The cell- 35 Flashcards
Membrane function and membrane lipids
What is the function of membranes?
-Semipermeable barrier
-Detects and interprets changes in extracellular environment
-Provide anchorage sites for extracellular proteins and cytoskeleton
-Provides an alternative environment to the cytoplasm
What type of cells are compatmenalised? How?
Eukaryotic cells
Compartments are enclosed in membranes. Membrane proteins are important for functions.
Describe membranes? Give a model example.
Membranes are semi-fluid, not static.
Fluid mosaic model.
What is the function of a particular membrane defined by?
The protein and complexes which reside in it. E.g. lipids
How much of membranes do lipids make up?
There are ~5 x10^6 lipid molecules per 1um ^2 of lipid bilayer.
The plasma membrane of a ‘typical’ cell contains ~10^9 lipids.
E.g. phospholipids, glycolipids and cholesterol.
What are the key biological functions of lipids?
-Fuel for metabolism: triglycerides
-Membranes: phospholipids, glycolipids and cholesterol
-Signalling molecules- steroid hormones and eicosanoids
-Vitamins: A, D, E and K
What is the structure of lipids? How are lipids defined?
They are very diverse in structure.
They are defined by their hydrophobicity rather than structure. They are not soluble in water, but they are soluble in organ solvents e.g. chloroform.
What is the role of glycerol? Name 2 derivatives.
Storage of fuel for metabolism.
Triacyl glyceride and phosphogleride.
How are phospholipids amphiphilic/amphiphathic? What does this mean?
Polar/hydrophilic: water-liking
Non-polar/hydrophobic: water-fearing
Heads are hydrophilic and fatty acid chains are hydrophobic
Amphipathic: has both properties
What is the result of the hydrophobic part of lipids?
Hydrophobic parts exclude water.
Therefore:
-extensive
-close in on themselves, no edges
-self sealing
What is the length of hydrocarbon in a fatty acid?
14-24C
Most commonly 16 and 18.
What are the tails of phospholipids and triacyl glycerides made of?
Fatty acids.
What are the properties of fatty acids?
Can be unsaturated (single bonds) or saturated (double bonds).
Terminated with carboxylic acid group.
What are the ways to name a saturated fatty acid?
Chemical numbering system: 1, 2, 3
Biochemical: alpha, beta, y
Nutrition: w, w-1, w-2
What is the trend in saturated fatty acids?
Melting point increases with length.
Most fatty acids have even number of carbons.
Describe unsaturated fatty acids.
Have C=C double bonds.
They are usually cis. The difference in structure between cis/trans is at the double bond.
Written with delta and number, this indicated the position of double bond.
Describe the trend in unsaturated fatty acids.
As double bonds increase, the boiling point descreases.
What is a result of a double bond in the structure?
C=C introduces a kink in the chain. This causes irregular packing.
Irregular packing leads to lower melting point and more fluidity.
What is an essential fatty acid? Why are they important? Give examples.
Essential- must be obtained in diet.
Important function in cell membrane in signaling. Is a starting point for making arachidonic acid.
W-6 and w-3 fatty acid.
What is arachidonic acid? Why is it important?
Synthesised from linoleic acid.
Precursor for eicosanoids.
Important functions as part of phospholipids in membrane.
Plays an important role in inflammation.
How is eicosanoids important in pain and inflammation?
Inflammatory signal to membrane.
Arachidonic acid is released.
Aspirin/ibuprofen -> prostaglandin or other eicosanoids.
What can be modified in phospholipids?
Hydroxy group or O-
Phosphate group
What are common head groups?
Serine, choline, ethanolamine and linositol.
What is the general structure of a phospholipid?
Fatty acid, glycerol, phosphate, head group.
How do head groups have biological functions?
Phosphatidylcholine and phosphatidylinositol can be cleaved. Inositol and choline are important signalling molecules.
Signal transmits to phospholipase C (PLC). Only some pathways depend on phosphatidylserine. Other membrane proteins are also important.
Inositol phosphate is cleaved and transmits the signal into the cell.
What lipid does E. coli not contain?
Cholesterol.
How is sphingomyelin formed?
Sphingolipids are based on the amino alcohol sphingosine. One fatty tail and a hydrocarbon tail (instead of two fatty acid tails) and sphingosine (instead of glycerol). Amide bond between fatty acid and sphingosine (instead of ester).
Choline instead of -OH.
Describe the significance of lipids in myelinated axons.
Sphingomyelin is a major component in myelin sheath.
Myelin sheath increases speed of electrical impulse. Demyelination leads to disease.
What are glycolipids?
Sugar containing lipids. There is a sugar instead of phosphate group.
It can be more than one sugar unit.
In animal cells, they are derived from sphingosine not glycerol.
Sugar always on the outside of cell.
What is cholesterol? What does it have an important effect on?
Cholesterol is the only steroid in membranes (only in animals).
Cholesterol has important effects on membrane fluidity.
What is sterol? What is their common structure?
Modified steroid.
4 hydrocarbon rings.
What is the function of glycolipids?
Immune responses, cell-to-cell recognition and attachment.
What is the importance of sphingomyelin?
Major component in myelin sheath
Signal transduction
Apoptosis
