Cheatography
https://cheatography.com
The cheat sheet about cell transport and what involves in it.
This is a draft cheat sheet. It is a work in progress and is not finished yet.
Fluid mosaic membranes
Membranes do not only separate different areas but also control the exchange of material across them, as well as acting as an interface for communication |
Phospholipid structurally contain two distinct regions: a polar head and two nonpolar tails |
Membranes are partially permeable: substances can cross membranes by diffusion, osmosis and active transport |
The phosphate head of a phospholipid is polar (hydrophilic) and therefore soluble in H2O. The lipid tail is non-polar (hydrophobic) and insoluble in H2O |
Cellular membranes are formed from a bilayer of phospholipids which is roughly 7nm wide |
Phospholipid monolayer: If phospholipids are spread over the surface of H2O they form a single layer with the hydrophilic phosphate heads in the H2O and the hydrophobic fatty acid tails sticking up away from the H2O |
The fluid mosaic model describes cell membranes as mosaics because: The scattered pattern produced by the proteins within the phospholipid bilayer looks somewhat like a mosaic when viewed from above |
Micelle - If phospholipids are mixed/shaken with water they form spheres with the hydrophilic phosphate heads facing out towards the water and the hydrophobic fatty acid tails facing in towards each other |
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Phospholipid
- Form the basic structure of the membrane (phospholipid bilayer)
- Act as a barrier to most water-soluble substances
- This ensures water-soluble molecules such as sugars, amino acids and proteins cannot leak out of the cell
- Can be chemically modified to act as signalling molecules by:
- Moving within the bilayer to activate other molecules (eg. enzymes)
- Being hydrolysed which releases smaller water-soluble molecules that bind to specific receptors in the cytoplasm |
Cholesterol
Cholesterol regulates the fluidity of the membrane |
Cholesterol also contributes to the impermeabilty of the membrane to ions and increases mechanical strength and stability of membranes; without it membranes would break down and cells burst |
Cholesterol molecules sit in between the phospholipids, preventing them from packing too closely together when temperatures are low; this prevents membranes from freezing and fracturing. |
At higher temperatures it stops the membrane from becoming too fluid: cholesterol molecules bind to the hydrophobic tails of phospholipids, stabilising them and causing phospholipids to pack more closely together |
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Glycolipids & glycoproteins
Glycolipids and glycoproteins contain carbohydrate chains that exist on the surface, which enables them to act as receptor molecules
There are three main receptor types:
- signalling receptors for hormones and neurotransmitters
- receptors involved in endocytosis
- receptors involved in cell adhesion and stabilisation
Some act as cell markers or antigens, for cell-to-cell recognition |
Proteins
Transport proteins create hydrophilic channels to allow ions and polar molecules to travel through the membrane.
There are two types: channel (pore) proteins & carrier proteins
Each transport protein is specific to a particular ion or molecule. |
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