MODULE 39

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Questions and Answers

What occurs during prophase of mitosis?

Kinetochores bind to spindle fibers

Chromosomes condense and the nuclear envelope disappears (correct)

Chromosomes separate and move to opposite poles

Sister chromatids align at the metaphase plate

What distinguishes homologous chromosomes from sister chromatids?

Sister chromatids are present in haploid cells only

Homologous chromosomes are identical copies, while sister chromatids are different

Homologous chromosomes do not share a centromere, whereas sister chromatids do

Sister chromatids are formed after the S phase of the cell cycle (correct)

What is the role of the cohesin protein complex during mitosis?

It separates chromosomes at the poles

It condenses chromatin into chromosomes

It keeps sister chromatids together (correct)

It facilitates spindle fiber formation

What structure is responsible for organizing the microtubules during cell division?

Centrosome Signup and view all the answers

Which type of spindle fiber helps provide structure during anaphase?

Polar fibers Signup and view all the answers

What does the term 'tubulin flux' refer to in the context of mitosis?

The movement of tubulin subunits between the (+) and (–) ends of the microtubule Signup and view all the answers

What is the role of CENPE during mitosis?

It is important for the plus-end elongation. Signup and view all the answers

During which phase do chromosomes align at the metaphase plate?

Metaphase Signup and view all the answers

Which motor proteins are involved in chromosome movement during mitosis?

Chromokinesin and dynein Signup and view all the answers

What happens during telophase?

Nuclear envelope forms around the separated chromatids Signup and view all the answers

What happens during telophase in mitosis?

The spindle disappears. Signup and view all the answers

What is the importance of kinetochores in mitosis?

They bind to microtubules for chromosome movement Signup and view all the answers

What occurs in prometaphase during mitosis?

Chromosomes attach to spindle fibers at their kinetochores Signup and view all the answers

How does cytokinesis occur in animal cells?

Through a contractile ring formed by actin and myosin. Signup and view all the answers

What structure forms in plant cells during mitosis to assist in cell division?

Phragmoplast Signup and view all the answers

Which of the following statements is true regarding depolymerases in mitosis?

They remove tubulin subunits. Signup and view all the answers

What event occurs at the metaphase stage of mitosis?

Chromatids are aligned at the equatorial plane. Signup and view all the answers

What is the importance of the anaphase-promoting complex (APC) in mitosis?

It is essential for chromatid separation. Signup and view all the answers

How do plant cells differ from animal cells during mitosis regarding cytokinesis?

Plant cells need to form a cell wall afterward. Signup and view all the answers

What triggers the formation of the cleavage furrow during cytokinesis?

Actin and myosin contractile fibers Signup and view all the answers

What role does the anaphase-promoting complex (APC) play during anaphase?

It degrades securin, allowing separase activation. Signup and view all the answers

Which protein inhibits separase before anaphase begins?

Securin Signup and view all the answers

During anaphase A, what is the primary movement of the chromosomes?

Chromosomes move toward the poles. Signup and view all the answers

What happens if the chromosomes are not properly aligned during metaphase?

MAD protein prevents the degradation of securin. Signup and view all the answers

How do chromosomes stay connected to spindle fibers during tubulin loss?

Using a dam ring that hugs the plus end of the fibers. Signup and view all the answers

What is aneuploidy?

A condition where cells have an abnormal number of chromosomes. Signup and view all the answers

Which protein is likely serving a similar function to the dam ring in vertebrates?

CENP-E Signup and view all the answers

What is the effect of the degradation of securin during anaphase?

Activates separase to degrade cohesin. Signup and view all the answers

Which stage of mitosis is characterized by the shortening of spindle fibers for chromosome movement?

Anaphase Signup and view all the answers

What is the primary function of the APC with cdh1 after mitosis?

To allow cells to exit mitosis and re-enter the cell cycle. Signup and view all the answers

Which stage of mitosis involves the disappearance of the nuclear envelope?

Prophase Signup and view all the answers

What is the primary function of cohesin during mitosis?

To keep sister chromatids together Signup and view all the answers

Which structure is crucial for chromosome movement during mitosis?

Kinetochores Signup and view all the answers

What occurs to chromatin during prophase?

It compacts into chromosomes Signup and view all the answers

What is the significance of tubulin flux during mitosis?

It helps adjust chromosome positioning Signup and view all the answers

Which spindle fibers provide the structure necessary for chromosomes to separate during anaphase?

Polar fibers Signup and view all the answers

In which phase do chromosomes move to the metaphase plate?

Prometaphase Signup and view all the answers

What happens to sister chromatids at the end of anaphase?

They separate and move towards opposite poles Signup and view all the answers

What role does condensin play during mitosis?

Increasing chromatin organization Signup and view all the answers

What does the positive end of the spindle fibers attach to during mitosis?

Chromosomes at the kinetochore Signup and view all the answers

What is the role of the anaphase-promoting complex (APC) in the transition from metaphase to anaphase?

To activate separase by degrading securin Signup and view all the answers

What happens to tubulin subunits during anaphase in relation to chromosome movement?

They are lost from both the (+) and (–) ends of the spindle fibers. Signup and view all the answers

What is the primary consequence of a metaphase arrest due to misaligned chromosomes?

It ensures proper alignment and segregation of chromosomes. Signup and view all the answers

How does the MAD protein contribute to cell cycle regulation during mitosis?

It prevents the APC from degrading securin. Signup and view all the answers

What occurs during Anaphase A in relation to chromosome movement?

Chromosomes move toward the spindle poles. Signup and view all the answers

What does separase degrade to facilitate the separation of sister chromatids during anaphase?

Cohesin Signup and view all the answers

In the context of chromosomes and spindle fibers during anaphase, which statement is accurate?

Spindle fibers shorten by losing tubulin subunits from both ends. Signup and view all the answers

Which component likely fulfills a function similar to the dam ring for chromosome movement in vertebrates?

NDC80 Signup and view all the answers

What is the result of the degradation of securin prior to anaphase?

Separation of sister chromatids is allowed to occur. Signup and view all the answers

What is the primary role of motor proteins during mitosis?

To assist in chromosome movement Signup and view all the answers

What happens to the connection between the kinetochore and spindle fibers during tubulin loss?

It remains indirect as the fibers lose tubulin but maintain attachment. Signup and view all the answers

Which stage of mitosis is directly followed by the formation of a contractile ring?

Telophase Signup and view all the answers

What happens to the chromosomes during telophase?

They decondense and the spindle apparatus disappears Signup and view all the answers

What is the function of the phragmoplast in plant cells during mitosis?

To form new cell walls Signup and view all the answers

Which process is specifically inhibited by antibodies to actin and myosin?

Cytokinesis Signup and view all the answers

How are tubulin subunits involved in the chromosome movement during mitosis?

They are removed by depolymerases Signup and view all the answers

What is the primary consequence of chromosome condensation during mitosis?

Chromosomes align at the metaphase plate Signup and view all the answers

What structure provides the necessary organization for microtubules during cell division?

Spindle apparatus Signup and view all the answers

What role does the anaphase-promoting complex (APC) play in mitosis?

It regulates the progression through mitosis Signup and view all the answers

What cellular structure is crucial for plant cells to establish after mitosis?

Cell wall Signup and view all the answers

Study Notes

M Phase

M Phase consists of Mitosis & Cytokinesis
Mitosis stages include:
- Prophase: Chromosome condense, nuclear envelope disappears, spindle forms
- Prometaphase: Chromosomes move to the metaphase plate
- Metaphase: Chromosomes lined up at the metaphase plate
- Anaphase: Chromosomes and poles separate
- Telophase: Opposite events of prophase occur

Homologous Chromosomes & Sister Chromatids

Homologous Chromosomes: two copies of each chromosome found in diploid cells
Sister Chromatids: duplicated DNA of each homologous chromosome after S phase
Sister Chromatids form an X shape, connected by a centromere composed of two kinetochores

Chromosome Condensation & Kinetochores

Chromosome condensation: chromatin becomes tightly packed and organized
Cohesin: Holds sister chromatids together
Condensin: Responsible for chromatin compaction
Kinetochores: Distinct structures that bind factors involved in chromosome movement during mitosis

Spindle Fibers

Spindle Fibers are made up of:
- Kinetochore fibers: Attached to chromosomes, help move chromosomes
- Polar fibers: Provide structure to slide past each other in anaphase to separate poles
- Astral fibers: Localize the spindle apparatus in the cell
Positive end of fibers at the kinetochore, minus end at the microtubule organizing center (MTOC) at centrosome
Microtubule nucleation can occur at the MTOC and/or at the kinetochore

Tubulin Flux

Two types of tubulin flux:
- Constant slow addition of tubulin subunits to (+) end and slow loss at (–) end, subunits slowly move from (+) to (–) end
- Rapid flux to change the length of chromosome spindle fibers, adjusts chromosome position in prometaphase, in equilibrium in metaphase, shortens both ends in anaphase

Anaphase Promoting Complex (APC)

APC with cdc20 promotes transition from metaphase to anaphase
Securin inhibits separase
Separase degrades cohesin, allowing sister chromatids to separate
APC-cdc20 degrades securin, activating separase and degrading cohesin
APC with cdh1 allows cells to exit mitosis and re-enter the cell cycle

Anaphase A & Anaphase B

Anaphase A: Chromosomes move to the poles, during anaphase, chromosomal spindle fibers shorten by losing tubulin subunits from both ends
Anaphase B: Poles separate

Chromosome Movement

Kinetochore connection to chromosomes is indirect
Yeast: Dam ring extends from kinetochore at plus end surrounding and near plus end of fiber, allowing plus end to lose/gain tubulin subunits
Loss of tubulin subunits helps the sliding of the ring to the minus end, bringing the chromosomes with it
Vertebrates: Similar function likely fulfilled by NDC80 or CENP-E

Checkpoints

Metaphase arrest prevents aneuploidy (abnormal number of chromosomes)
MAD protein is recruited to misaligned chromosomes and prevents APC from degrading securin, stopping progression into anaphase until proper alignment

Chromosome Movement During Mitosis

Chromosome movement during mitosis is a combination of tubulin flux, motor proteins, and depolymerases
CENPE: Important for plus-end elongation
Dynein & chromokinesin: Motors
Depolymerases: Required to remove tubulin subunits

Telophase & Cytokinesis

Telophase: Opposite of prophase, nuclear envelope reforms, chromosomes decondense, and spindle disappears
Cytokinesis: Actin & myosin fibers form a contractile ring, forming a cleavage furrow between future daughter cells, pinches off to split parental cell, inhibited by antibodies to actin/myosin

Plant Cell Mitosis

Plant cells form a cell wall after mitosis
Phragmoplast: Array of microtubules forms where spindle was
Golgi-derived vesicles migrate to the border between future cells
Membrane of vesicles becomes a new cell membrane, content becomes new cell wall

Fundamental Points

Each step in metaphase is defined by specific events
After S phase and before mitosis, each homologous chromosome consists of two sister chromatids
Mitosis separates the chromatids into daughter cells
Chromosome condensation and tubulin flux are important events in mitosis
APC with various cofactors is critical in the progression through and out of mitosis
Cytokinesis depends on actin and myosin
Plant cell mitosis ends with the formation of a new cell wall involving the phragmoplast

Mitosis and Cytokinesis

M phase consists of mitosis and cytokinesis.
Mitosis stages:
- Prophase: chromosomes condense, nuclear envelope disappears, spindle forms.
- Prometaphase: chromosomes move to the metaphase plate.
- Metaphase: chromosomes lined up at the metaphase plate.
- Anaphase: chromosomes and poles separate.
- Telophase: opposite events of prophase occur.

Homologous Chromosomes and Sister Chromatids

Homologous chromosomes: two copies of each chromosome in diploid cells.
Sister chromatids: duplicated DNA of every single homologous chromosome after the S phase.
Centromere connects sister chromatids, composed of two kinetochores which are attachment points for microtubules.

Chromosome Condensation and Kinetochores

Chromosome Condensation: Chromatin is organized into tightly packed sections, facilitated by cohesin and condensin.
- Cohesin: keeps sister chromatids together.
- Condensin: responsible for chromatin compaction.
Kinetochores: have distinct structures that bind to factors important for chromosome movement in mitosis.

Spindle Fibers

Kinetochore fibers: attached to chromosomes and help move them.
Polar fibers: provide structure to the spindle and allow the poles to slide past each other in anaphase.
Astral fibers: localize the spindle apparatus in the cell.
Positive end: of the fibers is at the kinetochore.
Minus end: is at the microtubule organizing center (MTOC) at the centrosome.
Microtubule nucleation can occur at the MTOC and/or the kinetochore.

Tubulin Flux

Constant slow addition of tubulin subunits: to the (+) end and slow loss at the (–) end.
Subunits slowly move: from the (+) to the (–) end.
Rapid flux to change the length of chromosome spindle fibers: adjusts chromosome position in prometaphase, reaches equilibrium in metaphase, and shortens both ends in anaphase.
These changes in fiber length allow for chromosome movement.

Metaphase to Anaphase Transition

Anaphase Promoting Complex (APC) with cdc20: promotes the metaphase to anaphase transition.
Securin: normally inhibits separase.
Separase: degrades cohesin, allowing sister chromatids to separate.
APC-cdc20 complex degrades securin: activating separase, degrading cohesin, and separating chromatids.
APC with cdh1: allows cells to exit mitosis and re-enter the cell cycle, proceeding to G1.

Anaphase A and B

Anaphase A: chromosomes move to the poles.
Anaphase B: the poles separate.
Chromosomes move to the poles: as chromosomal spindle fibers shorten by losing tubulin subunits from both the (+) and (–) ends.

Chromosome Spindle Fiber Shortening

Connection between the kinetochore and chromosomes: indirect.
Dam ring (in yeast): extends from the kinetochore at the plus end, going around and near the plus end of the fiber, leaving the plus end free to lose/gain tubulin subunits.
Tubulin subunit loss: exerts force that slides the ring to the minus end, bringing the chromosomes with it (toward the pole).
Vertebrates: similar mechanism likely fulfilled by another factor (NDC80 or CENP-E).

Checkpoints

Metaphase arrest: prevents daughter cells from receiving the wrong number of chromosomes (aneuploidy).
MAD protein: recruited to misaligned chromosomes (due to misaligned forces pulling in different directions).
MAD protein prevents APC from degrading securin: stopping progression into anaphase until chromosomes properly align.

Chromosome Movement Mechanisms

Chromosome movement during mitosis: combination of tubulin flux, motor proteins, and depolymerases.
CENPE: important for plus-end elongation.
Dynein and chromokinesin: motor proteins.
Depolymerases: remove tubulin subunits.

Telophase and Cytokinesis

Telophase: opposite of prophase, nuclear envelope reforms, chromosomes decondense, spindle disappears.
Cytokinesis: actin and myosin fibers form a contractile ring.
Cleavage furrow: forms between the two future daughter cells.
Furrow eventually pinches off: splitting the parental cell into two daughter cells.
Antibodies to actin or myosin inhibit this process.

Plant Cell Cytokinesis

Plant cells form a cell wall after mitosis.
Phragmoplast: array of microtubules forms where the spindle was.
Vesicles (from Golgi): migrate to the border between the future cells.
Vesicle membrane: becomes a new cell membrane.
Vesicle content: gives rise to the new cell wall.

Fundamental Points

Metaphase occurs in defined steps: each with specific events.
After S-phase and before mitosis: each homologous chromosome consists of two sister chromatids.
Mitosis separates the chromatids: into the daughter cells.
Chromosome condensation and tubulin flux are important events in mitosis.
Anaphase-promoting complex (APC): critical for progression through and out of mitosis.
Cytokinesis depends on actin and myosin.
Plant cell mitosis ends with the formation of a new cell wall: involving the phragmoplast structure.

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Description

This quiz covers the M Phase of the cell cycle, focusing on the processes of mitosis and cytokinesis. It includes details on the stages of mitosis, homologous chromosomes, sister chromatids, chromosome condensation, and kinetochores. Test your understanding of these critical concepts in cell division.