membrane structure
- Created by: Sona16
- Created on: 14-05-21 14:23
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- properties of cell membrane
- The phospholipid head contains a negatively charged phosphate group which because of its charge is attracted water because of its polarity
- Cell membranes are composed of phospholipids that consist of a hydrophilic(attracted to water) head and a hydrophobic(repelled by water) tail
- membrane structure
- phospholipids
- A bilayer produced from huge numbers of molecules
- Composed of a three-carbon compound called glycerol
- Two of the glycerol carbons have fatty acids
- The third carbon is attached to a highly polar organic alcohol that includes a bond to aphosphate group
- cholesterol
- Allow membrane to function effectively at a wider range of temperatures
- • Most of the cholesterol molecule is hydrophobic and therefore embeds within the tails of the bilayer. A small portion (hydroxyl –OH group) is hydrophilic and is attracted to the phospholipid head
- Cholesterol is a lipid that belongs in the steroid group and is also a component of the cell membrane
- Cholesterol embedded in the membrane will reduce the fluidity making the membrane more stable by the hydrophilic interactions with the phospholipid heads
- • While cholesterol adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain its fluidity by disrupting the regular packing of the hydrocarbon tails.
- Therefore, cholesterol helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane
- proteins
- embedded in the fluid matrix of the phospholipid bilayer
- integral proteins Permanently embedded, go all the way through,
- peripheral Temporary association, bounded to the surface of the membrane
- glycoprotein Protein attached with a sugar chain
- Membrane protein functions
- Transport: Protein channels (facilitated) and protein pumps (active)
- Receptors: Peptide-based hormones (insulin, glucagon, etc.)binding------relay the message
- Anchorage: permanent or temporary junctions
- Cell recognition: MHC proteins and antigens
- Intercellular (between cells) joining's: Tight junctions, an identification label
- Enzymatic activity: Metabolic pathways (e.g. electron transport chain)
- phospholipids
- The fatty acid hydrocarbon tail has no charge and is therefore repelled by water
- When placed in water, the phospholipids naturally form a double layer with the heads facing outwards towards the water and the tails facing each other inwards (micelle or liposome)
- This forms a very stable structure that surrounds the cell because of the attractions and bonds that are formed between the heads to the water and to each other, and the hydrophobic interactions between the tails
- Even though it is a very stable structure, it is still fluid, as the phospholipids can move along the horizontal plane
- To increase stability, many cells have cholesterol imbedded between the phospholipids
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