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USMLE Step 1 > Cell Cycle > Flashcards

Cell Cycle Flashcards

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USMLE® Step 1 flashcards
1
Q

Mencione the cell cycle phases.

A

• Interphase
- G1
- S
- G2
• Mitosis
• G0

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2
Q

Tell me the characteristics of G1 phase.

A

Last from hours to months

Cell growth during this phase

There is one chromatide per chromosome

Synthesis of RNA

Occurs after mitosis

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3
Q

What’s the G0 phase?

A

Variable duration state

The cells enter after exiting G1 phase

Those cell are differeciated

Most mature cells are in this state

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4
Q

Mencione the Mitosis stages.

A

Prophase

Prometaphase

Metaphase

Anaphase

Telophase

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5
Q

Tell me the characteristics of G2 phase.

A

Last for 2 to 5 hours

Synthesis of proteins further necessary for mitosis

Repair of DNA replication errors

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6
Q

Tell the characteristics of S phase.

A

Last for 8 h

DNA replication results in two chromatide per chromosome

Synthesis of protein necessary for the DNA packing (histones)

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7
Q

Effects of EGF on the cell cycle.

A

• Promotion of the proliferation
- Trough its pathways it phosphorylate and mark to ubiquitilation the p27^Kipl. This inhibits Cyclin E- CDK 2 complex & Cyclin D- CDK 4/6. Necessary to the G1- S phase transition.

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8
Q

Effects of PDGF on the cell cycle.

A

• Promotion of proliferation. G1 to S phase by upregulating Cyclin D and CDK 4&6

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9
Q

Cyclin-dependent Kinase’s characteristics

A
  • A type of inactive kinease that most be activated in order to transition from a phase to another.
  • Present in all the phases.
  • Activated via binding to cyclins to form cyclins/CDK complex.
  • Inactivated by CDKIs (inhibitor proteins) if any error is detected.
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10
Q

Types of cyclins.

A

A to E

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11
Q

Tell examples of Tumor suppressors.

A
  • BRCA-1/BRCA-2 (DNA repair proteins) defect = breast cancer
  • NFI = neurofibromatosis type 1
  • p53 = Li- Fraumeni syndrome
  • APC = adenomatous polyposis
  • pRb = retinoblastoma
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12
Q

Tell me the basics principles of cell cycle regulation.

A
  • Insulin
  • EGF
  • EPO
  • Cyclins/CDK complex
  • Platelet-derived growth factor
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13
Q

Functions of the EGF.

A
  • Development: especially in tissues such as skin, lungs and gastrointestinal tract.
  • Wound healing: stimulating the proliferation of keratinocytes and fibroblasts.
  • Maintenance of epithelial tissue.
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14
Q

Clinical implications of over expression or mutation of EGF.

A
  • Non-small cell lung cancer
  • Colorectal cancer
  • Head & neck squamous cells carcinoma
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15
Q

Mencione Mitosis’ phases

A
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
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16
Q

Prophase’s key points

A
  • Chromosome condensation, mark the beginning of this phase.
  • Centrosome separation
  • Formation of the mitotic spindle
  • Formation of more organelles (mitochondria).
  • Degradation of the nucleus into small vesicles mark the end of this phase.
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17
Q

What’s the centrosome?

A

It’s a chromosomal region into wich proteins like kinetochore, the point of origin of the mitotic spindle. Form by two centrioles surrounded for a matrix from wich the microtubules emerge.

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18
Q

Prometaphase’s key points.

A
  • The mitotic spindle is fully formed.
  • The microtubules of the mitotic spindle attach to the kinetochore, emanating from opposite sides. When the chromosomes are aligned on the metaphase plate the metaphase phase has been reached.
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19
Q

Metaphase’s key points.

A
  • Maximal condensation of chromatin.
  • The chromosome must be aligned on the equator of the cell. (Mitotic spindle checkpoint).
  • When the link between sister chromatids breaks. Mark the end of this phase.
20
Q

Spindle checkpoint’s key points.

A
  • Mediated by a complex of proteins called the MCC (mitotic checkpoint complex)
  • Those proteins inhibits the APC/C until every chromosome is aligned.
21
Q

Dynein’s function.

A
  • It’s a motor protein.
  • Aid the attach to various microtubules of the mitotic spindle to chromosomes.
22
Q

Anaphase’s key points.

A
  • Cell elongation.
  • Begging of the cytokinesis.
  • Separation of sister chromatids, due to the dissolution of the centromere by the enzyme separase. Marks the transition to anaphase.
23
Q

Telophase’s key points.

A
  • Disintegration of the mitotic spindle.
  • Formation of a new nuclear membrane.
  • Decondensation of the chromosome.
  • Synthesis of Ribosomal RNA (rRNA).
  • Cytokinesis is almost complete by the end of this phase.
24
Q

Cyclin A key points.

A
  • Transcription begin at G1 and peak in the middle of S phase.
  • It’s complex with CDK 2 allow the transition from G1 to S.
  • It’s complex with CDK 1 allow the transition from S to G2.
25
Q

Function of Cyclin B.

A
  • Regulate G2 checkpoint.
26
Q

Function of Cyclin C.

A
  • Allow transition from G0 to G1, bind with CDK 3.
  • Regulate gen transcription by phosphorylated transcription factors and RNA polymerase II.
27
Q

Functions of CyclinD.

A
  • Transition from G1 to S bind with CDK 4,6.
  • Initiation of protein replication by inactivation of pRb.
28
Q

Cyclin E functions.

A
  • Allow the transit from G1 to S binding/activating CDK 2.
  • Initiation of the DNA synthesis along with CDK 2.
29
Q

G1 checkpoint key point.

A
  • Control of Nuclear/Cytoplasmic ratio.
  • Enough nutrients levels.
  • DNA damage.
  • Regulated by:
    • Cyclin D/CDK4.
    • p53 tumor suppressors.
    • Proapoptotic active proteins of the BCI-2 family, such as Bax and Bak.
30
Q

Function of p53 tumor suppressor in the regulation of G1 checkpoint.

A
  • If DNA damage is reparable, it activate the p21 causing the arrest of the cell cycle by the inactivation of the G1/S & S-CDK complexes through the inactivation of the pRb.
  • Also through the activation of the p27, this inactivate directly the Cyclins/CDK complexes.
  • If DNA damage is irreversible produce apoptosis trough active proteins of the family of BCI-2, such as Bax & Bak.
31
Q

G2 checkpoint highlights.

A
  • Check for DNA damage.
  • DNA replication if there is any errors.
  • Initiate mitosis by phosphorylation of various proteins.
32
Q

Regulation of G2 checkpoint.

A
  • By Mitosis Promoting Factor (MPF), composed by CDK1/cyclin B.
33
Q

M checkpoint key points.

A
  • Happen between metaphase and anaphase.
  • Ensure correct alignment of the chromosomes and sister chromatids at the equatorial plane before the separation of sister chromatids.
34
Q

Mencione the cell types according to it replication properties.

A
  • Labile cells.
  • Permanent cells.
  • Quiscent (Stable cells)
35
Q

Labile cells characteristics.

A
  • Rapidly dividing cells
  • Short G1
  • Lack of G0
  • Fast cell turnover makes these cell specifically vulnerable to chemotherapy.
36
Q

Labile cells examples.

A
  • Epithelial cells.
  • Germ cells.
  • Hematopoietic cells.
37
Q

Quiescent cells characteristics.

A
  • May enter G1 phase from G0 when stimulated.
38
Q

Quiescent cell’s examples.

A
  • Cells in endocrine and exocrine glands.
  • Hepatocytes.
  • Lymphocytes.
  • Periosteal cells.
  • Cells of the proximal covoluted tubule.
39
Q

Permanent cells key points.

A
  • Remain in G0 phase.
  • Regenerate via cell differentiation from steam cell.
40
Q

Permanent cells examples.

A
  • Skeletal & cardiac muscle cells.
  • Red blood cells.
  • Neurons.
41
Q

p53 tumor suppressor key points.

A
  • Encode by the TP53 gem.
  • Activated in response of:
    • cell stress
    • DNA damage
    • oxidative stress
    • oncogene activation
    • hypoxia.
  • Negative regulation: MDM2 by promoting its ubiquitilation and proteosomal degradation.
42
Q

Aurora Kinase’s functions.

A
  • Centrosome maturation.
  • Interactions of chromosomes with microtubules.
  • Activation of the contractile ring of actin myosin II filaments, necessary to cytokinesis.
43
Q

Cohesins key points.

A
  • Member of the structural maintenance of chromatin (SMC).
  • Bind to DNA on S phase, maintaining the linkage between sister chromatids following DNA replication.
  • Breakdown of the Golgi apparatus into vesicles.
  • It’s replace for condensins as the cell enter M phase, in most of the chromosomes but the centromere.
44
Q

Condensins key points.

A
  • Member of the family of the Structural Maintenance of Chromatin (SMC).
  • Induce chromatin condensation into DNA loops, leading to the formation of metaphase chromosomes.
45
Q
  • Function of the CDK1/cyclin B complex on the breakdown of the nuclear lamina.
A
  • Phosporilation of the lamins result in depolymerization of nuclear lamina into laminate dimers.
  • Phosporylates several proteins in the inner nuclear membrane and the nuclear pore complex.
  • Breakdown the Golgi apparatus into vesicles, absorbed by the ER or distributed to the daughter’s cells.
  • Activation of the APC/C ubiquitin ligase, produce the degradation of the securin, activating the separase, producing the final degradation of the cohesins.
46
Q

Aurora Kinase Family. Types, location and function.

A

Aurora A kinase.
- Location:
• Centromeres and spindle poles.
- Functions:
• Centromere maturation.
• Mitotic spindle assembly.
• Regulate Mitotic Spindle checkpoint.
• Promote Mitotic Entry through the phosphorylation of several substrates, such as some necessary to the Mitotic spindle formation.
Aurora B kinase.
- Location:
• Chromosomes.
- Functions:
• Chromosomes condensation on early stages of mitosis.
• Proper attachment of mitotic spindle microtubules to the kinetochore.
• Regulation of the M checkpoint.
• Regulation of the Cytokinesis.

USMLE Step 1 (6 decks)

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