LW

AP Bio Unit 2 AP Classroom

Plasma Membrane

Basics

  • function
    • transport
    • cell-cell recognition
    • enzymatic activity
    • signal transduction
    • intercelular joining
    • attachment for cytoskeleton
  • cell membrane is a barrier
  • structure fluid mosaic model
    • bilayer of phospholipids are fluid
    • not static
    • help by hydrophobic interactions not covalent bonds
    • some lipids/proteins can shift and flow along surface of the membrane/across the bilayer
    • cholesterol, type of steriod, and is wedged in membrane to regulate fluidity depending on environment
    • carbohydrates and lipids are spread out and function as markers
    • glycoproteins - 1+ carbohydrate attached to a membrane protein
    • glycolipid - lipid with a carb attached
  • proteins
    • peripheral proteins
    • loosely bound to surface
    • hydrophilic with charged and polar side groups
    • integral proteins
    • span the membrane
    • hydrophilic with charged and polar side groups
    • hydrophobic with non polar side groups that penetrate bilayer
  • Phospholipids
    • amphipathic = hydrophobic, tails, AND hydrophilic, head.
    • spontaneously form bilayer in an aqueous environment on the inside and outside of membrane

Membrane Permeability

  • selectively permeable
    • small non polar molecules pass freely
    • N2, O2, CO2
    • hydrophillic substance can not move across freely
    • use transport proteins
      • channel proteins -hydrophilic tunnel allows specific target molecules to pass
      • carrier proteins - changes shape to move molecule to one side to other
    • small polar molecules likeH2O can move freely in small amounts
    • structural boundary
    • protects maintains cell shape
    • prevents cellular rupture when high water pressure
    • helps plant stand up against gravity
    • permeable barrier
    • plasmodesmata - small holes between plant cells that allows the transfer of nutrient, waste, and ions
    • cell wall - compromised of complex carbs in plants, fungi, and prokaryotes

Membrane transport

  • concentration gradient - when a solute is more concentrate than another
  • passive transport
    • movement of high to low with no energy needed
    • diffusion - movement of small non polar molecules to pass freely N2, O2, CO2
    • facilitated diffusion - movement of molecules through transport proteins allowing hydrophilic and ion to pass
  • Active transport
    • requires direct energy to move molecules from low to high
    • established and maintains concentration gradients
    • endocytosis -cell uses energy to take in macromolecules by forming vesicles
    • phagocytosis - cell takes in large particles
    • pinocytosis - cell takes extracellular fluid containing dissolved substances
    • Receptor-mediated endocytosis - proteins on cell membrane capture specific molecules
    • exocytosis
    • internal vesicles use energy to fuse with membrane and secrete macromolecules out
    • ex proteins, hormones, waste
    • Cotransport secondary active transport using energy from electrochemical gradient to transport 2 dif ions
    • symport - 2 dif ions move in same direction
    • antiport - 2 dif ions move opposite
    • can be polarized by movement of ions/from electrical chemical gradient due to membrane potential (electrical potential difference)
  • Facilitated diffusion
    • needs transport protein to move from low to high
    • move large and small polar molecules using channel/carrier proteins, large quantities of water using aquaporin, charge ions (Na+ and K+) needs gated ion channel

tonicity/osmosis

  • osmosis
    • is diffusion of free water across membrane
    • large quantities move via aquaporin
    • osmolarity = total solute concentration
    • water has high solvency
    • solute is substance being dissolved
    • solvent is substance that dissolves a solute
  • tonicity
    • measurement of relative concentrations of solute between 2 solutions
    • hypo, iso, hyper
    • water and solute concentration are inversely related since water moves from a lower solute concentration to high
    • in plant cells osmoregulation maintains water balance and allows control of internal solute composition/water potential
    • Environmental hypertonicity or more cell water less cell solute = plasmolysis
    • isotonic solution or equal solute and water = flaccid
    • Environmental hypotonicity or more cell solute and less water = turgid
      • this cause water to flow into plant expanding the cell wall which then exerts pressure on cell aka tugor pressure
      • This is OPTIMUM state for plant cells
    • in animals cells osmoregulation maintains water balance and allows control of internal solute composition/water potential
    • Environmental hypertonicity = shriveled
    • isotonic = normal
    • Environmental hypotonicity = lysed or to burst
  • water potential
    • water potential measure tendency of water to move by osmosis
    • more negative water potential the more likely water will move into the negative area
    • osmoregulation allows organism to control their internal solute composition and water potential
    • water potential and pressure potential directly proportional and amount of solute is indirectly proportional
    • i = ionization constant sucrose = 1 and NaCl=2
    • the addition of solutes = to a more negative solute potential

Cell basics

Sub cellular components

  • all cells have ribosomes and genomes

    • need to store/pass along genetic infro
    • ribosomes synthesize proteins from genome

  • ribosomes not membrane enclosed

  • ER network of membrane tubes

    • mechanical support, transport
    • rough - have ribosome, compartmentalizes the cell, packages proteins made by ribosomes on them
    • smooth - not ribosomes, detoxification and lipid synthesis

  • Golgi complex series of flattened membrane bound sacs

    • correct folding and chemical modifications of proteins and packaging protein
    • UPS of protein trafficking
    • have vesicles - membrane containers move things around cell

  • Lysosomes membrane-enclosed sac containing hydrolytic enzymes

    • Intercellular digestion- damaged cell parts or macromolecules, recycle organic material, programmed cell death aka apoptosis
    • lycel

  • vacuoles membrane sacs

    • storage of water, macromolecules and release of waste, water, macromolecules

    • in plants - aid retention of water for turgor pressure

    • turgor pressure- internal cellular force,

      b has more tp

      b has more tp

  • Mitochondria - capture energy from macromolecules

    • double membrane- out smooth and inside folded so more surface area(more efficent) and separate different metabolic reactions
    • electron transport and ATP synthesis in inner membrane
    • krebs cycle occurs in matrix in-inside

  • chloroplast

    • double membrane
    • capture sun energy and produce sugar aka photosynthesis
    • 2 distict compartments
    • thylakoid - foldable membrane stacks (increase efficiency of reactions) or grana, contain chlorophyll pigments, light-dependent reaction occur
    • Stroma - fluid between inner membrane and thylakoids, carbon fixation reaction occurs

compartmentalization

  • eukaryotic cells have plasma membrane on outside of cell AND have membrane bound organelles
    • this allows for various reactions to occur → more efficient
  • lysosomes contain hydrolytic enzymes with an acidic environment separate from cytoplasm
  • membrane folding in mitochondria or chloroplast allows more atp or photosynthesis processes
  • mitochondria and chloroplast evolved from free living prokaryotes

Cell Size

  • smaller cells have larger SA:V ratio
    • Efficient exchange of materials
    • Small SA:V high demand for resources bc volume is to big for SA
  • increase surface area
    • membrane folding
    • root hairs on plants
    • outer lining of small intestine creates projections or Villi
    • villi have microvilli to increase absorption
    • increase in volume → decrease heat exchange
    • elephant makes up for big ears
    • leaves have stomata-small openings- to efficiently obtain CO2 and release O2 and H2O