Biochemistry and Cellular Structure & Function Notes

Biochemistry: Molecular Structure and Enzyme Function

Molecules in Living Things

Organic compounds are carbon-containing and are fundamental to all living organisms.

Carbohydrates
  • Major source of short-term energy.
  • Involved in animal and plant structures (exoskeleton and cell wall).
  • Examples: Sugars.
  • Composed of carbon, hydrogen, and oxygen in a 2:1 ratio of hydrogen to oxygen.
  • Monomer: Monosaccharide (e.g., glucose).
Proteins
  • Made of chains of amino acids (20 different types).
  • Functions include enzymes, hormones, antibodies, and structural components (muscles).
Lipids
  • Water-insoluble (fats, waxes, and oils).
  • Composed of carbon, hydrogen, and oxygen; glycerol and fatty acids are the building blocks.
  • Provide insulation, long-term energy storage, and cushioning for internal organs; found in cell membranes.
  • Types: Saturated (single bonds) and unsaturated (double bonds).
Nucleic Acids
  • Store and transmit genetic information.
  • Two types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
  • Composed of nucleotides (sugar, nitrogenous base, and phosphate group).

Enzymes: Biological Catalysts

Function
  • Special proteins that regulate biochemical reactions; different reactions require different enzymes.
  • Aid in digestion and break down complex molecules (substrate = reactant).
  • Act as catalysts: they speed up chemical reactions without being used up or altered.
  • Lower the activation energy for chemical reactions.
Factors Affecting Enzymes
  • pH: Enzymes are affected by changes in pH. Optimum pH is the most favorable pH value at which the enzyme is most active.
  • Temperature: The rate of an enzyme-catalyzed reaction generally increases with temperature. However, most animal enzymes denature at temperatures above 40∘C40^\circ C.
  • Quantity: Enzyme activity is also affected by enzyme concentration.
Activation Energy

Enzymes lower the activation energy required for a reaction to proceed.

Water: Properties Supporting Life

Polarity
  • Water is polar, with a slight positive charge on hydrogen atoms and a slight negative charge on oxygen atoms.
  • This polarity allows it to dissolve other polar molecules effectively.
Cohesion and Adhesion
  • Cohesion: Water molecules are attracted to each other.
  • Adhesion: Water is attracted to other molecules; example: capillary action-water climbs and moves up a tree.
  • These properties are crucial for water movement in plants (transpiration).
High Heat Capacity
  • Water holds heat to regulate temperature, contributing to homeostasis.
High Heat of Vaporization
  • Sweating cools the body due to the high heat of vaporization.
Density
  • Water is less dense as a solid than as a liquid (ice floats), insulating lakes and allowing aquatic organisms to survive in winter.
Solvent Properties
  • Water is an excellent solvent, dissolving nutrients and facilitating biological reactions.

Key Water Properties

  • Cohesive behavior (attraction between water molecules).
  • Ability to moderate temperature.
  • Expansion upon freezing.
  • Versatility as a solvent.
  • Hydrogen bonding.

Cellular Structure and Function

Cell Theory

Development
  • Matthias Schleiden (1838): All plants are composed of cells.
  • Theodor Schwann (1839): All animals are composed of cells.
  • Rudolph Virchow (1855): All cells come from pre-existing cells.
  • Robert Hooke: First to observe cells using a primitive microscope.
Principles
  • Cells are the basic units of structure and function in all living things.
  • All organisms are composed of cells.
  • All cells come from pre-existing cells.

Laws vs. Theories

  • Law: Simple statement about a phenomenon that never requires verification.
  • Theory: Scientific explanation of an observed phenomenon; explains why things are the way they are; can never become laws.

Prokaryotic vs. Eukaryotic Cells

Prokaryotic Cells
  • No nucleus.
  • No membrane-bound organelles.
  • Small in size.
  • Examples: Bacteria, Archaea.
  • Cell/plasma membrane, ribosomes and cell wall are present.
Eukaryotic Cells
  • Have a nucleus.
  • Have membrane-bound organelles.
  • Large in size.
  • Examples: Animals, Plants, Fungi, Protists.
  • Cell/plasma membrane and ribosomes are present.

Eukaryotic Cell Structures

Animal Cell
  • Nucleus: Contains genetic material.
  • Nuclear Envelope: Double membrane enclosing the nucleus.
  • Nucleolus: Site for ribosome subunit assembly.
  • Chromatin: Complex of protein and DNA.
  • Ribosome: Site of polypeptide synthesis.
  • Mitochondrion: Site of ATP synthesis.
  • Cytoskeleton: Protein filaments providing shape and aiding in movement.
  • Lysosome: Site where macromolecules are degraded.
  • Peroxisome: Site where hydrogen peroxide and other harmful molecules are broken down.
  • Golgi Apparatus: Site of modification, sorting, and secretion of lipids and proteins.
  • Cytosol: Site of many metabolic pathways.
  • Plasma Membrane: Controls movement of substances into and out of the cell; site of cell signaling.
  • Rough ER: Protein synthesis, contains ribosomes.
  • Smooth ER: Detoxification and lipid synthesis.
Plant Cell
  • Same as animal cell, plus:
  • Cell Wall: Provides support for the cell (made of cellulose).
  • Vacuole: Contains cell sap, a weak solution of sugar and salts.
  • Chloroplasts: Contain chlorophyll for photosynthesis.

Cell Membrane and Transport

Structure
  • Phospholipid bilayer (glycerol head and two fatty acid tails).
Transport
  • Passive Transport: Movement across the membrane without energy (high to low concentration).
    • Diffusion: Movement from high to low concentration.
    • Osmosis: Diffusion of water from high to low concentration.
      • Hypotonic: Water moves in; cell bursts.
      • Hypertonic: Water moves out; cell shrivels.
      • Isotonic: No net movement; cell maintains equilibrium.
    • Facilitated Transport: Carrier molecule transports substance across the membrane.
  • Active Transport: Requires energy and carrier molecules (low to high concentration).
  • Endocytosis: Large particles brought into the cell.
  • Exocytosis: Large particles leave the cell.
Homeostasis
  • Internal equilibrium; plasma membrane regulates what enters and leaves the cell.
  • Selectively permeable membrane only allows certain substances to pass through.

Cellular Energy

  • Mitochondria: Convert chemical energy into ATP for cellular activities.
  • Chloroplasts: Capture light energy for photosynthesis.