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Cell Biology and Energy Metabolism Lecture Review

Cells and Microscopy

  • Early microscopes: Robert Hooke (1665) identified "cells" in cork; Anton von Leeuwenhoek observed living cells from blood, sperm, and pond water.
  • Light Microscope (LM): Light passes through a specimen, glass lenses, projected to eye. Magnification up to 1000x.
  • Magnification: Increase in an object's image size vs. actual size.
  • Resolution: Clarity of an image; ability to show two nearby objects as separate.
  • Limitations: Human eye and LM have limits of resolution, restricting detailed small structure view.
  • Cell Theory (1800s): All living things are composed of cells, and all cells come from other cells.
  • Electron Microscopes (EM) (1950s): Use a beam of electrons; resolve structures down to 2 nm; magnify up to 100,000x.
    • Scanning Electron Microscope (SEM): Studies detailed architecture of cell surfaces.
    • Transmission Electron Microscope (TEM): Studies internal cell structure.
  • Differential Interference Light Microscopes: Amplify density differences, making living cells appear 3D.
  • Cell Size: Must be large enough for organelles (DNA, proteins) but small enough for adequate surface-to-volume ratio for exchange.

Plasma Membrane

  • Flexible boundary between living cell and surroundings.
  • Phospholipid bilayer: Hydrophilic heads face outward (exposed to water), hydrophobic tails point inward (shielded from water).
  • Membrane proteins: Embedded in lipid bilayer; form channels for ions/hydrophilic molecules or act as pumps (active transport).

Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic Cells: Bacteria and Archaea; simpler, smaller, no membrane-enclosed nucleus or organelles.
  • Eukaryotic Cells: All other forms of life; distinguished by membrane-enclosed nucleus and many membrane-enclosed organelles.
  • Common to Both:
    • Plasma membrane.
    • Cytosol (thick, jelly-like fluid).
    • One or more chromosomes (DNA).
    • Ribosomes (make proteins).
    • Cytoplasm (entire interior of cell; in eukaryotes, region between nucleus and plasma membrane).
  • Prokaryotic specifics:
    • DNA coiled into nucleoid region (no membrane).
    • Rigid cell wall (protects, maintains shape).
    • Surface projections: Short (attachment) or long (flagella, for propulsion).
  • Eukaryotic specifics:
    • Membrane-enclosed nucleus and other organelles.
    • Four basic functions of organelles:
      1. Genetic control (nucleus, ribosomes).
      2. Manufacture, distribution, breakdown of molecules (ER, Golgi, lysosomes, vacuoles, peroxisomes).
      3. Energy processing (mitochondria, chloroplasts).
      4. Structural support, movement, communication (cytoskeleton, plasma membrane, cell wall).

Eukaryotic Organelles - Animal vs. Plant

  • Animal Cells Only: Lysosomes, centrosomes (containing centrioles).
  • Plant Cells Only:
    • Rigid cell wall (contains cellulose, support).
    • Plasmodesmata (cytoplasmic channels connecting adjacent cells).
    • Chloroplasts (photosynthesis).
    • Central vacuole (stores water, chemicals).

Nucleus and Ribosomes

  • Nucleus: Contains most cell DNA, controls activities by directing protein synthesis (via mRNA).
    • Chromosomes: DNA associated with proteins.
    • Chromatin: Complex of proteins and DNA when cell is not dividing (diffused mass).
    • Nuclear envelope: Double membrane with pores (regulates entry/exit, connects with ER).
    • Nucleolus: Prominent structure; site of ribosomal RNA (rRNA) synthesis.
  • Ribosomes: Cellular components that use mRNA instructions to build proteins.
    • Free ribosomes: Suspended in cytosol.
    • Bound ribosomes: Attached to ER or nuclear envelope.

Endomembrane System

  • Includes: Nuclear envelope, ER, Golgi apparatus, lysosomes, vacuoles, plasma membrane.
  • Components are physically connected or linked by vesicles (sacs of membrane).
  • Endoplasmic Reticulum (ER): Extensive network of flattened sacs and tubules.
    • Smooth ER: Lacks ribosomes; synthesis of lipids, oils, phospholipids, steroids; processes drugs/alcohol; stores calcium ions.
    • Rough ER: Has bound ribosomes; makes additional membrane; makes secretory proteins.
  • Golgi Apparatus: Molecular warehouse and processing station for ER products.
    • Receives products via transport vesicles from ER.
    • Modifies products as they move through stacks.
    • Ships products in new vesicles to other sites.
  • Lysosomes: Membrane-enclosed sacs of digestive enzymes (made by rough ER, processed in Golgi).
    • Fuse with food vacuoles to digest food.
    • Fuse with vesicles containing damaged organelles for recycling.
    • Destroy bacteria engulfed by white blood cells.
  • Vacuoles: Large vesicles with varied functions.
    • Contractile vacuoles (protists): Eliminate excess water.
    • Plant vacuoles: Digestive functions, contain pigments/poisons, store water/chemicals.
  • Peroxisomes: Metabolic compartments; break down fatty acids for fuel; not part of endomembrane system.

Energy-Converting Organelles

  • Mitochondria: Carry out cellular respiration in nearly all eukaryotic cells.
    • Converts chemical energy in food to ATP.
    • Intermembrane space: Narrow region between inner/outer membranes.
    • Mitochondrial matrix: Contains mitochondrial DNA, ribosomes, many enzymes for respiration.
    • Cristae: Folds of inner mitochondrial membrane; increase surface area for ATP production.
  • Chloroplasts: Photosynthesizing organelles of plants and algae.
    • Converts light energy to chemical energy (sugar).
    • Intermembrane space: Between inner/outer membranes.
    • Stroma: Thick fluid inside inner membrane; contains chloroplast DNA, ribosomes, enzymes.
    • Thylakoids: Network of interconnected sacs; contain chlorophyll; site of solar energy capture.
    • Granum: Stack of thylakoids.
  • Endosymbiont Theory: Mitochondria and chloroplasts were formerly small prokaryotes that began living within larger cells.

Cytoskeleton and Cell Surfaces

  • Cytoskeleton: Network of protein fibers organizing cell structure and activities.
    • Microtubules (tubulin): Shape/support cell, act as tracks for organelle movement.
      • Grow from centrosome (animal cells), containing centrioles (ring of microtubules).
    • Intermediate filaments: Reinforce cell shape, anchor organelles; more permanent.
    • Microfilaments (actin filaments): Support cell shape, involved in motility.
  • Cilia and Flagella: Short, numerous appendages (cilia) or longer, fewer appendages (flagella) for propulsion.
    • Common structure: Microtubules wrapped in plasma membrane.
    • 9+2 pattern: Ring of nine microtubule doublets surrounding a central pair.
    • Anchored in basal body (nine microtubule triplets in a ring).
    • Movement: Bending of motor proteins (dynein feet) causing microtubules to slide.
  • Extracellular Matrix (ECM) (Animal Cells): Secreted by animal cells; holds cells in tissues, protects, supports membrane.
    • Attaches via glycoproteins binding to integrins (membrane proteins).
  • Animal Cell Junctions:
    • Tight junctions: Prevent fluid leakage across epithelial cell layer.
    • Anchoring junctions: Fasten cells together into strong sheets.
    • Gap junctions: Channels allowing small molecules to flow through protein-lined pores between cells.
  • Plant Cell Wall: Rigid (cellulose), protects, provides skeletal support.
  • Plasmodesmata (Plant Cells): Cell junctions allowing sharing of water, nourishment, chemical messages.

Membrane Structure and Function (Review)

  • Fluid Mosaic Model: Patchwork of diverse protein molecules embedded in a phospholipid bilayer.
  • Selective Permeability: Plasma membrane regulates passage of substances.
  • Membrane Proteins Functions:
    • Enzymes: Carry out sequential reactions.
    • Attachment proteins: Attach to ECM and cytoskeleton; support membrane, coordinate changes.
    • Receptor proteins: Bind signaling molecules, relay messages inside cell.
    • Transport proteins: Allow specific ions/molecules to enter/exit (channels or pumps).
    • Junction proteins: Form intercellular junctions.
    • Glycoproteins: Serve as ID tags for cell recognition.
  • Self-Assembly: Phospholipids spontaneously form membranes.

Membrane Transport

  • Diffusion: Tendency of particles to spread out evenly in available space; move down concentration gradient until dynamic equilibrium.
  • Passive Transport: Diffusion across a membrane without energy expenditure (e.g., oxygen, carbon dioxide).
  • Osmosis: Diffusion of water across a selectively permeable membrane.
  • Tonicity: Ability of surrounding solution to cause cell to gain or lose water (depends on solute concentration relative to cell).
    • Isotonic solution: Solute concentration same on both sides; cell volume unchanged (normal for animal cells, flaccid for plant).
    • Hypotonic solution: Lower solute outside cell; water moves in; animal cell bursts (lysis), plant cell becomes turgid (normal for plant).
    • Hypertonic solution: Higher solute outside cell; water moves out; animal cell shrivels (crenation), plant cell shrivels (plasmolysis).
  • Osmoregulation: Control of water balance (for animal cells in hypotonic/hypertonic environments).
  • Facilitated Diffusion: Movement of polar/charged substances across membranes with help of specific transport proteins; no energy required; relies on concentration gradient.
    • Aquaporins: Protein channels for rapid water diffusion.
  • Active Transport: Cell expends energy (ATP) to move solute against its concentration gradient.
  • Bulk Transport (Large Molecules):
    • Exocytosis: Exports bulky molecules (proteins, polysaccharides) in vesicles.
    • Endocytosis: Takes in large molecules in vesicles.
      • Phagocytosis: Engulfment of a particle by cell membrane wrapping around it (forming vacuole/pseudopods).
      • Receptor-mediated endocytosis: Uses membrane receptors for specific solutes; forms coated pit/vesicle (e.g., cholesterol uptake).

Energy and Metabolism

  • Energy: Capacity to cause change or perform work.
    • Kinetic energy: Energy of motion (thermal energy/heat, light).
    • Potential energy: Energy matter possesses due to location or structure (chemical energy).
  • Chemical energy: Potential energy available for release in chemical reactions; most important for living organisms.
  • Thermodynamics: Study of energy transformations.
    • First Law of Thermodynamics (Conservation): Energy in the universe is constant.
    • Second Law of Thermodynamics: Energy conversions increase disorder (entropy) of the universe.
  • Exergonic reactions: Release energy (e.g., burning wood, cellular respiration).
  • Endergonic reactions: Require input of energy, yield products rich in potential energy (e.g., photosynthesis).
  • Metabolism: Total of an organism's chemical reactions.
  • Metabolic pathway: Series of chemical reactions that build or break down complex molecules.
  • Energy coupling: Uses energy from exergonic reactions to drive endergonic reactions, typically using ATP.
  • ATP (Adenosine Triphosphate): Powers nearly all forms of cellular work.
    • Consists of adenosine and a triphosphate tail.
    • Hydrolysis of ATP releases energy by transferring its third phosphate to another molecule (phosphorylation).
    • Drives chemical, mechanical, and transport work.
    • ATP Cycle: Energy from exergonic reactions (e.g., glucose breakdown) regenerates ATP from ADP.

Enzymes

  • Energy barrier (activation energy): Must be overcome for chemical reactions to begin.
  • Enzymes: Biological catalysts (mostly proteins) that increase reaction rate by lowering activation energy without being consumed.
  • Specificity: Enzyme shape determines its specificity; specific reactant (substrate) fits into active site.
  • Induced fit: Substrate snugly fits into active site, causing slight shape change.
  • Optimal Conditions: Temperature (most human enzymes best at 35-40^{\circ}C), pH (most near neutrality, ~7).
  • Cofactors: Non-protein helpers that bind to active site and function in catalysis.
    • Inorganic (e.g., zinc, iron, copper ions).
    • Organic (coenzymes, e.g., most vitamins).
  • Inhibitors: Chemicals that interfere with enzyme activity.
    • Competitive inhibitors: Block substrates from active site, reducing productivity.
    • Noncompetitive inhibitors: Bind to enzyme elsewhere, changing active site shape, preventing substrate binding.
  • Feedback Inhibition: Product acts as an inhibitor of an enzyme in its own metabolic pathway.
  • Applications: Many drugs (ibuprofen, blood pressure meds, antibiotics, HIV proteases) and some pesticides/poisons are enzyme inhibitors.