Cell membranes Flashcards
What does it mean that cell membranes are partially permeable?
They let some substances cross via diffusion, osmosis or active transport.
Describe the fluid mosaic structure
Phospholipid molecules form a bilayer
Cholesterol molecules
Channel proteins scattered (allow large molecules and ions to pass)
Receptor proteins (detect chemicals from other cells)
Polysaccharide chain (glycoproteins, glycolipids)
Name the role of phospholipids in the cell membrane
Hydrophobic head and hydrophilic tail
Heads face out
Doesn’t allow water-soluble molecules through and act as a barrier
Name the role of cholesterol in the cell membrane
It's a type of lipid, not found in bacterial membranes Fit between phospholipids Bind to tails Pack more closely together Less fluid and more rigid
Permeability at temperatures below 0 degrees
Phospholipids have little energy, packed close and rigid. Channel/carrier proteins deform making it more permeable. Ice crystals may pierce.
Permeability at temperatures 0-45 degrees
Phospholipids can move and are less packed. Membrane is partially permeable. As temp increases so does permeability due to more energy in phospholipids.
Permeability at temperatures above 45 degrees
Phospholipid bilayer begins to melt and becomes more permeable. Water expands and puts pressure on membrane and channel/carrier proteins deform.
What is Fick’s law?
rate of diffusion = (surface area X concentration)/ diffusion pathway
Talk about facilitated diffusion
Use of carrier proteins and channel proteins
They passively move molecules which are too big or ionic
How do carrier proteins work?
Large molecules attaches to the carrier protein
Causes the protein to change shape
Releasing a molecule on the other size
How do channel proteins occur?
Form pores in the membrane
Allowing a pathway for charged particles to pass
What factors does simple diffusion depend on?
The concentration gradient
Thickness of the exchange surface
The surface area
What factors does facilitated diffusion depend on?
The concentration gradient
The amount of channel/ carrier proteins available
What does the rate of osmosis depend on?
The water potential gradient
The thickness of exchange surface
The surface area of exchange surface
Describe how carrier proteins are involved in active transport
A molecule attaches to the carrier protein
The protein changes shape moving the molecule
The molecule is released using energy from ATP
Unlike other types of diffusion this can happen against a concentration gradient
Describe how co transporters are involved in active transport
The protein binds to two molecules at the same time
The concentration gradient of one of the molecules allows the other molecule to move against its gradient
The protein changes shape and moves both molecules to pass the membrane
Describe how glucose can be absorbed using co transport
Sodium ions are actively transported into the blood (sodium-potassium pump)
Causes sodium ions to diffuse into the epithelial cells down the concentration gradient, via co transporter proteins
The co transporter protein also carries glucose into the cell so glucose concentration increases inside the cell
Finally glucose diffuses out the cell down its concentration gradient through a protein channel (facilitated diffusion)
