Section 2: Chapter 4: Transport across cell membranes Flashcards
What is the function of phospholipids in the membrane?
- Lipid-soluble substances can enter and leave.
- Prevents water-soluble substances to enter or leave.
- Makes membrane flexible.
What 2 places are proteins found in the phospholipid bilayer?
1) surface of the bilayer.
2) Spanning the bilayer (protein channels and carrier proteins).
What are the functions of proteins in the cell-surface membrane?
- Structural support.
- Protein channels - transporting water-soluble substances.
- Carrier proteins - active transport.
- Cell-surface receptors.
What are the functions of cholesterol in the cell-surface membrane?
- Strength.
- Limits phospholipid movement by pulling together fatty acid tails.
- Hydrophobic - prevents water leaking.
What are the functions of glycolipids in the membrane?
- Recognition sites.
- Stability.
What are glycolipids made up of?
A carbohydrate covalently bonded with a lipid.
What are the functions of glycoproteins in the membrane?
- Recognition sites.
- Help cells attach to each other.
What is the fluid-mosaic model of the cell-surface membrane?
- Fluid - phospholipid molecules make the membrane flexible.
- Mosaic - proteins embedded in the bilayer.
What are the two types of diffusion?
Simple and facilitated.
Is simple diffusion a type of passive or active transport?
Passive.
Define diffusion.
Net movement of molecules from high to low concentration.
Explain facilitated diffusion.
- Still passive and down conc. gradient.
- Protein channels form hydrophilic channels for water-soluble ions to pass through.
- Ions bind to the protein, causing it to change shape and open on other side of membrane.
- Carrier proteins - mol (eg/ glucose) binds to it, changing it’s shapes the mol can be released onto other side of membrane.
What type of molecules can be transported via simple diffusion?
Small, non-polar molecules eg/ oxygen.
Is facilitated diffusion a type of passive or active transport?
Passive.
What molecules do protein channels let through?
Water-soluble molecules.
What molecules do carrier proteins let through?
Glucose etc.
Define osmosis.
Movement of water from high to low Ψ through a selectively permeable membrane.
What is the Ψ of water?
0.
What units is water potential measured in?
KiloPascals - kPa.
How would you find the water potential of cells or tissues?
Place the tissue in a series of solutions of different Ψ. No net gain or loss of water = tissue same Ψ as solution.
What will happen to a cell if placed in a hypertonic solution?
The cell is plasmolyzed, it will shrink and shrivel up.
What is an isotonic solution?
Ψ is the same in the cell as in the solution.
What will happen to a cell if placed in a hypotonic solution?
The cell will become turgid and eventually burst.
What is a hypertonic solution?
Ψ of solution lower (more negative) than cell.
