Lipids Flashcards
Classification of lipids
Simple and complex
Simple lipid definition
An ester of fatty acids with alcohol and no other molecule
Complex lipid definition
An ester of fatty acids with alcohol and other molecules such as phosphates, nitrogenous base,
General structure of fatty acids
Follow general formula Ch3-(CH2)n-COOH
Saturated fatty acid with no double bond, straight chains.
Unsaturated fatty acid with double bond, forming a kink. . If more than one fatty acid is present then a methylene group often separates them.
Alternatives to structure of fatty acids and where are they found?
Cyclic structure found in microorganisms and seeds, branched fatty acids in wax
How are the carbons numbered?
Numbered 1-n from the carbon in the carboxyl group.
What is an essential fatty acid?
One that cannot be synthesised by the body and must be supplied with the diet. Examples include polyunsaturated linoleic, linolenic and arachidonic FAs.
Sources of fatty acid
Diet and de-novo synthesis
Where in diet?
Present in animal fats such as duck fat, lard and butter or vegetable fats such as coconut oil, sunflower oil and rapeseed oil.
De-novo synthesis explained
The synthesis of complex molecules from simple molecules such as sugars. Enzyme Acetyl CoA carboxylase introduces a carboxyl group to acetyl CoA, forming malonyl CoA. Fatty Acid Synthase enzyme then turns malonlyl-CoA into fatty acid chains.
Key complex lipid examples
phospholipids, phosphatidyls, sphingolipids and sterols
Phospholipid structure
Constituted by an alcohol, Fatty Acids and phosphoric acid.
What is the most abundant phospholipid? + location
Glycerophospholipid, where the alcohol is a glycerol molecule. Found in high abundance in cell membranes and small quantities in fat stores
Glycerophospholipid structure
2 hydroxyl groups esterase by fatty acids, with the one at C2 commonly an arachidonate. Third hydroxyl esterified by phosphoric acts. C2 of the glycerol moiety is asymmetric, producing stereoisomerism
How does a phosphatidyl vary?
One of the OH groups on the phosphate moiety is esterified with another component, generating diffing glycerophospholipids .
Different classes of phospholipids
Phosphatidic Acid (PA), Phosphatidylethanolamine (PE), Phosphatidylcholine (PC), Phosphatidylserine (PS), Phosphatidylinositol (PI) and Cardiolipin (CL)
Phosphatidic acid structure + function
Compounds formed of a molecule of glycerol with two hydroxyl esterified by fatty acids and the other by phosphoric acid. Due to small highly charged head group lipid introduces high curvature in lipid bilayers. Produced as intermediates in the synthesis of triacylglycerols and glycerophospholipids.
Phosphatidylethanolamine structure + function
Primary amine phospholipid, ethanol amine added to head group. Major structure in cell membranes
Phosphatidylcholine structure + function
Amino acid choline esterified as head group. Important in packing cell membranes due to its can shape and zwitterionic (overall neutral) existence.
Phosphatidylserine structure + function
Amino acid serine esterified as head group. Especially present in enriched brain tissue, considered to be involved in cognitive development. Also anchors proteins to the cell membrane, including PKC
Phosphatidylinositol structure + function
Cyclic hexalcohol is head group. Important in signalling, especially in the brain. Commonly in the structure of phosphatodylinositol biphosphates, with C4 and C5 on the inositol groups being phosphorylated.
Cardiolipin structure + function
Essentially two Phosphatidic acids glued together by a glycerol. Found predominantly in the mitochondrial inner membrane and I important in stabilising proteins in the electron transport chain.
Overall functions of phospholipids
Form phospholipid bilayers due to their amphipathic molecules, with a polar head comprised of the OH groups on the phosphoric acid moiety, while the non polar region comprises of the tails of the carbon chains of fatty acids. Allows the molecules to arrange as a double layer, with their polar heads facing towards the aqueous medium and the non polar acyl chains orientated towards the membrane interior. Enable organelles to function and cells.
Also act as detergents, reduce the water surface tension and stabilise the dispersion of hydrophobic compounds in aqueous solutions.
Phospholipid degradation definition
Specific phospholipases hydrolyse bonds in phospholipids. Components can then be used in physiological functions and pathophysiological processes.
Name three phospholipases
Phospholipase A1, A2 and C
Roles of each phospholipase
A1- removes the 1-acyl, hydrolyse phospholipid into fatty acids, producing a fatty acid and a lysophospholipid. Act as digestive enzyme
A2- cleave fatty acid in position 2, recognises the sn-2 acyl bond, releasing arachidonic acid which is modified into eicosanoids including prostaglandins- inflammatory mediator.
C- removes phosphorylated head group, important in signal transduction pathways.
Sphingolipid definition
A lipid composed of an alchohol called a sphingosine, a fatty acid, phosphoric acid and choline
Most common sphingolipid
Sphingomyelin
Sphingosine structure
18 carbon atoms, alcohol group at C1, amine at C2, secondary alcohol at C3 and a double bond between C4 and C5 and the rest is a saturated hydrocarbon chain.
How are sphingolipids formed from spingoserine
FA binds to C2 amine via an amide function, forming a ceramide. Phosphoric acid esterifies the -OH at C1 and choline binds to the phosphate.
Sphingomyelin function
Forms myelin sheaths of nervous tissues.
Two most common types of glycolipids + original lipid
Derived from sphingomyelin- cerebrosides and gangliosides
Cerebroside structure + function
Neutral compound formed of a ceramide (sphingosine and fatty acid) with a monosaccharide, usually galactose, bound to C1 of esfingol. Gallactose containing lipids are found in plasma membrane of neuronal cells, glucose in non neuronal cells.
What is a globoside?
Glycosphingolipid with a more complex carbohydrate portion.
Ganglioside structure
Ceramide with the carbohydrate portion at C1 being very complex, oligosaccharides composed of several hexoses and silica acid residues.
A chain of hexose monosaccharides, usually beginning with glucose, galactose, N-acetyl-galactosamine and another glucose or galactose.
Sialic acid is bound to one of the monosaccharides on the chain.
Ganglioside function
Structural component of cell membranes and acts as a cell marker and specific binding site for interferons.
Sterol definition
Cyclopentanoperhydrophenanthrene derivatives .All structures that have this chemical ring structure are called steroids.
Cholesterol structure
Formed of 3 6 membered rings and one 5 membered ring a short aliphatic chain and hydroxyl group.
Amphiphillic nature due to hydroxyl group
Cholesterol’s derivatives
steroid hormones and bile
Steroid hormone synthesis
Synthesised from cholesterol in the gonads and adrenal glands.
Bile synthesis
Bile salts are derived from cholesterol, then become conjugated in the liver with glycine and taurine to form bile acids.
Bile salts and acids have higher hydrophilicity than cholesterol so become excreted into the intestine to emulsify lipids to aid digestion.
