The Eukaryotic Cell Cycle
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Questions and Answers

What role do checkpoint proteins play in the cell cycle?

  • They speed up the process of cytokinesis.
  • They act as sensors to determine if the cell is ready to divide. (correct)
  • They increase the levels of cyclins throughout the cycle.
  • They trigger apoptosis when the cell is damaged.

    • Which checkpoint is considered the most critical for determining if a cell can enter the division cycle?

  • G2/M checkpoint
  • Cytokinesis checkpoint
  • G1/S checkpoint (correct)
  • Metaphase checkpoint

    • What structure is primarily responsible for organizing and sorting chromosomes during mitosis?

  • Mitotic spindle (correct)
  • Golgi apparatus
  • Cleavage furrow
  • Centrosome

    • How do sister chromatids move to opposite poles during mitosis?

    <p>By depolymerizing at the kinetochore ends.</p> Signup and view all the answers

    What occurs during cytokinesis in animal cells?

    <p>The cleavage furrow constricts like a drawstring.</p> Signup and view all the answers

    What is the composition of the mitotic spindle?

    <p>Microtubules made of tubulin proteins.</p> Signup and view all the answers

    What does the G0 phase signify for a cell?

    <p>The cell has exited the cycle and is inactive.</p> Signup and view all the answers

    Which type of microtubule stabilizes the spindle apparatus but does not attach to chromosomes?

    <p>Polar microtubules</p> Signup and view all the answers

    What is the primary purpose of mitosis in eukaryotic cells?

    <p>To produce genetically identical cells</p> Signup and view all the answers

    Which phase follows the G1 phase in the cell cycle?

    <p>S phase</p> Signup and view all the answers

    What characteristic distinguishes human sex chromosomes from autosomes?

    <p>They may not have homologs.</p> Signup and view all the answers

    What is the role of sister chromatids during mitosis?

    <p>They remain joined at the centromere.</p> Signup and view all the answers

    Which of the following correctly describes the G2 phase?

    <p>Proteins needed for mitosis are synthesized.</p> Signup and view all the answers

    What occurs at the G1 checkpoint in the cell cycle?

    <p>The cell assesses conditions to divide.</p> Signup and view all the answers

    What is the outcome of cytokinesis following mitosis?

    <p>Division of the cytoplasm into two cells.</p> Signup and view all the answers

    Which statement about homologous chromosomes is correct?

    <p>They are present in diploid cells only.</p> Signup and view all the answers

    How many total chromosomes are present in a human somatic cell?

    <p>46</p> Signup and view all the answers

    What is a karyotype used to analyze in a dividing cell?

    <p>Number and structure of chromosomes</p> Signup and view all the answers

    Study Notes

    The Eukaryotic Cell Cycle

    • Cells are the fundamental units of life
    • The continuity of life relies on genetic material transfer between cells

    Why Do Cells Divide?

    • Reproduction
    • Growth and development
    • Cell replacement and tissue renewal

    Types of Cell Division in Humans

    • Asexual (genetic clones):
      • Mitosis conserves chromosome number
    • Sexual (genetic variation):
      • Meiosis occurs only in gamete (sex cell) production
      • Reduces chromosome number

    Eukaryotes and Chromosomes

    • Human somatic cells have 23 pairs (46 total) of chromosomes
      • Autosomes: 22 pairs
      • Sex chromosomes: 1 pair (XX or XY)
        • Diploid (2n)
    • Human gametes have 1 member of each chromosome pair (23 total) - Haploid (n)

    Homologous Chromosomes

    • Members of a chromosome pair are called homologs (homologous chromosomes)
    • They are nearly identical in size and genetic composition
    • Example: Both carry eye color genes, but one may have brown and the other blue

    Sex Chromosomes

    • Not true homologs
    • X and Y chromosomes differ significantly in size and genetic composition

    Two Types of Nuclear Division

    • Mitosis and Meiosis
    • Mitosis leads to identical diploid daughter cells for growth and repair.
    • Meiosis leads to haploid gametes for sexual reproduction.
    • Diagrams of the cell cycle shown.

    Genome and Chromosomes

    • Genome usually exists as chromatin
    • Chromosomes condense only to prepare for division
    • DNA is organized into multiple genes along chromosomes
    • Centromere: is the narrow region where replicated chromosomes join

    Karyotype

    • Karyotype reveals chromosome number, size, and form in dividing cells

    Cell Cycle (Life Cycle of a Cell) Phases

    • Interphase:
      • G1 (first gap): Cell growth and development; commitment to division at G1 checkpoint
      • S (synthesis): DNA replication
      • G2 (second gap): Protein and structure synthesis for mitosis
      • G0: cells postponing division or never dividing again
    • M (mitosis and cytokinesis)

    S Phase

    • Each chromosome replicates
    • Replicated chromosomes are called sister chromatids
    • Sister chromatids remain attached at the centromere
    • Human cells have 46 chromosomes in G1 phase and 92 sister chromatids in G2 phase

    G2 Phase

    • Synthesizes proteins and structures needed during mitosis and cytokinesis

    Mitosis

    • Nuclear division, separation of sister chromatids
    • Followed by cytokinesis to form two daughter cells

    Control of Cell Division

    • External factors: environmental conditions, signaling molecules, determines if a cell divides
    • Internal factors: cell cycle control molecules, checkpoints.
      • Internal checkpoints: G1/S, G2/M, Metaphase

    Internal Checkpoints

    • G1/S checkpoint (restriction point): determines if conditions are favorable and if DNA is undamaged
      • Cells that fail checkpoint exit cycle to G0
    • G2/M checkpoint: Checks DNA replication; monitors protein levels needed for mitosis
    • Metaphase (spindle) checkpoint: Ensures all chromosomes are attached to the spindle apparatus

    Checkpoint proteins

    • Cyclins and cyclin-dependent kinases (cdks) advance cells through checkpoints.
    • Cyclin levels vary; Cdks are constant but require binding to a cyclin to be active
    • Checkpoint proteins act as sensors determining if the cell is ready for cell division

    Mitosis Stages

    • Interphase
    • Prophase
    • Prometaphase
    • Metaphase
    • Anaphase
    • Telophase
    • Cytokinesis

    Mitotic Spindle

    • Crucial for segregation of chromosomes into daughter cells - Ensures each daughter cell receives correct # chromosomes
    • Mitotic spindle apparatus/spindle is responsible for organizing and sorting the chromosomes during mitosis.
    • Centrosomes are microtubule organizing centers

    Spindle Microtubules

    • Comprised of tubulin proteins
    • Three types
      • Astral microtubules
      • Polar microtubules
      • Kinetochore microtubules.

    Chromosome movement during mitosis

    • Motor proteins attached to chromosomes move during mitosis by de-polymerizing at kinetochore ends.

    Cytokinesis

    • Division of cytoplasm to form two new cells
      • Animals: Cleavage furrow constriction
      • Plants: Cell plate forms cell wall.

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    Related Documents

    The Eukaryotic Cell Cycle Mitosis PDF

    Description

    Explore the fascinating processes of the eukaryotic cell cycle, including the reasons for cell division and the types of cell division in humans. Understand the roles of mitosis and meiosis, as well as the structure and significance of chromosomes and homologous chromosomes.

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