Lipids 2 Flashcards
What is Glycerolphospholipids composed of ?
Alcohol, Phosphate, Glycerol and 2 Fatty acids
Fatty acids form ester linkages with the first and second hydroxyl groups of ?
L-glycerol-3-phosphate
The phosphate group is ?
Charged at physiological pH
Where does biosynthesis of membrane phospholipids occur ?
In cytosol
Phospholipid head is attached to ? and by what ?
Phospholipid head is attached to diacylglycerol by a phosphodiester bond
PLA2 can release ?
Inflammatory mediators such as histamine, prostaglandins & leukotrienes
What happens in absence of strict regulation of PLA2 ?
A disproportionate release of inflammatory mediators can take place
What does Glucocorticoids upregulate ?
Lipocortin which inhibits PLA2 and reduce the inflammatory response
What is Lecithin ?
They are mixtures of glycerol phospholipids that contain the amino alcohol choline e.g. phosphatidylcholine
Where is Lecithin found ?
Found in egg yolks, wheat germ & soybeans
Lecithin is extracted and used as emulsifying agent in food because ? and what does this enable ?
Extracted & used as emulsifying agent in food because it has both polar & non-polar properties. This enables it to mix other fats & oils with water
What does Cephalin contain?
The amino alcohols serine or ethanolamine
Where are cephalins found?
Found in most cell membranes, particularly brain tissue (e.g. Phosphatidyl ethanolamine)
Cephalin is important in ?
The blood coagulation process, found in blood platelets (e.g. Phosphatidyl ethanolamine & Phosphatidyl serine work to increase thrombin)
Difference between Lecithin and Cephalin ?
Lecithin contains the amino alcohol - choline. Whereas, Cephalins contain the amino alcohol – ethanolamine (or serine)
Sphingolipids have a backbone of ?
Sphingosine (a derivative of ceramide)
Sphingosine is a ?
18-C amino alcohol with unsaturated hydrocarbon tail
What Sphingolipids contain?
Choline, Phosphate, Sphingosine (with built in hydrocarbon tail) and Fatty acid
Polar head group is connected to ?
Sphingosine by a glycosidic or phosphodiester linkage.
Where are Sphingolipids found ?
Found largely in the outer face of plasma membranes
Biological relevance of Sphingolipids ?
- 60+ human sphingolipids identified in cell membranes
- Prominent in neurons & cell recognition sites
- Define human blood groups
Ceramide is the precursors to ?
Sphingolipids
What is Ceramide formed by?
Fatty acid attached to carbon 2 via an amide bond
What are Sphinglipidoses ?
They are disorders of sphingolipid metabolism Eg. Nieman-Picks disease
Ceramide + Water =
Fatty acid + Sphingosine
What are Sphingolipids subdivided into ?
Sphingomyelins, Glycosphingolipids (neutral glycolipids) and Gangliosides
Phosphatidylcholine (a glycerophospholipid) and sphingomyelin (a sphingolipid) have similar ?
3D structure & physical properties
What different roles to they plan in membranes ?
Sphingomyelin is abundant in myelin sheath that surrounds some nerve cells in animals
What is Glycosphingolipids subdivided into ?
Glycosphingolipids (Glycolipids) One or more sugars connected directly to the ceramide
- Cerebrosides – 1 sugar
- Globosides – 2+ sugars
Gangliosides Complex sphingolipids with oligosaccharide polar head & 1> sialic acid termini (-ve charge at pH7).
Galactose + ceramide =
Galactocerebroside
What does Cerebroside contain ?
Monosaccharides, Sphingosine (with attached hydrocarbon tail) and fatty acid
What does Ganglioside contain ?
NANA (Sialic acid), Sugar(s), Sphingosine (with attached hydrocarbon tail) and fatty acid
Where is the highest sialic acid concentration ? and why important role does it play ?
The brain has highest sialic acid concentration where it plays an important role in neural transmission & ganglioside structure
What can Glycosphingolipids determine and using what part?
Blood groups (O, A, B) determined in part by oligosaccharide head group of glycosphingolipids
Simply explain Fat (Triacylglycerols - TAGs) ?
Simplest storage lipids (energy source) constructed from fatty acids & alcohol
What are lipids divided into?
Lipids that contain fatty acids (complex lipids)
- storage lipids: Triacylglycerols
- membrane lipids: Phospholipids & Glycolipids
Lipids that do not contain fatty acids e.g. cholesterol, vitamins, pigments.
What is the advantage of fats over polysaccharides ?
- Fatty acids carry more energy per carbon because they are more reduced.
- Fatty acids carry less water per gram because they are nonpolar.
- Glucose & glycogen are for short-term energy needs & quick delivery
- Fats are for long-term (months) energy needs, good storage and slow delivery.
Explain the structure of TAGs?
- A triglyceride (TG, triacylglycerol – TAG or triacylglyceride) is an ester derived from glycerol & 3-4 Fatty Acids
- All 3 hydroxyl groups of glycerol are esterified
- Many different types: mainly division between saturated & unsaturated
- The primary storage form of lipids (body fat)
- Less soluble in water than FA due to esterification of carboxylate group
- Less dense than water: fats & oils float
High levels of triglycerides in the bloodstream have been linked to ?
Atherosclerosis and the risk of heart disease & stroke
Properties of TAGs ?
- Neutral (no ionic groups)
- Non-polar & hydrophobic
- Insoluble in water
- Transported around the body shielded from water in plasma
- Carried by large lipid particles the lipoproteins
- Simple TAGs have 3 identical fatty acids esterified to glycerol backbone
- Mixed TAGS have 2-3 differing fatty acids
Basic structure of lipoprotein?
Non-polar lipid core containing TAG & cholesterol esters (cholesterol linked to fatty acid)
5 classes of Lipoproteins by increasing density:
- Chylomicrons (CM)
- Very low density (VLDL)
- Intermediate density (IDL)
- Low density (LDL)
- High density (HD)
What is are the TAGs & cholesterol esters surrounded by ?
Polar outer phospholipids shielding them from water
What is used to synthesise their membranes ?
Cells use fats and cholesterol to synthesise their membranes
TAGs cannot be absorbed by? but are broken into ?
TAGs cannot be absorbed by intestine, they are broken down into free fatty acids & glycerol by pancreatic lipase & colipase:
The activated complex works only at a water-fat interface
Must be emulsified by bile salts for excretion
What is the main function of bile acid ?
The main function of bile acid is to facilitate the formation of micelles, which promotes the processing of dietary fat
Bile salts are ?
Amphipathic molecules & very effective detergents
What do Bile Salt act to solubilise ?
They act to solubilise dietary lipids & also the lipid-soluble vitamins A, D, E and K
Soaps are ?
Salts of TAGs formed by breakdown in a strong base (saponification)
Solubility in water and grease/oil in a long non-polar hydrophobic hydrocarbon chain ?
Insoluble in water but soluble in grease/oil
Short polar carboxylate ion is? solubility in water and grease/oil ?
Short polar carboxylate ion is hydrophilic - water soluble but insoluble in grease/oil
Non-polar tails dissolve in?
Grease/oil surrounding a dirt particle & disperse or emulsify the particles which are then washed away
What are waxes ?
Carboxylic acid esters of long chain (C14-C36) saturated & unsaturated fatty acids with long chain alcohols (C16-C30)
Insoluble with high melting points involved in:
- storage of metabolic fuel in plankton
- protection & pliability for hair & skin in vertebrates
- waterproofing of feathers in birds
- protection from evaporation in tropical plants and ivy
- used by people in lotions, ointments, and polishes
Triacontanoylpalmitate, major component of beeswax, is ?
An ester of palmitic acid with the alcohol triacontanol
Waxes form ?
Protective coats on leaves / fruits and on birds & mammals. Bees use wax in the construction of their larval chambers
Biological waxes e.g. lanolin/beeswax & Carnuba wax (palm) are widely used in?
Lotions, ointments & polishes
What are sterols ?
Structural membrane lipids with 4 fused carbons
Cholesterol and related sterols are present in ?
The membranes of most eukaryotic cells
- modulate fluidity and permeability
- thicken the plasma membrane
- no sterols in most bacteria
Mammals obtain cholesterol from ?
Food or synthesise it de novo in the liver
Cholesterol, bound to proteins, is transported to ?
Tissues via blood vessels
- Cholesterol in low-density lipoproteins tends to deposit and clog arteries
Many hormones are derivatives of ?
Sterols
What cannot synthesise sterols ?
Bacteria cannot synthesise sterols
Vitamin D is derived from?
Vitamin D is derived from cholesterol in a series of reactions, one of which requires UV light to break the bond between two C atoms
Steroids are oxidised derivatives of ?
Sterols
Steroids have the ? but lack?
Steroids have the sterol nucleus but lack the alkyl chain found in cholesterol
Steroids are more polar than?
Cholesterol
Steroid hormones are synthesised from ?
Cholesterol in gonads and adrenal glands
How are they carried through ?
They are carried through the body in the bloodstream, usually attached to carrier proteins
Many of the steroid hormones are ?
Male and female sex hormones
