Lecture 13 Review

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Questions and Answers

What occurs during telophase?

The sister chromatids are pulled apart to opposite poles

The chromosomes align at the cell equator

The nuclear envelopes reassemble around each set of chromosomes (correct)

The spindle fibers begin to disassemble

Which type of microtubule is primarily responsible for the movement of chromosomes toward the poles during anaphase?

Interpolar microtubules

Kinetochore microtubules (correct)

Polar microtubules

Astral microtubules

What initiates cytokinesis in animal cells?

Disassembly of the mitotic spindle

Reassembly of the nuclear envelope

Separation of chromatids

Formation of a contractile ring (correct)

Which motor proteins are involved in the movements of microtubules during anaphase?

Dyenin and kinesin Signup and view all the answers

What is the primary function of the contractile ring during cytokinesis in animal cells?

To divide the cell cytoplasm Signup and view all the answers

Which phase of mitosis is characterized by the separation of chromosomes?

Anaphase Signup and view all the answers

What happens during the S-phase of the cell cycle?

The genome is replicated. Signup and view all the answers

What is the role of cohesin proteins during the S-phase?

They bind to the genome and hold sister chromatids together. Signup and view all the answers

What is the spindle-assembly checkpoint responsible for during mitosis?

Ensuring chromosomes are properly bi-oriented. Signup and view all the answers

Which phase of mitosis involves the preparation for the physical separation of chromosomes?

Metaphase Signup and view all the answers

What role do microtubules play during mitosis?

They facilitate chromatid segregation. Signup and view all the answers

During which phase of the cell cycle are centrosomes duplicated?

S and G2 phases Signup and view all the answers

What distinguishes condensin proteins from cohesin proteins?

Condensin facilitates chromosome condensation, while cohesin holds sister chromatids together. Signup and view all the answers

What occurs during cytokinesis?

Division of the cytoplasm to form two cells. Signup and view all the answers

Which structure assembles during prophase to assist with chromosome movement?

Kinetochore Signup and view all the answers

What happens to chromosomes at the end of interphase?

They are replicated and held together by cohesins. Signup and view all the answers

What is the primary function of the mitotic spindle during mitosis?

To segregate duplicated chromosomes. Signup and view all the answers

What is the significance of the spindle-assembly checkpoint during metaphase?

It confirms all chromosomes are attached to the spindle before anaphase. Signup and view all the answers

What role do kinetochores play during cell division?

They link microtubules to centromeres. Signup and view all the answers

What stabilizes the attachment of microtubules to kinetochores during metaphase?

Tension in the microtubules Signup and view all the answers

What happens at the Spindle-Assembly Checkpoint when all kinetochores are properly attached?

The Anaphase Promoting Complex is activated. Signup and view all the answers

What prevents the exit from metaphase when there are unattached kinetochores?

Signaling from the unattached kinetochores Signup and view all the answers

What is the main purpose of cohesins in cell division?

To hold chromatids together Signup and view all the answers

How does the APC/C affect M-cyclin and cohesins?

It leads to their degradation. Signup and view all the answers

During which phase are chromosomes aligned on the metaphase plate?

Metaphase Signup and view all the answers

What is the primary indicator that the Spindle-Assembly Checkpoint is satisfied?

All kinetochores are bi-oriented. Signup and view all the answers

What is the primary purpose of the mitotic spindle during cell division?

It segregates sister chromatids into separate nuclei. Signup and view all the answers

During which phase do microtubules begin attaching to kinetochores?

Prometaphase Signup and view all the answers

What component is NOT part of the mitotic spindle?

Ribosomes Signup and view all the answers

What initiates the breakdown of the nuclear envelope during prometaphase?

Phosphorylation of nuclear lamins Signup and view all the answers

What is a spindle pole in the context of the mitotic spindle?

Each centrosome with its microtubules Signup and view all the answers

Which of the following correctly describes the spindle-assembly checkpoint?

It ensures that chromosomes are properly attached to the spindle apparatus. Signup and view all the answers

Which is NOT a characteristic of microtubules in the mitotic spindle?

They connect to the nuclear envelope directly. Signup and view all the answers

Study Notes

Exam Instructions

Computer screens must be in BRIGHT MODE and Canvas displayed in full screen.
Only Canvas software should be running.
Do not highlight any text on your Canvas site.
Turn off phones, smartwatches, and calculators, and keep them in backpacks until 1:15.
Use colored paper as scrap paper, but do not write on it before the exam starts.
Leaving the seat during the preliminary exam is allowed only in emergencies.
The exam duration is 45 minutes.
Close your laptop or turn your tablet upside down upon finishing and submitting the exam.
If you finish the exam before 1:00 pm, you can leave the exam room after showing your submission page at the exit and returning the scrap paper.
Remain in the exam room in exam mode (no phones) until 1:15 if you finish after 1:00 pm

Mitosis Learning Objectives

Understand the organization of microtubules in the mitotic spindle and which associate with centrosomes and kinetochores.
Understand the events that occur in each phase of mitosis.
Understand how chromosomes become attached to appropriate microtubules: "bi-orientation."
Understand the mitosis checkpoint (spindle-assembly checkpoint) and how it's satisfied.

Today's Topics (M-Phase)

Overview of events in M-phase and preparation for M-phase.
Prophase and the mitotic spindle.
Chromosome attachment in prometaphase and the spindle-assembly checkpoint in metaphase.
Anaphase (separation of chromosomes).
Telophase and cytokinesis (cell division).

The Cell Cycle

The cell cycle is divided into four phases: interphase (G1, S, G2), and M-phase (mitosis and cytokinesis).
G1 phase: Growth and preparation for S phase.
S phase: DNA replication.
G2 phase: Growth and preparation for mitosis.
M phase: Mitosis (nuclear division) and cytokinesis (cytoplasmic division)

S-Phase Details

The genome is replicated (duplicated) by DNA polymerase during S phase.
Cohesin proteins bind to the genome forming rings that hold duplicated sister chromatids together.
Sister chromatids are exact copies of the same chromosome, consisting of DNA and histone proteins.

Centrosome Replication

The centrosome is replicated during S and G2 phases.
Centrosomes are microtubule organization centers (MTOCs) composed of γ-tubulin complexes.
Microtubules play a critical role in chromatid segregation.

Mitotic Spindle

The mitotic spindle is responsible for segregating sister chromatids into separate nuclei.
It's made of microtubules, motors, and the two centrosomes.
It has a built-in quality control system - the spindle-assembly checkpoint.

Prometaphase

The nuclear envelope breaks down and microtubules begin attaching to chromosomes during prometaphase.
Phosphorylation of nuclear lamins and nuclear pore proteins breaks down the nuclear envelope into vesicles.
Microtubules attach to kinetochores.

Kinetochore Microtubules

The kinetochore links centromeres to kinetochore microtubules.
The centromere(s) is/are a special region of DNA within each chromosome.
The kinetochore is a protein complex that attaches microtubules to the centromere of each chromosome.

Metaphase

During metaphase, chromosomes are arranged on the "metaphase plate."
The metaphase plate is positioned midway between the spindle poles.

Anaphase Details

Anaphase is characterized by two simultaneous processes: anaphase A and anaphase B.
- Anaphase A: Shortening of kinetochore microtubules pulling chromosomes towards the spindle poles.
- Anaphase B: Pushing and pulling of poles apart through interpolar microtubules.
Microtubules depolymerize at the kinetochore pulling the chromosome to the pole, which causes separation.
A sliding force and a pulling force between interpolar microtubules drive the poles apart.

Telophase

During telophase, nuclear envelopes reassemble around each set of chromosomes producing two nuclei.
Cytokinesis is initiated, including the formation of a contractile ring in animal cells.

Cytokinesis

During cytokinesis, the cell completes the division process by separating the cytoplasm, creating two daughter cells.
This process differs between plant and animal cells. Animal cells have a contractile ring.

Spindle Assembly Checkpoint Overview

The spindle assembly checkpoint ensures all chromosomes are correctly attached to spindle fibers before anaphase.
If not, the checkpoint prevents anaphase promoting complex (APC) activation – and with it chromosome separation.

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Description

Test your knowledge on key concepts of mitosis, including the phases, microtubule functions, and cytokinesis in animal cells. This quiz covers essential details such as the role of cohesin proteins and the spindle-assembly checkpoint. Perfect for students studying cell biology!