Membranes

ANSC 360 - anatomy and physiology

what are membranes composed of

Phospholipids

what do the membrane phospholipids consist of

diacylglycerol, nitrogen, phosphate

what is an example of a phospholipid

phosphatidyl choline

which part of a phospholipid is hydrophilic

head

which part of a phospholipid is hydrophobic

tail

what are the three sponateously aggregate phospholipid shapes

Micelles, Bilayers, Liposomes

What do micelles look like

-spheres

-heads on surface

-tails inside

-complete sphere not hollow

What do bilayers look like

-sheets

-tails inside

-heads on surface

-very simple membrane

-about 10nm thick

what are Liposomes like

-spheres

-formed by closing of a bilayer

-water trapped inside and surrounding outside

-heads are in contact with water

-represents a simple cell

what two other components do natural membranes contain

cholesterol and proteins

what does cholesterol do in a membrane

intercalates between tails

binds them together

structure

what do proteins do in a membrane

inserted into membrane

partial or spanning

carry out membrane processes

what is the fluid mosaic model

a sea of phospholipids with ships of proteins floating around in it

what substances can pass through a membrane

hydrophobic and non-polar molecules

• O2, N2, lipids

small uncharged polar molecules

• H2O, CO2, glycerol, urea

what substances cannot pass through a membrane

large polar molecules

• sugars, amino acids

Ions

• H+, Na+, K+, HCO3-

what are the two types of transport proteins

channel proteins

carrier proteins

What are channel proteins like

aqueous pathways through membrane

molecules diffuse based on concentration

what are the two subtypes of channel proteins

1. open (leak)

• always open

• molecules pass at will if a gradient

• tens of millions/second

2. gated

what are the three subtypes of gated channels

ligand

voltage

mechanically

what is a ligand gated channel protein like

normally closed

binding with a controlling molecule

what is a voltage gated channel protein like

gate normally closed

opens in response to a change in electrical charge

what is a mechanically gated channel protein like

opens in responsse to mechanical force (stretch or compression)

what are carrier proteins like

membrane-bound enzymes

• bind and transport molecule

exhibit high specificity and saturation kinetics

what are the two types of carrier proteins

diffusion facilitators

• carry molecules through membrane

• only in direction of concentration gradient

• energy input is from concentration gradient

active transporters

• primary active- move molecules against a concentration gradient

• secondary active

what is the Na+ and K+ concentration interstitial

[Na+] = 145mM

[K+] = 5 mM

what is the Na+ and K+ concentration intracellular

[Na+] = 15mM

[K+] = 140mM

what ion will move out of the cell - efflux

K

what ion will move in the cell- influx

Na

how many more K channels are there than Na channels

40x

what are the net charges inside and outside surfaces of a cell membrane

net negative on the inside

net positive on the outside

what is the most important enzyme in physiology

Sodium-potassium ATPase

what happens each cycle of the sodium potassium pump

-one atp split

-3 Na+ removed from cell

-2 K+ added to cell

what is antiport transporter

moves some molecules in while simultaneously moving others out

what is a symport transporter

moves two types of ions in the same direction

what are the two mechanisms for transporting macromolecules

proteins

lipids

what is exocytosis

moves stuff out of cell

what is endocytosis

moves stuff into cell

what are the two types of endocytosis

pinocytosis (cell drinking)

phagocytosis (cell eating)