Cell Structure And Function-Cell Cycle And Cell Division

Cell Cycle: NCERT Reference: Chapters 10 and 11, Class 11 Biology

• Phases of the cell cycle:

• Interphase (G1, S, G2 phases)

• Prophase

• Metaphase

• Anaphase

• Telophase

• Cytokinesis

• Significance of cell cycle checkpoints:

• Ensure accurate replication and segregation of DNA during cell division

• Prevent transmission of damaged DNA to daughter cells

• Regulate cell growth and differentiation

Cell Division:

NCERT Reference: Chapter 10, Class 11 Biology

Mitosis:

• Significance of mitosis:

• Growth and tissue repair

• Asexual reproduction

• Vegetative propagation

• Stages of mitosis:

  • Prophase: Condensation of chromosomes, formation of mitotic spindle
  • Metaphase: Alignment of chromosomes at the metaphase plate
  • Anaphase: Separation of sister chromatids and their movement to opposite poles
  • Telophase: Uncoiling of chromosomes, reformation of nuclear envelope
  • Cytokinesis: Division of the cytoplasm to form two daughter cells

• Mitotic spindle apparatus:

• Centrosomes: Organize microtubules and initiate spindle fiber formation

• Centromere: Region of the chromosome where spindle fibers attach

• Spindle fibers/microtubules: Dynamic structures made of tubulin, responsible for chromosome movement

Meiosis:

NCERT Reference: Chapters 9, 10 and 11, Class 12 Biology

• Significance of meiosis:

• Sexual reproduction

• Production of haploid gametes

• Genetic diversity and variation

• Synapsis and crossing over in meiosis:

• Synapsis: Pairing of homologous chromosomes during prophase I

• Crossing over: Exchange of genetic material between homologous chromosomes, leading to genetic recombination

• Stages of meiosis:

• Meiosis I:

  • Prophase I: Synapsis and crossing over, formation of tetrads
  • Metaphase I: Alignment of homologous chromosome pairs at the metaphase plate
  • Anaphase I: Separation of homologous chromosome pairs and their movement to opposite poles
  • Telophase I: Uncoiling of chromosomes, formation of two daughter cells with haploid chromosome number

• Meiosis II:

• Prophase II: Condensation of chromosomes

• Metaphase II: Alignment of sister chromatids at the metaphase plate

• Anaphase II: Separation of sister chromatids and their movement to opposite poles

• Telophase II: Uncoiling of chromosomes, formation of four haploid daughter cells

• Segregation and independent assortment of chromosomes in meiosis:

• Segregation: Separation of homologous chromosomes during meiosis I and sister chromatids during meiosis II

• Independent assortment: Random orientation of homologous chromosome pairs and sister chromatids at the metaphase plate, leading to genetic diversity

Genetic material and DNA Replication

NCERT Reference: Chapters 6, 7, and 8, Class 12 Biology

• Structure and composition of DNA:

• Double helix structure

• Composed of deoxyribonucleotides (Adenine, Thymine, Guanine, Cytosine)

• Nitrogenous bases: Purines (Adenine and Guanine) and Pyrimidines (Thymine and Cytosine)

• Base pairing: Adenine with Thymine and Guanine with Cytosine

• Nucleotides: Sugar-phosphate backbone with nitrogenous bases

• DNA replication:

• Semi-conservative replication: Each daughter molecule consists of one original and one newly synthesized strand.

• Unidirectional replication: DNA synthesis occurs in one direction only, from the 5’ to 3’ end

• Replication fork: Y-shaped region where DNA replication is actively taking place

• Enzymes involved: DNA polymerase, Helicase, RNA primase, DNA ligase

Mutation

NCERT Reference: Chapter 10, Class 12 Biology

• Types of mutation:

• Gene mutations:

  • Point mutations: Substitution, deletion, or insertion of a single nucleotide
  • Deletion: Loss of a segment of DNA
  • Insertion: Addition of a segment of DNA
  • Duplication: Repetition of a segment of DNA
  • Translocation: Transfer of a segment of DNA from one chromosome to another
  • Inversion: Reversal of the orientation of a segment of DNA within a chromosome

• Chromosomal mutations:

• Numerical mutations: Changes in the number of chromosomes, such as aneuploidy (gain or loss of one or more chromosomes) and polyploidy (multiple sets of chromosomes)

• Structural mutations: Changes in the structure of chromosomes, such as deletions, insertions, inversions, and translocations