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Cell transport Cheat Sheet (DRAFT) by

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

The fluid mosaic model


- 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

Fluidity of membrane


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

Membrane structure

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


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.

Transport proteins