Mitosis and the Cell Cycle

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Questions and Answers

What is the primary difference between quiescence and senescence in cells?

Quiescence is irreversible, while senescence is reversible.

Senescence allows for cell division, while quiescence does not.

Quiescence is a temporary state, but senescence is permanent. (correct)

Senescence involves metabolically active cells, while quiescence does not.

What is the primary function of the G2 checkpoint in the cell cycle?

To ensure DNA replication is complete

To promote rapid protein synthesis

To initiate mitosis

To assess for DNA damage (correct)

During which phase of interphase does DNA synthesis occur?

G1 phase

S phase (correct)

M phase

G0 phase

Which phase of the cell cycle immediately follows DNA replication?

G2 phase Signup and view all the answers

What happens to the amount of DNA in a cell during the S phase?

DNA content doubles, but the number of chromosomes remains unchanged. Signup and view all the answers

What activity characterizes the G1 phase of interphase?

High biosynthetic activity with an increase in size and organelles. Signup and view all the answers

What role do cyclins play in the regulation of the cell cycle?

They activate CDKs by binding to them Signup and view all the answers

Which statement accurately describes cyclin-dependent kinases (CDKs)?

They require a cyclin for activation Signup and view all the answers

What primarily occurs during the S phase of the cell cycle regarding histones?

Most histone synthesis occurs to support new chromatin formation. Signup and view all the answers

How many key CDKs are particularly important for cell cycle regulation in vertebrates?

4 Signup and view all the answers

What is the primary purpose of the cell cycle in eukaryotic cells?

To support growth, development, and tissue repair. Signup and view all the answers

Which phase of the cell cycle is characterized by the duplication of DNA?

S phase Signup and view all the answers

What event occurs during the G0 phase of the cell cycle?

Cells exit the cell cycle and stop dividing. Signup and view all the answers

Which molecules play a crucial role in regulating the cell cycle?

Cyclins and cyclin-dependent kinases (CDKs) Signup and view all the answers

Which cell cycle checkpoint is responsible for assessing whether conditions are favorable for DNA replication?

G1/S checkpoint Signup and view all the answers

What is the main role of tumor suppressor proteins like p53 in the cell cycle?

Prevent errors and regulate cell division. Signup and view all the answers

In prokaryotic cells, what does the D period of the cell cycle represent?

Binary fission and cell division. Signup and view all the answers

The process of cytokinesis occurs during which phase of the cell cycle?

M phase Signup and view all the answers

Which type of cells are least likely to enter the G0 phase?

Skin epithelial cells Signup and view all the answers

What does the term 'quiescent' refer to in the context of cell cycles?

Cells that have stopped dividing. Signup and view all the answers

What roles do BRCA1 and BRCA2 proteins play in the cell cycle?

They repair DNA double-strand breaks. Signup and view all the answers

Which phase of the cell cycle is primarily responsible for DNA replication?

S phase Signup and view all the answers

How do cyclins and CDKs affect the cell cycle?

They regulate transitions between cell cycle phases. Signup and view all the answers

Which of the following correctly describes a function of the p53 tumor suppressor?

It inhibits cell growth. Signup and view all the answers

What is the main purpose of cell cycle checkpoints?

To prevent errors during cell division. Signup and view all the answers

Which technique is used for analyzing cell cycle phases and progression?

Flow cytometry Signup and view all the answers

What distinguishes mitosis from cytokinesis in the cell cycle?

Mitosis involves chromosome separation, while cytokinesis divides the cytoplasm. Signup and view all the answers

Which of the following cancers is associated with mutations in BRCA1 and BRCA2?

Breast cancer Signup and view all the answers

Which cyclin activates CDK2 during the G1/S transition?

Cyclin E Signup and view all the answers

What is the primary function of the G1 checkpoint?

To verify nutrient availability and DNA integrity Signup and view all the answers

Which phase of mitosis involves the chromosomes aligning at the metaphase plate?

Metaphase Signup and view all the answers

Which of the following roles does p21 serve in the cell cycle?

Inhibits cyclin-CDK complexes in response to DNA damage Signup and view all the answers

Which process ensures that chromosomes are properly attached to the spindle before anaphase begins?

Metaphase checkpoint Signup and view all the answers

What happens to the cyclin levels at the end of telophase?

They drop, inhibiting CDKs Signup and view all the answers

In which phase do the centrosomes move to opposite poles of the cell?

Prophase Signup and view all the answers

What process occurs during cytokinesis in animal cells?

Formation of a cleavage furrow Signup and view all the answers

When does cyclin A activate CDK1?

At G2/M transition Signup and view all the answers

What occurs during anaphase?

Sister chromatids are pulled to opposite poles Signup and view all the answers

Study Notes

Cell Division and the Cell Cycle

Fundamental for growth, development, and tissue repair in organisms.
Prokaryotic division occurs in a cycle consisting of B, C, and D periods, while eukaryotic division includes interphase and M phase (mitosis and cytokinesis).
Checkpoints are crucial for ensuring accuracy and preventing errors during cell division.

Prokaryotic Cell Division

Comprises three distinct periods:
- B period: Time from cell birth to initiation of DNA replication.
- C period: DNA replication starts at oriC and progresses bidirectionally.
- D period: Time between the end of DNA replication and cell division via binary fission.

Eukaryotic Cell Cycle

Strongly structured, consisting of four phases: G1 (first gap), S (synthesis), G2 (second gap), and M (mitosis).
Each phase activation depends on the completion of the prior phase.
G0 phase represents quiescence, where differentiated, non-dividing cells reside.

G0 Phase

Reversible resting phase for differentiated cells such as red blood cells, neurons, and muscle cells.
Most epithelial cells regularly divide without entering G0; some may enter semi-permanently for repair as needed.

Quiescence vs. Senescence

Quiescent cells are metabolically active and can re-enter the cell cycle; senescent cells permanently exit due to DNA damage or stress.

Interphase: Phases Overview

G1 Phase: Growth phase; involves protein and organelle synthesis, cell size increase; contains a restriction point to decide progression to S phase.
S Phase: DNA replication occurs, resulting in two sister chromatids for each chromosome; minimal RNA transcription and protein synthesis.
G2 Phase: Prepares cell for mitosis through protein synthesis and growth; the G2 checkpoint checks for DNA damage.

Regulation of the Eukaryotic Cell Cycle

Key regulators include cyclins, cyclin-dependent kinases (CDKs), and inhibitors.
Checkpoints assess readiness for phase transitions in the cell cycle.

Cyclins and CDKs

CDKs modify protein substrates and are inactive without cyclin partners.
Vertebrates possess 20 CDKs; key ones include CDK1, CDK2, CDK4, and CDK6.
Major cyclins (A, B, D, E) help regulate distinct phases of the cell cycle.

Cell Cycle Checkpoints

G1 Checkpoint: Reviews cell size, nutrient availability, and DNA integrity before S phase.
G2 Checkpoint: Validates completion of DNA replication and DNA damage before mitosis.
Metaphase Checkpoint: Ensures all chromosomes are attached to the spindle apparatus prior to anaphase.

Tumor Suppressor Network

p21, inactivated by DNA damage, halts the cell cycle in G1, allowing time for repair or triggering cell death if damage is severe.
p53 plays a crucial role in regulating p21 and cell cycle control; mutations can lead to uncontrolled progression, promoting tumorigenesis.

Mitosis: Phases Overview

Sequence includes Prophase, Prometaphase, Metaphase, Anaphase, and Telophase, leading to the separation of chromosomes into two identical sets.
Variability exists, with fungi and yeast performing closed mitosis.

Mitosis Detailed Steps

Prophase: Chromosomes condense; spindle fibers form; nuclear envelope begins disassembly.
Prometaphase: Chromosomes move toward the cell equatorial plane; fragmentation of ER and Golgi occurs.
Metaphase: Chromosomes align along the metaphase plate; spindle assembly checkpoint ensures readiness for separation.
Anaphase: Sister chromatids separate; spindle poles move apart, elongating the cell.
Telophase: Chromosomes de-condense; nuclear envelopes reform; preparation for cytokinesis occurs.

Cytokinesis

Cytoplasm and organelles divide into two distinct daughter cells. In animal cells, a cleavage furrow is formed.
In plant cells, a cell plate forms due to rigid cell walls; lacks centrosomes for spindle formation.

Cell Cycle Disorders: Cancer

BRCA1 and BRCA2 genes are critical in repairing DNA; mutations increase risks for various cancers.
Abnormalities occur in approximately 1 in 400 Australians, with heightened risk in Ashkenazi Jewish communities (1 in 40).

Research Techniques

Flow cytometry is used to analyze cell cycle phases and progression.
Microscopy provides insights into mitosis and identifies abnormalities.

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Description

This quiz covers the essential concepts of mitosis and the cell cycle, focusing on cellular biology and genetics. Students will explore the stages of cell division and the regulation of the cell cycle, gaining a deeper understanding of these fundamental biological processes.