Mol bio lecture 3

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Questions and Answers

Which event occurs during prophase?

Chromosomes align at the metaphase plate

Nuclear envelope disassembly

Chromatin condenses into chromosomes (correct)

Sister chromatids are pulled apart

What is a critical event in prometaphase?

Chromosomes begin decondensation

All spindle fibers attach to kinetochores (correct)

Centromeres split

Nuclear envelope reformation

During which phase do chromosomes align at the metaphase plate?

Anaphase

Metaphase (correct)

Telophase

Prometaphase

What happens to sister chromatids during anaphase?

They are pulled apart towards opposite poles Signup and view all the answers

Which statement describes telophase accurately?

Spindle fibers disassemble and reformation of the nuclear envelope occurs Signup and view all the answers

What is the main role of the spindle checkpoint during metaphase?

To verify spindle fibers are attached correctly to chromosomes Signup and view all the answers

What event is characterized by chromatin decondensation?

Telophase Signup and view all the answers

Which structure is crucial for chromosome movement during prometaphase?

Spindle fibers Signup and view all the answers

What is not a characteristic of prophase?

Nuclear envelope disappears Signup and view all the answers

What happens to the centromeres during anaphase?

They split to allow chromatids to be pulled apart Signup and view all the answers

What is the primary role of cohesin during metaphase?

Maintains adhesion of sister chromatids at the metaphase plate Signup and view all the answers

What happens during the metaphase checkpoint if a single kinetochore is unattached?

Mitosis is stalled due to lack of CDC20 activation Signup and view all the answers

What is the first major step in sister chromatid separation?

Securin is degraded by APC Signup and view all the answers

Which statement accurately describes APC's role in cell cycle regulation?

APC promotes the degradation of securin and cyclins Signup and view all the answers

What is the consequence of an error during prophase related to chromosome condensation?

Cell stalls at the G2/M checkpoint Signup and view all the answers

How does MAD2 contribute to spindle attachment checkpoint regulation?

It sequesters CDC20 at unattached kinetochores Signup and view all the answers

What initiates the synthesis of G1 cyclin following APC activation?

Inactivation of m-phase cyclin Signup and view all the answers

Which of the following events would stall a cell at the spindle attachment checkpoint?

A single kinetochore remains unattached Signup and view all the answers

What is the role of separase in the process of sister chromatid separation?

To cleave cohesin, allowing separation Signup and view all the answers

What characterizes symmetric cytokinesis?

It leads to perfectly split organelles and cytoplasm. Signup and view all the answers

Which of the following involves the creation of the cleavage furrow?

Contraction of the Contractile Ring Signup and view all the answers

During embryogenesis, what role do polarity proteins play?

They help establish concentration gradients for materials. Signup and view all the answers

What is one result of asymmetric cell division during embryogenesis?

One daughter cell becomes more concentrated in materials. Signup and view all the answers

Which protein complex is responsible for positioning the contractile ring?

Centralspindlin complex Signup and view all the answers

What occurs during the final separation phase of cytokinesis?

The midbody ring coordinates the abscission of daughter cells. Signup and view all the answers

In somatic mitosis, how is the distribution of organelles and cytoplasm managed?

They are evenly split to ensure cell viability. Signup and view all the answers

Which step of cytokinesis follows the formation of the contractile ring?

Contraction of the contractile ring Signup and view all the answers

Which statements about cytokinesis during embryogenesis are true?

It enables the development of uniquely fated cells. Signup and view all the answers

What is the consequence of improper alignment of chromosomes during metaphase?

Aneuploidy in daughter cells Signup and view all the answers

Which stalling point is associated with errors during anaphase?

Failure to separate sister chromatids Signup and view all the answers

What may result from the failure of cytokinesis?

Multinucleated cells with cellular dysfunction Signup and view all the answers

How do microtubules contribute to anaphase?

By pulling sister chromatids apart Signup and view all the answers

What could be a consequence if spindles fail to pull chromatids apart?

Undergoing apoptosis or unchecked cell cycle Signup and view all the answers

What role do actin and myosin play in cytokinesis?

They form a contractile ring to split the cell. Signup and view all the answers

What happens if a significant issue triggers a post-mitotic checkpoint?

The cell may proceed to apoptosis. Signup and view all the answers

What defines the final step in the cell cycle?

Cytokinesis process Signup and view all the answers

What can occur as a consequence of aneuploidy during cell division?

Developmental disorders or cancer risk Signup and view all the answers

Which error is most closely associated with incomplete chromosome segregation?

Incorrect spindle fiber attachment Signup and view all the answers

Study Notes

Mitosis Phases and Major Events

Prophase: Chromatin condenses into visible chromosomes with sister chromatids; nucleus remains intact; spindle apparatus begins formation from centrosomes.
Prometaphase: Nuclear envelope disassembles; spindle fibers attach to kinetochores at chromosome centromeres; chromosomes start moving toward the metaphase plate.
Metaphase: Chromosomes align at the metaphase plate; spindle checkpoint ensures all chromosomes are correctly attached to spindle fibers before proceeding.
Anaphase: Sister chromatids are pulled apart toward opposite poles once the centromeres split; cell elongates as microtubules push against each other.
Telophase: Chromosomes reach poles and decondense; nuclear envelope reforms around each chromosome set; spindle apparatus disassembles.
Cytokinesis: Division of the cytoplasm, creating two daughter cells; differs in animals (cleavage furrow) and plants (cell plate formation).

Metaphase Checkpoint and Chromosome Separation

Alignment is driven by kinetochore attachment; an unattached kinetochore can stall mitosis via the anaphase promoting complex (APC).
Cohesin complex holds sister chromatids together until anaphase; degradation of securin frees separase to cleave cohesin, enabling separation.
Rate limiting steps include CDC20 synthesis and APC phosphorylation.

Consequences of APC Activation

Activation of APC leads to the degradation of securin, freeing separase to cleave cohesin for chromatid separation.
APC activation facilitates the degradation of m-phase cyclin and initiates G1 cyclin synthesis.

Spindle Attachment Checkpoint

Ensures all chromosomes are properly attached before separation; a single unattached kinetochore can inhibit CDC20, stalling mitosis.
MAD2 proteins sequester CDC20 at unattached kinetochores, blocking the progression into anaphase.

Errors in Mitosis

Prophase Errors: Failure in chromosome condensation or spindle formation can lead to incomplete segregation; stalling at the G2/M checkpoint.
Metaphase Errors: Improper alignment can cause aneuploidy; stalling occurs at the metaphase checkpoint if chromosomes are misaligned.
Anaphase Errors: Failure to separate chromatids results in uneven distribution, leading to potential aneuploidy; errors may trigger apoptosis or unchecked cell growth.
Telophase/Cytokinesis Errors: Incomplete reformation of the nuclear envelope or failed cytokinesis may cause multinucleated cells or chromosomal abnormalities; potential post-mitotic checkpoint may lead to apoptosis.

Cytokinesis Features and Steps

Final stage of cell division, dividing cytoplasm into two daughter cells after mitosis.
Actin and myosin filaments form a contractile ring that pinches the cell into two; divisions can be symmetric or asymmetric.

Steps for Proper Cytokinesis

Formation of Contractile Ring: Positioning at the equator through signals like Rho-GEF and Ect-2; microtubules guide the central spindle complex.
Contraction of Contractile Ring: Actin and myosin tighten the ring to form a cleavage furrow.
Cleavage Furrow Formation: Actin and microtubules guide spatial distribution for even cell division.
Final Separation: The midbody ring coordinates the separation of daughter cells.
Distribution of Organelles: Ensures equal division of organelles and cytoplasm for viability.

Differences in Cytokinesis: Somatic Mitosis vs. Embryogenesis

In somatic mitosis, division is nearly even; each daughter cell receives approximately equal cytoplasmic contents.
In embryogenesis, asymmetrical divisions create concentration gradients; polarity proteins and Rho-GTPases contribute to unique material distribution affecting cell fate, crucial for morphogenesis and specialization.

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Description

This quiz covers the sequential phases of mitosis, detailing the major events that occur in each stage. You will learn about prophase, metaphase, anaphase, and telophase, along with the instrumental role of spindle fibers in cell division. Dive into the essentials of mitotic processes.