Membrane Structure Flashcards
What are biological membranes composed of?
Lipid bilayer
Describe the lipid composition
Phospholipids=> hydrophilic head + hydrophobic tail
Cholesterol
Glycolipids => have a fatty acid + large hydrocarbon component important in cell recognition + stability of cell
What are the factors that affect fluidity?
Temperature=> as temp increases, the energy associated with phospholipid molecules increases so they move
Fatty acid composition=> saturated fatty acid= molecule compact close together. Unsaturated fatty acid= cannot compact close together therefore affects fluidity
What affect does temperature have on cholesterol?
Low temperature Cholesterol will interact with phospholipid Increases fluidity High temperature Maintains membrane stability Decreases fluidity
What are 3 enzymes involved with membrane synthesis lipids?
Floppase => moves phospholipids from inner to outer leaflet. Requires ATP
Flippase => move phospholipid from outer to inner leaflet
Scramblase=> bidirectional movement. Doesn’t require ATP
What is meant by apoptosis?
Means programmed cell death
What takes place in apotosis?
Distribution of phosphatidylserine changes significantly
Phosphatidylserine is expressed in outer surface membrane
Macrophage will recognise apoptotic cell due to eat me signal
What are 2 major populations of membrane proteins?
Integral proteins
Peripheral proteins
What are integral proteins?
Penetrate hydrophobic interior of lipid bilayer
Strong non-covalent bonds
Transmembrane domain often an a-helix
Can be predicted from sequence
What are peripheral membrane proteins?
Weekly associated with membrane
Located on extracellular or cytosolic membrane
Associated by non-covalent bonds
Can associate with membrane protein or lipid
What are lipid anchored membrane protein?
Covalently linked to lipid molecule e.g. glycero-phosphatidylinositol
What are membrane carbohydrates?
Carbohydrates associated with both membrane lipids + proteins
Carbohydrates on all membrane faces away from cytosol
Form 2-10% of membrane weight
Often involved in cell-cell interactions or cellular recognition
In RBC, 8% of weight is carbohydrate
A phospholipid is an …….. molecule
What does the missing word mean?
Amphipathic
= means that it has both hydrophilic region + hydrophobic region
What is meant by fluid mosaic model?
Membrane is a fluid structure with mosaic of various proteins embedded in or attached to bilayer of phospholipids
