Module 4 Flashcards
Lipids and membrance
What are lipids?
Compounds that are low solubility in water. (generally non-polar
Energy storage, structural components in biological membranes, signals and cofactors
What is the glycerol of the fatty acids
O at the end of the M shaped carbon
What are the storage lipids
Fatty acids, triacylglycerol, waxes
What are the membrane lipids
phospholipids, glycolipids, cholesterol
What are the signaling and cofactor lipids
Phospholipid derivatives, steroid hormanes, eicosanoids, lipid soluble vitamins(Vit A)
What are the properties of carboxylic acids
fatty acids
almost have an even number of carbon bonds, most natural fatty acids are unbranched
What are saturated fatty acids
no double bonds between carbons in the chains
What are monounsaturated fatty acids
one double bond between carbons in the alkyl chain
What are polyunsaturated fatty acids
more than one double bond in the alkyl chain
What properties as carbon skeleton increase
Melting point increase, solubility decrease.
Properties of a saturated fatty acid
Usually a fully extended conformation, almost a crystalline array stabilized by extensive hydrophobic interactions of the hydrocarbon chain. Longer chain need more energy to disrupt packing
Properties of unsaturated fatty acids
Usually cis configuration, usually not conjugated, pack less orderly due to the disorder. Takes lesser energy to disrupt chain
What are trans fatty acids used for
Formed by dehydrogenation of unsaturated fatty acid, increase shelf life or stability at high temperature of oil.
What does trans double bond do?
allow fatty acid to adopt extended conformation, packed more regularly and show higher melting points than cis forms. rise of cardiovascular disease
What are omega-3 acids
essential nutrients
ALA, DHA and EPA
3rd carbon from the end
What are omega-6 fatty acids
6th carbon from the end
What are simple triacylglyceral?
3 fatty acids are identical
e.g. tristearin, triolein
What are mixed triacylglycerols fatty acids
fatty acids differs
Properties of triacylglycerols
-hydrophobic
-provide stored energy and insulation
Adventages
-Higher energy yield than oxidation of other fuel sources such as starch or glycogen
-Not hydrated (lighter)
How well does lipids store energy
reduce compounds: lots of available energy through oxidation
-hydrophobic nature : good packing
How does lipid insulate from environment
Low thermal conductivity
high heat capacity
mechanical protection
Are lipids water repellant
yes, hydrophobic nature
What are the compounds that are in the outer biological membrane
Glycolipid, oligosaccharide chans of glycoprotein, GPI-anchored protein
What compounds are in the inner biological membrane
Sterol, integral protein(through the inner and outer), peripheral protein(both inner and outer)
What are phospholipids
Phosphate group within their polar head group
2 classes of it
Glycerophospholipids (glycerol molecule)
sphingolipids (based on sphingosine)
What is the structure of Glycerophospholipids
glycerol connected to 2 fatty acid and phophate with a alcohol
What is the structure of sphingolipids
a L shaped sphingosine connected to a fatty acid and a phosphate with choline group
What is the structure of choline
N connected with 4 carbons and connects to one carbon then the O of the phosphate
What are the fatty acids connected by in the lipids
ester linkages
What are the range of charges for Glycerophospholipids
-4 - 0
What are Glycerophospholipids important for
structural and signalling lipids
What are the roles of sphingolipids
Distinctive structural and signalling roles
do not always contain phosphate group but can also fall into a glycolipid grouping
What are the roles of glycolipids
Contribute to sites of biological recognition (blood type)
What are glycolipids
Contains mono or oligosaccharide units in their head group
what are oligosaccharide?
polymer containing sugars(carbohydrate)
What are sterols
4 fused carbon rings (A, B & C =6 carbon rings, D= 5 carbon ring near fatty acid chain) with a polar head
Amphipathic
What is the main sterol in animal tissues
Cholesterol
What role does sterol play in the membranes
Structural roles, acting as a precursor for steroid hormones
What experiment are done to show that the biological membranes are lipid bilayer
electron microscopy of cell membranes
What is the fluid mosaic model
Protein embedded in the bilayer sheet by hydrophobic interactions. interaction are noncovalent(allowing fluid, dynamic properties), charges of the lipid head group contribute significantly to surface properties of membranes
What determines the packing arrangements
Shape(cross section of head group relative to side chain)
How fatty acids form micelles
Wedge shaped lipid unit
What form bilayers
phospholipid (creat cylindrical shape)
How are vesicle form
folding back on itself
What happens to membrane as temperature increases?
Phase transition temperature, becomes fluid when temperature increase. biological membranes are fluid at 37 degrees
What are the movement of lipids in membrane
uncatalyzed lateral diffusion(lateral movement and rapid), uncatalyzed transverse diffusion(flipflop slow)
The two monolayer can have different composition
Properties of lateral diffusion
Stay within the plane of the leaflet and exchange places with neighbours
Can be measured by Fluorescence recovery after photobleaching(FRAP)
How does TRANSBILAYER MOVEMENT work?
Specialised protein needed(catalysis)
Flippases (from outside)
Floppase (from inside)
Scramblase (either direction, towards equilibrium)
How are biological membrane distributed
Asymmetry of distribution, therefore flip-flop(movement between layer) not favoured
What can sterols do in the membrane
Prevent phospholipid packing, its concentration modulate membrane fluidity
What is membrane raft(lipid raft or microdomains) made of
Sterols and sphingolipids
What are the properties of membrane rafts
Slightly thicker, more ordered(less fluid) and harder to dissolve in non-ionic detergent.
Possible for lateral diffusion
Many lipid modified protein
What roles do membrane proteins play?
- Permit selective entry and exit of molecules from cell eg. via transporters
- Provide recognition signals e.g. receptors for growth factors
- Provide structural support to the cell
How do proteins interact with the membrane?
- Integral membrane protein 2. Peripheral protein
Most membrane proteins are free to diffuse laterally in lipid matrix
What are Integral membrane proteins
Inbetween membrane
what are Peripheral membrane proteins
Associated with outside surfaces
How can we distinguish between the types of membrane proteins?
- the chemical nature of the interaction between protein and membrane
- the position of the protein relative to the face of the membrane
How does peripheral membrane proteins associate with membranes
ionic interactions and H-bonding with:
• polar head groups of lipids
• integral membrane proteins
How does Integral membrane proteins interact with membranes
hydrophobic interactions with:
• acyl chains of membrane lipids
Properties of Peripheral Membrane Proteins
- high salt
- change pH
- chelating agent
Released from membrane by reagents that disrupt ionic interactions
Properties of Intergral membrane proteins
Released from membrane by reagents that disrupt hydrophobic interactions eg detergents (SDS)
How does detergent work in membrane protein?
Dissolves membrane and maintain extracted protein in solution by interacting with hydrophobic regions of protein
Does all membrane proteins have a unique orientation in the membrane
Yes
How can we determine orientation/ arrangement of membrane proteins?
Protease sensitivity of proteins from intact cells
trypsin cleaves carbonyl side of lysine and arginine
Only has access to outer layer.
analyse remaining protein
Based on sequence can we predict transmembrane protein domains?
Yes by Genome sequencing projecting
How do we know which transmembrane protein domain?
– sequence will consist of hydrophobic amino acids
– conformation will be an α-helix
– span (segment of protein) equal to width of membrane
What is the thickness of membrane and number of residues in alpha helix in membrane
3nm
20 hydrophobic residues
How to determine the number of protein and which is in the membrane
using hydropathy index
Which substance are permeable to membrane?
Only a few eg O2, CO2, mostly impermeable
What are responsible for transferring small water soluble molecules across lipid by layer
Transport proteins
What are the classes of membrane transport proteins
Carriers(transporter) and channels
How does passive carrier protein transport
undergo conformational change
Examples of Passive transporter
GLUT 1( glucose down a concentration gradient, no other substance)
What is the mechanism of glucose transport
two conformation, Binding of glucose (from blood plasma) may induce a conformation change from T1 to T2
Mechanism of active transporters
Requires energy
Example of active transporter
P-type ATPases
What is P-type ATPases
membrane proteins that uses ATP hydrolysis to pump ions across membranes
What doe p-type ATPases pump
- Na+-K+ ATPase (pumps Na+ out, ↑K+ in cell)
- H+-K+ ATPase (pumps H+ out, K+ in; acidifies stomach)
- Ca2+ ATPase (pumps Ca2+ out of cytosol)
What maintain cell volume and create transmembrane electrical potential
Na and K gradient in animal cells
