Biology: Structure of Chromosomes and Nucleosomes
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Questions and Answers

What is the primary function of telomeres?

  • To prevent the formation of sister chromatids
  • To allow continued replication of DNA (correct)
  • To increase the size of DNA molecules
  • To code for proteins

    • DNA molecules in sister chromatids are genetically different.

    False

    What is a gene?

    A section of DNA that codes for one protein.

    The size of a DNA molecule is approximately _______ nm.

    <p>2</p> Signup and view all the answers

    Match the following components with their functions.

    <p>Telomerase = Completes copying of meaningful DNA Sister chromatids = Contain identical genes DNA size = Approximately 2nm Gene = Codes for one protein</p> Signup and view all the answers

    What is the primary function of nucleosomes?

    <p>To compress DNA into a compact unit</p> Signup and view all the answers

    Telomeres are found in the middle of chromosomes.

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

    What are chromosomes made of?

    <p>DNA and proteins</p> Signup and view all the answers

    The protective sequence of nucleotides at the ends of chromosomes is known as __________.

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

    Match the following terms with their definitions:

    <p>Chromatid = One half of two identical copies of a replicated chromosome Centromere = The region where spindle microtubules attach during cell division Histones = Proteins that DNA winds around to form nucleosomes Chromatin = A complex of DNA and proteins that makes up chromosomes</p> Signup and view all the answers

    How long is the total length of DNA in 46 human chromosomes?

    <p>1.8m</p> Signup and view all the answers

    Histone proteins are acidic in nature.

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

    What is the width of a centromere?

    <p>11 nm</p> Signup and view all the answers

    What is the role of centromeres during mitosis?

    <p>They assist in the separation of chromatids</p> Signup and view all the answers

    In plant cells, daughter cells are separated by a cleavage furrow.

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

    What is the term used to describe the ability of a stem cell to produce different cell types?

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

    A __________ is an agent that causes cancer, such as UV radiation or nuclear fallout.

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

    Match the following terms related to cancer with their definitions:

    <p>Oncogene = A gene that causes uncontrolled cell division Proto-oncogene = A normal gene that can become an oncogene Mutation = A change in the DNA sequence Tumor = An irregular mass of cells</p> Signup and view all the answers

    What structure forms across the equator of a plant cell during cytokinesis?

    <p>Cell plate</p> Signup and view all the answers

    Cytokinesis in animal cells involves the formation of a cell plate.

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

    What is the primary function of centrioles during cell division?

    <p>To assemble and contract spindle fibers</p> Signup and view all the answers

    During mitosis, the __________ ensures chromosome stability by moving chromosomes to the poles of the cell.

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

    Match the following cell division processes with their characteristics:

    <p>Cytokinesis in Plant Cells = Formation of a cell plate Cytokinesis in Animal Cells = Formation of a cleavage furrow Centrosome = Microtubule organizing center Centrioles = Assist in spindle fiber assembly</p> Signup and view all the answers

    Which of the following statements is true about stem cells?

    <p>They can differentiate into various cell types.</p> Signup and view all the answers

    Animal cells contain both centrioles and centrosomes.

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

    What is the role of the contractile ring during animal cell cytokinesis?

    <p>To push the equator of the cell inwards, forming a cleavage furrow.</p> Signup and view all the answers

    What is the primary purpose of mitosis?

    <p>Growth and repair</p> Signup and view all the answers

    Interphase is the shortest phase in the cell cycle.

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

    During which phase do centrosomes migrate to opposite poles?

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

    The process by which DNA is duplicated is called the ______ phase.

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

    Match each phase of mitosis with its description:

    <p>Prophase = Chromosomes condense and the nuclear envelope disappears Metaphase = Chromosomes align at the cell's equator Anaphase = Sister chromatids are pulled apart Telophase = Nuclear envelope re-forms around each set of chromosomes</p> Signup and view all the answers

    Which of the following statements about the G1 phase is true?

    <p>Cells make RNA and proteins needed for growth</p> Signup and view all the answers

    In anaphase, chromosomes line up at the equator of the spindle.

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

    What occurs during the G2 phase?

    <p>The cell continues to grow and checks DNA for errors.</p> Signup and view all the answers

    The mitotic spindle is made up of ______ required for chromosome movement.

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

    What is formed at the end of the M phase?

    <p>Two genetically identical daughter cells</p> Signup and view all the answers

    Study Notes

    The Structure Of A Chromosome

    • Chromosomes are thread-like structures made of DNA
    • The total length of DNA in a human cell is about 1.8m
    • DNA is wound around proteins called histones.
    • Histone proteins associate with DNA to form nucleosomes.
    • Nucleosomes condense DNA into chromatin.
    • Chromatin is a complex of DNA and RNA, as well as proteins that compress DNA.

    Structure of a Chromosome

    • A chromatid is one half of a replicated chromosome
    • The centromere is the region of a chromosome where microtubules attach during cell division.
    • Telomeres are protective sequences of nucleotides found at the ends of chromosomes.

    Structure of a Nucleosome

    • 11nm wide and 6nm long.
    • Made up of 8 histone molecules.

    Structure of Telomeres

    • Cap the ends of chromosomes.
    • Are required for successful cell division.
    • Allow continued replication.
    • Prevent the loss of genes.
    • Made of DNA with short base sequences repeated multiple times.

    The Cell Cycle

    • The cell cycle is a series of events that take place in a cell leading up to its division.

    Interphase

    • The longest phase of the cycle
    • The cell grows to its normal size.
    • When the cell performs its normal functions
    • The time spent between cell division

    G1 Phase

    • Cells make RNA, enzymes, and other proteins needed for growth.
    • At the end of G1, the cell becomes committed to either dividing or not.

    S Phase

    • DNA synthesis takes place
    • The DNA in the nucleus replicates, so each chromosome consists of 2 identical chromatids.
    • This is known as DNA replication.

    G2 Phase

    • The cell continues to grow.
    • New DNA is checked, and any errors are repaired.
    • Preparations are made to start cell division.

    M Phase (Mitosis)

    • Nuclear division that produces 2 genetically identical daughter cells.
    • Maintains genetic stability.
    • Ensures cells retain function
    • Maintains chromosome number

    Functions of Mitosis

    • Growth
    • Cell replacement
    • Repair of tissues
    • Asexual reproduction
    • Immune response (clonal selection of B and T-lymphocytes)

    The Stages of Mitosis

    • Prophase, metaphase, anaphase, telophase

    Prophase

    • Centrosomes migrate to opposite poles of the cell.
    • Chromatin begins to condense.
    • The nuclear envelope and nucleolus begin to disappear.
    • Centrosomes and migrate to opposite poles of the cell.
    • Asters and spindle fibers form.

    Metaphase

    • Centrosomes are at the poles of the cell and organize the production of spindle microtubules.
    • Chromosomes line up across the equator of the spindle.
    • Each chromosome splits at its centromere.
    • Chromosomes start to be pulled apart by microtubules.

    Anaphase

    • Chromatids move to opposite poles.
    • Centromeres are first pulled by microtubules.
    • Spindle fibers contract and chromosomes are pulled to opposite ends.

    Telophase

    • Nuclear envelope and nucleolus reforms.
    • Nucleus divides.
    • Chromosomes are at the poles of the cell.

    Cytokinesis

    • The division of cytoplasm
    • Cytoplasm is divided into two cells.

    Cytokinesis In Plant Cells

    • Cell plate forms across the equator of the cell, cellulose, and cell wall laid down.

    Cytokinesis In Animal Cells

    • A contractile ring forms.
    • The contractile ring pushes the equator of the cell inwards, forming a cleavage furrow.
    • The cleavage furrow deepens as active filaments in the ring contract.
    • Eventually, the cell splits into two cells.

    Differences in Plant and Animal Cell Mitosis

    • Plant cells have no visible centriole or aster.
    • Daughter cells get separated by a cell plate, there is no cleavage furrow formation.

    Centromeres, Centrosome, Centrioles

    Centromere

    • Needed for separation of chromatids during mitosis
    • Site of attachment of spindle microtubules
    • Each metaphase chromosome has 2 kinetochores at its centromere and microtubules
    • Kinetochore is a protein molecular complex that binds to DNA and microtubules.
    • Bundles of microtubules called spindle fibers extend from the kinetochores to the poles of the spindle during mitosis.

    Centrosome

    • Found in animal cells.
    • Acts as the microtubule organizing center for the construction of the spindle.
    • Located at the poles of the cells.

    Centrioles

    • Act as microtubule organizing centers.
    • Assemble and form spindle fibers during prophase.
    • Contraction of spindle fibers during anaphase separates sister chromatids.

    Stem Cells

    • Can divide an unlimited number of times by mitosis.
    • The extent of the power that a cell has to produce different types of cells is called its potency.
    • Stem cell therapy is the introduction of new adult stem cells into damaged tissue to treat disease or injury.

    Cancer

    • Results from uncontrolled mitosis.
    • Cancer cells divide repeatedly and form a tumor.
    • Carcinogens are agents that cause cancer.

    Cellular Changes that Occur in the Development of Cancer

    • A mutation occurs in a gene responsible for cell division.
    • This leads to the formation of an oncogene from a proto-oncogene.
    • This causes uncontrolled cell division.
    • The coordination of the cell cycle is lost. The signal to stop dividing is not received by the cell.
    • Loss of function and lack of specialization occurs.
    • A tumor is formed, an irregular mass of cells that show an abnormal change in shape.

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