Cell Division and Mitosis Quiz

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Questions and Answers

What is the primary role of the mitotic checkpoint?

To activate the anaphase-promoting complex

To promote the destruction of Cohesins

To complete mitosis regardless of chromosome attachment

To ensure all chromosomes are attached to the mitotic spindle (correct)

What effect does Mad2 binding have during cell division?

Promotes the cleavage of Cohesins

Delays the metaphase-anaphase transition (correct)

Inhibits the destruction of Securin

Increases the activity of Cdc20-APC

Which protein's destruction is triggered by the activated anaphase-promoting complex (APC)?

Separase

Mad2

Securin (correct)

Cohesin

What happens if the mitotic checkpoint is activated for an extended period?

It leads to cell death Signup and view all the answers

How does Separase contribute to the separation of sister chromatids?

By cleaving the Cohesin complexes Signup and view all the answers

What is one of the main functions of cell division?

Reproduction of cells Signup and view all the answers

During which phase of the cell cycle does DNA replication occur?

S phase Signup and view all the answers

Which checkpoint in the cell cycle is considered the primary decision point for many cells?

G1 checkpoint Signup and view all the answers

What marks the beginning of cytokinesis?

Cleavage furrow formation Signup and view all the answers

What is the consequence if a cell does not receive a go-ahead signal at the G1 checkpoint?

The cell enters the G0 nondividing state. Signup and view all the answers

What happens during prophase?

Chromatin fibers become tightly coiled Signup and view all the answers

Which type of cells is most likely to divide frequently throughout life?

Skin cells Signup and view all the answers

Which stage of mitosis involves the alignment of chromosomes at the cell's equator?

Metaphase Signup and view all the answers

What role do external factors play in the regulation of cell division?

They include signals from outside the cell. Signup and view all the answers

What is a key role of the mitotic spindle during cell division?

Attach to kinetochores Signup and view all the answers

At which phases do the major checkpoints in the cell cycle occur?

G1, G2, M Signup and view all the answers

Which phase of the cell cycle occurs after the S phase?

G2 phase Signup and view all the answers

What happens during anaphase of mitosis?

Sister chromatids separate Signup and view all the answers

What could be a potential internal signal that influences the G1 checkpoint decision?

Cell size Signup and view all the answers

Which of the following best describes the G0 phase of the cell cycle?

A nondividing state. Signup and view all the answers

What is a key characteristic of mature nerve and muscle cells in relation to cell division?

They do not appear to divide at all after maturity. Signup and view all the answers

What is required for the activity of Cdk?

Phosphorylation at a specific site Signup and view all the answers

How are cyclins regulated in terms of their abundance?

Through protein degradation via ubiquitylation Signup and view all the answers

What role does activated p53 protein play in the cell cycle?

Stimulates transcription of the p21 gene Signup and view all the answers

What triggers the activation of protein phosphatase in the Cdk complex?

Removal of all inhibitory phosphate groups Signup and view all the answers

What can a cell decide at the G1 checkpoint?

Commit to dividing into two Signup and view all the answers

Which of the following statements about Cdk inhibitor proteins is correct?

They can respond to DNA damage. Signup and view all the answers

What is the function of maturation promoting factor (MPF) in the cell cycle?

Triggers M phase by phosphorylating various proteins Signup and view all the answers

What happens to cyclins after they execute their function in the cell cycle?

They are targeted for destruction through ubiquitylation. Signup and view all the answers

What initiates the activation of M-Cdk at the end of G2?

Dephosphorylation by Cdc25 Signup and view all the answers

Which site modification is essential for M-Cdk to become active?

Both phosphorylation and dephosphorylation Signup and view all the answers

What is the role of Cdc25 in the activation of M-Cdk?

It removes inhibitory phosphates from M-Cdk. Signup and view all the answers

How does M-Cdk promote its own further activation?

Through a positive feedback loop Signup and view all the answers

What is the main function of the spindle-attachment checkpoint?

To block sister chromatid separation if kinetochores are improperly attached Signup and view all the answers

What action does activated M-Cdk take against the inhibitory kinase Wee1?

It directly inhibits the activity of Wee1. Signup and view all the answers

Which proteins are recruited to unattached kinetochores during improper attachment?

Mad2 Signup and view all the answers

What is the role of the SCF complex in cell cycle regulation?

To target specific cyclins and some CKIs for degradation Signup and view all the answers

What is required for the activation of cyclin-dependent kinases (Cdks)?

Binding of cyclins Signup and view all the answers

Which type of cyclin assists in promoting passage through the restriction point in late G1 phase?

G1-cyclins Signup and view all the answers

How do cyclin levels change throughout the cell cycle?

They are low during interphase and peak during mitosis. Signup and view all the answers

What is NOT a mechanism of regulation for the cyclin-Cdk complex?

Cdk binding to DNA Signup and view all the answers

What is necessary for a Cdk to be fully active?

Phosphorylation at one site and dephosphorylation at two sites Signup and view all the answers

Which class of cyclins binds to Cdks during S phase and is required for initiating DNA replication?

S-cyclins Signup and view all the answers

What event triggers the entry into M phase?

Increased levels of M-cyclins Signup and view all the answers

Which statement is incorrect regarding the cyclin-Cdk complex?

It is always active during the cell cycle. Signup and view all the answers

Study Notes

Cell Cycle Overview

The cell cycle is a series of events that leads to cell division
Cell division is crucial for reproduction, growth, and tissue repair
Cells duplicate their genetic material before dividing to ensure each daughter cell receives an exact copy
The cell cycle is regulated by checkpoints which help prevent errors and allow time for accurate duplication

Learning Outcomes

Describe the overall purposes of cell division
Describe the structural organization of a eukaryotic genome
Explain cytokinesis
List the phases of the cell cycle and describe the events in each phase
Describe the roles of checkpoints, cyclin, Cdks, and MPF in the cell cycle control system
Describe internal and external factors influencing the cell cycle control
Explain how abnormal cell division of cancerous cells escapes normal cell cycle control

Functions of Cell Division

Reproduction (example: bacteria, amoeba)
Growth and development (example: embryos)
Tissue renewal (example: skin, blood)

The Cell Cycle

The cell division process is a part of the cell cycle
A cell duplicates its contents and divids into two
Each new cell receives a copy of the genetic material (DNA)
Cells duplicate their genetic material before division

Phases of the Cell Cycle

Mitotic Phase:
- Mitosis: division of the nucleus
- Cytokinesis: division of the cytoplasm
Interphase:
- G1 phase: cell growth and preparation for DNA synthesis
- S phase: DNA replication
- G2 phase: preparation for mitosis

Stages of Mitotic Cell Division

Prophase: chromatin fibers coil, nucleoli disappear, centrosomes move apart, mitotic spindle forms
Prometaphase: nuclear envelope fragments, microtubules interact with chromosomes, kinetochores attach to microtubules
Metaphase: centrosomes at opposite poles, chromosomes align at the metaphase plate, kinetochores of sister chromatids attach to microtubules
Anaphase: paired centromeres separate, sister chromatids move to opposite poles
Telophase: daughter nuclei form, chromatin fibers decondense, cytokinesis occurs

Cytokinesis

Cytoplasm divides; resulting in two daughter cells
In animal cells, characterized by a cleavage furrow
In plant cells, characterized by a cell plate

Interphase

G1 Phase: Post-mitotic phase. Cell growth and accumulation of energy
S Phase: Synthesis phase. DNA and centriole replication
G2 Phase: Pre-mitotic gap phase. Synthesis of RNA and proteins

The Cell Cycle Control System

Cell cycle events are directed by a cell-cycle control system
Checkpoints are critical control points in the cell cycle
- Checkpoints in G1, G2, and M phases
- Control cell cycle progression through chemical signals
Checkpoints monitor cell size, DNA replication, chromosome attachment errors and nutrients in the exterior environment

The G1 Checkpoint

Major decision point
If the cell has a go-ahead signal, it continues through the cell cycle
- Internal signals: cell size, nutrition signals for metabolism
- External signals: growth factors
If the cell does not receive a go-ahead signal, it may halt or enter a nondividing state (G0)

External Signals

Factors/signals outside of cell affecting the division process
Chemical factors: nutrients, presence of growth factors
Physical factors: density-dependent inhibition (cells stop dividing when crowded), anchorage dependence (cells need a surface to divide)
Anchorage to substrate controlled by membrane protein-cytoskeleton interactions

Growth Factors

Proteins that stimulate division in other cells
Bind to receptors that trigger cell growth
Cells usually respond to a combination of growth factors

Internal Factors

Kinases: enzymes that transfer phosphate groups to molecules
Cyclins: proteins that activate kinases
Control cell cycle progression

Maturation Promoting Factor (MPF)

Triggers entry into M phase
Oscillates during the cell cycle in Xenopus embryos

G2 Checkpoint

Ensures all DNA replicated and any errors are fixed

Checkpoint: Spindle Assembly

Mitosis only completes when all chromosomes are attached to the mitotic spindle
Delaying anaphase prevents chromosome segregation errors

The APC

Triggers separation of sister chromatids by promoting the destruction of cohesins
Holds sister chromatids together in the replicated chromosome
Cleaves cohesin complexes, allowing movement of chromosomes to opposite poles

DNA Damage Arresting the Cell Cycle in G1

DNA damage initiates a response that halts the cell cycle
Activates p53, which leads to the production of p21
p21 inhibits kinases associated with cell cycle progression causing arrest in G1

Regulation of Cyclin-Cdk Complexes

Cyclin levels alter based on cell phase, activating or deactivating kinases
Phosphorylation (adding phosphate groups) and dephosphorylation (removing phosphate groups) impact the activity of cyclin-dependent kinases (Cdks)
Ubiquitination and subsequent degradation regulates abundance of cyclins

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Description

Test your knowledge about the cell division process, focusing on the mitotic checkpoint, roles of key proteins, and various phases of mitosis. This quiz covers essential concepts in cell cycle regulation and the implications of checkpoints on cell division. Perfect for biology students at any level.