Fluid Mosaic Membrane Model Flashcards
Membranes…
- cover the surface of every living cell
- form an intricate network with the cytoplasm
- surround most cell organelles
- same in all eukaryotes
Visible under microscopes?
- optical -> barely visible
* electron -> visible
Phospholipid bilayer size
7nm
Glycocalyx width
0.5nm
Cell surface membrane width
7.5nm
Properties of phospholipid bilayer
- 45% lipid, 45% protein, 10% carbohydrate
* most of the lipid is phospholipid
Phospholipid bilayer
- each phospholipid molecule has a hydrophobic tail of 2 fatty acids, and a hydrophilic phosphate head
- arrange themselves in a 2 molecule layer
- hydrophobic tails point inwards
- oily
- allows passage of certain lipid-soluble substances through the membrane (semi-permeable) - this is its function
Why do hydrophobic tails point inwards?
away from the watery environments both inside and outside of the cell
Why is the phospholipid bilayer oily?
• gives membrane flexibility and fluidity
Proteins in the cell membrane - the basics
- need to have R-groups that anchor it in place and ones that facilitate movement of molecules
- hydrophilic/hydrophobic interactions
- intrinsic proteins
- extrinsic proteins
- glycoproteins
- channel protein
- carrier protein
- can act of pumps
- enzymes - digestion or microvilli
Intrinsic proteins
- Span the width of the membrane
- carrier molecules
- enzymes
Extrinsic proteins
- confined to the outer or inner surface
- combine with carbohydrate groups to form glycoproteins
- those on the inner surface attach onto the cytoskeleton right anchor the membrane in place
Carbohydrate groups
Extend from the membrane
Glycoproteins
cell signalling, cell recognition, binding cells together
Channel proteins
- protein with a specific shape that complements the shape of a substance to be transported across the membrane
- used in facilitated diffusion
Carrier proteins
- protein with a specific shape that complements the shape of a substance to be transported across the membrane
- used in facilitated diffusion and active transport
- allow the transport of water soluble and polar molecules
Lipids in the cell membrane not involved in phospholipid bilayer
combine with carbohydrate groups to form glycolipids
Glycolipid
- cell signalling, cell recognition (and cell-surface antigen recognition)
- receptors
Cell signalling
- réceptors on cells bind to hormones, drugs and other cells
- leads to a series of reactions within the cell
Cholesterol
- restricts the movement of other molecules
- regulates membrane fluidity and stability
- keeps phosphates in the bilayer
Glycocalyx
- layer of carbohydrates on the outside of the bilayer
* glycoproteins/glycolipids
Why call it the fluid mosaic model?
- fluid -> everything vibrates (esp. bilayer)
* mosaic -> made up of lots of different components
How was the FMM discovered?
- freeze-fracturing using SEM on RBCs
- wanted to etch away at the membrane to investigate what it was made of
- blobs on image were glycoproteins sticking out
Specialisations of the cell membrane
- properties, functions and capabilities depend on glycoproteins, carrier proteins, and channel proteins
- folds increase SA for transport/absorption (microvilli)
- fluidity allows membranes to be folded by the cytoskeleton to form vesicles; part of endocytosis; requires ATP
- vesicles can fuse with the membrane in exocytosis
Functions of cell membranes
1) forms a barrier between the watery cell and its watery surroundings
2) controls transport of molecules into and out of cells (semi-permeable); fuse with itself for bulk transport
3) recognition of other cells
4) receptor sites for hormones and neurotransmitters
5) transmission of nerve impulses
6) insulation of nerves (resting potential maintenance)
Properties of the barrier necessary
- strong -> offers mechanical support
- flexible -> allow cells to move, grow and divide
- self-sealing -> division without lysis
Hydrophobic tails
Barrier to water soluble molecules
Intracellular membranes
Proportions of molecules greatly vary
Functions of intracellular membranes
- reaction surface
- intracellular transport system
- compartmentalisation; isolates différent chemical reaction pathways to avoid interference and maintain high substrate concentrations
- hold enzymes
- forms ATP with ATPase
- prevents disruption to the cell (e.g. lysozomes)
- formation of vesicles
- ER, Golgi
- exocytosis
- chloroplasts - contain chlorophyll
How temperature affects cell membrane function
- affects permeability
- increase kinetic energy of component molecules and the transporting substances; membrane becomes more permeable
- too high - denature proteins - changes shape - destruction
Kidney permeability - extra
- aquaporins (protein water channel) allow water to return to the medulla
- micelles fuse with the membrane
- ions cannot gets through because they’re charged
- lipid soluble substances can (hormones, O2, CO2, urea, glycerol)
- large molecules (glucose, amino acids) cannot
- water can, despite the hydrophilic tails
