Ch. 3

1. Cell:

   1. Basic unit of life composed of a plasma membrane and cytoplasm, includes a nucleus and cytoplasmic organelles

2. Plasma (cell) membrane:

   1. Outer boundary that allows the cell interaction with its external environment

3. Cytoplasm

   1. Located between the plasma membrane and the nucleus

   2. Contains organelles that perform specific functions

4. Nucleus

   1. Directs cell activities

Functions of Cell

1. Metabolism and energy use

2. Synthesis of molecules

3. Communication

4. Reproduction and inheritance

Plasma Membrane

1. Function

   1. Boundary separating intracellular substances from extracellular environments

   2. Encloses and supports cell contents

   3. Attaches to the extracellular membrane or other cells

   4. Ability to recognize and communicate with other cells

   5. Determines what moves in and out of cells

2. Parts

   1. Phospholipid Bilayer

      1. Polar heads facing water in the interior and exterior of the cell (hydrophilic)

      2. Nonpolar tails facing each other on the interior of the membrane (hydrophobic)

   2. Cholesterol

      1. Interspersed among phospholipids

      2. Amount determines the fluid nature of the membrane, providing stability to the cell.

   3. Integral Membrane Proteins

      1. Extend deeply into the membrane, often extending from one surface to another

      2. Can form channels through the membrane

   4. Peripheral Membrane Proteins

      1. Attached to integral proteins at either the inner or outer surfaces of the lipid bilayer or to polar heads of phospholipids

      2. Functions depend on 3-D shape and chemical characteristics

         1. Can be markers, attachment sites, channels, receptors, enzymes, or carriers

   5. Channel Proteins

      1. Integral membrane proteins that form tiny channels through membrane

      2. Channel determines the size, shape, and charge of what can pass through

      3. The charge of the hydrophilic tunnel determines the types of ions that can move through

   6. Enzymes

      1. Some act to catalyze reactions at outer/inner surface plasma membrane

      2. Some membrane-associated enzymes are always active while others are acitve by receptors or G protein complexes

3. Movement

   1. Plasma membrane is selectively permeable

      1. Only allows specific substances to pass through

      2. Must maintain homeostasis through the composition inside and outside the cell are different

   2. Passive transport

      1. Cell does not expend energy

      2. Movement from higher conc. to lower conc.

         1. Diffusion

            1. Movement of a substance from an area of high conc. to one of low conc.

            2. Net movement of solutes from an area of higher conc. to lower conc. in a solution

            3. Concentration Gradient

               1. Concentration difference between 2 points

               2. Solutes move down their conc. gradient until and equilibrium is established

         2. Osmosis

            1. Diffusion of water (solvent) across a selectively permeable membrane

            2. Aquaporins

               1. Water channel proteins

            3. Osmotic Pressure

               1. Force require to prevent water from moving across a membrane by osmosis

            4. With Cells

               1. Isotonic

                  1. Cell neither shrinks nor swells when places in a solution

               2. Hypertonic

                  1. Cell shrinks when placed in solution; water to move out of cell

               3. Hypotonic

                  1. Cell swells and may rupture (lyse) when in a solution; water moves into cell

         3. Facilitated diffusion

            1. Mediated transport process carried out by carrier/channel proteins; no ATP required

            2. Move large, water-soluble molecules or electrically charged molecules across a plasma membrane

            3. Amino acids and glucose in, manufactured proteins out

   3. Active Transport

      1. Requires energy to move from a lower conc. to a higher conc.

      2. Active transport

      3. Secondary active transport

         1. Use of potential energy in concentration gradient of one substance (established by primary transport) to help move another substance

   4. Vesicular Transport

      1. Uses membrane-bound sac

      2. Movement of larger substances by formation or release of a vesicle

      3. Endocytosis

         1. Movement into cell

         2. Phagocytosis

            1. Solid particle is ingested and large vesicle is formed

         3. Pinocytosis

            1. Dissolved molecules ingested and small vesicles are formed

      4. Exocytosis

         1. Movement out of cell