Lectures 6-7 - Cells and Cell Cycle

Quote

• "There is no elevator to success. You have to take the stairs."

The Eukaryotic Cell Cycle, Mitosis, and Meiosis

• Chapter 16, Brooker Overview:

  • Key concepts of eukaryotic cell cycle include:

    • The Eukaryotic Cell Cycle

    • Mitotic Cell Division

    • Meiosis

    • Sexual Reproduction

    • Variation in Chromosome Structure and Number

  • Related Course: BIOL 1113, Organisms and their Environment

Unit Overview

• Central Dogma of Molecular Biology

• Concepts to Review:

  • Mitosis

  • Meiosis

  • Life Cycles

  • Ploidy (Refer to Chapter 4 – Features of Cells, pp 78-104)

Cell Theory (Chapter 4)

• Basic Principles:

  • All living organisms are composed of one or more cells

  • Cells are the smallest units of life

  • New cells arise only from pre-existing cells through cell division

  • Cell Structure was reviewed in the last class by Dr. Allen

Types of Cells

• Prokaryotic Cells:

  • E.g., bacteria

  • Lack internal compartmentalization and a membrane-enclosed nucleus

  • Typically small (1-10 µm)

• Eukaryotic Cells:

  • Have internal compartmentalization (membrane systems)

  • Examples:

    • Nucleus (contains DNA)

    • Endoplasmic Reticulum

    • Mitochondria (energy)

    • Plant cells (with chloroplasts)

  • Features:

    • Nucleoid (contains DNA)

    • Cell membrane

    • Cytoplasm

    • Cell wall

    • Ribosomes (synthesize polypeptides)

    • Animal cells lack cell walls and chloroplasts

Structure of Typical Bacterial Cell

• Inside Plasma Membrane:

  • Cytoplasm

  • Nucleoid Region (DNA location)

  • Ribosomes (protein synthesis)

• Outside Plasma Membrane:

  • Cell wall (provides support and protection)

  • Glycocalyx (traps water, provides protection, helps evade immune system)

  • Appendages:

    • Pili (attachment)

    • Flagella (movement)

Eukaryotic Cell Features

• DNA and Organelles:

  • DNA is housed in a membrane-bound nucleus

  • Various organelles, each with unique structure and function

  • Shape, size, and organization of eukaryotic cells vary considerably

  • Differences exist between species and specialized cell types

Key Cell Structures

• Components:

  • Rough Endoplasmic Reticulum

  • Nucleus (with nuclear pores, nucleolus, chromatin)

  • Golgi apparatus

  • Mitochondria (energy production)

  • Ribosomes

  • Cytoskeleton (microfilaments, intermediate filaments, microtubules)

Keith Porter: The Father of the Cell

• Biography:

  • BA in Biology & Chemistry, Acadia 1934

  • Notable contributions to cell biology through Transmission Electron Microscopy

  • Researched and described many parts of cells

Fields of Genetic Study

• Cytogenetics:

  • Involves microscopic studies of chromosomes

• Transmission Genetics:

  • Study of gene passage from one generation to the next (Mendelian Genetics)

• Population Genetics:

  • Examines genetic variation among individuals

• Quantitative Trait Genetics:

  • Focuses on measurable traits with continuous variation

• Molecular Genetics:

  • Investigates molecular processes of gene structure and function

• Epigenetics:

  • Studies modifications in gene expression not caused by changes in DNA sequence

• Genomics and Bioinformatics:

  • Covers entire genomic complement of an organism and data analysis

Criteria for Genetic Material

• Four necessary criteria:

  • Information storage

  • Ability to replicate

  • Transmission across generations

  • Variation among organisms

• Historical overview:

  • Late 1800s: Biochemical basis of heredity introduced

  • 1920s-1940s: Chromosomes expected to be genetic material

Nucleic Acid Structure

• Levels of DNA Structure:

  • Nucleotides (building blocks)

  • Strands (linear polymers of DNA/RNA)

  • Double helix formation (two strands of DNA)

  • Chromosomes (DNA associated with proteins)

  • Genome (complete genetic material of an organism)

Central Dogma of Molecular Biology

• Key Processes:

  • DNA replication: copying genetic information

  • Transcription: DNA to messenger RNA (mRNA)

  • Translation: mRNA to polypeptides (protein synthesis)

Genetic Information Encoding

• Chromosomes and Genes:

  • Each chromosome contains many genes responsible for genetic information

  • Humans: 23 pairs of chromosomes

    • One pair determines sex (XX or XY)

    • Other 22 pairs (autosomes) determine other traits (e.g., eye color)

Eukaryotic Cell Cycle

• Highlights:

  • "Omnis cellula e cellula" – All cells come from existing cells

  • Series of regulated events leading to cell division via mitosis and meiosis

Eukaryotic Chromosomes

• Cytogenetics:

  • Field focused on microscopic examination of chromosomes

  • Karyotype reveals number, size, and form of chromosomes

Chromosome Ploidy

• Humans:

  • 23 pairs (46 total chromosomes)

  • Diploid (2n) with 23 pairs

  • Haploid (n) gametes with 23 total chromosomes

Homologous Chromosomes

• Definition:

  • Homologs are members of a pair of chromosomes in diploid species

  • Autosomal pairs: Similar in size and genetic composition

  • Sex chromosomes: X and Y differ in size and composition

Stages of the Cell Cycle

• Phases of the Eukaryotic Cell Cycle:

  • G1 (First Gap): Cell growth

  • S (Synthesis): DNA replication

  • G2 (Second Gap): Preparing for mitosis

  • M (Mitosis): Division occurs

  • Interphase includes G1, S, and G2 phases

Mitosis and Cytokinesis

• Mitosis Process:

  • Cell divides producing two genetically identical cells

  • Involves separation of sister chromatids and cytoplasm division

  • Mitosis: critical for growth, development, and asexual reproduction

Comparison of Mitosis and Meiosis

• Mitosis:

  • Produces 2 identical diploid daughter cells

• Meiosis:

  • Produces 4 varied haploid daughter cells through two rounds of division (meiosis I and II)

Meiosis Process

• Overview:

  • Meiosis involves combination and separation of homologous chromosomes leading to genetic diversity

  • Key phases include Prophase I, Metaphase I, Anaphase I, and Telophase I

Crossing Over and Genetic Variation

• Mechanism:

  • Crossing over introduces genetic variation through the exchange of chromosome segments

  • Formation of bivalents or tetrads occurs during meiosis I

Summary of Meiosis II

• Comparative Aspects:

  • Resembles mitosis; sister chromatids separate during anaphase II

  • Result: four genetically diverse haploid cells