LECTURE 2: FUNCTIONS OF CELLULAR MEMBRANES, SOLUTE AND WATER TRANSPORT THROUGH THE MEMBRANE Flashcards
FUNCTION OF PM PROTEINS
FUNCTION OF PM LIPIDS
CLASSIFICATION OF TRANSPORT PROCESSES THROUGH THE PM
- SIMPLE DIFFUSION:
- PASSIVE, DRIVING FORCE= CHEMICAL GRADIENT (CONC. DIFF) I.E FACILITATED DIFFUSION - PROTEIN MEDIATED MEMBRANE TRANSPORT:
- SOLUTE CARRIERS (FACILITATED DIFF)
- ATP DEPENDENT CARRIERS (PUMPS)
- H20 CHANNELS
3. VESICULAR TRANSPORT - ENDOCYTOSIS (PINOCYTOSIS, PHAGOCYTOSIS, RECEPTOR MEDIATED ENDOCYTOSIS)
- EXOCYTOSIS
****O2, CO2, NO****
*****UREA, HYDROPHOBIC HORMONES****
NOT PEPTIDES, NOT PROTEINS, NOT DISACCHARDIES
MOLECULAR MODELS OF SEVERAL MEMBRANE TRANSPORT PROTEINS
CARRIERS FUNCTION DIFFERENTLY TO ION CHANNELS, WHY?
channel=gate
carrier= enzyme- facilitated (PASSIVE) or active transport (ENERGY METABOLISM)
*DIRECT=primary active pump
*INDIRECT= secondray active pump; ie. works together with a pump
NB
Classification of membrane carriers
mechanism of diffsion?
random movement of solute due to brownian motion
spontaneous process: molecuels move from HIGH to LOW concentration
driven by thermal motion
**Ficks first law**
Ficks first law on diffusion
Movement of molecules across membrane
Diffusion coefficient takes into a/c thermal energy of the molecule
diffusion depends on: hydrophobicity and SIZE of molecule!!!
-spherical molecules: D= stokes einstein equation
properties of simple diffusion?
protein mediated membrane transport(carriers)
faciliated: integral plasma proteins
movement via transport of proteins show saturation kinetics:
because the value of km, the cells that have glucose transporter have glucose in the whole range!
cells with GLUT 1: glucose all the time e.g. RBC always has GLUT 1=> always supplied by glucose
GLUT 2: km value increases: only saturated because of physiological range of glucose
rate of diffusion: depends if glucose high or low
Beta cells of pancreas (glucose sensor cells)
GLUT 4: insulin senstive cells= localisation of PM if glucose present (allowing glucose uptake= pulls glucose from RBC
**skeletal muscle, adipocytes**
facilitated transport (f. diffusion)
water transport through the membrane
permeability of lipid bilayer is low because hydrophobic cells
**aquaporins arer a protein tht provide H20 across PM**
**osmosis= h20 flows from LOWER conc. to HIGHER
osmotic water movement and generation of osmotic pressure
** osmosis= lower concentration to higher
von hoff’s law of osmotic pressure
nacl contains 145 mM/L
osm?
nacl contains 145 mM/L
= 145x2=290 mOsm/L
practice these calculations:
tonicity of solution:
isotonic solution= when cell volume does not change
hypertonic= shrinking
hypotonic= swelling and lysis
***isoosmotic urea= lysis and swelling! —>does not pass PM (ineffective osmole)
***nacl and sucrose= isotonic
