Cell cycle (van Weerink)

35 important questions on Cell cycle (van Weerink)

Why do cells divide?

  • Wound healing
  • Organ maintenance

Which phases happen during the interphase?

  • G1 phase
  • S phase
  • G2 phase

What is the function of the cell-cycle control system?

The cell-cycle control system switches all the machinery on and off at the correct time, thereby coordinating the various steps of the cycle.
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How are DNA replication, mitosis, and cytokinesis regulated or initiated?

The regulation of DNA replication, mitosis, and cytokinesis is carried out through the phosphorylation and dephosphorylation of proteins involved in these essential processes.

Which proteins carry out dephosphorylation?

Protein phosphatases

What is the function of Cdks and cyclin?

A Cdk must bind a regulatory protein called a cyclin before it can become enzymatically active. This activation also requires an activating phosphorylation of the Cdk. Once activated, a cyclin-Cdk complex phosphorylates key proteins in the cell that are required to initiate particular steps in the cell cycle. The cyclin also helps direct the Cdk to the target proteins that the Cdk phosphorylates.

What is the function of M cyclin? Which cyclin is an M cyclin?

M cyclin is the cyclin that acts in G2 to trigger entry into M phase.
Cyclin B is an M cyclin.

What is the function of G1 cyclin? Which cyclins are G1 cyclins?

G1 cyclin helps drive the cell through G1 toward S phase.
Cyclin D is a G1 cyclin.

What are the three checkpoints of the cell cycle? And what happens at these points?

  • G1-S: It is checked if the external factors are OK for cell division and if the DNA is undamaged.
  • G2-M: It is checked if the DNA is duplicated correctly
  • M metaphase-anaphase: It is checked if the chromosomes are correctly attached to the spindles

How are Cdks returned to their inactive state?

The anaphase-promoting complex tags the Cdks with a chain of ubiquitin. Proteins marked with ubiquitin are rapidly degraded.

What triggers the abrupt activation of cyclin-Cdk complexes?

Cyclin-Cdk complexes contain inhibitory phosphates, and to become active, the Cdk must be dephosphorylated by a specific protein phosphatase.

How can the activity of a cyclin-Cdk complex be blocked?

The activity of a cyclin-Cdk complex can be blocked by the binding of a Cdk inhibitor protein.

How is the DNA prepared for duplication in the G1 phase?

During G1, the Cdc6 binds to the ORC (origin recognition complex), and together these proteins load a pair of DNA helicases to form the prereplicative complex.

How is DNA duplicated in the S phase?

At the start of the S phase, S-Cdk triggers the firing of the loaded replication origin by guiding the assembly of the DNA polymerase and other proteins that initiate DNA synthesis at the replication fork. S-Cdk also blocks re-replication by helping to phosphorylate Cdc6, which marks the protein for degradation.

What process prevents re-replication of the DNA?

The phosphorylation of Cdc6. By doing this, Cdc6 is marked for degradation. Eliminating Cdc6 helps ensure that DNA replication can not be reinitiated later in the same cell cycle.

What is the process of the checkpoint from the G2 to the M phase?

If DNA replication succeeded Cdc25 will dephosphorylate the M-Cdk complex and the cell can continue to the M phase. However, if DNA is damaged or incompletely replicated the Cdc25 is inhibited. M-Cdk is not dephosphorylated (remains inactive) and the cell remains in the G2 phase until the DNA is repaired or replication is completed.

How are chromosomes split over daughter cells?

By interaction with microtubules.

What is one of the function of M cyclin to proceed from the G2 to the M phase?

M cyclin expresses survivin, this is critical to form the microtubule spindles.

What is the function of condensin?

Condensin makes chromatin more compact.

What is the role of duplicating centrioles?

The duplication of centrioles happens because of spindle formation.

What does the contractile ring consist of?

The contractile ring consists mainly of actin filaments and myosin filaments arranged in a ring around the equator of the cell.

What makes that the nuclear envelope disappears and is re-formed?

During prometaphase the nuclear envelope disappears because the nuclear lamins were phosphorylated. During the telophase the nuclear lamins are dephosphorylated, causing the nuclear envelope to be formed again.

How are chromosomes separated by the movement of microtubules during the anaphase?

The chromosomes are separated by 2 types of microtubule movement.The kinetochore microtubules are shortened, in this way the chromosomes come closer to the spindle pole. The interpolar microtubules become longer, so the two spindle poles move away from each other.

How are chromosomes separated by APC/C?

M-Cdk binds to active APC/C. This binds to active separase, which breaks down cohesin between the two sister chromatids.

What triggers cytokinesis?

Cytokinesis is triggered by the dephosphorylation of Cdks and cyclin breakdown by APC/C ubiquitination.

What is the final contact between the two cells?

The midbody

What are the critical cytoskeletal filaments during mitosis and cytokinesis?

Mitosis: microtubules
Cytokinesis: actin

What is wrong with syndactyly patients?

They have a defect in apoptosis.

What prevents cytochrome C release from mitochondria?

Bcl-2

What can cytochrome C do?

Cytochrome C can activate caspase 9 to induce the caspase cascade.

What can block apoptosis?

Survival factors, IAP (inhibitors of apoptosis) like Bcl-2

External signals can stimulate apoptosis by activating a set of cell-surface receptors known as?

Death receptors

What is the metaphase-anaphase checkpoint?

Cdc-20-APC/C interaction is blocked when kinetochore is not associated to the chromosomes.

What is the function of APC/C?

APC/C resets all cyclins by triggering cyclin degradation. APC/C is an E3-ligase: ubiquitin ligase for proteins, especially cyclins.

What is the process of cytokinesis?

Cytokinesis is the process by which the cytoplasm is cleaved in two. This is the last step of the M phase.

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