Exchange Across Cell Membranes Flashcards
Why are cell membranes described as having a fluid mosaic structure?
Fluid - phospholipids constantly moving
Mosaic - proteins scattered throughout bilayer
What are glycoproteins?
Proteins with a carbohydrate (polysaccharide) attached
What are glycolipids?
Lipids with a polysaccharide chain attached
Why does the phospholipid bilayer not allow water soluble substances to pass through?
Head is hydrophilic - attracts water
Arrange themselves automatically into bilayer
Water can’t pass through hydrophobic tails
What is the role of cholesterol in the membrane?
Provide stability
How does cholesterol provide stability in the membrane?
Bind to hydrophobic tails of phospholipids
Packed closer together
Restricts movement - less fluid
Why is cholesterol particularly important in animal cells?
They do not have a cell wall so helps maintain shape of cell
What is diffusion
The random, net movement of particles from an area of higher concentration to an area of lower concentration
Is diffusion active or passive?
Passive
What is facilitated diffusion?
Diffusion using carrier proteins and protein channels
Is facilitated diffusion active or passive?
Passive
Describe the role of carrier proteins in facilitated diffusion
Attach to large molecule
Protein changes shape
Releases molecule on opposite side of membrane
Describe the role of channel proteins in facilitated diffusion
Form pores in membrane
Charged/water soluble particles
Different proteins for different particles
What three factors affect the rate of simple diffusion?
concentration gradient
Thickness of exchange surface
Surface area
What two factors affect the rate of facilitated diffusion?
Concentration gradient
Number of channel/carrier proteins
What is osmosis?
The diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential
What is the water potential of pure water?
Zero
What three factors affect the rate of osmosis?
Water potential gradient
Thickness of exchange surface
Surface area
What are two methods of making up solutions of exact concentrations?
Scale factors
Serial dilutions
What is active transport
The movement of particles across a membrane from an area of low concentration to an area of high concentration
Active transport is active. What provides energy for this process?
ATP from respiration
Active transport only uses one type of protein. What is this protein?
Carrier protein
What are co transporters?
A type of carrier protein which binds two molecules at a time
How do co transporters work?
The concentration gradient of one molecule is used to move the other molecule AGAINST their concentration gradient
