The Membrane Bilayer Flashcards
How much protein, lipid and carbohydrate does a membrane usually contain?
Protein = 60% Lipid = 40% Carbohydrate = 1-10%
What percentage of the total weight of a membrane is water?
20%
What is the name of a phospholipid based on?
It’s head group
How long are the fatty acids chains usually in phospholipids?
C16 - C18
What makes sphingomyelin different to the other phospholipids?
No glycerol backbone
What are the 2 types of glycolipids?
Cerebrosides and gangliosides
What is a cerebroside?
A glycolipid whose head group is a sugar monomer
What is a ganglioside?
A glycolipid whose head group is a oligosaccharide.
What are some of the functions of biological membranes?
Selectively permeable barrier, control of enclose environment, communication, recognition and signal generation.
Do phospholipids more naturally form micelles or bilayers?
Bilayers
What motions are available to phospholipids?
Flexion
Rotation
Lateral diffusion
Flip-flop (rare)
How does cholesterol integrate itself into the membrane?
The cholesterol OH group forms hydrogen bonds with the phospholipid.
How does cholesterol increase membrane fluidity?
Reduces phospholipid packing
How does cholesterol decrease membrane fluidity?
Reduces phospholipid chain motion
What functions of the membrane give us evidence for presence of proteins?
Facilitated diffusion
Ion gradients
Specificity of cell responses
What are the biochemical methods of testing for proteins in the membrane?
Fractionation and electrophoresis
Freeze fracture
What movements are available to proteins in the membrane?
Conformational changes
Rotation
Lateral diffusion
What restricts the movement of proteins in the membrane?
Aggregates
Tethering
Interaction with other cells
Where do you find more proteins in a membrane?
In cholesterol poor regions
How do we remove peripheral proteins?
Changes in pH or ionic strength
How do we remove integral proteins?
Use agents that compete for non-polar interactions (eg. Detergents)
Approximately how many amino acids are needed to span a membrane?
18 - 22 amino acids
Often TMDs are which shape?
Alpha helical
What do hydropathy plots tell us?
The relative hydrophobicity or hydrophilicity of amino acids in the protein and then we can work out where those amino acids will reside. (Eg. Which ones are in the TMDs)
Describe hereditary spherocytosis
Spectrin deficiency
RBCs become spherical
Leads to increased lysis therefore leads to anaemia
Must have frequent blood transfusions
Describe hereditary elliptocytosis
Defect in spectrin
Unable to form properly
RBCs are elliptic
More prone to lysis therefore anaemia occurs
What molecule is sphingomyelin based on and where is it found in the highest concentrations?
Sphingosine
Nervous tissue
Briefly describe cholesterol
Steroid alcohol 4 fused hydrocarbon rings Modulates fluidity of cell membranes Very hydrophobic Synthesised by virtually all tissues in humans
Give examples of hydrophobic molecules that can easily pass through the cell membrane
Oxygen (O2)
Nitrogen (N2)
Carbon dioxide
Benzene
What is passive transport dependent on?
Permeability
Concentration gradient
