Molecular Biology Lesson 3

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Questions and Answers

In which phase of mitosis do chromosomes align at the metaphase plate?

  • Metaphase (correct)
  • Anaphase
  • Prophase
  • Telophase

Cytokinesis refers to the process of nuclear division.

False (B)

What is the primary result of meiosis?

four daughter cells

During ____ phase, spindle fibers pull apart the chromatids towards opposite poles of the cell.

<p>anaphase</p>
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Match the following processes or phases with their descriptions:

<p>Prophase = Chromatins condense into chromosomes Telophase = Chromatids reach the opposite poles Cytokinesis = Division of the cytoplasm Meiosis = Production of genetically different gametes</p>
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How many pairs of chromosomes are found in the human body?

<p>23 pairs (D)</p>
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The S-phase of interphase is responsible for DNA replication.

<p>True (A)</p>
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What are the two major phases of the cell cycle?

<p>Interphase and M-phase</p>
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The cell spends approximately _______ hours in interphase.

<p>24</p>
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What is the purpose of the G2 phase in interphase?

<p>Energy replenishment and preparation for cell division (A)</p>
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Match the stages of mitosis with their key events:

<p>Prophase = Chromosomes condense and nuclear envelope breaks down Metaphase = Chromosomes align at the cell equator Anaphase = Sister chromatids are pulled apart Telophase = Nuclear membranes reform around two sets of chromosomes</p>
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Cytokinesis is the division of the nucleus during cell division.

<p>False (B)</p>
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What type of cells undergo mitosis?

<p>Somatic or body cells</p>
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What does DNA stand for?

<p>Deoxyribonucleic acid (C)</p>
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Mitosis and meiosis are the same processes of cell division.

<p>False (B)</p>
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What are genes recognized as?

<p>The basic physical and functional unit of heredity.</p>
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DNA consists of two strands that wind around each other to form a double ______.

<p>helix</p>
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What is the structural role of histones in chromosomes?

<p>To support the structure of DNA (C)</p>
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Telomeres are made of coding DNA sequences.

<p>False (B)</p>
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The term 'chromosome' comes from the Greek words 'khroma' meaning color and 'soma' meaning ______.

<p>body</p>
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Match the terms with their definitions:

<p>Gene = A sequence of nucleotides that encodes a gene product Chromosome = Condensed structure made of DNA that carries genetic material DNA = Biological molecule that carries hereditary materials Telomere = Protective end of a chromosome made of non-coding DNA</p>
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What process does meiosis I include that allows for genetic diversity?

<p>Crossing over (C)</p>
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During Telophase II, the chromosomes de-condense back into chromatin.

<p>True (A)</p>
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What happens during Anaphase I?

<p>Homologous chromosomes are pulled apart to opposite ends of the cell.</p>
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The stage between Meiosis I and Meiosis II that does not involve DNA replication is called __________.

<p>interkinesis</p>
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Match the stage of meiosis with its description:

<p>Prophase I = Chromosomes condense and crossing over occurs Anaphase II = Chromatids are pulled to opposite poles Metaphase I = Homologous chromosomes align at the center Telophase I = Nuclear membrane reintegrates and cleavage furrow forms</p>
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In which stage of meiosis do spindle fibers attach to the centromeres of chromosomes?

<p>Metaphase II (B)</p>
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Meiosis II is essentially the same process as mitosis but occurs in haploid cells.

<p>True (A)</p>
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During __________, centrosomes duplicate and start producing spindle fibers in both meiosis I and II.

<p>prophase</p>
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Flashcards

What are genes?

Basic units of heredity; sequences of nucleotides encoding for RNA or protein synthesis.

What is DNA?

Carries hereditary material and genetic instructions, organized into a double helix structure.

What are chromosomes?

Condensed DNA structures containing genetic material, coiled around histones for support.

What are telomeres?

Protective caps at chromosome ends composed of repetitive non-coding DNA sequences.

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What is the cell cycle?

The series of ordered events leading to cell growth and division into two daughter cells.

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What is Interphase?

Longest stage of the cell cycle where the cell grows and prepares for division.

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What is the G1 phase?

Growth phase where structural proteins and enzymes are synthesized.

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What is the S-phase?

The phase where DNA replication occurs, doubling the genetic material.

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What is the G2 phase?

Phase where the cell prepares for division, replenishing energy and duplicating organelles, includes checkpoints to correct errors in duplicated chromosomes.

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What is the G0 phase?

Non-dividing state that can be permanent.

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What is mitosis?

Cell division that gives rise to two identical daughter cells (2n) from somatic cells.

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What happens in Prophase?

Chromatin condenses into visible chromosomes; nuclear membrane disintegrates; spindle fibers begin forming.

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What happens in Metaphase?

Chromosomes align at the metaphase plate; spindle fibers attach to centromeres.

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What happens in Anaphase?

Chromatids separate and move to opposite poles of the cell as spindle fibers shorten.

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What happens in Telophase?

Chromatids reach poles and decondense; nuclear membranes reform, and cleavage furrow begins to form.

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What is Cytokinesis?

Final division of the cytoplasm into two daughter cells.

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What is Meiosis?

Occurs in germ cells, halving chromosome number from diploid (2n) to haploid (n) across two divisions.

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What happens in Interphase I?

Cells undergo a preparatory growth phase, similar to the interphase in mitosis, but DNA is not replicated again.

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What happens in Prophase I?

Nuclear membrane disintegrates; spindle fibers form; includes crossing over between homologous chromosomes.

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What happens in Metaphase I?

Homologous chromosomes align at the cell's center.

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What happens in Anaphase I?

Homologous chromosomes are pulled apart to opposite poles.

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What happens in Telophase I?

Chromosomes decondense, nuclear membrane reforms; cleavage furrow starts to form.

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What is Interkinesis?

Brief stage without DNA replication where cell growth occurs.

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What is Meiosis II?

Resembles mitosis, separating chromatids similar to mitotic phases.

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What is the result of Mitosis?

Produces two identical daughter cells (2n).

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What is the result of Meiosis?

Results in four genetically diverse daughter cells (n).

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Where does Mitosis occur?

Occurs in somatic cells.

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Where does Meiosis occur?

Occurs in gametes.

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What is the purpose of mitosis?

The division of cells that results in two identical daughter cells.

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Study Notes

Molecular Biology: Lesson 3 Study Notes

  • Connection between DNA, Genes, and Chromosomes

    • Genes are the basic units of heredity, sequences of nucleotides in DNA or RNA encoding for RNA or protein synthesis.
    • DNA (deoxyribonucleic acid) carries hereditary materials and genetic instructions, organized into a double helix structure made of nucleotides.
    • Chromosomes are condensed DNA structures that contain genetic material, coiled around histones for structural support; humans have 46 chromosomes (23 pairs).

  • Telomeres

    • Telomeres protect chromosome ends with repetitive non-coding DNA sequences.
    • They shorten with each cell division, ultimately limiting further divisions once they become critically short.

Cell Cycle Overview

  • Definition and Phases

    • The cell cycle is a series of ordered events leading to cell growth and division into two daughter cells.
    • Comprises two main phases: Interphase and M-phase (mitosis).

  • Interphase

    • Longest stage (approximately 24 hours); accounts for about 90% of a cell's life.
    • Stages of Interphase:
      • G1 Phase: Growth phase where structural proteins and enzymes are synthesized; cellular contents duplicated (excluding chromosomes).
      • S-phase: DNA replication occurs, doubling genetic material before division.
      • G2 Phase: Cell prepares for division, replenishing energy and duplicating organelles; includes checkpoints to correct errors in duplicated chromosomes.
      • G0 Phase: Non-dividing state that can be permanent.

M-phase: Cell Division

  • Mitosis and Cytokinesis
    • Mitosis gives rise to two identical daughter cells (2n) from somatic cells.
    • Stages of Mitosis:
      • Prophase: Chromatin condenses into visible chromosomes; nuclear membrane disintegrates; spindle fibers begin forming.
      • Metaphase: Chromosomes align at the metaphase plate; spindle fibers attach to centromeres.
      • Anaphase: Chromatids separate and move to opposite poles of the cell as spindle fibers shorten.
      • Telophase: Chromatids reach poles and decondense; nuclear membranes reform, and cleavage furrow begins to form.
    • Cytokinesis: Final division of the cytoplasm into two daughter cells.

Meiosis: Sexual Cell Division

  • Definition and Process

    • Meiosis occurs in germ cells, halving chromosome number from diploid (2n) to haploid (n) across two divisions.
    • Results in four genetically diverse daughter cells.

  • Stages of Meiosis:

    • Interphase: Cells undergo a preparatory growth phase, similar to the interphase in mitosis, but DNA is not replicated again.
    • Meiosis I:
      • Prophase I: Nuclear membrane disintegrates; spindle fibers form; includes crossing over between homologous chromosomes.
      • Metaphase I: Homologous chromosomes align at the cell's center.
      • Anaphase I: Homologous chromosomes are pulled apart to opposite poles.
      • Telophase I: Chromosomes decondense, nuclear membrane reforms; cleavage furrow starts to form.
    • Interkinesis: Brief stage without DNA replication where cell growth occurs.
    • Meiosis II: Resembles mitosis, separating chromatids similar to mitotic phases (Prophase II, Metaphase II, Anaphase II, Telophase II), resulting in four unique haploid cells.

Key Differences between Mitosis and Meiosis

  • Mitosis produces two identical daughter cells (2n).
  • Meiosis results in four genetically diverse daughter cells (n).
  • Mitosis occurs in somatic cells, whereas meiosis occurs in gametes.

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