Biology Notes (Exam Guide 6)

Important features of membrane structure

• fluid mosaic model

• phospholipids

• proteins

• carbohydrates

membrane components

• primarily phospholipids

- phospholipid bilayer forms spontaneously due to amphipathic structure which has polar/non polar sides, they are held together by hydrophobic interactions (Van Der Waals), selectively permeable (blocks some things while letting others in)

transmembrane

span membrane

• some membrane proteins can move, others can’t

functions of membrane proteins

1. transport materials

2. enzymatic activity

3. signal transduction (control time of gene expression)

4. cell-cell recognition

5. intercellular joining

6. attachment to the cytoskeleton and extracellular matrix (ECH)

carbohydrates

• polysaccharides attached to protein (glycoprotein) or lipid (glycolipid), cell identification 

fluid mosaic model

membrane components can move laterally within one layer of the membrane

- lipids, proteins, and carbs

plasma membrane

• selectively permeable and there are 2 basic types of transport

1. passive- doesn’t use metabolic energy (ATP), moves with the gradient (bike downhill)

2. active- does use metabolic energy (ATP), moves against the gradient (bike uphill), from low concentration to high

passive transport

• includes simple diffusion, osmosis, and facilitated (uses protein)

- net movement is down concentration gradient, no ATP required, spontaneous, results in dynamic equilibrium

diffusion 

the tendency for molecules of a substance to fill available space 

- small gases: O2, CO2, and N2

- small non polar molecules: including hydrocarbons

- small polar uncharged molecules: including H20

dynamic equilibrium

no net movement at equilibrium

- different substances diffuse independently

osmosis

diffusion of water accrosss selectively permeable membrane

- water diffuses from lower to higher (solute) or from higher to lower (H2O), salt sucks

ability of a solution to cause a cell to gain or lose water 

1. isotonic solution 

2. hypertonic solution 

3. hypotonic solution 

1. isotonic solution

(equal), (iso=same), the solute outside the cell is the same as the solute inside the cell means there is no net H2O movement

2. hypertonic solution

the solute outside the cell is more than the solute inside the cell

3. hypotonic solution

the solute outside the cell is less than the solute inside the cell

what can’t diffuse directly across a membrane?

• large molecules

• non small polar molecules - hydrophilic

• ions charged

- cells have evolved ways to transport these materials involve transport proteins- several mechanisms

facilitated diffusion

large molecules or ions (H+, Ca2+, Na+) that transport proteins (integral proteins), channel proteins which then (ion channel) , carrier proteins which then specific to what each protein is transporting

active transport

• works against the gradient

• large epolar molecules

• requires ATP

• facilitated by proteins

• carries or pumps or bu;l transport of molecules

- sodium potassium pump: 3 Na+ out, 2 K+ in, establishes electrical gradient

Bulk transport

• type of active transport 

• requires ATP 

• transport many molecules at once with vesicles

• enter/exit cell without crossing through the lipid bilayer 

• exocytosis/endocytosis

exocytosis “out”

things like waste, proteins, and secretory products 

• vesicle fuses with plasma membrane , releases contents from cell

- vesicle fuses with PM which is the primary mechanism for growing plasma membrane 

endocytosis “in

material being taken into cell by forming vesicles from plasma membrane, phagocytosis and pinocytosis

phagocytosis

“cellular eating”, cell engulfs large particle, non specific

pinocytosis 

“cellular drinking”, ingestion of fluid and dissolved material, non specific