Biological Membranes, 2.5 Flashcards
What is a partially permeable membrane?
Separates the cell and regulates substances moving in an out.
What is the role of the plasma membrane?
Regulate molecules. Separate. Contains enzymes. Antigens. Release chemicals. Contains receptors.
What is the phospholipid bilayer?
Consists of two layers of phospholipids. Hydrophilic heads in contact with water. Hydrophobic tails point inwards.
What proteins would you find in the plasma membrane?
- Channel proteins - allow ions through
- Carrier proteins - specific, change shape
- Receptors - recognise and bind to molecules
How thick is plasma membrane?
5 - 10 nm
What is glycolax?
Formed from carbohydrates attached to lipids or proteins.
What is the role of glycolipids?
On external surfaces. Cell to cell recognition.
What is cholesterol and why is it in the plasma membrane?
Steroids. Regulates fluidity.
Define diffusion
Molecules moved from an area of high concentration to an area of low concentration down a concentration gradient. No energy required.
What can pass through the plasma membrane by diffusion?
Oxygen, carbon dioxide, small substances - fat soluble can dissolve through
What can’t pass through the plasma membrane?
Water - polar and insoluble. Have to use water channel proteins. Molecules with charges and large molecules
What effects diffusion?
Temperature - more kinetic energy. Distance. Surface area. Size of molecules.. Concentration gradient.
What molecules will use facilitated diffusion?
Molecules with charges (ions) - use channel proteins. Larger molecules (glucose) - use carrier proteins.
How does a channel protein work?
Pores in the membrane. On type of molecule. Water filled.
How does a carrier protein work?
Molecule binds to transmembrane carrier protein. Protein changes shape so molecules can pass through. Specific.
Define osmosis
Movement of water molecules from a region of higher water potential to an area of lower water potential. Down a water potential gradient. Across a partially permeable membrane.
What is water potential?
Measure of the tendency of water molecules to diffuse from one region to another.
What is ‘free’ water?
Water thats not bound to any substance.
What has the highest water potential/
Pure water
What is a solute?
Substance that can be dissolved
What is a solvent?
Liquid that solutes dissolve in
What is a solution?
Solute dissolved in a solvent
Is osmosis passive or active?
Passive
What factors effect osmosis?
Temperature. Water potential difference. Pressure. Concentration gradient.
What can be dissolved in cells?
Sugars and salts
What happens when a plant cell has lots of water?
It is turgid. Cell wall prevents it from bursting.
What happens when a plant cell loses water?
Cytoplasm shrinks and membrane pulls away from the cell wall. Described as plasmapheresis or flaccid.
What happens when animal cells are full of water?
Cell will swell and burst - cytolysis
What happens when animal cells lose water?
Shrivels - crenated
What is active transport?
Movement of substances against their concentration gradient with ATP
How is a carrier protein involved in active transport?
Specific regions to allow molecules through. Has regions that bind to ATP to release energy.
What is bulk transport?
Transport large substances through the membrane using ATP
What is endocytosis?
Large molecule into the cell. Segment of membrane encloses a particl bringing it into a vesicles.. ATP is needed
What is exocytosis?
Large molecules out of the cell. Vesicles fusses with plasma membrane
How does temperature affect the membrane?
Molecule gain energy - fluidity increase. Permeability increases. Effects function of embedded proteins. Change the ability of cells to signals
Effect of decreasing the temperature on the membrane?
Fatty acids are compressed. Unsaturated fats push phospholipids away with their tails maintaining fluidity. Cholesterol prevents phospholipids from packing to closely together.
What will organic solvents such as acetone and ethanol do to the membrane?
Damage it. Dissolve the lipids.
