chapter 3 (notes)

• Organelle


  Specialized structure in cells that perform specific functions
• Organelles


  • nucleus, mitochondria, ribosomes
• Cell membrane


  Also termed the plasma membrane, a structure that encloses the cytoplasm
• The cell membrane is the outermost component of a cell
• The cell membrane forms a boundary between material inside the cell and the outside
• Materials inside the cell are intercellular and those outside are extracellular
• Cell membrane


  Acts as a selective barrier
• Fluid-mosaic model


  The model used to describe the cell membrane structure
• The cell membrane contains phospholipids, cholesterol, proteins, and carbohydrates
• Phospholipids form a bilayer
• Phospholipids


  Have a polar head region that is hydrophilic and a nonpolar tail region that is hydrophobic
• The polar region is exposed to water around the membrane
• The nonpolar region is facing the interior of the membrane
• Selective permeability


  The cell membrane allows only certain substances to pass in and out of the cell
• Substances such as enzymes, glycogen, and potassium are found in higher concentrations inside the cell
• Substances such as sodium, calcium, and chloride are found in higher concentrations outside the cell
• The vesicle must fuse with the cell membrane for transport
• Passive membrane transport


  Does not require the cell to expend energy
• Active membrane transport


  Does require the cell to expend energy, usually in the form of ATP
• Passive membrane transport mechanisms

  • Diffusion, osmosis, and facilitated diffusion
• Active membrane transport mechanisms


  • Active transport, secondary active transport, endocytosis, and exocytosis
• Diffusion


  Generally involves the movement of substances in a solution down a concentration gradient
• Solution


  Generally composed of two major parts, solutes and the solvent
• Solutes


  The substances dissolved in a predominant liquid or gas, which is called the solvent
• Concentration gradient


  The difference in the concentration of a solute in a solvent between two points divided by the distance between two points
• Concentration gradient


  Is said to be steeper when the distance is large and/or the distance is small
• Leak channels


  Constantly allow ions to pass through
• Gated channels


  Limit the movement of ions across the membrane by opening and closing
• Osmosis


  The diffusion of water (solvent) across a selectively permeable membrane from a region of higher water concentration to one of lower water concentration
• Osmotic pressure


  The force required to prevent movement of water across cell membrane
• Isotonic


  A cell immersed in an isotonic solution has the same solute concentrations inside and outside the cell
• Hypotonic


  A hypotonic solution has a lower concentration of solutes and a higher concentration of water relative to the cytoplasm of the cell
• Hypertonic


  The cytoplasm of a cell in a hypertonic solution has a lower solute concentration and higher water concentration than the surrounding solution
• In a hypotonic solution, water moves by osmosis into the cell, causing it to swell and potentially rupture (lysis)
• In a hypertonic solution, water moves by osmosis from the cell into the hypertonic solution, resulting in cell shrinkage or crenation
• Carrier-mediated transport


  Involves carrier molecules, which are proteins within the cell membrane, to transport water-soluble, electrically charged or large-sized particles that cannot enter or leave through the cell membrane by diffusion
• Substances that require carrier-mediated transport

  • Amino acids, glucose, and some polar molecules produced by the cell
• Carrier-mediated transport mechanisms


  Facilitated diffusion and active transport
• Osmosis


  Water moves by osmosis into the cell, causing it to swell
• Lysis


  If the cell swells enough, it can rupture