Retta - L13

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Questions and Answers

What year did the scientists receive the Nobel Prize in Chemistry for the discovery of ubiquitin-mediated protein degradation?

2004 (correct)

2007

2001

2010

Which of the following proteins is specifically referred to as M cyclin in the context of the M phase?

Cyclin A

Cyclin B (correct)

Cyclin E

Cyclin D

What role does ubiquitination primarily serve in cellular processes?

Facilitating protein synthesis

Regulating protein degradation (correct)

Enhancing signal transduction

Promoting cell division

Which aspect of proteins can vary significantly due to ubiquitination?

Their half-life Signup and view all the answers

Ubiquitination has a similar regulatory role to which other post-translational modification?

Phosphorylation Signup and view all the answers

How is the degradation of cyclins primarily classified in cellular processes?

As a post-translational modification Signup and view all the answers

What role does the M-Cdk complex play during the M phase of the cell cycle?

It induces chromosome condensation and spindle assembly Signup and view all the answers

How is the M-Cdk complex activated at the onset of mitosis?

Through the removal of inhibitory phosphate groups by Cdc25 phosphatase Signup and view all the answers

Which molecule is responsible for keeping the M-Cdk complex in an inactive state?

Wee1 kinase Signup and view all the answers

What happens to M cyclin levels during the G2 and M phases of the cell cycle?

They increase due to constant synthesis without degradation Signup and view all the answers

What structural changes facilitative role do cohesins and condensins provide during mitosis?

They help configure duplicated chromosomes for segregation Signup and view all the answers

Which of the following statements about the phosphorylation of the M-Cdk complex is true?

The M-Cdk complex is kept inactive by additional phosphorylation from Wee1 Signup and view all the answers

What is the relationship between the M-Cdk complex and the Cdc25 phosphatase?

Cdc25 is directly activated by M-Cdk, leading to its own positive feedback Signup and view all the answers

What role does cohesin play during mitosis?

It maintains the sister chromatids together. Signup and view all the answers

Which statement accurately describes condensin's function?

It facilitates the condensation of chromosomes during mitosis. Signup and view all the answers

What happens to cohesin as the cell progresses through mitosis?

It remains near the centromere until sister chromatids are separated. Signup and view all the answers

Which component is essential for the physical separation of daughter cells during cytokinesis?

Actomyosin ring contractility. Signup and view all the answers

What is the primary characteristic of M phase?

It includes both mitosis and cytokinesis. Signup and view all the answers

How are condensins and cohesins structurally similar?

Both form a ring structure. Signup and view all the answers

What is the function of the mitotic spindle during cell division?

It provides tension necessary for the separation of chromatids. Signup and view all the answers

In the S phase of the cell cycle, what is primarily occurring with regard to chromosomal structure?

DNA is duplicated and sister chromatids are formed. Signup and view all the answers

What experimental technique was used to visualize the distribution of condensin along chromosomes?

Electron microscopy with immunohistochemistry. Signup and view all the answers

What is the role of kinesins during mitotic spindle assembly?

They facilitate the sliding of microtubules towards the poles. Signup and view all the answers

Which statement best describes the function of the M-Cdk complex?

It phosphorylates proteins to initiate spindle assembly. Signup and view all the answers

How does the presence of Ran-GTPase affect microtubule dynamics during mitosis?

It promotes the attachment of microtubules to the kinetochores. Signup and view all the answers

What major event happens to the nuclear envelope during mitosis?

It undergoes breakdown due to phosphorylation of lamin proteins. Signup and view all the answers

What is a significant characteristic of microtubules during metaphase?

Their dynamic instability decreases upon attachment to kinetochores. Signup and view all the answers

Which protein complex is crucial for the extensive condensation of mitotic chromosomes?

Condensin Signup and view all the answers

What effect does M-Cdk phosphorylation have on centrosome components?

It activates them to enhance spindle assembly. Signup and view all the answers

What is the primary outcome of increased microtubule instability during mitosis?

It leads to the efficient separation of chromosomes. Signup and view all the answers

What is the primary function of kinetochore microtubules during mitosis?

To pull chromosomes to opposite poles. Signup and view all the answers

Which type of microtubules plays a key role in separating sister chromatids during anaphase?

Kinetochore microtubules Signup and view all the answers

How does the duplication of centrosomes relate to DNA duplication in the cell cycle?

Both initiate during the G1-S phase. Signup and view all the answers

Which motor protein is responsible for the anti-parallel sliding of interpolar microtubules during spindle elongation?

Kinesin 5 Signup and view all the answers

What is the orientation of the plus-ends of all microtubules during mitosis?

Projected away from the centrosome. Signup and view all the answers

What is a unique feature of dynein motor proteins compared to kinesins?

Dyneins move toward the minus-end of microtubules. Signup and view all the answers

How do interpolar microtubules contribute to the overall function of the mitotic spindle?

By promoting the elongation of the spindle through sliding. Signup and view all the answers

What mechanism is shared by both DNA duplication and centriole duplication?

They utilize a semi-conservative mechanism. Signup and view all the answers

What role do kinesin 14 motor proteins play during mitosis?

They move toward the minus-end in leading the opposing force in the spindle. Signup and view all the answers

What is the consequence of improper segregation of sister chromatids during mitosis?

Potential genomic instability and disease. Signup and view all the answers

Study Notes

Discovery of Ubiquitin

Nobel Prize in Chemistry awarded in 2004 for the discovery of ubiquitin-mediated protein degradation.
Ubiquitination is a critical post-translational modification involved in the turnover of proteins, including cyclins.
Proteins have varying half-lives: some last 24 hours, while others degrade within minutes.
This process is crucial for regulating protein levels and cell cycle progression.

M-Cyclin CDK Complex

M cyclin, specifically cyclin B, forms the M cyclin CDK complex with CDK1.
Regulates entry into and exit from the M phase of the cell cycle, essential for mitosis.
M-Cdk induces mitotic spindle assembly and chromosome attachment to the spindle.
Activates chromosome condensation and nuclear envelope breakdown.

Activation and Regulation of M-Cdk

M cyclin accumulates during the cell cycle, particularly in G2 and M phases.
Ubiquitination influences the stability and degradation of M cyclin; decreased ubiquitination allows accumulation.
Activation requires dephosphorylation: inhibitory phosphate groups added by Wee1 kinase must be removed by Cdc25 phosphatase.
The M-Cdk complex exhibits a positive feedback loop, facilitating rapid progression into mitosis.

Cohesins and Condensins

Cohesins form rings that hold sister chromatids together until anaphase.
Condensins aid in DNA condensation, forming loops that compact chromatin into metaphase chromosomes.
Both proteins work together to ensure proper chromosome organization during mitosis.

Cytoskeletal Structures in M Phase

The mitotic spindle, composed of microtubules, is essential for chromosome segregation.
Actin filaments form a contractile ring during cytokinesis for daughter cell separation.
Cytokinesis follows mitosis, facilitating the division of cytoplasm into two cells.

Microtubules in M Phase

Kinetochore microtubules attach to the centromeres of chromosomes, facilitating their movement during mitosis.
Interpolar microtubules stabilize the spindle and aid in separating sister chromatids.
Astral microtubules help position the spindle apparatus within the cell.

Centrosome Duplication

Centrosomes duplicate alongside DNA during interphase to prepare for mitosis.
Centrioles duplicate in a semi-conservative manner, serving as templates for new centrioles.
This duplication is crucial for maintaining proper cell structure and function during cell division.

Role of Motor Proteins

Motor proteins, like kinesins and dyneins, facilitate microtubule dynamics and chromosome movement.
Kinesins move toward the plus-end of microtubules, promoting elongation and alignment of chromosomes.
Dyneins move toward the minus-end, contributing to microtubule organization and centrosome separation.
Proper function of these motor proteins is vital for accurate chromosome segregation and cytokinesis.### Kinesin Movement and Motor Protein Functions
Kinesin 5 exhibits bidirectional movement on microtubules, with motor domains enabling movement toward both minus and plus ends.
Reciprocal sliding between antiparallel microtubules occurs due to the action of multimeric motor proteins, essential for mitotic spindle assembly.
Two primary functions of these motor proteins include promoting microtubule sliding toward spindle poles and facilitating microtubule focalization at the centrosome.

Role of Cyclin-CDK Complex in Mitosis

Cyclin-CDK complex (M-Cdk) is crucial for bipolar mitotic spindle assembly, phosphorylating proteins including condensins and lamins.
Condensins facilitate the condensation of chromosomes, while lamin phosphorylation leads to nuclear envelope breakdown during mitosis.
M-Cdk influences microtubule dynamics and centrosome maturation, ensuring accurate chromosome separation.

Microtubule Instability and Dynamics

Microtubule instability increases during mitosis, crucial for the formation of the mitotic spindle and interaction with chromosomes.
Metaphase microtubules have a half-life of 15 seconds compared to 5 minutes in interphase, showing reduced dynamic instability when attached to kinetochores.
Interpolar, kinetochore, and astral microtubules display different stability characteristics and functions during mitosis.

Chromosome Contribution to Microtubule Nucleation

Ran-GTPase protein accumulates around mitotic chromosomes, aiding microtubule attachment to kinetochores.
Activated by GEF (RCC1), Ran promotes the exchange of GDP for GTP, enhancing nucleation and microtubule attachment at kinetochores.
Chromosomes serve as nucleation points for microtubule formation even in the absence of centrosomes.

Mechanism of Microtubule Nucleation

Nucleation occurs at the centromeric region, with active Ran GTP promoting recruitment of proteins essential for microtubule assembly.
Microtubules elongate toward the plus end and stabilize at kinetochores, facilitating proper chromosome alignment and segregation.
The process is governed by concentration gradients of Ran-GTP, displaying differences in microtubule behavior depending on their origin.

Kinetochore Structure and Function

Kinetochore microtubules bind to the centromere region of chromosomal proteins, forming during chromosome condensation.
Variability exists among species regarding the number of microtubules attached to kinetochores, with simpler organisms exhibiting fewer attachments.
Kinetochore evolution reflects diversity in protein complexes, influencing the functionality and efficiency during cell division.

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Description

This quiz explores the discovery of ubiquitin and its crucial role in molecular biology, particularly during the M phase of mitosis. Learn about the Nobel Prize-winning research that highlighted ubiquitin-mediated proteolysis and its implications in cell cycle regulation and cellular functions.