Structure of Cell Membrane

B2.1.1-B2.1.3 ,, B2.1.5- B2.1.17

define amphipathic

a molecule that has both hydrophobic & hydrophilic regions

amphipathic molecules (lipids) in a plasma membrane include:

• phospholipids

• cholesterol

describe the polarity and amphipathic(ness) of the plasma membrane

• the core of the plasma membrane is the hydrophobic and non-polar region

• the outer layers (phosphate heads) are hydrophilic & polar regions

what type of molecules do not pass through the plasma membrane

• large molecules

• hydrophilic particles (polar)

• ions

examples of large molecules that have low permeability of the plasma membrane

• proteins

• starch

• glycogen

• cellulose

polar molecules that have low permeability of the plasma membrane

• glucose

• amino acids

define diffusion

net movement of particles (liquid or gases) from a region of higher concentration to lower concentration as a result of a conc. gradient

is diffusion passive or active transport

passive — not energy requiring bc of gradient

what are the two types of proteins in plasma membranes

integral & peripheral

integral proteins (location)

embedded in the phospho bilayer

peripheral proteins

attached to the phospho bilayer surface on one side or the other

structure of glycoproteins

polypeps that have carbohydrate(s) attached

structure of glycolipids

lipids with carbs attached (short chain of1-4 subunits)

roles of glycoproteins & glycolipids

cell adhesion & cell recognition

cell adhesion & glycolipids/proteins

together form a glycocalyx (a carb-rich layer on outer face of animal cell)

• adjacent glycocalyx can fues attaching cells tgthr + preventing tissue from falling apart

cell recognition & glycoproteins & glycolipids

difference in types of glycoproteins and glycolipids within the membrane allows for cell recognition in which are harmful (pathogens) or not

how do particiles dissovle in water

forming H bonds (or other intermolecular interactions) w water molecules

define osmosis

the net movement of water from a region of low solute concentration to high solute concentration across a semi-permeable membrane

what are aquaporins

transmembrane proteins with a pore that allow water molecules to pass across a membrane in either direction — still passive trasnport

define active transport

the movement of substances across membrane using energy from ATP — against a concentration gradient

pump proteins

carry out active transport

• use ATP to transition into the less table orientation (allowing the substance to exit the pump)

• then transition back into the stable orientation — this transition does not requite ATP

channel proteins

carry out facilitated diffusion

• are specific to one type/group of particle(s)

• some channels’ pores can be temporarily closed to control diffusion

describe the structure of a phospholipid

head — phosphate & glycerol (hydrophilic)

tails ; one unsaturated fatty acid chain + one unsaturated fatty acid chain (hydrophobic)

6 functions of membrane bound proteins

1. enzyme activity

2. receptor

3. transport

4. recognition

5. adhesion

6. anchorage

role of cholesterol in membrane @ high temperatures

helps maintain orderly arrangement of phospholipids — prevents too fluidity

role of cholesterol in membrane @ low temps

ensures saturated fatty acids tails do not solidify — prevents viscocity & inflexibility

define endocytosis

formation of vesicles in the cytoplasm by pinching off a piece of plasma membrane

define exocytosis

fusing of vesicles w the plasma membrane, expelling content from the cell