LECTURE 2: FUNCTIONS OF CELLULAR MEMBRANES, SOLUTE AND WATER TRANSPORT THROUGH THE MEMBRANE

Question 1

FUNCTION OF PM PROTEINS

Answer 1

Question 2

FUNCTION OF PM LIPIDS

Answer 2

Question 3

CLASSIFICATION OF TRANSPORT PROCESSES THROUGH THE PM

Answer 3

1. SIMPLE DIFFUSION:
   - PASSIVE, DRIVING FORCE= CHEMICAL GRADIENT (CONC. DIFF) I.E FACILITATED DIFFUSION
2. 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

Question 4

MOLECULAR MODELS OF SEVERAL MEMBRANE TRANSPORT PROTEINS

Answer 4

Question 5

CARRIERS FUNCTION DIFFERENTLY TO ION CHANNELS, WHY?

Answer 5

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

Question 6

NB

Classification of membrane carriers

Answer 6

Question 7

mechanism of diffsion?

Answer 7

random movement of solute due to brownian motion

spontaneous process: molecuels move from HIGH to LOW concentration

driven by thermal motion

**Ficks first law**

Question 8

Ficks first law on diffusion

Answer 8

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

Question 9

properties of simple diffusion?

Answer 9

Question 10

protein mediated membrane transport(carriers)

Answer 10

faciliated: integral plasma proteins

Question 11

movement via transport of proteins show saturation kinetics:

Answer 11

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**

Question 12

facilitated transport (f. diffusion)

Answer 12

Question 13

water transport through the membrane

Answer 13

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

Question 14

osmotic water movement and generation of osmotic pressure

Answer 14

** osmosis= lower concentration to higher

Question 15

von hoff’s law of osmotic pressure

nacl contains 145 mM/L

osm?

Answer 15

nacl contains 145 mM/L

= 145x2=290 mOsm/L

Question 16

practice these calculations:

Answer 16

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