Unit 5 - Cell Membrane and Cellular Transport

Phospholipid

Main structural component of cell membrane; hydrophilic phosphate head (1a) and hydrophobic fatty acid tails (1b)

Cholesterol

Provides fluidity to membrane; prevents phospholipid coagulation

Membrane Proteins

Perform various functions; some are along the edge of the membrane (peripheral proteins 3b); some are within the bilayer (integral proteins 3a)

Glycocalyx

Surface “fuzz” involved in cell to cell recognition; made of short carbohydrate chains (oligosaccharides 4) attached to proteins (glycoproteins 5a) and lipids (glycolipid 5b)

Channel Protein

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

Enzyme

Enzymes 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”

Isotonic Environment

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

Hypotonic Environment

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)

Isotonic environment example

Environment: 95% H2O, 5% solute

Cell: 95% H2O, 5% solute

Hypotonic environment example

Environment: 99% H2O, 1% solute

Cell: 95% H2O, 5% solute

Hypertonic environment example

Environment: 75% H2O, 25% solute

Cell: 95% H2O, 5% solute

Hypertonic

More solute

Hypotonic

More water

Osmosis

Passive Transport of water across a membrane from high concentration to low concentration (hypotonic to hypertonic)

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 turgor pressure

Plasmolysis

shrinking of a Cell from loss of water in a hypertonic environment

Cytolysis

swelling and bursting of a cell caused by internal pressure

Active Transport

passage of a substance across a semi-permeable membrane that requires the use of ATP energy. May also be the movement of materials against the concentration gradient or movement of molecules two 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

Example: Sodium-Potassium Pump

Endocytosis

Taking in large molecules by a cell without moving through pores of the cell membrane. Formation of vesicles as the cell membrane pinches around the substance

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 without going through pores of the cell membrane. Vesicles fuse with the cell membrane as the molecule is released outside the cell

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

Rate of Diffusion

Due to diffusion pressure, mass of molecule, and temperature

• Fast diffusion: low mass + high temp

• Slow diffusion: high mass + low temp

Semi-permeable membrane

• lets only selected substances through

• based on size and polarity of molecules

Facilitated diffusion

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

Factors affecting rate of diffusion

• mass of particle

• Concentration Gradient

• Temperature

Factors affecting the ability to diffuse

• Molecular volume

• Polarity

Plasma membrane

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

Phospholipid

Specialized triglyceride that makes up most of the membrane