Ch 6) Cell Membranes

how are the structure of biological membranes described?

fluid mosaic model

what is the structure of a phospholipid?

hydrophilic head and a hydrophobic fatty acid tail. They all vary in fatty acid chain length, degree of unsaturation, and phosphate groups

what is characteristic of the inside of a cell membrane?

it is somewhat fluid which allows for lateral movement of molecules

what does phospholipid membrane fluidity depend on?

lipid composition and temperature, cholesterol and saturated fatty acids pack tightly which makes the membrane less fluid, and unsaturated fatty acids create kinks in the chain because they are less tightly bonded together

what is needed to maintain constant cell fluidity in the cell membrane

more saturated fatty acids at higher temperatures

how does membrane fluidity decrease as temperature drops?

organisms change the lipid content of cell membranes when they get cold, replacing saturated with unsaturated fatty acids and using fatty acids with shorter tails.

what is a peripheral membrane protein?

lack hydrophobic regions and do not penetrate the bilayer

what is an anchored membrane protein?

covalently attached to fatty acids or other lipids

what is a transmembrane protein?

extend all the way through the phospholipid bilayer, can have different domains called transmembrane domains

what serves as a recognition site for other cells and molecules?

Glycolipids—carbohydrate + lipid

Glycoproteins—carbohydrate

(oligosaccharide) + protein; proteo-

glycans have a higher percentage of

carbohydrates.

how do cells arrange themselves?

by cell recognition and cell adhesion (using those glycolipids and glycoproteins)

what is a cell junction?

specialized structures that hold cells together

what does a tight junction do?

helps ensure directional movement of materials

what does a desmosome?

provides structural security and tensile strength

what does a gap junction do?

connect the cytoplasm of adjacent cells which allows for communication

what does the protein integrin do?

it is a transmembrane protein that binds to the matrix outside epithelial cells and to actin filaments inside the cell

what is passive transport?

no energy input is required as it uses a concentration gradient

what is active transport?

energy is required (ATP) and movement of substances against a concentration gradient occurs, is directional

what is diffusion?

random movement towards equilibrium, it goes from high concentration to low concentration

what does diffusion rate depend on?

• Size and mass of the molecules or ions

• Temperature of the solution

• Density of the solution

• Concentration gradient

• Area and distance

Number of carrier proteins in the cell membrane

what is simple diffusion?

small molecules pass through the lipid bilayer

what can diffuse across the cell membrane?

lipid soluble molecules

what cannot diffuse across the cell membrane?

electrically charged and polar molecules

what is osmosis?

diffusion of water

what does osmosis depend on?

the relative concentration of water molecules

what is an isotonic solution?

equal concentrations of solute and solvent

what is a hypertonic solution?

higher solute concentration than solvent

what is a hypotonic solution?

higher solvent concentration than solute

what is facilitated diffusion?

polar and charged molecules diffuse with concentration gradients and channel proteins or carriers

what is a channel protein?

integral membrane proteins that form a tunnel

what is a carrier protein?

bind some substances and speed their diffusion through the bilayer

what are the three proteins involved in active transport?

• Uniporter—moves one substance in one

direction.

• Symporter—moves two diff substances in

one direction.

• Antiporter—moves two diff substances in

opposite directions.

what is primary active transport?

requires the hydrolysis of ATP

what is secondary active transport?

uses its energy from the primary active transport

what is a sodium potassium pump?

pumps 2 K+ ions into the cell for every 3 Na+ ions outside of the cell, example of primary active transport

secondary active transport example

sodium-potassium pump, passive diffusion of some sodium back into the cell from the concentration gradient provides energy which is used for the transport of glucose into the cell

how do macromolecules enter and leave the cell?

through membrane vesicles

what is endocytosis?

bring molecules and cells into a eukaryotic cell, the cell membrane folds inward around the material

what is phagocytosis?

molecules or entire cells are engulfed, a food vacuole (phagosome) fuses with a lysosome to digest the contents of the phagosome

what is pinocytosis?

vesicle forms to bring small dissolved substances or fluids into the cell, vesicles are smaller than the ones found in phagocytosis

what is receptor mediated endocytosis?

macromolcules are brought into the cell via binding to receptors

what is exocytosis?

materials packaged in vesicles exit the cell membrane by the vesicle contacting the cell membrane