Study Notes on Cells: The Living Units

Chapter 3: Cells - The Living Units

Overview

  • Introduction to cells as the fundamental units of life.
  • Importance of microscopy for cell visibility.

Microscopy

  • Microscope Types:
    • Light Microscope
    • Utilizes light to magnify images of cells.
    • Electron Microscope
    • Uses electron beams for high-resolution imaging of cell structures.

Cell Types and Functions

  • Variability in Cell Types:
    • Cells are specialized; form fits function:
    • Smooth Muscle Cells: Contraction for movement.
    • Blood Cells: Transport of oxygen and carbon dioxide.
    • Bone Cells: Structural support of the body.
    • Sperm Cells: Male reproductive cells.
    • Oocyte (Egg) Cells: Female reproductive cells.
    • Intestinal Tract Cells: Absorption of nutrients.
    • Neurons: Signal transmission in the nervous system.
    • Fat Cells: Energy storage.
  • Total Cell Count:
    • The human body contains approximately 10 trillion cells.

Fundamental Cell Structure

  • Basic Parts of a Cell:
    1. Nucleus:
    • Contains genetic material (DNA).
    1. Plasma Membrane:
    • Surrounds the cell; regulates entry and exit of substances.
    1. Cytoplasm:
    • Gel-like fluid filling the cell; contains organelles.

Plasma Membrane Structure

  • Phospholipids:
    • Composed of a hydrophilic (polar) head and hydrophobic (fatty acid) tails.
  • Proteins:
    • Integral (Transmembrane) Proteins: Span the membrane, function as channels or transporters.
    • Peripheral Proteins: Positioned on the membrane surface, involved in signaling and maintaining cell shape.
  • Glycoproteins and Glycolipids:
    • Composed of carbohydrate and lipid/protein; involved in cell recognition.
  • Cholesterol:
    • Stabilizes the membrane fluidity.

Functions of Plasma Membrane

  • Enzymatic Activity:
    • Catalyzes biochemical reactions at the membrane surface.
  • Receptors:
    • Bind to signaling molecules, inducing changes within the cell.
  • Attachment and Cell Junctions:
    • Form connections with adjacent cells (e.g., tight junctions, gap junctions).
  • Cell Recognition:
    • Essential for immune response and cell communication.
  • Transport Mechanisms:
    • Passive Transport: Moves substances without energy.
    • Simple Diffusion: Movement of small, non-polar molecules through the membrane.
    • Facilitated Diffusion: Uses specific transporter proteins for larger molecules.
    • Osmosis: Movement of water across a selectively permeable membrane.
    • Active Transport: Requires energy (ATP) to move substances against their concentration gradient.
    • Pumps: Proteins that move substances from low to high concentration.
    • Vesicular Transport:
      • Endocytosis: Cellular uptake of materials.
      • Exocytosis: Release of materials from the cell.

Osmosis and Tonicity

  • Osmotic Solutions:
    • Isotonic: Equal concentrations of solutes inside and outside the cell; water enters/leaves at equal rates.
    • Hypotonic: Lower concentration of solutes outside the cell; water enters the cell, potentially causing it to rupture.
    • Hypertonic: Higher concentration of solutes outside the cell; water leaves the cell, causing it to shrivel.

Cytoplasm Composition

  • Components of Cytoplasm:
    1. Cytosol:
    • Aqueous gel with dissolved solutes.
    1. Organelles:
    • Specialized structures that perform distinct functions within the cell.

Organelles in Eukaryotic Cells

  • Key Organelles:
    • Rough Endoplasmic Reticulum (ER):
    • Site of protein synthesis and modification.
    • Smooth ER:
    • Involved in lipid synthesis and detoxification.
    • Golgi Apparatus:
    • Modifies and packages proteins for export.
    • Mitochondria:
    • Powerhouse of the cell; site of ATP production via aerobic respiration.
    • Lysosomes and Peroxisomes:
    • Involved in digestion and detoxification, respectively.
    • Centrioles:
    • Assist in cell division by organizing microtubules.
    • Cytoskeleton:
    • Provides structure, support, and facilitates intracellular transport.

Cell Cycle and Division

  • Phases of the Cell Cycle:
    • Interphase: Preparation phase.
    • G1 Phase: Cell growth and normal activities.
    • S Phase: DNA replication occurs.
    • G2 Phase: Further growth and preparation for mitosis.
    • M Phase: Mitosis, involving:
    • Prophase, Metaphase, Anaphase, Telophase
    • Cytokinesis: Cytoplasmic division occurs following mitosis.
  • DNA Synthesis in S Phase:
    • DNA unzips; each strand serves as a template for a new strand, resulting in two identical DNA strands.
  • Outcome of Mitosis:
    • Results in two genetically identical daughter cells.

DNA and Protein Synthesis

  • DNA Functions:
    • Heredity and Protein Synthesis.
  • Protein Synthesis Process:
    1. Transcription: DNA gene template is used to create complementary mRNA.
    2. Translation: mRNA is read by ribosomes, assembling amino acids into proteins.
  • Genetic Code:
    • Consists of codons, which correspond to specific amino acids; structured as triplets of nucleotides.

Conclusion: Understanding the Cell

  • Knowledge of cell structure and functions is essential in biology and understanding life processes.
  • Comprehensive comprehension of the cell cycle and protein synthesis is pivotal in research and medicine.