2.5 BIOLOGICAL MEMBRANES Flashcards
State the 3 roles of plasma membranes
1) partially permeable barriers between cells and environment/organelles and cytoplasm
2) site of chemical reactions
3) site cell communication/signalling
Why is the plasma membrane called “fluid-mosaic”?
- Mosaic = proteins, glycoprotiens, glycolipids, cholesterol are scattered throughout the phospholipid bilayer
- Fluid = membrane components are free to move
How does the plasma membrane have a role in cell signalling?
- contains membrane-bound receptors for hormones and drugs to bind
Describe the phospholipid bilayer
- hydrophobic, nonpolar tails on inside
- hydrophilic, polar heads on outside
Role of glycoproteins and glycolipids?
- maintain stability and facilitate cellular recognition
Which molecules CAN get through the partially permeable plasma membrane? (3)
- Gases
- Hydrophobic molecules (are uncharged/nonpolar/fat soluble)
- Small polar molecules
Which molecules CANNOT get through the partially permeable plasma membrane? (2)
- Large polar molecules
- Ions (charged molecules)
Which two factors affect membrane structure and permeability?
Temperature and Solvents
How does high temperature affect the plasma membrane?
- Increases kinetic energy, phospholipids move more, fluidity of membrane increases, membrane more permeable and structure breaks down
How do organic solvents (alcohol) affect the plasma membrane?
- Alcohols will dissolve lipids and break the phospholipid bilayer
Describe simple diffusion
- The passive net movement of particles form an area of higher concentration to an area of lower concentration, down a concentration gradient
- Occurs as particles have kinetic energy, ATP not required
- Stops when equilibrium is reached
Which particles use simple diffusion across plasma membranes?
- Small, lipid soluble (nonpolar) molecules
Describe facilitated diffusion
- The passive net movement of particles from an area of higher concentration to lower concentration across a partially permeable membrane using protein channels/carriers
- no ATP required
Role of channel proteins?
- for charged/polar molecules
- fills with water so polar molecules/ions can dissolve in water and diffuse over
Role of carrier proteins?
- for large molecules
- when molecule binds the carrier protein opens and changes shape then releases molecule on other side
Which particles use facilitated diffusion via channel proteins across partially permeable plasma membranes?
- water soluble ions (charged)