Lesson 1

• The Cell and Organization of the Human Body
• Protoplasm


  Water, electrolytes, proteins, lipids, carbohydrates
• Water


  70%-85% of most cells (except fat cells) that acts as principal medium and diluent for suspended solid particulates and dissolved chemicals
• Electrolytes


  • K+, Mg2+, PO4-, SO4-, HCO3+, Na+, Cl-, and Ca2+
• Proteins


  2nd most abundant substance (10%-20%) - structural and functional proteins
• Structural proteins


  Mainly in the form of long filaments that are polymers of many individual protein molecules
• Functional proteins


  Composed of combinations of a few molecules in tubular-globular form, mainly the enzymes of the cell and are often mobile in the cell fluid
• Lipids


  Several types of substances that are grouped together because of their common property of being soluble in fat solvents (i.e., phospholipids and cholesterol ~2% of total cell mass)
• Triglycerides


  Neutral fats that represents the body's main storehouse of energy-giving nutrients that can later be used to provide energy wherever in the body it is needed
• Carbohydrates


  Play a major role in nutrition of the cell, minimal role in structural function
• Glucose


  Dissolved glucose - always present in the surrounding extracellular fluid so that it is readily available to the cell
• Glycogen


  An insoluble polymer of glucose that can be depolymerized and used rapidly to supply the cells' energy needs
• Membranous structures


  • Cell membrane
  • Nuclear membrane
  • Membrane of the endoplasmic reticulum
  • Membranes of the mitochondria, lysosomes, and Golgi apparatus
• Cell membrane


  Consists of phospholipids, cholesterol, and proteins, with oligosaccharide chains covalently linked to many of the phospholipids and proteins
• Cell membrane


  • 55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, 3% carbohydrates
  • Visible only with EM [7.5-10nm] but may be appreciated in LM as line between adjacent cells
• Sphingolipids


  Present in small amounts in CM (nerve cells) and also has hydrophobic and hydrophilic groups; functions: protection from harmful environmental factors, signal transmission, and as adhesion sites for extracellular proteins
• Integral membrane proteins


  • Proteins that protrude all the way through the membrane, functioning as: channels (pores) to allow diffusion of molecules between fluid compartments via preferential diffusion, carrier proteins for transporting substances that otherwise could not penetrate the lipid bilayer, receptors for water-soluble chemicals, ligands and second messengers for communication about the environment to the cell interior
• Peripheral membrane proteins


  • Proteins attached to integral proteins that function almost entirely as enzymes or as controllers of transport of substances through the cell membrane "pores"
• Glycocalyx


  The entire outside surface of the cell often has a loose carbohydrate coat; functions: gives most cells an overall negative surface charge that repels other negatively charged objects, attaches to the glycocalyx of other cells, act as receptor substances for binding hormones, some carbohydrate moieties enter into immune reactions
• Mechanisms of Transport


  1. Diffusion

  2. Osmosis

  3. Facilitated diffusion

  4. Active transport

  5. Vesicular transport
• Cytosol


  Fluid portion inside the cell membrane that bathes the organelles
• Organelles


  Metabolically active structures inside the cell
• Cytoskeleton


  Determine's cell shape and motility
• Ribosomes


  Primary function: assemble polypeptides from AA of tRNA in a sequence specified by mRNA; 2 subunits: smaller (core) rRNA with 30 unique proteins, and larger subunit with 3 other rRNA molecules and 50 basic proteins; polyribosomes or polysomes - larger complexes of ribosomes that are seen in protein synthesis that bind to same mRNA strand
• Endoplasmic Reticulum


  Convoluted flat membranous network of organelles that extends from the surface of the nucleus throughout most of the cytoplasm; cisternae - intercommunicating channels enveloped by the network (reticulum); major site for biosynthesis of proteins (RER), sequestration of calcium ions, synthesis of steroid and phospholipids (SER)
• Golgi Apparatus


  Consists of many smooth membranous saccules, some vesicular, others flattened, but all containing enzymes and proteins being processed; small Golgi complexes are located near the nucleus; completes post-translational modifications of proteins from RER; 2 functional sides: cis face (receiving region where transport vesicles merge) and trans face (shipping region at the opposite side)
• Lysosomes


  Membrane-limited vesicles that contain about 40 different hydrolytic enzymes (mostly acid hydrolases); spherical, ~0.05 – 0.5 µm and appear uniformly granular, electron-dense in TEM; sites of intracellular digestion & turnover of cellular components; autophagy: secondary function of lysosomes; excess organelles or large groups of nonfunctional macromolecules in cytoplasm are degraded
• Lysosomal storage diseases


  • Hurler syndrome (MPS I)
  • McArdle syndrome
  • Tay-Sachs
  • Gaucher
  • I-cell disease
• Peroxisomes


  Membrane-bound spherical organelle that contains enzymes (oxidases) producing and degrading H2O2; formed in 2 ways: budding of precursor vesicles from the ER or growth and division of preexisting peroxisomes; major function is to catabolize LFA
• Proteasomes


  Minute abundant non-membrane bound protein complexes that appear cylindrical of (4) stacked rings, each composed of 7 proteins with a regulatory particle at each end; degrades denatured and nonfunctional polypeptides and other proteins; restricts the activity of a specific protein (as individual molecules)
• Secretory Granules


  Condensing vesicles in the GA and are found in cells that store a products until its release by exocytosis; membrane-bound with secretory products; zymogen granules: secretory granules with dense contents of digestive enzymes
• Mitochondria


  Membrane-bound with enzymes needed for aerobic respiration and ATP production (powerhouse of the cell); elongated structures with diameter of 0.5-1µm but lengths of up to 10x greater; highly plastic and changing shape, fusing with other mitochondria, dividing, and moving throughout with microtubules
• Cytoskeleton


  Protein polymers (fibrillar proteins) that determine the shape of cells, movements of organelles and vesicles, and movement of the entire cell; composed of microtubules, microfilaments (actin filaments), and intermediate filaments
• Nucleus


  Largest organelle and usually the most striking feature in LM; contains genetic material (DNA) arranged as chromosomes; contains the genetic blueprint for all proteins and command center of the cell
• Nuclear Envelope


  Selectively permeable barrier between the nuclear and cytoplasmic compartments; composed of 2 membranes separated by perinuclear space, together with outer nuclear membrane, is continuous with the extensive RER cytoplasmic network
• Nucleolus


  Spherical, basophilic subdomain of nuclei in cells actively engaged in protein synthesis; consists of DNA and all other associated proteins involved in the organization and function of DNA
• Chromatin


  Euchromatin: lightly basophilic, finely dispersed; Heterochromatin: coarse, highly basophilic
• Inclusions


  Accumulated metabolites or other substances with little to no metabolic activity; most are transitory structures and are not membrane bound; lipid droplets, glycogen granules, pigments (melanin, lipofuscin, hemosiderin)
• Perinuclear space


  Space between two nuclear membranes, continuous with the extensive RER cytoplasmic network
• Nucleus


  • Spherical, basophilic subdomain of nuclei in cells actively engaged in protein synthesis