What can pass the lipid bilayer? (WEEK 1)

The lipid bilayer is permeable to…

small hydrophobic molecules
small uncharged polar molecules

The lipid bilayer is impermeable to…

large polar molecules
ions

O2

permeable

CO2

permeable

N2

permeable

benzene

permeable

H2O

permeable

glycerol

permeable

ethanol

permeable

amino acids

impermeable

glucose

impermeable

nucleotides

impermeable

H+

impermeable

Na+

impermeable

HCO3-

impermeable

K+

impermeable

Ca2+

impermeable

Cl-

impermeable

Mg2+

impermeable

What makes the lipid bilayer selectively permeable? 

transport proteins

What is the purpose of the cytoskeleton? 3 components of Cytoskeleton are . . .

To provide cell shape and movement; F actin, intermediate filaments, microtubules(tubulin)

F actin (build of, rate limiting step, purpose, size, ATP dependent?) 

• Made up of: ATP bound G-actin subunits

• Rate limiting step: Nucleation 

• Purpose: supports cell’s plasma membrane → microvilli formation

• Size: 7-9 mm 

• ATP dependent; ATP G actin hydrolyzed to add G actin to polar double helical filament

treadmilling

F-ACTIN!!! Cytosolic concentration of ATP-bound G-actin is higher than the critical concentration at the (+) end, and lower than the critical concentration at the (-) end (Cc- > C cyto > Cc+)
no overall filament change 

Profilin

G actin (+) regulator

Adds ATP to G actin

Thymosin

G actin (-) regulator

Deactivates G actin ATP —> No filament growth 

Cofilin

G actin (-) regulator

Destabilizes (-) end of F actin—> (-) end depolymerization

Capping Proteins

Protects F actin (+) end from depolymerization
look at picture (yellow ball) 

Nucleators/Nucleation Promoting Factors/Formins

Formins
Nucleator necessary for the nucleation of actin filaments at (+ end/cell periphery)

look at picture (blue ring)

Arp2/3 complex w/ WASP

Protein complex necessary for formation of branches actin filaments
-associated with (-) end

look at picture (purple ball with orange disk)

What color is F actin out of the 3 cytoskeletal elements?

Red (7-10nm) 
Supports plasma membrane (also microvilli) 

What color is Intermediate Filaments out of the 3 cytoskeletal elements?

Blue (10nm) 
Structural role; found everywhere in the cell
connects between cells 

What color are Microtubules out of the 3 cytoskeletal elements?

Green (25nm) 

nucleated @ Microtubule Organizating Center (MTOC) 

radiates towards cell periphery 

AMINO ACIDS!!! nonpolar, negative, positive, uncharged polar

write out and compare