1. Lipids, Proteins and Membrane Structure Flashcards
What proportion of the dry weight of a membrane do lipids make up?
40%
Why would different regions of a cell membrane have different proteins?
Different regions can have different functions e.g. Adherence, secretion/absorption, synapses, interaction with basement membrane etc.
What proportion of the dry weight of the membrane do proteins make up?
60%
What else makes up the dry weight of the membrane bilayer.
Carbohydrates
When hydrated, how much of the total weight does water make up and how is water associated with the membrane?
20%
Hydrogen bonded to the cell membrane surface
What four groups make up a phospholipid molecule?
Polar head group
Phosphate group
Glycerol
Fatty acid chains
What are the most predominant lengths of fatty acid chains?
C16
C18
What can produce a kink in the phospholipid?
Cis orientated double bond in a fatty acid tail
What four chemicals can act as polar heads?
Choline
Amines
Amino acids
Sugars
What makes a glycolipid different to a phospholipid?
Carbohydrate molecule instead of a phosphate head
What are the two types of glycolipid?
Cerebrosides
Gangliosides
What type of head group is present on a ganglioside glycolipid?
Oligosaccharide
What type of head group is present on a cerebroside lipid?
Sugar monomer
What are the forces that interact between hydrophobic tails in a membrane?
Van der Wall’s forces
What are the two types of lipid bilayers that can form?
Phospholipid bilayer
Lipid mycelle
What 4 types of motion can phospholipids undergo?
Flexion (vibration)
Rotation
Lateral diffusion
Flip flop
Which type of phospholipid motion requires the most energy and why?
Flip flop as it is the least thermodynamically favourable
What do the Cis bonds in the fatty acid tails of phospholipids result in?
Reduced phospholipid packing
More movement
More fluidity of membrane
What does our diet need to include for phospholipids and where can we get this from?
Polyunsaturated fats
Vegetable oils
Tuna/Salmon
Seeds
What property does the planar ring in cholesterol have?
Rigidity
What percentage of lipids in a phospholipid bilayer are cholesterol?
45%
How does cholesterol interact with the phospholipid bilayer?
Locks onto adjacent phospholipid via a hydrogen bond
How does cholesterol reduce fluidity of the membrane at high temperatures?
Reduces the phospholipid’s fatty acid chain’s motion
How does cholesterol increase fluidity of the membrane at low temperatures?
Reduced phospholipid packing
What is cholesterol’s overall effect on the membrane?
Maintains a constant fluidity at a wide range of temperatures
What are the 3 functional pieces of evidence for proteins existence in the membrane?
Facilitated diffusion
Ion gradients
Specificity of cell responses
What are the 2 biochemical pieces of evidence for protein existence in the membrane?
Membrane fractionation
Freeze fracture
What type of mobility can proteins NOT do in membrane bilayers and why?
Flip flop
Requires too much energy as they have large hydrophilic moieties which associate with the polar heads and water on the outsides of the membrane
What are the 3 types of mobility proteins can do in bilayers?
Conformational change
Rotation
Lateral diffusion
What restricts protein movement in bilayers?
Protein aggregation
Tethering (e.g. Cytoskeleton)
Interaction with other cells
What are peripheral membrane proteins and how do they bond?
Proteins bound to the surface of a membrane
Hydrogen bonds
Electrostatic bonds
Disulphide bonds
How can peripheral proteins be removed from the membrane?
pH change
Ionic strength
What are integral proteins?
Proteins that interact extensively with hydrophobic domains of the lipid bilayer (can be transmembrane proteins)
How can integral proteins be removed from the membrane?
Detergents
Organic solvents
What type of secondary structure do transmembrane domains often have and how many residues does it take to cross the membrane?
Alpha helix
18 - 22 amino acid residues
What is a hydropathy plot?
Checking individual residues to check how hydrophobic/hydrophilic their R groups are
18-22 hydrophobic residues indicates a membrane cross hence a hydropathy plot can be used to tell how many times a protein crosses the membrane
What forms the cytoskeleton network on the erythrocyte membrane?
Actin
Alpha and beta spectrin molecules wound together to form a heterotetramer
Which adapter proteins do band 3 and glycophorin A attach to respectively?
Ankyrin and band 4.1
Which integral proteins do ankyrin and band 4.1 bind to respectively?
Band 3 and glycophorin A
What is hereditary spherocytosis and what is it’s cause?
Erythrocytes become more spherical hence are less resistant to lysis and get cleared by the spleen
Cause by a 50% depletion in spectrin due to one allele not being expressed
What is hereditary eliptocytosis and what is its cause?
Erythrocytes are fragile eliptoid shaped cells
Caused by defect in spectrin molecule stopping heterotetramers from forming
What are the main signs/symptoms of haemolytic anaemias?
Low erythrocyte count hence low Hb
Fatigue
What is the treatment for haemolytic anaemias?
Blood transfusions
What is the sequence of hydrophobic amino acids called which cause that section of the synthesised protein to stay in the membrane?
Stop transfer signal
