Unit 5 – Cell Membrane and Cellular Transport

Plasma Membrane

controls the movement of materials in/out of the cell; key regulation of homeostasis of cell and maintenance of life functions

Phospholipid

1.  specialized triglyceride that makes up most of the membrane 

Plasma membrane Structure/ Proteins

multiple other structures reside within the plasma membrane to aid its function

Phospholipid Function:

Main structural component of the cell membrane

Cholesterol

Provides fluidity to membrane; prevents phospholipid coagulation

Membrane Proteins

Perform various functions; some are along the edge of the membrane (peripheral proteins); some are within the bilayer (integral proteins)

Glycocalyx

Surface “fuzz” involved in cell to cell recognition; made of short carbohydrate chains (oligosaccharides) attached to proteins (glycoproteins) and lipids (glycolipid)

Channel Protein

Provides passage of small, polar molecules across membrane by simple diffusion; substances pass through the channel unimpeded by nonpolar region

Enzyme

promote chemical reactions; found as integral or peripheral proteins

Carrier Protein

Facilitate passage of large and/or polar molecules through membrane; may function via simple diffusion (passive transport) or by ATP (active transport)

Marker Protein

Specialized protein involved in cell to cell recognition; help form the glycocalyx

Receptor Protein

Specialized protein involved in “Receptor mediated endocytosis”

Passive Transport

movement of materials across a membrane which requires no energy other than kinetic energy of molecules

 Simple Diffusion

- driven completely by kinetic energy of particles

- may or may not include a membrane

- movement of materials from area of high concentration to area of low concentration

Concentration Gradient

exists when there is a difference in concentrations over a distance or across a membrane

Equilibrium

No concentration gradient; equal concentrations

Rate of  Diffusion Caused by

due to diffusion pressure, mass of molecule, and temperature

Semi-permeable membrane

- lets only selected substances through

- based on size and polarity of molecules

Factors affecting rate of diffusion

Mass of Particle

Concentration Gradient

Temperature

Factors Affecting Ability to Diffuse:

Molecular Size

Polarity

Facilitated Diffusion

form of passive transport in which substances move from an area of high conc. to an area of low conc. with the assistance of proteins within the membrane

Osmosis

passive transport of water across a membrane from high concentration to low concentration

Isotonic Environment

state of equilibrium, equal concentrations throughout, both inside and outside the cell.  No concentration gradient exists, zero diffusion pressure.

Hypotonic

concentration of solutes outside is lower than concentration of solutes inside the cell (therefore water is greater outside)

Hypertonic Environment

concentration of solutes outside the cell is greater than the concentration inside the cell (therefore water outside is less)

Turgor Pressure

pressure that builds up in a cell due to the inward flow of water; some organisms use a contractile vacuole to expel excess water to lessen this

Plasmolysis

shrinking of a cell from loss of water

Cytolysis

 swelling and bursting of a cell caused by internal pressure

Active Transport

passage of a substance across a semipermeable membrane that requires the use of ATP energy.  May also be the movement of materials against the concentration gradient or movement of molecules too large for the membrane pores.

. Ion Pumps

• carrier proteins used to move ions across the membrane against the concentration gradient

• - conformational change of carrier proteins require ATP

- used to maintain steep concentration gradient of ions across a cell membrane

 Endocytosis

taking in large molecules by a cell w/out moving through pores of the cell membrane.  Formation of vesicles as the cell membrane pinches around the substance.

Receptor–Mediated Endocytosis

acquiring specific materials from. the environment through use of receptor proteins found at specific sites (coated pits) on the outer surface of the cell membrane

Phagocytosis

engulfing whole cells or one-celled organisms; formation of vacuoles, broken down by digestive enzymes of lysosome

Pinocytosis

taking in liquids or dissolved solutes by a cell; formation of vacuoles, broken down by digestive enzymes of lysosome

Exocytosis

passage of large molecules to the outside of the cell w/out going through pores of the cell membrane.  Vesicles fuse with the cell membrane as the molecule is released outside the cell

Endomembrane System:

The fluid plasma membrane works in conjunction with all other membrane bound organelles to promote both exocytosis and endocytosis of materials.