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Questions and Answers
What occurs during the pachytene stage of meiosis?
What occurs during the pachytene stage of meiosis?
Which process ensures genetic variability through the exchange of genetic material?
Which process ensures genetic variability through the exchange of genetic material?
What is the possible number of combinations of 23 chromosome pairs that can be present in gametes?
What is the possible number of combinations of 23 chromosome pairs that can be present in gametes?
What happens to chromosomes during anaphase I of meiosis?
What happens to chromosomes during anaphase I of meiosis?
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What is the primary consequence of nondisjunction during meiosis?
What is the primary consequence of nondisjunction during meiosis?
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How does meiosis differ from mitosis regarding chromosome number?
How does meiosis differ from mitosis regarding chromosome number?
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Why is crossing over ensured by homologous recombination during meiosis?
Why is crossing over ensured by homologous recombination during meiosis?
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During which phase does the synaptonemal complex begin to break down?
During which phase does the synaptonemal complex begin to break down?
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What is the defining characteristic of telophase I in meiosis?
What is the defining characteristic of telophase I in meiosis?
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How is somatic mosaicism defined?
How is somatic mosaicism defined?
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What genetic condition is primarily caused by nondisjunction during meiosis?
What genetic condition is primarily caused by nondisjunction during meiosis?
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Which element is critical for the formation of double stranded breaks in homologous recombination?
Which element is critical for the formation of double stranded breaks in homologous recombination?
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What is the role of chiasmata during meiosis?
What is the role of chiasmata during meiosis?
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What is the primary cause of triploidy in humans?
What is the primary cause of triploidy in humans?
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What are the stages of Meiosis I in the correct order?
What are the stages of Meiosis I in the correct order?
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What is a key event that occurs during Prophase I of meiosis?
What is a key event that occurs during Prophase I of meiosis?
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What is the primary outcome of nondisjunction during meiosis?
What is the primary outcome of nondisjunction during meiosis?
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Which of the following best describes genetic recombination?
Which of the following best describes genetic recombination?
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How does meiosis differ from mitosis?
How does meiosis differ from mitosis?
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During which phase of meiosis does the cleavage furrow form?
During which phase of meiosis does the cleavage furrow form?
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What is the purpose of crossing over during meiosis?
What is the purpose of crossing over during meiosis?
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What is the result of incomplete cytokinesis during meiosis?
What is the result of incomplete cytokinesis during meiosis?
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What role do motor proteins play during meiosis?
What role do motor proteins play during meiosis?
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Which type of cell undergoes meiosis?
Which type of cell undergoes meiosis?
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What is a key checkpoint during meiosis that ensures chromosomes are correctly aligned?
What is a key checkpoint during meiosis that ensures chromosomes are correctly aligned?
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Which of the following describes an outcome of meiosis?
Which of the following describes an outcome of meiosis?
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What is a potential consequence of nondisjunction during Meiosis I?
What is a potential consequence of nondisjunction during Meiosis I?
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During which meiotic phase do homologous chromosomes align at the metaphase plate?
During which meiotic phase do homologous chromosomes align at the metaphase plate?
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Study Notes
Cytoskeleton
- Consists of microtubules, microfilaments (actin filaments), and intermediate filaments
- Microtubules: Largest filament type, composed of α-tubulin and β-tubulin subunits, approximately 25 nanometers in diameter. Assembled into linear protofilaments. Can rapidly grow or shrink in size due to polymerization or depolymerization, respectively.
- Microfilaments: Smallest filament type, composed of actin protein, around 8 nanometers in diameter. Common in muscle cells.
- Intermediate filaments: Composed of various protein subunits, around 10 nanometers in diameter. Associated with specific cell types (neurofilaments, desmin, keratins).
Functions of Cytoskeleton
- Maintains cell shape and resists deformation
- Transports intracellular cargo (e.g., vesicles)
- Facilitates cell movement and migration
- Aids in cell communication
- Assists in cell division.
Microtubules (Continued)
- Protofilaments (10-15 in number, 14 in mammalian cells) assemble to form a hollow cylinder, approximately 24 nanometers wide
- Contain y-tubulin, capping proteins, + and - ends to control growth
Motor Proteins
- Utilize ATP hydrolysis to generate movement and force
- Examples include kinesin (moves towards cell membrane), dynein (moves components inward), myosin (muscle contractions, cytokinesis, endocytosis, exocytosis)
Cell Division in Eukaryotes (Mitosis and Meiosis)
- Mitosis: Somatic cell division resulting in two genetically identical daughter cells. Involves 5 phases: Prophase, Prometaphase, Metaphase, Anaphase, and Telophase.
- Meiosis: Germ cell division, producing haploid gametes. Involves two rounds of cell division (Meiosis I and Meiosis II). Essential for sexual reproduction.
Regulation of Mitosis
- Cyclin-dependent kinases (CDKs) regulate the cell cycle, including the M phase.
- Kinases add phosphate groups to other molecules.
- CDKs are active only when associated with cyclin proteins. Cyclin concentration fluctuate
Regulation of Mitosis
- Cyclin-dependent kinases (CDKs) are crucial for accurate cell cycle progression. These enzymes add phosphate groups to other molecules (specifically, the amino acids serine, threonine, or tyrosine). CDKs are inactive unless bound to specific cyclin proteins, whose concentrations fluctuate throughout the cell cycle.
Mitosis (Stages)
- Prophase: Chromosomes condense, nuclear envelope breaks down, and the mitotic spindle begins to form.
- Prometaphase: Chromosomes attach to microtubules of the mitotic spindle.
- Metaphase: Chromosomes align along the metaphase plate (equatorial plane).
- Anaphase: Sister chromatids separate and move to opposite poles.
- Telophase: Chromosomes decondense, nuclear envelopes reform, and cytokinesis begins (division of cytoplasm).
Telophase and Cytokinesis
- Physical process completing the division of parent cell into two identical daughter cells.
- Signal for cytokinesis is the dephosphorylation of proteins, which are targets of CDKs.
- Cell membrane pinches in at the equator.
- Action of a contractile ring of actin and myosin filaments forms the cleavage furrow.
Meiosis (Stages)
- Prophase I: Homologous chromosomes pair up (synapsis), crossing over occurs (exchange of genetic material).
- Metaphase I: Homologous pairs (bivalents) line up at the metaphase plate.
- Anaphase I: Homologous chromosomes separate and move to opposite poles.
- Telophase I and Cytokinesis: Two haploid cells are formed.
- Meiosis II: Similar to mitosis, but with haploid cells. Sister chromatids separate, resulting in four haploid gametes.
Cell Division and Human Pathology
- Aneuploidy (abnormal chromosome number) is a common cause of human genetic disorders.
- Non-disjunction (failure of chromosomes to separate correctly) during meiosis is a major cause of aneuploidy. Examples include Down syndrome (trisomy 21).
- Mosaicism involves the presence of different cell populations within an individual, each with a different genetic makeup.
Chromosomes
- Chromosomes condense into compact structures during prophase.
- Condensins attach to chromosomes for compaction.
- Nuclear envelope disintegrates.
- Cohesins holds sister chromatids together.
- H3 and H1 histone phosphorylation are crucial for chromosome condensation and attachment.
- Centrosomes move to opposite poles to facilitate the process.
- Microtubule organizing centers (MTOCs) are essential structures, with the centrosome being the primary MTOC.
- Centrioles, duplicated during S phase, are part of the centrosome.
- Spindle fibers and microtubules are critical for chromosome alignment and movement during cell division.
Microtubules in Mitosis
- Astral microtubules position the mitotic spindle and orientation.
- Kinetochore microtubules attach to chromosomes; facilitate chromosome movement.
- Interpolar microtubules extend across the equator and have a sliding action to separate poles.
Motor Proteins in Mitosis
- Eg5 (Kinesin-5) is responsible for pole separation.
- Dynein performs pole focusing and transport.
- Chromokinesins (Kinesin-4, -10) facilitates ejection, and CENP-E helps transport chromosomes to the equator.
Mitochondrial Mosaicism
- Mitochondrial populations are heterogenous due to high mutation rate.
- Mitochondrial segregation occurs randomly during cell division.
- Variability in mitochondrial DNA (mtDNA) distribution in cells.
Tumorigenesis
- Tumor cells often possess genomic instability characterized by widespread DNA alterations, chromosome breaks, and aneuploidy.
- Aneuploidy can contribute to tumorigenesis by creating extra copies of oncogenes or deleting tumor suppressor genes.
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Description
This quiz covers the components and functions of the cytoskeleton, including microtubules, microfilaments, and intermediate filaments. Understand how these structures maintain cell shape, assist in movement, and transport cargo within cells. Test your knowledge of cell biology related to the cytoskeleton.
