Membrane Structure and Function
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5 features of all membranes
• Flexible • Self-sealing • Selectively Permeable • They define boundaries • They divide internal spaces
4 functions of membranes defined by their molecular composition
• Transport • Cell recognition • Cellular Communication • Metabolic regulation
Meaning of amphipathic
Hydrophilic and hydrophobic part included
Where does synthesis of the phospholipid take place
Cytoplasmic surface of the membrane
How are phospholipids transported from one side of the membrane to the other
Use ABC transporter (ATP Binding cassette transporters), enable movement of highly charged head group across hydrophobic region.
Which 3 enzymes are used in phospholipid distribution, and what type of movement do they promote
• Floppase - Inner to outer leaflet • Flippase - Outer to inner leaflet • Scramblase - Bidirectional
5 factors that affect membrane fluidity
• Temperature • Fatty acid composition • Chain length • Degree and extent of saturation • Cholesterol content
How does temperature affect membrane fluidity
As temp increases, energy associated with phospholipid molecules will increase, and so will their movement
How does fatty acid composition affect membrane fluidity
More unsaturated fatty acids are bent, making molecules less compact and therefore increased fluidity
How does cholesterol content affect membrane fluidity
At lower temperatures, cholesterol increases fluidity due to reduced covalent lipid interactions. At high temperatures, molecules have more energy and move more. The cholesterol helps stabilise the membrane by maintaining interactions.
What happens in spur cell anaemia and what is it’s effect
Cholesterol content increases by 25-65%, leading to decreased membrane fluidity. The cells can then get trapped and rupture.
4 features of integral membrane proteins
• Single or multi pass • Strong non-covalent bonds • Trans-membrane domain often an alpha helix • Can be predicted from sequence
Features of the peripheral membrane proteins
• Located on both the extracellular cytosolic membrane • Associated by non-covalent bonds
Name a membrane protein other than the integral or peripheral proteins
Lipid anchored membrane protein (has COVALENT bond to lipid molecule)
State the interactions of the integral and peripheral proteins
• Integral proteins interact with the lipid bilayer • Peripheral proteins interact with integral proteins or lipid polar head groups
State the amount and functions of membrane carbohydrates in membranes
• Forms 2-10% of membrane weight • Involved in cell-cell interactions or cellular recognition.
What type of molecule are blood group antigens?
Glycolipids