CELLS

• Cells


  The basic living units
• 3 Major Parts of Cells

  • Plasma Membrane
  • Cytoplasm & Organelles
  • Nucleus

  
• Plasma Membrane


  • Outer surface of the cell
  • Separates intracellular from extracellular

  
• Cytoplasm & Organelles


  • Contents between the membrane and nucleus
  • Have distinct jobs for the cell
• Nucleus


  • Largest organelle
  • Contains most of the genetic material
• Over 250 types of cells in the body with a variety of shapes, sizes, and functions
• An average adult has ~ 37,000,000,000,000 cells in their body
• Cyto-


  Means "cell"
• Extracellular Materials


  • Body Fluids
  • Cell Secretions
  • Extracellular Matrix

  
• Body Fluids act as transport and dissolving media
• Cell Secretions aid in lubrication and digestion
• Extracellular Matrix is a gelatinous composition of proteins & polysaccharides organized in a mesh holding cells together

  
• Total body mass is 45% solids and 55% fluids for females, and 40% solids and 60% fluids for males

  
• Total body fluid is 67% intracellular and 33% extracellular

  
• Extracellular fluid is 80% interstitial and 20% plasma
• Plasma Membrane


  Separates intracellular fluid from extracellular fluid
• Plasma Membrane


  • Can best be depicted as the fluid mosaic model - phospholipid bilayer with proteins

  
• Multiple Functions of the Plasma Membrane

  • Mechanical Barrier
  • Selective Permeability
  • Cell Communication
  • Cell Signaling
  • Electrochemical Gradient
• Plasma Membrane Lipids


  • Phospholipids (saturated or unsaturated)
  • Cholesterol
  • Glycolipids (part of glycocalyx)
• Phospholipids


  • Polar phosphate group, non-polar fatty acid tails
  • On both inner and outer membrane surfaces
  • Comprise ~75% of membrane lipids
• Cholesterol


  • Hydrocarbon rings are between phospholipid tails
  • Stabilizes the membrane, phospholipid mobility and, thus, membrane fluidity
  • Comprise ~20% of membrane lipids
• Glycolipids


  • Polar sugar groups, non-polar fatty acids
  • Only on outer membrane surface
  • Comprise ~5% of membrane lipids
• Plasma Membrane Proteins


  • Integral Proteins
  • Glycoproteins (part of glycocalyx)
  • Peripheral Proteins

  
• Integral Proteins


  • Firmly inserted transmembrane proteins
  • Include transporters, receptors, and enzymes
• Glycoproteins


  • Abundant proteins with sugar groups
  • Cell-cell interactions and cell-cell recognition
• Peripheral Proteins


  • Loosely attached to integral proteins
  • Include cytoskeleton and extracellular matrix proteins, and motor proteins
• Blood Types


  • Type O
  • Type A
  • Type B
  • Type AB

  
• Plasma Membrane Junctions


  • Tight Junctions ("Impermeable")
  • Gap Junctions ("Communication Nexus")
  • Desmosomes ("Anchoring")
• Tight Junctions


  • Occludins in membranes of adjacent cells fuse together, forming mostly impermeable junctions that encircle each cell
• Gap Junctions


  • Membranes of adjacent cells are very close and connected by connexons
• Desmosomes


  • Two parts arise from cytoplasmic plaques: 1) intermediate (keratin) filaments 2) linker (cadherin) proteins
  • 3 factors bind cells together: 1) glycocalyx 2) wavy shape of cell membranes 3) cell junctions
• The plasma membrane is selectively permeable
• Because of the selective permeability of the membrane


  The "recipe" for fluids inside & outside the cell membrane are different
• Cells are like salty bananas
• Resting Membrane Potential


  • Difference in electrical charge between two points referred to as potential (voltage)
  • Voltage occurs only at membrane surface; the rest of cell and extracellular fluid are neutral
  • Membrane voltages range from -50 to -100 mV in different cells

  
• Resting membrane potential is negative because: 1) There is a net loss of 1 positive ion per pump (3 positive out, 2 positive back in) 2) Many negatively charged proteins inside
• Resting membrane potential is maintained through the action of Na+-K+ pumps, which continuously eject 3 Na+ out of the cell and bring 2 K+ back inside
• Gradients Used for Transport

  • Chemical (Concentration) Gradients
  • Electrical Gradients
  • Electrochemical Gradients
• No energy is required for transport down chemical, electrical, or electrochemical gradients
• Transport Through the Plasma Membrane

  • Passive Transport
  • Active Transport