topic 3: membranes

fluid mosaic model

describes teh plasma membrane as a polar/hydrophilic head and a nonpolar/hydrophobic tail

what is the plasma membrane primarily comprised of?

• lipids (phospholipids + cholesterol)

• carbohydrates

• proteins

phospholipids

a molecule consisting of glycerol, two fatty acids, and a phosphate linked head group

where are phospholipids hydrophilics?

the head

where are phospholipids hydrophobic?

the tails

integral proteins/integrins

proteins that integrate completely into the membrane structure, they are found in the tail

glycoproteins

located on the membranes exterior surface, basically carbohydrates attach to proteins

cholesterol

made of 4 fused carbon rings, located next ti the phospholipids on the tails, these lower the temperature and organize proteins

diffusion

net flow of a substance down its concentration gradient until it reaches equilibrium, this is a form of passive transport

facillitated diffusion

diffusion with the help of a transport protein which acts as a carrier or a channel (channels are specific to the substance)

aquaporins

transport/channel proteins that helps water cross membranes (water has difficulty crossing bc its so polar)

osmosis

net flow/diffusion of water down its concentration gradient across a differentially permeable membrane, deals with an aqueous solution

aqeuous solution

water (solvent) + a solute

hypotonic solution

solute is low

ex. .45% NaCl for dehydration

hypertonic solution

solute is high

ex. .9% NaCl + .5% glucose for low blood sugar

isotonic solution

solution is in equilibrium

ex. .9% NaCl for comatose people

active transport

requires energy in the form of ATP

1. solute binds to the binding site

2. ATP phosphorylates the transport protein

3. the transport protein changes shape and releases the solute on the other side

4. phosphate group detaches and the transport protein changes back to its original shape

Na+ K+ Pump

basically cells need high K and low Na inside them to do stuff so Na’s gradient drives into the cell and the K’s gradient also goes down into the cell but this causes the K to go out of the cell