Flashcards in Lipid Structure and Classification_Molecules Deck (78):
What is a lipid?
1) A heterogenous class of naturally occurring organic compounds on the basis of common solubility properties
What are the common solubility properties of lipids?
1) Non polar/hydrophobic - soluble in organic solvents but NOT water
2) largely hydrocarbon in nature
3) Can be amphipathic (mainly non polar/hydrophobic but with some hydrophilic/polar groups)
What are the major classes of lipid?
1) Fatty acids (and their derivates)
2) Triacylglycerols (triglycerides)
3) (Glycero) phospholipids
What are the 5 major functions that lipids have physiological importance for humans?
1) Serve as structural components of biological membrane
2) Provide energy reserves, predominantly in the form of Triacylglycerols
3) Both lipids and lipid derivatives serve as vitamins and hormone
4) Bile acids aid in lipid solubilisation
5) Biological signalling molecules
What are examples of lipids and lipid derivatives serving as vitamins and hormone?
1) Fat soluble vitamins
2) Eicosanoids (e.g. prostaglandins)
3) Steroid hormones
What are fatty acids composed of?
Long hydrocarbon chains (C10-C24) with a terminal carboxylate (COO-) group
Most naturally occurring FA have how many numbers of C atoms?
Even number of C atoms
Most fatty acids are branched or unbranched?
What are the properties of Fatty Acids?
1) Highly reduced (energy dense)
2) C-C double bonds in naturally occurring FA are cis (not trans)
3) Soem FA are essential and must be consumed in our diet
4) May be saturated (all C-C bond are single) or unsaturated (one or more C-C double bonds)
If there is 1 C-C double bond, what is it called?
If there are 2 or more C-C double bond, what is it called?
What is the general structure of a fatty acid?
Position of C-C double bond may be denoted in relation to the C number (with 1 being the C atom of the -COO- group)
Position of C-C double bond may be denoted in relation to omega C atom e.g. omega3, omega6, omega9 etc.
A saturated Fatty Acid doesn't have what?
No C = C double bonds
Most naturally occurring double bonds are what confirmation?
(Trans isomer is some but rare)
Chemical/Industrial production of MUFA and PUFA (hydrogenated fats) yield what? What is the effect?
Yield trans isomer (dietary trans FA)
Effect: Appear to increase risk of coronary heart disease in party by raising LDL cholesterol
Unsaturated FA have how many C=C double bond?
1 or more C=C double bond
What do trans FA do?
Makes fat more solid or 'spreadable', helps to prolong the shelf life of the food and maintain flavour stability
What are the effects of FA (De)saturation on structure of lipid aggregates?
- Saturated FA chains pack tightly and form more rigid, organised aggregates
- Cis unsaturated FA chains bend and pack in a less ordered way, with greater potential for motion i.e. more fluid - trans unsaturated chains are more straighter
Why is FA saturation important?
Important déterminant of membrane fluidity
What are essential fatty acids?
PUFAs with >= 2 double bonds at least 1 of which is beyond C9
Why is PUFAs with >= 2 double bonds at least 1 of which is beyond C9 considered an essential fatty acid?
As human and animal species cant introduce double bonds into FA after C9, some FA are essential and must be consumed in our diet
What are examples of essential fatty acids?
Linolenic acid (C18:3) - omega 3 fatty acid
Linoleic acid (C18:2) - omega 6 fatty acid
How do FA with double bonds after C9 become consumed in our diet to become beneficial to our body?
Converted by elongation and desaturation to PUFA with essential biological roles
What are examples of FA converted by elongation and desaturation to PUFA with essential biological roles?
Linoleic acid -> arachidonic acid (C20:4) - ARA
Linolenic acid -> eicosapentaeonic acid (C20:5) - EPA
What are ARA and EPA
Serve as precursors for synthesis of eicosanoids
What is a fatty acid derivatives?
What is eicosanoids derived from?
From C20 conditionally essential PUFAs
What are the C20 conditionally essential PUFA is needed to make eicosanoids?
1) C20:3 eicosatrienoic acid (ESA)
2) C20:4 arachadonic acid (ARA)
3) C20:5 eicosapentaenoic acid (EPA)
can be synthesised from essential FAs - linoleum acid (C18:2) and linolenic acid (C18:3)
What are the synthetic pathways that can create eicosanoids?
Cyclooxygenase (COX) pathway (prostaglandins and thromboxane)
Lipooxygenase (LOX) pathway (leukotriene)
What do eicosanoids do?
Exert their actions by binding to specific plasma membrane receptors
What are examples of a subclass of Eicosanoids, essentially a metabolite of arachidonic acid?
LT (Leukotrienes) and PG (Prostaglandins)
What do LT and PG do?
Function as local signalling molecules and play important roles in:
1) inflammation (COX2) inhibitors are widely prescribed NSADs e.g. aspirin)
2) regulation of vascular tone
What is a triacylglycerols (triglycerides)?
3C alcohol (glycerol) esterified to 3 FA through -COOH group
What is triacylglycerols used for?
A major energy storage form in animals
1) stored in adipose tissue,
2) highly reduced (energy dense) form of carbon,
3) no solvation (take up less space than highly hydrated CHO)
What are other advantages of triacylglycerols?
What does it mean for there to be highly reduced form of carbon?
1 g of triacylglycerols yields about 38 kJ of energy (twice as much as CHO or protein)
What is triglyceride structure?
1) Lipases cleave ester bonds and release the FA
2) FA may all be the same or different and may be saturated, unsaturated or both
What is the simplest GPL [(Glycerol)Phospholipids]?
What is the structure of the simplest GPL which is phosphatidate?
Glycerol 3 phosphate esterified with 2 FA (diacylglycerol with a PO4 at 3rd -OH Group)
If GPL contains an unsaturated FA, where would it be?
Be at C2
What is unique about (glycerol)phospholipids (GPL)?
A variety of polar alcohol compounds can be esterified to the PO4 group of phsophatidate
What are the variety of polar alcohol that can be esterified to the PO4 group of phosphatidate?
1) Choline (phosphatidylcholine aka lecithin)
2) Serine (phosphatidylserine)
3) Ethanolamine (phosphatidylethanolamine)
4) Inositol (phosphatidylinositol)
5) Glycerol (Phosphatidylglycerol)
What is do venoms of poisonous snakes like the Indian cobra contain
Venoms of poisonous snakes contain large amounts of phospholipase A2
What is lysolecithin?
A breakdown product of this reaction (phospholipase breakdown of GPL)
What does lysolecithin do?
Acts as a biological detergent and dissolves the membranes of red blood cells, causing them to rupture
What are (glycerol)phospholipid properties?
GPLS are amphipathic molecules
- polar head: PO4 and alcohol groups
- non polar tail: hydrophobic FA chains
What are the benefits of the GPL having amphipathic properties?
Integral to the role of GPL in biological membranes
What does unsaturated fatty acids do?
Change the fluidity and permeability of membrane
What does phospholipid bilayer with many unsaturated fatty acids have?
What is an important determinant of membrane fluidity?
What is the effect of temperature and membrane fluidity?
Increase in temperature, increase in fluidity
- Lipids acquire thermal energy when they are heated up; energetic lipids move around more, arranging and rearranging randomly, making the membrane more fluid
What does cholesterol do to membrane fluidity?
1) Cholesterol decreases membrane fluidity near membrane surface
2) acts as a 'spacer' allowing greater fluidity deeper inside the lipid bilayer
What do the main class of glycolipids contain?
Contain sphingosine and one or more sugars (glycophingolipids - GPL)
What is the simplest glycosphingolipids?
What is glycosphingolipids particularly abundant in?
In nerve cell membrane
What does glycosphingolipids being particularly abundant in nerve cell membrane help with?
1) Nerve impulse transmission
2) Cell-cell recognition
3) Molecular recognition (binding glycoprotein homeones and bacterial toxins)
What are genetic defects in glycosphingolipid metabolism respsonsible for?
For several fatal neurological disorders (sphingolipidoses)
What are sphingolipids?
Membrane lipids based on an 18C amino alcohol (sphingosine) rather than glycerol
What is the parent compound of sphingolipids?
What is ceramide consisted of?
FA joined to the nitrogen of sphingosine in an amide linkage
What are categories under Glycosphingolipids?
What are cerebrosides?
Ceramide + 1 sugar
What are examples of cerebrosides?
What are Globosides?
Ceramide + 2 or more sugars not including NANA
What are examples of globosides?
What are gangliosides?
Ceramide + 3 or more sugars one of which is N acetylneuraminic aka NANA
What are sphingomyelin?
Abundant membrane lipid in nerve cells phosphorylcholine or phosphorylethanolamine esterified to C1 -OH of ceramide
What does sphingomyeline have and don't have?
Phospholipid but not glycerophospholipid
What is the core structure of cholesterol?
Consists of three 6 membered rings and one 5 membered ring with 8C side chain
What type of molecule is cholesterol?
Hydrophobic molecule apart from weakly polar -OH group on C3 (amphipathic lipid)
What is cholesterol comprised of?
30-40% of plasma membrane lipids,
What is the cholesterol do?
1) playing a critical role in regulating membrane fluidity
2) Serves as a precursor for synthesis of many other biological molecules such as steroid hormones and bile salts
What are the major cholesterol derivatives and what is the hormone they play apart of?
1) Mineralocorticoids - Aldosterone
2) Glucocorticoids - Cortisol
3) Androgens - Testosterone
4) Estrogens - Estradiol
5) Progestagens - Progesterone
6) Calciferols - 1,25 dihydroxy vitamin D2
7) Bile salts- chalk acid/deoxycholic acid
What type of molecule are lipids?
Lipids are predominantly hydrophobic molecules that can be esterified but cannot polymers
Which is more dense fatty acid or carbohydrates?
Fatty acids are more energy dense than carbohydrates and can be stored in a more compact form
What type of molecules are glycerophospholipids?
Amphipathic molecules that can form the lipid bilayer component of cell membrane
What is bilayer fluidity dependent on?
On length and saturation of its lipids and on the presence of cholesterol