Eukaryotic Cell Cycle and Division
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Questions and Answers

What is the role of maturation-promoting factor (MPF) in the cell cycle?

  • It regulates the progression of the cell cycle. (correct)
  • It breaks down the spindle apparatus at the end of mitosis.
  • It initiates DNA replication during interphase.
  • It ensures the daughter cells are genetically distinct.

During which phase of the cell cycle are sister chromatids produced?

  • S phase (correct)
  • M phase
  • G1 phase
  • G2 phase

What is a function of the spindle apparatus during cell division?

  • It organizes and sorts the chromosomes. (correct)
  • It creates cytoplasmic structures.
  • It forms the cell membrane around daughter cells.
  • It helps in the replication of DNA.

What occurs during cytokinesis?

<p>The cell splits into two genetically identical daughter cells. (D)</p> Signup and view all the answers

Which structure is responsible for defining the two poles of the spindle apparatus?

<p>Centrosomes (D)</p> Signup and view all the answers

What is the primary outcome of meiosis compared to mitosis?

<p>Meiosis produces four haploid cells. (B)</p> Signup and view all the answers

How many chromosomes would a diploid cell with 6 chromosomes produce after meiosis?

<p>4 daughter cells with 3 chromosomes each. (A)</p> Signup and view all the answers

Which principle of the chromosome theory of inheritance states that the nucleus of a diploid cell contains pairs of chromosomes?

<p>The nucleus contains two sets of homologous chromosomes. (D)</p> Signup and view all the answers

During meiosis, what happens to the homologous chromosomes?

<p>They segregate independently into daughter nuclei. (B)</p> Signup and view all the answers

What is the correct sequence of phases in the eukaryotic cell cycle?

<p>G1 → S → G2 → M (A)</p> Signup and view all the answers

What occurs during the S phase of the cell cycle?

<p>Each chromosome is replicated. (A)</p> Signup and view all the answers

What role do gametes play in the process of fertilization?

<p>They each provide a complete set of chromosomes to the offspring. (B)</p> Signup and view all the answers

Which of the following correctly describes the chromosome theory of inheritance?

<p>The chromosome behavior during meiosis explains the inheritance pattern of traits. (A)</p> Signup and view all the answers

Which type of chromosomes are referred to as homologs in diploid species?

<p>Pairs of chromosomes nearly identical in size and genetic composition. (B)</p> Signup and view all the answers

What process divides one cell nucleus into two during the cell cycle?

<p>Mitosis (B)</p> Signup and view all the answers

Which statement correctly summarizes a key aspect of Mendel’s laws?

<p>They rely on the independent assortment and segregation of traits. (C)</p> Signup and view all the answers

In a cell with a diploid number of 6, how many chromosomes are present in each gamete after meiosis?

<p>3 chromosomes. (D)</p> Signup and view all the answers

Which of the following statements about gametes is true?

<p>They contain a total of 23 chromosomes. (B)</p> Signup and view all the answers

What do cytogenetics primarily focus on?

<p>Microscopic examination of chromosomes (B)</p> Signup and view all the answers

During which phase of the cell cycle does a cell prepare for division by synthesizing proteins?

<p>G2 phase (C)</p> Signup and view all the answers

What is the total number of chromosomes in most human cells?

<p>46 (B)</p> Signup and view all the answers

What occurs in the cell cycle's G1 phase?

<p>Molecular changes promote progression through the cycle. (A)</p> Signup and view all the answers

Which of the following best defines a karyotype?

<p>A photographic representation of chromosomes. (A)</p> Signup and view all the answers

What is the duration of the G1 phase for a cell that divides in 24 hours?

<p>11 hours (D)</p> Signup and view all the answers

Which proteins are essential for controlling advancement through the cell cycle?

<p>Cyclins and Cyclin-dependent kinases (D)</p> Signup and view all the answers

What is the primary function of the G1 checkpoint in the cell cycle?

<p>Determine if conditions are favorable for cell division (B)</p> Signup and view all the answers

Which phase of the cell cycle is most likely to be the shortest in rapidly dividing mammalian cells?

<p>M phase (A)</p> Signup and view all the answers

What role do cyclins play in the cell cycle?

<p>Their levels fluctuate to regulate cell cycle progression. (C)</p> Signup and view all the answers

What do checkpoint proteins in the cell cycle primarily function as?

<p>Sensors to monitor cell conditions (A)</p> Signup and view all the answers

Which checkpoint verifies the integrity of the spindle apparatus?

<p>Metaphase checkpoint (B)</p> Signup and view all the answers

During which cellular phase do cyclins and cdks form active complexes to push the cell cycle forward?

<p>G1 phase (C)</p> Signup and view all the answers

What is the primary outcome of meiosis in terms of chromosome number?

<p>Four haploid daughter cells (B)</p> Signup and view all the answers

During which phase of meiosis does crossing over occur?

<p>Prophase I (D)</p> Signup and view all the answers

In terms of genetic identity, how do the daughter cells produced by mitosis compare to each other?

<p>Genetically identical to each other (B)</p> Signup and view all the answers

What is the function of the synapsis during meiosis I?

<p>To facilitate crossing over (B)</p> Signup and view all the answers

How many rounds of cell division occur during meiosis?

<p>Two (B)</p> Signup and view all the answers

What happens to homologous chromosomes during Anaphase I?

<p>They segregate to opposite poles (D)</p> Signup and view all the answers

What is the number of different random alignments of chromosomes possible during metaphase I in humans?

<p>2^23 (D)</p> Signup and view all the answers

What is the connection point between homologous chromosomes that have crossed over called?

<p>Chiasma (B)</p> Signup and view all the answers

How does the chromosome number in daughter cells at the end of meiosis II compare to the original diploid cell?

<p>Half of diploid (A)</p> Signup and view all the answers

What is the major difference in chromosome behavior between meiosis II and mitosis?

<p>Sister chromatids separate in both processes (C)</p> Signup and view all the answers

What occurs during prophase of mitosis?

<p>Nuclear membrane begins to dissociate and chromatids condense. (D)</p> Signup and view all the answers

What is characteristic of the metaphase stage?

<p>Sister chromatids align along the metaphase plate. (D)</p> Signup and view all the answers

What happens during anaphase in mitosis?

<p>Sister chromatids are pulled apart towards opposite poles. (D)</p> Signup and view all the answers

How does cytokinesis differ in animal cells compared to plant cells?

<p>Animal cells involve actin, whereas plant cells utilize microtubules for separation. (C)</p> Signup and view all the answers

What describes the transition from prometaphase to metaphase?

<p>Sister chromatids align along the metaphase plate. (D)</p> Signup and view all the answers

What role do microtubules play during cytokinesis?

<p>They assist in the cleavage furrow of animal cells. (A)</p> Signup and view all the answers

During telophase, which of the following occurs?

<p>Nuclear membranes reform around two separate nuclei. (D)</p> Signup and view all the answers

Which statement is true about the timing of mitosis and cytokinesis?

<p>Cytokinesis always occurs after mitosis. (A)</p> Signup and view all the answers

Flashcards

MPF (Maturation-Promoting Factor)

A protein complex crucial for advancing the cell cycle. It's composed of a mitotic cyclin and a cyclin-dependent kinase (cdk).

Mitotic Cell Division

A process where a single cell divides into two genetically identical daughter cells. It involves mitosis (nuclear division) and cytokinesis (cytoplasm division).

Sister Chromatids

Two identical copies of a chromosome connected at the centromere. Created during DNA replication in preparation for cell division.

Centrosome

A microtubule-organizing center (MTOC) responsible for forming the spindle apparatus during cell division. Each cell has two.

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Spindle Apparatus

A structure made of microtubules that organizes and separates chromosomes during cell division. It originates from the centrosomes.

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What are the phases of mitosis?

Mitosis occurs as a continuum of phases: prophase, prometaphase, metaphase, anaphase, and telophase.

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Prophase

Chromatids condense into visible structures; nuclear membrane starts breaking down; nucleolus disappears.

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Prometaphase

Nuclear envelope fragments completely; spindle apparatus fully forms; sister chromatids attach to microtubules from opposite poles.

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Metaphase

Sister chromatids line up in a single row at the metaphase plate, halfway between the poles.

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Anaphase

Connections between sister chromatids break; kinetochore microtubules shorten, pulling chromosomes to opposite poles.

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Telophase

Chromosomes reach poles, decondense; nuclear membranes reform, creating two separate nuclei.

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Cytokinesis

Division of the cytoplasm into two daughter cells. Occurs differently in animals and plants.

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How does cytokinesis differ in animals and plants?

Animals: Cleavage furrow constricts like a drawstring; Plants: Vesicles form a cell plate that becomes a cell wall.

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Cell Cycle Duration

The time it takes for a cell to complete one cycle of growth and division. Varies greatly depending on cell type, ranging from minutes in embryos to months in adult cells.

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Cell Cycle Phases

The distinct stages of the cell cycle, including G1, S, G2, and M. Each phase has a specific function and is governed by specific proteins.

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Cyclins and Cdks

Two types of proteins that control the cell cycle. Cyclins fluctuate in concentration throughout the cycle, while cyclin-dependent kinases (cdks) are enzymes that activate other proteins.

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Cell Cycle Checkpoints

Points in the cell cycle where proteins monitor for critical events, ensuring the cell divides only when conditions are favorable and all processes are completed correctly.

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Cell Cycle

A highly regulated series of events leading to cell division. Includes phases of growth, DNA replication, and division.

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Karyotype

A photographic representation of chromosomes arranged in pairs by size and shape.

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Chromosome Sets

Eukaryotic organisms have sets of chromosomes. Humans have 23 unique chromosomes, forming a set (n). Two sets (2n) make up the diploid state, found in most cells. Gametes (sperm/egg) are haploid (n).

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Homologs

Chromosomes in a pair (diploid) are called homologs, nearly identical in size and DNA content, but with slight variations. They ensure genetic diversity.

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Mitosis

A process of nuclear division where duplicated chromosomes are divided into two new nuclei, each receiving a complete set.

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Mitosis: Daughter Cells

Two daughter cells are produced during mitosis, each with the same number of chromosomes as the original mother cell. These daughter cells are genetically identical to each other and the original cell.

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Meiosis: Diploid to Haploid

Meiosis is the cell division process that reduces the number of chromosomes in a diploid cell to produce haploid cells. For example, in humans, a diploid cell with 46 chromosomes divides into gametes (sperm or egg) with 23 chromosomes.

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Synapsis

Synapsis is the pairing of homologous chromosomes during the early stages of meiosis I (prophase I). These paired chromosomes are called bivalents or tetrads.

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Crossing Over

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during synapsis. This exchange occurs at points called chiasmata.

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Meiosis I: Homolog Separation

Meiosis I separates homologous chromosomes into two daughter cells. Each daughter cell receives one chromosome from each homologous pair.

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Metaphase I: Random Alignment

In metaphase I, the bivalents (paired homologs) line up randomly along the metaphase plate, allowing for various combinations of maternal and paternal chromosomes in the daughter cells.

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Anaphase I: Homolog Segregation

During anaphase I, the connections between the bivalents break, and each homologous chromosome, with its attached sister chromatids, moves to opposite poles.

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Meiosis II: Sister Chromatid Separation

Meiosis II separates the sister chromatids of each chromosome. It's similar to mitosis, but starts with half the number of chromosomes.

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Outcome: Haploid Gametes

The end product of meiosis is four haploid cells (gametes, like sperm or egg) with only one chromosome from each pair, unlike the original diploid cell.

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Meiosis vs. Mitosis: Chromosome Count

Meiosis reduces the chromosome number in half, creating four haploid daughter cells from one diploid cell. Mitosis produces two diploid daughter cells that are genetically identical.

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Meiosis: Chromosome Number Example

If a cell has 6 chromosomes in 3 homologous pairs (2n=6), mitosis will produce 2 daughter cells with 6 chromosomes. Meiosis will produce 4 daughter cells with 3 chromosomes.

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Mendel's Laws and Meiosis Relationship

Mendel's laws, which govern inheritance patterns, can be explained by the pairing and segregation of homologous chromosomes during meiosis.

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Chromosome Theory of Inheritance: Who?

The chromosome theory of inheritance, proposed by Theodor Boveri and Walter Sutton, explains how the inheritance of traits is determined by the behavior of chromosomes during meiosis.

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Chromosome Principle: DNA as Genetic Material

The chromosome theory states that chromosomes contain DNA, which is the genetic material. Genes are found within these chromosomes.

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Chromosome Principle: Replication and Transmission

Chromosomes are replicated and passed down from parent to offspring and from cell to cell during multicellular development.

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Chromosome Principle: Homologous Pairs

The nucleus of a diploid cell has two sets of chromosomes, forming homologous pairs. One member of each pair is inherited from the mother, and the other from the father. Each set carries a complete set of genes.

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Chromosome Principle: Segregation and Independent Assortment

During meiosis, one chromosome from each pair segregates into one daughter nucleus, and its homologue goes into the other. Members of different chromosome pairs also segregate independently, contributing to genetic diversity.

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Study Notes

The Eukaryotic Cell Cycle, Mitosis and Meiosis

  • The adult human body contains between 10 to 50 trillion cells.
  • Except for rare mutations, DNA sequences of all chromosomes in all cells are the same.
  • Careful reproduction of cells ensures the integrity of the genetic material through two processes: mitosis and meiosis.
  • A cell cycle is a highly regulated series of events that leads to cell division.
  • When cells get ready to divide, chromosomes become compact enough to be seen with a light microscope.
  • Cytogenetics is the field of genetics involving microscopic examination of chromosomes.
  • Karyotype: A photographic representation of chromosomes. This shows the complete set of chromosomes from a single cell.

Cell Division

  • The eukaryotic cell cycle has four main phases: G1, S, G2, and M.
    • G1 (Gap 1): Cell growth and preparation for DNA replication.
    • S (Synthesis): DNA replication occurs.
    • G2 (Gap 2): Preparation for mitosis.
    • M (Mitosis): Cell division.
  • A cell may also exit the cell cycle and enter a nondividing phase called G0.
  • Cell cycle length differs depending on cell type. (e.g., several minutes in embryos to several months in slow-growing cells). The length of a cell cycle can vary from 10 to 24 hours for fast-dividing cells in adults.

Control of the Cell Cycle

  • Advancement through the cell cycle is controlled by cyclins and cyclin-dependent kinases (cdks).
  • Cyclin levels fluctuate during the cell cycle.
  • Cyclins and cdks combine to form an activated cyclin/cdk complex that phosphorylates and activates other proteins.

Cell Cycle Checkpoints

  • Checkpoint proteins control whether a cell advances through the cell cycle.
  • G1 checkpoint (restriction point): Checks for favorable conditions and DNA damage.
  • G2 checkpoint: Checks for DNA damage and ensures all DNA has been replicated.
  • Metaphase checkpoint: Checks for the integrity of the spindle apparatus and accurate chromosome attachment.

Overview of Meiosis

  • Meiosis is the process by which haploid cells are produced from a cell that was originally diploid.
  • In humans, a diploid cell has 46 chromosomes (23 pairs). After meiosis, gametes (haploid egg or sperm) have 23 chromosomes.
  • Meiosis involves one round of DNA replication followed by two rounds of cell division.
  • Two key events at the beginning of meiosis I are the pairing of homologous chromosomes and crossing over.
  • Crossing over exchanges segments of DNA between homologous chromosomes, increasing genetic variation.
  • Meiosis I involves the separation of homologous chromosomes.
  • Meiosis II involves the separation of sister chromatids.

Mitosis

  • Mitosis is the division of one nucleus into two nuclei, followed by cytokinesis.
  • This leads to the production of two new, genetically identical daughter cells.
  • Mitosis is used for asexual reproduction and development/growth of multicellular organisms.
  • DNA is replicated, producing identical sister chromatids. Sister chromatids are tightly associated at the centromere. The spindle apparatus, composed of microtubules, is responsible for organizing and sorting chromosomes. Mitosis occurs in a series of phases (prophase, prometaphase, metaphase, anaphase, telophase).

Cytokinesis

  • The process of division of the cytoplasm into two daughter cells, following mitosis.
  • Cytokinesis is different in animals and plants.
  • Animal cells use a cleavage furrow to separate the cells, while plant cells use a cell plate.

End Results

  • Two daughter cells with the same number of chromosomes as the mother cell are produced.
  • Barring mutations, the two cells are genetically identical.

Sexual Reproduction

  • Two haploid gametes unite in a fertilization event to create a diploid cell (zygote).
  • After zygote formation, rounds of mitosis create many more diploid cells, forming a multicellular organism.
  • Sexual reproduction differs from asexual reproduction by the fusion of gametes and the contribution of genetic material from two parents, which contrasts to the single parent in asexual reproduction.

Life Cycles

  • The sequence of events that produce another generation of organisms.
  • For sexually reproducing organisms, it involves an alternation between haploid and diploid cells or organisms.
  • Diploid-dominant species: Most animals, multicellular organisms are diploid, produces haploid cells in reproductive organs).
  • Haploid-dominant species (many fungi and some protists): Multicellular organism is haploid, haploid cells unite to form a zygote, zygote undergoes meiosis immediately to make four haploid spores.

Chromosome Theory of Inheritance

  • The chromosome theory of inheritance shows how traits can be explained by chromosome behavior during meiosis. The chromosome theory proposes five fundamental principles:
    • Chromosomes contain DNA, which is the genetic material.
    • Chromosomes are replicated and passed from parent to offspring and from cell to cell.
    • The nucleus of a diploid cell contains two sets of chromosomes which are found in homologous pairs. Each homolog pair is inherited from one parent (one from the mother, one from the father).
    • At meiosis, one member of each chromosome pair segregates into one daughter nucleus and the other into the opposite daughter nucleus. Pairs segregate independently.
    • Gametes are haploid cells that combine to form a diploid cell during fertilization.

Chromosomes & Segregation

  • Locus: Physical location of a gene on a chromosome.
  • Each homologous chromosome carries an allele of the same gene at the same locus.
  • A gene can exist as two or more different alleles.

Comparing Mitosis and Meiosis

  • Mitosis produces two genetically identical diploid daughter cells.
  • Meiosis produces four genetically unique haploid daughter cells.
  • Key differences include chromosome replication, synapsis and crossing over, homologous chromosome segregation and sister chromatid separation.

Crossing Over

  • Crossing over is a crucial part of meiosis that exchanges segments of DNA between chromosomes, increasing genetic variation.
  • During prophase I, homologous chromosomes pair up, forming a structure called a tetrad.

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Description

Explore the intricacies of the eukaryotic cell cycle, including the phases of mitosis and meiosis. This quiz delves into the structure and function of chromosomes, the process of cell division, and the significance of cytogenetics. Test your knowledge on how cells ensure genetic integrity during division.

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