BioChem - Intro to Cell

• Cell


  Basic structural unit of the human body
• Cells


  • Carry out chemical activities necessary to sustain life
  • Function in the production, repair and regeneration of tissues
• Generalized cell


  Describes cell features that are common to most cells
• Robert Hooke


  Discovered the cube-like structures and called them "cells"
• Theodore Schwann and Matthias Jakob Schleiden


  Proposed the Cell Theory in the 18th century
• Cell Theory


  • The cell is the basic unit of structure and function life
  • All living things are composed of one or more cells
  • New cells arise from pre-existing cells through cellular division
• Expanded Cell Theory


  • Cells carry genetic material passed to daughter cells during cellular division
  • All cells are essentially the same in chemical composition
  • Energy flow (metabolism and biochemistry) occurs within cells
• Cell Types


  • Eukaryotes
  • Prokaryotes
• Prokaryotes


  • Small; size ranges 0.1 to 10 μm
  • No true nucleus; DNA is bounded in the nucleoid
  • Single circular chromosome condensed in cytoplasm
  • Cytosol contains macromolecules (enzymes, mRNA, tRNA, and ribosomes), organic compounds and ions
• Prokaryotes


  • Eubacteria
  • Archaebacteria
• Eubacteria


  • Peptidoglycan cell walls and cell membranes with a lipid bilayer
  • Larger genome sequences

  
• Archaebacteria


  • Lower organization
  • Lower genome sequence
  • Cell walls have repeating subunits of N-Acetylglucosamine and N-Acetyltalosaminuronic acid
  • No peptidoglycans in cell wall; but polysaccharides

  
• Bacteria


  • Peptidoglycan cell wall protects cell from mechanical and osmotic pressure
  • Some antibiotics target enzymes that synthesize the cell walls
  • Gram-positive bacteria have thick cell walls surrounded by plasma membrane
  • Gram-negative bacteria have thinner cell wall and outer membrane

  
• Eukaryotes


  • With real, well-defined nucleus
  • Higher structural organization
  • Larger; with membrane-bound organelles
  • With more than one chromosome
  • Make up eukaryotic and/or other multicellular organisms; plants, animals, fungi
• Saccharomyces cerevisiae


  A unicellular eukaryote

  
• Cell Membrane


  • The outermost component of the cell
  • Encloses the cytoplasm forming the cellular boundary between cell's interior and exterior
  • Acts as a protective barrier regulating cellular entry and exit
• Cell Membrane


  • Structural components: major molecules like proteins, phospholipids, including cholesterol and carbohydrates
  • Phospholipids form a double layer of molecules
  • Polar phosphate-containing ends of the phospholipids are hydrophilic, while fatty acid tails are hydrophobic
  • The double-layer also has a liquid property giving it its semi-permeable identity

  
• Membrane Channels


  • Consist of large protein molecules extending from one surface of cell membranes to the other
  • The size, shape, and charge of a molecule all determine whether it can pass through each kind of channel
• Membrane Channels


  • Some channels constantly allow ions to pass through (leak channels)
  • Some channels limit movement of ions across the membrane by opening and closing (gated channels)
• Passive Transport


  • Fundamental movement of ions and other molecular substances within cells
  • Tendency of molecules to move from an area of higher concentration to an area of low concentration
• Diffusion


  • Substances move from an area of higher concentration to an area of lower concentration
  • Does not require energy (ATP) to accomplish transport
• Osmosis


  • The diffusion of water (a solvent) across a selectively permeable membrane
  • Movement flows from a region of higher water concentration to one of lower concentration
  • A form of passive transport
• Osmosis in Hypotonic, Hypertonic and Isotonic Solutions

  • Hypotonic solution: lower concentration of solutes and a higher concentration of water relative to the cytoplasm of the cell
  • Isotonic solution: concentrations of various solutes and water equal on both sides of the cell membrane
  • Hypertonic solution: causes water to move by osmosis, resulting in cell shrinkage, or crenation
• Carrier-Mediated Transport Mechanisms


  Move substances across the cell membrane from an area of higher concentration to an area of lower concentration
• Carrier-Mediated Transport Mechanisms


  • Facilitated Diffusion
  • Active Transport
  • Secondary Active Transport
• Facilitated Diffusion


  • Carrier molecules move large, water-soluble molecules or electrically charged ions across the cell membrane
  • Carrier-mediated transport mechanisms exhibit specificity; where only specific molecules are transported by the carriers
• Active Transport


  • Moves substances across the cell membrane from regions of lower concentration to a higher concentration against a concentration gradient
  • Requires energy in the form of ATP
• Active Transport


  • Primary Active Transport
  • Secondary Active Transport
• Primary Active Transport


  • Responsible for moving ions across a membrane creating a difference in charge across that membrane
  • Example: Sodium-Potassium Pump (Na⁺−K⁺)
• Secondary Active Transport


  • Also called co-transport
  • Allows an exchange of transport between two different solutes
  • Uses electrochemical gradient as energy source
• Endocytosis


  The uptake of material through the cell membrane by the formation of a vesicle
• Steps of Endocytosis


  1. Plasma membrane folds inward forming a cavity that is filled in by the desired materials

  2. Plasma membrane folds back, trapping the desired materials inside it

  3. Vesicle containing the material pinches off from the cell membrane
• Active Transport


  Requires energy in the form of ATP
• Active Transport


  • Primary Active Transport
  • Secondary Active Transport
• Carrier-Mediated Transport Mechanisms


  Responsible for moving ions across a membrane creating a difference in charge across that membrane
• Primary Active Transport


  Example: Sodium-Potassium Pump (Na⁺−K⁺)
• Secondary Active Transport


  Allows exchange of transport between two different solutes, uses electrochemical gradient as energy source
• Endocytosis


  1. Plasma membrane folds inward forming a cavity filled with desired materials

  2. Plasma membrane folds back, trapping the desired materials inside

  3. Vesicle pinches off the cell membrane
• Receptor-Mediated Endocytosis


  Cell membrane contains specific receptor molecules that bind to specific substances, triggering endocytosis
• Phagocytosis


  A "cell-eating process" where white blood cells and other cell types ingest bacteria, cell debris, and foreign particles