

A

Chromosomes organize on mitotic spindle

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15
Q

What occurs in metaphase?

A

Chromosomes line up on metaphase plate

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16
Q

What occurs in anaphase?

A

Chromosomes separate

17
Q

What occurs in telophase/cytokinesis?

A
  • Spindle breaks down
  • Cell divides
18
Q

Give some examples of points at which there is a checkpoint / restriction point in the cell cycle?

A
  • G1-S (prior to S phase entry)
  • G2-M (prior to Mitosis)
  • M phase (prior to anaphase/cytokinesis)
19
Q

Cyclin dependent kinases rely on cyclins which are regulatory proteins.

What do cyclin-Cdk complexes do?

A

Phosphorylate regulatory proteins
- Activate E2F proteins (transcription factors)
- Allow progression through cell cycle by binding to DNA prometer regions -> progression to S phase

20
Q

What extracellular proteins activate Cdk?
Explain how this process works

A

Mitogens
- Interact with cell surface receptors
- Activate intracellular pathways
- Increase G1 cyclin levels
- Increase cdk activity

21
Q

What do cyclin-Cdk complexes activate specifically?

A

E2F proteins
- Transcription factoes which activate genes for S phase

22
Q

What proteins can inhibit E2F and therefore progression to S phase?

A

Retinoblastoma proteins (Rb)

23
Q

What is Rb known as?

A

A tumor suppressor

24
Q

What do cyclin-Cdk complexes phosphorylate specifically?

A

Retinoblastoma proteins
- Activating E2F (TFs)

25
Q

What can arrest cell division at G1-S checkpoint?

A

DNA damage
- Allows for repair and prevension of mutant cells/cancer

26
Q

What are 2 pathways which cause cell cycle arrest at the G1-S checkpoint?

A
  • ATM pathway (ds breaks)
  • ATR pathway (ss breaks)
27
Q

What do ATM and ATR pathways lead to?

A

Phosphorylation of proteins
- Causes cell cycle / growth arrest at G1/S point

28
Q

What is ATM pathway triggered by?

A

Double strand breaks

29
Q

What is the ATR pathway triggered by?

A

Single strand breaks

30
Q

A mutation in ATM pathway leads to what condition?

A

Ataxia Telangiectasia

31
Q

What protein is stimulated (phosphorylated) by the ATM/ATR systems?

A

p53

32
Q

p53 induces the transcription of what proteins?

A

p21 proteins

33
Q

What does p21 (activated by p53) bind to to cause arrest of the cell cycle?

A

Cdks
- They therefore cannot activate E2F proteins
-> Arrest of cell cycle

34
Q

What are p53/p21 known as?

A

Tumor suppressors

35
Q

What is p53 generally stimulated by to cause arrest of the cell cycle?

A

DNA damage

36
Q

Retinoblastoma is a mutation of what gene?

A

RB1
- Codes for Rb protein
- Abnormal Rb -> unregulated cell growth

37
Q

Li-Fraumeni syndrome is a mutation of what gene?

A

TP53
- Codes for p53 protein

38
Q

What are the main cancers that are caused by Li-Fraumeni Syndrome?

A

SBLA
- Sarcoma
- Breast
- Leukemia
- Adrenal gland

USMLE Biochemistry (44 decks)

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