24 Questions
What is the purpose of the synaptonemal complex during meiosis?
To align the homologs with remarkable precision
What occurs during meiosis I: Anaphase I?
Homologous chromosomes move to opposite poles
What is the result of crossing-over during meiosis?
Recombination of genetic material
What occurs during meiosis II: Prophase II?
Chromosomes condense and the nuclear envelope breaks down
What is the purpose of the chiasmata during meiosis?
To mark the sites of crossing-over
What is the result of meiosis I?
Cells with half the number of chromosomes, each consisting of two sister chromatids
What occurs during meiosis II: Anaphase II?
Centromeres divide and sister chromatids move to opposite poles
What is the similarity between meiosis II and mitosis?
Both involve the separation of sister chromatids
What is the main function of the centrosome during interphase?
To duplicate and migrate to the nucleus
What type of microtubules are involved in the attachment to kinetochores?
Kinetochore microtubules
During which phase of mitosis do the chromosomes become apparent?
Prophase
What is the function of the kinetochores during mitosis?
To hold replicated sister chromatids together
What is the main function of the mitotic spindle during mitosis?
To separate chromosomes during anaphase
During which phase of mitosis does the nuclear membrane break down?
Prometaphase
What is the result of the cytokinesis process?
Formation of new cell membranes
Which type of cells do not have centrosomes?
Plant cells
What is the primary mechanism responsible for the rapid degradation of cyclin concentration during mitosis?
Ubiquitin-dependent proteolytic system
What is the role of the anaphase promoting complex (APC) in mitosis regulation?
To add ubiquitin to cyclin and other proteins involved in mitotic regulation
Which of the following cyclin-Cdk complexes is responsible for triggering the entry into the S phase?
S-cyclin-Cdk complex
What is the consequence of cyclin degradation in the cell cycle?
Inactivation of Cdk activity
What is the role of M-Cdk in its own deactivation?
It contributes to its own deactivation
What is the primary function of the proteasome in the context of cyclin regulation?
To degrade ubiquitinated cyclin proteins
What is the consequence of APC complex activation during mitosis?
Ubiquitination and degradation of M-cyclin
What is the role of different cyclin-Cdk complexes in the cell cycle?
They trigger different steps in the cell cycle
Study Notes
Meiosis I: Synapsis
- The synaptonemal complex, also known as the "zipper", aligns homologous chromosomes with remarkable precision, bringing together corresponding genetic regions of the chromosome pair.
- Sister chromatids do not undergo recombination.
- The sites of crossing-over are called chiasmata (singular, chiasma), resulting in the recombination of genetic material.
- No genetic information is lost or gained, and all chromatids retain their original size.
Meiosis I: Metaphase I, Anaphase I, and Telophase I
- Homologous chromosomes move to opposite poles.
- Nuclear envelope reforms.
- Resultant cells have half the number of chromosomes, each consisting of two sister chromatids.
Meiosis II
- Resembles Mitosis, with prophase, metaphase, anaphase, and telophase stages.
- Chromosomes condense, centrioles move towards the poles, and the nuclear envelope breaks down at the end of prophase II.
- Chromosomes align at the metaphase plate.
- Sister chromatids attach to the spindle fibers from opposite poles.
- Centromeres divide, and sister chromatids move to opposite poles.
Cell Cycle Regulation
- The sudden drop in cyclin concentration during mitosis is due to its rapid degradation by the ubiquitin-dependent proteolytic system.
- The anaphase promoting complex (APC) adds ubiquitin to cyclin and other proteins involved in mitotic regulation.
- M-Cdk contributes to its own deactivation.
- Different cyclin-Cdk complexes trigger different steps in the cell cycle.
- E.g., M-cyclin-Cdk complex acts in the G2 phase and triggers the entry into the M phase, while S-phase cyclins are responsible for the entry into the S phase.
Mitosis
- Chromosomes are lined up at the metaphase plate, an imaginary structure at the midway point between the spindle's two poles.
- Centrosomes duplicate during Interphase, and each centrosome migrates during prophase to either side of the nucleus to form spindle poles.
- Plant cells do not have centrosomes.
- Kinetochores are protein complexes associated with centromeres, and microtubules attach to kinetochores found at the centromere.
- Mitosis is conventionally divided into five phases: prophase, prometaphase, metaphase, anaphase, and telophase.
- Cytokinesis is the division of cytoplasm, resulting in the formation of new cell membranes and the separation of cells.
Learn about the process of synapsis in meiosis I, including the role of the synaptonemal complex and the formation of chiasmata. Understand how this process leads to genetic recombination.
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