Cell Membrane Strucutre n 1 Phospholipid bilayer n

Cell Membrane Strucutre n 1. Phospholipid bilayer n a. hydrophilic heads point out (phosphate) n b. hydrophobic tails in center (fatty acid) n c. amphipathic (both philic and phobic) n c. held together by hydrophobic interactions n d. capable of rapid lateral movement

Selective Permeability n A) Molecules can pass through membrane phospholipids on their own n i) small or non-polar (H 2 O, O 2, CO 2, Lipids) n n ii) Large polar molecules get through only very slowly (glucose) or via transport proteins iii) ions seldom cross on their own n B) More rapid transport requires proteins

Cell Membrane Structure n 2. Cholesterol n a. found in animal cells n b. maintains membrane fluidity n 1. high temp restrains p-lipid movement n n 2. low temp: prevents close packing

Cell Membrane Structure n 3. Membrane Proteins a. Integral (penetrate into CM) n some are transmembrane n b. Peripheral n May be held in Place by cytoskeleton Or ECM n n (Extracellular matrix)

Membrane Proteins (p 97) 1. Membrane Enzymes n a. often grouped in teams n b. active in metabolism n c. bind to cytoplasmic substrates

Membrane Proteins 2. Attachment proteins n a. bind to ECM n b. bind to cytoskeleton n c. maintain cell shape and location n d. non-covalent bonds

Membrane Proteins 3. Recognition proteins/lipids n a. sort cells in embryo n b. immune system self-recognition n c. often glycoproteins (glycolipids) n d. differ between species, individuals, cell types n e. A B O blood types

Membrane Proteins 4. Intercellular Joining n a. gap junctions n b. adhering junctions n

Membrane Proteins 5. Receptor Protiens aid Signal Transduction a. receptors – bind to chemical messenger (hormones, c. AMP) n b. binding signal molecule changes protein shape n c. signals inside of cell by binding cytoplasmic protein causing transduction

Receptor Protein example

G protein example

Membrane Proteins 6. Transport proteins n a. channel proteins (aquaporin) n b. carrier proteins (glucose transporter & protein pumps) n c. all are specific

2 Types of Cellular Transport n n 1) Passive Transport = no energy needed mol. flow high concentration low conc. 2) Active Transport = n takes energy n molecules pumped n Low conc. high conc. n n Exocytosis/endocytosis

3 Types of Passive Transport n n all high conc. low conc. due to… a) potential energy of concentration gradient b) thermal energy causing Brownian motion. n 1) n n 2) n n 3) n Diffusion (any molecule, random motion) Facilitated Diffusion (diffusion through channel protein) Osmosis (diffusion of water through membrane)

1. Diffusion n Dynamic equilibrium = no net movement

2. Facilitated Diffusion n Molecules too big /polar / charged n must go through transport protein. Either n Channel protein or carrier protein n (aquaporin) (glucose carrier) n Some channel proteins gated

3. Osmosis n Diffusion of water n must cross a membrane

Tonicity = n Ability of surrounding solution to make a specific cell gain or lose water n No net movement = n isotonic (same solute) n Water moves into cell = n hypotonic solution (less solute in solution) n Water moves out = n hypertonic solution (more solute in solution)

Osmoregulation n Control of solute and water concentrations inside a cell n Contractile vacuoles n aquaporin

Diffusion Rates Affected by: n 1. concentration n 2. size of molecule n 3. temperature n 4. electric gradient n 5. pressure gradient n 6. # pores

3 Types of Active Transport can be low conc. high conc. n All require energy input n Pumps move individual molecules n Endo/exocytosis do ‘bulk transport’

n Transport 1. Protein Pumps proteins that require energy n Protein pushes molecules into areas where they are in high concentration. n ATP is the energy used n Proton pumps Pump H+ ions

2. Exocytosis n How n n n cells secrete materials like hormones a. transport vesicle buds from golgi body b. vesicle moved to C. M. by motor protein c. vesicle fuses with CM d. contents spill out into extracellular space

Endocytosis n Cell takes in molecules by forming new vesicles at CM n a. phagocytosis = takes in food n b. pinocytosis = takes in water n c. receptor mediated = triggered by molecule binding to membrane receptor n * helps concentrate rare molecules