Plasma membrane

Fluidity Mosaic • Hydrophobic interactions (weak)

• Lateral movements of PL (not fixed)

• Asymmetrical protein embedding

• Many functions of proteins

Factors Affecting Fluidity Of Membrane1) Temperature

temp kinetic energy lateral motion fluidity• Low temp – gel phase (phase transition)• High temp – fluid phase

2) Length of FA length hydrophobic interXn heat energy meltg pt• > Solid / gel like at room temperature

3) Degree of FA saturation saturation kinks packing fluidity

4) Amt of cholesterol mol (intracellular membranes= rare) stability

• Chol intercalated/wedged in PM, enhancing mechanical stability• Regulates Fluidity (Dual effects on the fluidity – temp buffer)

• High temp = interfere w PL’s motions, so fluidity• Low temp = packing of PL = fluidity

• Affects permeability11 permeability by filling in spaces, so plugging transient gaps 2) Prevent small polar mol & ions from going thru

*** Transport across Membranes ***cell = s + p

The net movement of freely moving water mol from a region of LESS NEGATIVE water potential to a region of MORE NEGATIVE water potential through a selectively permeable membrane

0-20 -40

Water potential

[solute]

Hypotonic Isotonic HypertonicLess Neg Equal More Neg

- H20 > -

- H20 enters

- lysis

- H20 =

- No net change in cell volume

- H20 < -

- H20 leaves

- shrivelled

- H20 > -

- H20 enters

- Turgid

- H20 =

- No net change in cell volume

- H20 < -

- H20 leaves

- Flaccid /

plasmolysed

Cell Wall

Maintains shape

10nm

amphipathic

hydrophillic hydrophobic

Intrinsic/Integral

• largely hydrophobic

• Deeply embedded

• Weak hydropho interXn

• protein can move (fluidity)

• Detergents & solvents

Peripheral

• hydrophillic

• loosely bound

• cytoskele of cell

• ECM’s fibres

• pH / ionic changes

Stabilize PM & shape

anchorage recognition enzymatic receptor joining

Cell identity3 f(x)

sequential Chem signals communication

1 protein may more than 1 function

p= pressure the wall is exerting on the cell’s content, pushes water out, so its (+)

s : affected by [solute]

Hydrophobic

O2, CO2 N2 Benzene, H2O

Small Uncharged Polar

Urea, glycerol, H2O

Charged Polar

H+ Na+ HCO3- K+

CA2+ Cl- Mg2+

Large Uncharged Polar

Glucose, Sucrose

- Concentration gradient concentration = rate

- DISTANCE over wh diffusion occurs ↓ distance = rate

- AREA across wh diffusion occurs area = rate

- STRUCTURE through wh diffusion occurs

# of pores/ channels / carriers = rate

- SIZE and TYPE of diffusing molecule ↓ size = rate

- Temperature Temperature = KE = rate

Factors affecting diffusion rate

Bulk transport

Facilitated diffusionDiffusion/

osmosis

Active

GatedChannel

Passive

Uniport

Symport

Antiport

Specific binding sites

Transport Proteins

• Help polar mol cross hydrophobic PM

• mol move down or against conc grad

• specificity makes PM specific in transport jobs

Active Transport

Ingestion of bact by wbc Mucus secretion Ca2+ secretion

KIV nervous system

‘nursing’ of human egg cells

Cholesterol uptake

KIV cell signaling & homeostasis

Na+/K+ pump

Proton Pump

Glu pump

Conformation change

• http://www.youtube.com/watch?v=vh5dhjXzbXc

• http://www.youtube.com/watch?v=ldRZcmppQM8&feature=PlayList&p=5873AAE7F8787C04&playnext=1&playnext_from=PL&index=5