30 Questions
What is responsible for the appropriate division of a cell into two daughter cells?
Cell division
Which regulatory processes primarily control cell cycle progression?
Phosphorylation by cyclin-dependent kinases and dephosphorylation by phosphatases
What is the period between two mitotic divisions known as?
Interphase
What causes one of the most devastating diseases of this era?
Cell proliferation
What combines DNA replication with chromosomal segregation in an oscillatory manner during the cell cycle?
Cell cycle
What are specific proteins phosphorylated by in the regulation of cell cycle progression?
Cyclin-dependent kinases
What happens during interphase in a cell?
There is a continuous increase of RNA and protein.
What event typically occurs during the mitotic phase of the cell cycle?
Replicated DNA and contents are separated.
When does the division of the cytoplasm typically begin?
During cytokinesis
What is the main role of cell cycle checkpoints?
To control the ability of the cell to progress by determining earlier stages completion
How are daughter cells produced during cytokinesis?
Each daughter cell ends up with an identical set of chromosomes and half of the organelles.
What controls the phases of the cell cycle according to Benjamin Lewin in Genes VIII?
Discrete events that happen during G1, S phase, and mitosis
What is the primary role of cyclin-dependent kinases (CDKs) in the cell cycle?
To transduce extracellular signals and promote cell cycle progression
Which of the following statements about cyclins is correct?
They regulate the activity of CDKs by forming complexes with them
What is the primary function of checkpoints within the cell cycle?
To prevent progression to the next stage if there are problems with DNA integrity
Which of the following statements about CDKs is incorrect?
They are responsible for checking DNA integrity during S phase
What is the primary role of checkpoints at S phase?
To prevent replication from continuing if there are problems with DNA integrity
Which of the following statements about the regulation of cell cycle progression is correct?
CDK-cyclin complexes are central regulators of cell cycle progression
What is the role of RB protein in resting cells?
Prevents cell entry into S phase by binding to transcription factor E2F
What happens to RB protein in actively cycling cells?
Undergoes hyperphosphorylation
Which protein is involved in halting cell cycle progression for DNA repair?
p21
What is the consequence of further phosphorylation of RB by cyclin E-CDK2?
Allows cell to move out of G1 phase
Which proteins are activated upon DNA damage and play a role in apoptosis?
CKI and p21
What is the role of E2F when RB is hyperphosphorylated?
Binds to DNA and activates genes important for S phase
Which of the following cyclins are critical for progression through the restriction point?
D-type cyclins (cyclins D1, D2, D3)
Which of the following statements about cyclins is correct?
Their concentrations rise and fall throughout the cell cycle due to synthesis and degradation.
Which of the following cyclins are involved in regulating the S phase of the cell cycle?
Cyclin E and cyclin A
Which of the following statements about CDKs (cyclin-dependent kinases) is correct?
CDKs are activated by binding to their partner cyclins.
Which of the following statements about CDKs (cyclin-dependent kinases) is correct?
CDKs are serine/threonine kinases that are present in constant amounts during the cell cycle.
Which of the following statements accurately describes the activation of CDKs?
The specific cyclin binds first to the CDK, and then CDK-activating kinase (CAK) phosphorylates the CDK on a threonine residue, completing its activation.
Study Notes
Cell Cycle Regulation
- Cell division is a highly regulated process that ensures the appropriate division of a cell into two daughter cells.
- Cell proliferation is necessary for growth, development, and regeneration of eukaryotic organisms, but it also causes cancer.
Phases of the Cell Cycle
- The cell cycle combines DNA replication with chromosomal segregation in an oscillatory manner.
- The period between two mitotic divisions defines the somatic cell cycle.
- Interphase is the period from the end of one mitosis to the start of the next.
- M phase is the period of actual division, corresponding to the visible mitosis.
Interphase
- During interphase, there is little visible change in the appearance of the cell.
- The nucleus increases in size predominantly during S phase, when proteins accumulate to match the production of DNA.
- Chromatin remains a compact mass in which no change of state is visible.
Mitosis (M)
- Mitosis is the phase in which a cell undergoes cell division.
- During mitosis, the replicated DNA and contents are separated, and the cytoplasm is typically partitioned by cytokinesis.
Cytokinesis
- Cytokinesis is the division of the cytoplasm, usually starting around the same time as telophase.
- It results in two new identical cells (daughter cells) that have the same number of chromosomes as the original parent cell.
Cell Cycle Checkpoints
- Cell cycle checkpoints control the ability of the cell to progress through the cycle by determining whether earlier stages have been completed successfully.
- Checkpoints for specific events related to the individual stage occur at S phase and at mitosis.
- DNA damage is checked at every stage of the cycle.
Regulation of the Cell Cycle
- The phases of the cell cycle are controlled by discrete events that happen during G1, at S phase, and at mitosis.
- The progression to the next stage of the cell cycle is controlled by a kinase that consists of a catalytic subunit and a regulatory (cyclin) partner.
Cyclin-Dependent Kinases (CDKs) and Cyclins
- CDKs are activated by binding to their partner cyclins.
- CDKs are also negatively regulated by CDK inhibitors, which are commonly referred to as “CKIs.”
- Cyclins are expressed in a periodic manner and regulate a series of CDKs, whose phosphorylation of key substrates promotes cell cycle progression.
Regulation of the Cell Cycle by CDKs and Cyclins
- Cyclin D-CDK4/6 complexes are activated and phosphorylate RB, allowing the cell to move out of G1.
- Cyclin E-CDK2 phosphorylates RB, allowing the cell to enter S phase.
- p53: Tumor suppressor protein plays a major regulatory role in G1 when DNA is damaged.
Types of Cyclins
- D-type cyclins (cyclins 01, 02, and 03) are G1 regulators that are critical for progression through the restriction point.
- S phase cyclins include type E cyclins and cyclin A.
- Mitotic cyclins include cyclins B and A.
Explore the regulation of the cell cycle, focusing on the process of cell division and proliferation in eukaryotic somatic cells. Learn about the significance of cell proliferation for growth, development, and regeneration in organisms.
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