fluid mosaic model Flashcards
what does the cell surface membrane consist of
- bilayer of phospholipids
- proteins
- carbohydrate chains (attached to protein/ phospholipid, in contact with external environment)
details about phospholipid
- two fatty acid chains bonded to 2 of the 3 carbons in glycerol molecule
- phosphate group attached to last carbon
- fatty acid chains are hydrophobic
- phosphate group is polar, it is hydrophillic
how do phospholipids arrange themselves
- cytosol and external environment are both aqueous.
- hydrophillic head in contact with aqueous environment (external facing)
- hydrophobic tails shielded from aqueous environment. (internal facing)
what is meant by “fluid” in fluid mosaic model?
phospholipids and proteins moving freely and laterally within the phospholipid bilayer.
what is meant by “mosaic” in fluid mosaic model?
protein and cholesterol (animals only) molecules that are randomly embedded and scattered among the phospholipid molecules, resulting in mosaic arrangement of components.
types of proteins found in cell membrane
- channel protein: allows passage of specific ion/molecules across membrane
- carrier protein: allows passage of specific ion/molecules across membrane
- enzymes
- receptors: specific binding sites that bind to chemical messengers to relay a message into cell
- glycoproteins: cell recognition and cell adhesion, protein + carbohydrate
- glycolipids: cell recognition
what affects fluidity of membrane?
- increases at high temperature
- increases due to unsaturated fatty acids
- decreases due to saturated fatty acids
- cholesterol increases membrane fluidity at low temperature but decreases at high temperature
ways molecules/ions can pass through the cell surface membrane
- simple diffusion (passive)
- facilitated diffusion (proteins, passive)
- active transport (active)
simple diffusion allows what to pass through membrane
- small molecules
- lipid soluble substances
- oxygen
- carbon dioxide
- nitrogen
- water
- glycerol
NOTE: water and glycerol are polar. large polar molecules cannot cross cell membrane as they are hydrophillic. water and glycerol can cross however because they are small
what happens in facilitated diffusion
- passive process, down a concentration gradient, with the help of transport proteins (channel and carrier)
- transport proteins are very specific. they transport specific substances
how do CHANNEL proteins help with facillitated diffusion
provides a hydrophillic passage for specific hydrophillic molecules to move across hydophobic core of cell membrane.
- etc: aquaporins facillitate passage of water molecules
how do CARRIER proteins help with facilitated diffusion
- alternates between shapes, moving molecule by a change of shape.
- shape change is triggered by the binding and release of molecule at its binding site.
- molecule is shielded from hydrophobic core of cell membrane
what happens in active transport across cell membrane
- against concetration gradient –> high concentration to low concetration
- energy from hydrolysis of ATP is required.
- cells that constantly transport molecules using active transport require a lot of energy, hence they have large number of mitochondria
- carrier proteins required
process of active transport
- molecule is present in higher concentation inside cell
- molecules have to be actively transported into cell with the help of carrier proteins
- hydrolysis of ATP provides carrier protein with energy needed to change its shape to transport molecule across cell membrane
