Biological Membranes Flashcards
Structure and function of cell membrane
Phospholipid bilayer
Partially permeable membrane
Site of chemical reactions
Role in cell communication
What is the fluid mosaic model
The mixture and movement of the phospholipids, proteins, glycoproteins and glycolipids that the membrane is made of
Features of the fluid mosaic model
Phospholipids arranged as a bilayer due to hydrophilic heads being attracted to water and hydrophobic tails being repelled by water.
Proteins within the cell surface membrane can be intrinsic or extrinsic
What are extrinsic proteins
They provide mechanical support, or they make glycoproteins and glycolipids
The function is cell recognition as receptors
What are intrinsic proteins
protein carriers or channel proteins involved in the transport of molecules across the membrane
Difference between protein channels and carrier proteins
protein channels form tubes that fill with water to enable water soluble ions to diffuse whereas the carrier proteins will bind with other ions and larger molecules such as glucose and amino acids and change shape to transport them to the other side of the membrane
What is the function of cholesterol in membranes
Restricts the lateral movement of other molecules in the membrane, this makes the membrane less fluid at high temperatures and prevents water and dissolved ions from leaking out of the cell
What are the factors affecting structure and permeability
Temperature - high temperatures increase the kinetic energy of the phospholipids so that they move even more. This increases the fluidity of the membrane and the structure can start to break which makes it easier for particles to cross the membrane
High temperatures also denature carrier and channel proteins in the membrane
Solvents - Organic solvents like alcohol dissolve the phospholipid bilayer in membranes, this damage causes the fluidity of the membrane to increase and become more permeable
What are the six key modes of transport in and out of cells
Simple diffusion
Facilitated diffusion
osmosis
active transport
endocytosis
exocytosis
Describe simple diffusion
The net movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. This process does not require ATP
For molecules to diffuse across a membrane they must be lipid soluble and small
Describe facilitated diffusion
A passive process, down the concentration gradient through proteins
The movement of ions and polar molecules which cannot simply diffuse can be transported across membranes by facilitated diffusion using protein channels and carrier proteins
Describe osmosis
The movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane
What is an isotonic solution
When the water potential of the solution is the same in the solution and the cell (no water potential gradient so no net movement of water)
Example is red blood cell
What is a hypotonic solution
When the water potential of a solution is more positive than the cell
(water diffuses from solution into cell causing hemolysis or swelling)
What is a hypertonic solution
When the water potential of a solution is more negative than the cell
(water diffuses from cell into solution which causes cremation (shrivelled) or plasmolysis)
