bio quiz

• Plasma membrane


  A thin barrier that forms a boundary, separating an individual cell from the external environment
• Plasma membrane


  • Described as fluid mosaic
  • Lipids and proteins can move relative to each other within the membrane
• Components of the cell membrane

  • Phospholipids
  • Proteins
  • Carbohydrates
  • Cholesterol
• Phospholipids


  A molecule consisting of glycerol, two fatty acids and phosphate-linked head group
• Amphiphilic


  A molecule with the arrangement of a positively or negatively charged area and an uncharged, or non polar area
• Proteins in the plasma membrane

  • Integral proteins
  • Peripheral proteins
• Integral proteins


  • Integrated completely to the membrane structure
  • Single-pass integral membranes usually have hydrophobic transmembrane segment that consist of 20-24 amino acids
  • Complex proteins are composed of up 12 segments of a single protein, which are extensively folded and embedded in the membrane
• Peripheral proteins


  • Found on exterior and interior surface of membranes, attached either to integral proteins or phospholipids
  • Sometimes referred to as "cell-specific" proteins
• Carbohydrates in the plasma membrane

  • Always found on the exterior surface of cells and are bound either proteins (forming glycoprotein) or to lipids (forming glycolipids)
  • Composed of 2-60 monosaccharide units and can be either straight or branched
  • Form specialized sites on the cell surface that allow cells to recognize each other
• Glycocalyx


  The carbohydrates in the exterior surface of the cell - components of both glycoprotein and glycolipids
• Glycocalyx


  • Highly hydrophilic and attracts large amount of water to the surface cell
• Cholesterol


  • Composed of four fused carbon rings
  • Found alongside the phospholipids in the core of the membrane
• Factors that affect a molecule's ability to cross the cell membrane


  • Size (macromolecules and micromolecules)
  • Charge (non-polar and polar molecules)
  • Solubility (lipid-soluble molecules or not)
• Cell membrane


  • Provides structure for the cell, protects cytosolic contents from the environment, and allows cells to act as specialized units
  • Determines what molecules can move into or out of the cell, and so is responsible for maintaining the delicate homeostasis of each cell
• Some cells function best at a pH of 5, while others are better at pH 7
• The steroid hormone aldosterone is made in the adrenal gland, but affects mostly the kidney
• Sodium is more than ten times more concentrated outside of cells rather than inside
• Cell membranes are semipermeable, meaning they have control over what molecules can or cannot pass through
• Ways molecules can move across a membrane

  • Passive mechanisms (diffusion)
  • Active transport (requires energy)
• Diffusion


  The movement of particles down their gradient (an imbalance in concentration)
• Simple diffusion


  Molecules move down their gradients through the membrane without requiring energy
• Facilitated diffusion


  Diffusion that is helped along by a membrane transport channel (glycoproteins)
• GLUT4


  A glucose transporter found in fat and skeletal muscle that is triggered by insulin to insert into the membranes so glucose can be taken in from the blood
• Active transport


  Movement of molecules against their gradient, using energy (ATP) to power the transport
• Sodium-potassium pump (Na+/K+ ATPase)


  A protein that uses the energy released from hydrolysis of ATP to pump three sodium ions out of and two potassium ions into the cell
• Secondary active transport


  Moves multiple molecules across the membrane, powering the uphill movement of one molecule(s) (A) with the downhill movement of the other(s) (B)
• Symporter


  A secondary active transporter that allows molecules to go in the same direction
• Antiporter


  A secondary active transporter that allows molecules to go in opposite directions
• Sodium/calcium exchanger


  An antiporter used to restore cardiomyocyte (heart cell) calcium concentrations after an action potential
• Digoxin


  A heart disease medication that inhibits the sodium/potassium pump, leading to the accumulation of intracellular sodium and causing the sodium/calcium pump to change directions, making heart contractions stronger
• Semipermeable


  A trait of cell membranes that allows some substances to pass through while preventing others
• Forms of passive transport

  • Diffusion
  • Facilitated diffusion
  • Osmosis
• Diffusion


  Molecules move across a membrane from an area of high concentration to an area of low concentration, down a concentration gradient, until equilibrium is reached
• Facilitated diffusion


  Occurs when an ion or molecule diffuses across a membrane faster than expected, either through a specific channel protein or with the assistance of carrier proteins that change shape
• Osmosis


  Diffusion of water across a membrane, facilitated by specialized proteins called aquaporins
• Active transport


  Requires energy in the form of ATP to pump molecules or ions from an area of low concentration to an area of high concentration
• Pumps


  A form of protein which force molecules or ions to move against their concentration gradient
• Bulk transport


  Movement of larger substances into or out of the cell, using vesicles
• Types of endocytosis


  • Phagocytosis (large particles like bacteria or food)
  • Pinocytosis (small liquid or particle uptake)
  • Receptor-mediated endocytosis (molecules bind to specific receptors)
• Exocytosis


  The opposite of endocytosis, where membrane-bound vesicles fuse with the plasma membrane and release their contents to the outside of the cell