Cell Cycle, Cell Division, and Chromosome Structure
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Questions and Answers

What material makes up the fibre of a chromosome?

  • Chromatin (correct)
  • RNA and proteins
  • Histone octamer
  • DNA and lipids

    • Who first observed the structures named 'chromosomes'?

  • Walther Flemming (correct)
  • Francis Crick
  • Rosalind Franklin
  • James Watson

    • When do chromatin fibres become distinguishable as chromosomes?

  • During translation
  • During apoptosis
  • During transcription
  • During mitosis (correct)

    • What are the components of nucleosomes?

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

    What did Watson and Crick contribute to the study of DNA?

    <p>Double-helix structure of DNA</p> Signup and view all the answers

    What percentage of histones make up chromatin?

    <p>60%</p> Signup and view all the answers

    What term describes the complex of DNA and proteins in its coiled form?

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

    What are the three components of a nucleotide?

    <p>Phosphate, deoxyribose, base</p> Signup and view all the answers

    Which of the following scientists discovered chromosomes?

    <p>Walther Flemming</p> Signup and view all the answers

    What is the primary function of the centromere during cell division?

    <p>To attach chromosomes to spindle fibres</p> Signup and view all the answers

    Which nitrogenous base is unique to RNA?

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

    Which components form the structure of a nucleotide?

    <p>Phosphate group, pentose sugar, nitrogenous bases</p> Signup and view all the answers

    In which phase of mitosis do spindle fibres first appear?

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

    During cell division, sister chromatids are separated at the:

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

    During which phase of mitosis does the nuclear membrane reappear?

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

    Which of the following sequences encodes particular proteins and is inherited from parents to offspring?

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

    Which structure remains attached to each chromosome during metaphase?

    <p>Spindle fibre</p> Signup and view all the answers

    Who proposed the 'double helical' model of DNA?

    <p>Watson and Crick</p> Signup and view all the answers

    What initiates the separation of sister chromatids during mitosis?

    <p>Division of the centromere</p> Signup and view all the answers

    What percentage of the human genome is considered 'junk DNA'?

    <p>99%</p> Signup and view all the answers

    In which phase does the cleavage furrow start to deepen in an animal cell?

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

    At which stage are chromosomes visible as two chromatids joined at the centromere?

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

    What is the primary function of the centromere during cell division?

    <p>Attaching chromosomes to spindle fibers</p> Signup and view all the answers

    Which of the following best describes sister chromatids?

    <p>Identical chromatids joined by a centromere</p> Signup and view all the answers

    DNA fingerprinting is based on variations in which type of DNA?

    <p>Non-functional</p> Signup and view all the answers

    For what purposes can DNA fingerprinting be particularly useful?

    <p>Establishing paternity and criminal cases</p> Signup and view all the answers

    During which stage of mitosis are sister chromatids detached from each other?

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

    What happens to the number of chromosomes during mitosis?

    <p>It remains the same</p> Signup and view all the answers

    What is the role of genes on a chromosome?

    <p>To encode proteins</p> Signup and view all the answers

    Why is cell division important for growth?

    <p>To form new tissues and organs</p> Signup and view all the answers

    Which scientist proposed the chemiosmotic hypothesis in 1961?

    <p>Peter Mitchell</p> Signup and view all the answers

    What results from non-cyclic photophosphorylation?

    <p>ATP and NADPH</p> Signup and view all the answers

    During the light reaction, which molecule's photolysis occurs?

    <p>H₂O</p> Signup and view all the answers

    Where does photosynthetic ATP formation occur?

    <p>Within the thylakoid lumen</p> Signup and view all the answers

    What is the biosynthetic phase of photosynthesis primarily responsible for?

    <p>Fixing CO₂</p> Signup and view all the answers

    What process uses oxygen and releases CO₂ in plants?

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

    In which part of the chloroplast are ATP and NADPH used?

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

    What is the term used for photosynthetic ATP formation?

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

    Which cells in the human body last a lifetime once formed?

    <p>Eye lens cells</p> Signup and view all the answers

    What is the approximate lifespan of red blood cells?

    <p>120 days</p> Signup and view all the answers

    What is the average lifespan of bone cells in adults?

    <p>10 years</p> Signup and view all the answers

    Which step is NOT a part of karyokinesis?

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

    During which phase of the cell cycle does the division of the nucleus occur?

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

    How often are skin cells replaced in the human body?

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

    Which type of cell division leads to the production of haploid cells?

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

    What happens to the balance of cell production and cell death as humans grow old?

    <p>Cell death exceeds cell production</p> Signup and view all the answers

    Which process occurs during the S-phase of interphase?

    <p>Duplication of DNA</p> Signup and view all the answers

    What happens to DNA during cell division?

    <p>It is duplicated</p> Signup and view all the answers

    Which phase involves the synthesis of RNA and proteins necessary for cell division?

    <p>G2</p> Signup and view all the answers

    What is the primary activity of the First Growth Phase (G1) in the cell cycle?

    <p>Increase in cytoplasm volume</p> Signup and view all the answers

    Which of these cell types is replaced approximately every 120 days?

    <p>Red blood cells</p> Signup and view all the answers

    What occurs during the interphase of the cell cycle?

    <p>Cell growth and preparation for division</p> Signup and view all the answers

    Which organelles divide during the G1 phase due to having their own DNA?

    <p>Mitochondria and chloroplasts</p> Signup and view all the answers

    What is the fate of a cell that withdraws from the cell cycle in late G1 phase?

    <p>It enters a resting phase (R)</p> Signup and view all the answers

    Which cells in the human body are known to last a lifetime?

    <p>Cells of the eye lens and brain</p> Signup and view all the answers

    How long does the average life of epithelial cells lining the gut last?

    <p>Few days</p> Signup and view all the answers

    In which stage of animal cell mitosis do chromosomes align at the equatorial plane?

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

    What event marks the beginning of cytokinesis in animal cells?

    <p>Formation of a furrow at the middle of the cell membrane</p> Signup and view all the answers

    Which structure disappears during prophase in both animal and plant cells?

    <p>Nuclear membrane</p> Signup and view all the answers

    At what stage do sister chromatids separate and move towards opposite poles in animal cells?

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

    During which stage does the cleavage furrow deepen to complete cytokinesis in animal cells?

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

    How is the cytoplasm divided in plant cells during cytokinesis?

    <p>Growth of a cell plate from the center to the periphery</p> Signup and view all the answers

    Which stage in both animal and plant cells involves the disappearance of spindle fibres?

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

    During which stage do chromosomes appear as thread-like structures in both animal and plant cells?

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

    The X-shaped structure formed due to crossing over between the non-sister chromatids of paired homologous chromosomes is called?

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

    What process during meiosis results in genetic recombination?

    <p>Crossing over</p> Signup and view all the answers

    Where does mitosis occur in the body?

    <p>Somatic cells</p> Signup and view all the answers

    During which phase of mitosis do the chromosomes line up at the cell equator?

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

    What key event distinguishes meiosis from mitosis?

    <p>Reduction of chromosome number by half</p> Signup and view all the answers

    Which nitrogenous base is not found in DNA?

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

    How many daughter cells are produced from one parent cell during mitosis?

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

    In which stage of karyokinesis are sister chromatids separated and pulled to opposite poles?

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

    Which structure initiates cytokinesis in plant cells?

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

    What term describes a full set of chromosomes passed to each daughter cell during mitosis?

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

    What type of proteins are primarily associated with chromatin?

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

    During which phase of the cell cycle do chromatin fibers coil and condense to form chromosomes?

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

    Who was the first scientist to study chromosomes in animals?

    <p>Walther Flemming</p> Signup and view all the answers

    What year did Rosalind Franklin first work out the shape of the DNA molecule?

    <p>1952</p> Signup and view all the answers

    What macromolecule is described as having two complementary strands of nucleotides winding around each other?

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

    In which cells did Flemming first observe chromosomes?

    <p>Salamander larvae cells</p> Signup and view all the answers

    Which of the following best describes the form of chromatin in a non-dividing cell under an electron microscope?

    <p>Very long and thin fibre</p> Signup and view all the answers

    Which scientist is associated with the term 'mitosis'?

    <p>Walther Flemming</p> Signup and view all the answers

    Which phase does not belong to the interphase of the cell cycle?

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

    Which components make up each nucleotide in a DNA strand?

    <p>Phosphate, sugar, nitrogenous base</p> Signup and view all the answers

    Study Notes

    Structure of Chromosomes

    • Chromosomes are discrete units of DNA and proteins, making up chromatin.
    • Chromatin is formed of DNA (40%) and histones (60%).
    • Each chromosome contains one long DNA molecule and many proteins.
    • Chromatin fibres coil and condense to form chromosomes during cell division.

    Discovery of Chromosomes

    • Walther Flemming first studied chromosomes in animals in 1882.
    • He observed minute threads that divided lengthwise, calling their division mitosis.

    Structure of DNA

    • Rosalind Franklin and James Watson and Francis Crick worked out the double-stranded helical structure of DNA.
    • DNA is a macromolecule made up of two complementary strands of nucleotides.
    • Each nucleotide consists of phosphate, sugar, and a nitrogenous base.

    Nitrogenous Bases

    • Purines: Adenine (A) and Guanine (G)
    • Pyrimidines: Thymine (T), Cytosine (C), and Uracil (U) (only in RNA)

    Chromosome Structure

    • Each chromosome has two sister chromatids joined at a centromere.
    • Centromere serves as the point of attachment to spindle fibres during cell division.
    • Centromere also helps to detach sister chromatids during cell division.

    Genes

    • Genes are specific sequences of DNA that encode particular proteins.
    • Genes are the units of inheritance responsible for specific characteristics.

    DNA Fingerprinting

    • Regions between genes are known as "junk DNA" and show tremendous variations.
    • DNA fingerprinting is useful in establishing paternity and in criminal cases.

    Need for New Cells

    • Cells are produced for growth, replacement, and repair.
    • Cell division ensures the continued existence of an organism.

    Mitosis

    • Mitosis is a type of cell division that results in two daughter cells with the same number and kind of chromosomes as the parent cell.
    • Mitosis occurs in three stages: Interphase, Karyokinesis, and Cytokinesis.

    Interphase

    • Interphase is the stage where cells grow, synthesise materials, and duplicate DNA.
    • Interphase consists of three stages: G1, S, and G2.

    Cell Cycle

    • The cell cycle is a series of events that take place in a cell leading to the duplication of its DNA and the subsequent division of the cell.
    • The cell cycle consists of three stages: G1, S, and G2.

    Phases of Mitosis

    • Prophase: Chromosomes become visible, nuclear membrane and nucleolus disappear, and spindle fibres appear.
    • Metaphase: Chromosomes arrange on the equatorial plane, each attached to a spindle fibre.
    • Anaphase: Centromeres divide, separating sister chromatids, and chromatids are drawn apart towards opposite poles.
    • Telophase: Daughter chromosomes reach opposite poles, spindle fibres disappear, and a nuclear membrane forms.

    Cell Cycle and Cell Division

    • The cell cycle can stop temporarily or permanently.

    • There is a regulatory mechanism for the cell cycle.

    • Cells can be replaced or repaired in various ways, depending on the type of cell.### Significance of Meiosis

    • Chromosome number is halved in gametes (sex cells) to restore the normal number of chromosomes (2n) on fertilization.

    • Meiosis provides for mixing up of genes through two ways:

      • Maternal and paternal chromosomes mixing up during the first (reduction) division as they separate from homologous pairs.
      • Crossing over, which results in genetic recombination, occurs when chromatid material is exchanged between non-sister chromatids of paired homologous chromosomes.

    Mitosis vs. Meiosis

    • Mitosis occurs in somatic/vegetative (body) cells for growth, repair, and replacement.
    • Meiosis occurs in reproductive cells for gamete formation only.
    • Number of daughter cells produced:
      • Mitosis: 2 daughter cells
      • Meiosis: 4 daughter cells
    • Number of chromosomes passed on to each daughter cell:
      • Mitosis: Full set of chromosomes (diploid, 2n)
      • Meiosis: Half the number of chromosomes (haploid, n)
    • Number of nuclear divisions:
      • Mitosis: A single nuclear division after chromosome duplication
      • Meiosis: Two nuclear divisions after chromosome duplication
    • Identity of chromosomes and genes in daughter cells:
      • Mitosis: Identical
      • Meiosis: Randomly assorted between gametes, resulting in genetic variations

    Cell Structure and Division

    • Chromosomes are formed of very long fine DNA molecule wrapped around histone proteins.
    • Nucleosomes are groups of histone molecules with DNA wrapped around them.
    • Each DNA strand is composed of repeating nucleotides.
    • The four nitrogenous bases are adenine, guanine, thymine, and cytosine.
    • During replication, the DNA double helix gets unwound and separated.
    • Genes are specific sequences of nucleotides.
    • New cells need to be produced for growth and replacement.
    • Mitosis involves duplication of chromosomes, maintaining the chromosome number in all cells.
    • Mitosis occurs in two phases: Karyokinesis and Cytokinesis.
    • Karyokinesis occurs in four steps: prophase, metaphase, anaphase, and telophase.
    • Cytokinesis: In animal cells, by deepening of a furrow; in plant cells, a cell plate appears across the center.
    • Meiosis involves two divisions, reducing the number of chromosomes to half.
    • Meiosis also involves crossing over, resulting in genetic variations.

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    Description

    This quiz covers the structure of chromosomes, cell cycle phases including interphase and mitotic phase, and the process of cell division including mitosis and meiosis. It also touches on the significance and differences between these types of cell division.

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