Lecture 5 lipids Flashcards
(30 cards)
what are lipids
- component of homeostatic function
-hydrocarbon C-H
-made up of fatty acids (trig and phospholipds, and derivatives like sterols (CHOL, esters, hormones, bile acids Vitamin D) , Glycerol esters (mono-, di-, trig), fat soluble vitamins (VIT A, D, E ,K)
-Transported in blood as lipoproteins (particles made of protein and lipids) ex: HDL, LDL
-important in clinicals because they are associated with CVD, and Dyslipidemia
what is the biochemistry of lipids
-insoluble in water
-soluble in organic non polar solvents - Chloroform, ether, hexane, benzene
- Esters or potential esters of fatty acids - Esters formed by condensation of a fatty acid with an alcohol
O=C-OR
what is the function of a lipid
-energy storage and release -BETA -oxidation of fatty acids yields cellular ATP
Structural
* Cell membranes (phospholipids & lipoproteins)
* Brain tissue, nervous tissue
(glycolipids)
Protection & insulation
* Adipose tissue
* Padding to protect internal organs from shock
* Insulation to retain heat
Transportation
* vitamins A, D, E, K must be transported from the digestive tract (not soluble in plasma)
* dietary lipids dissolve vitamins & transport them across walls of intestinal tract
Synthesis
* used to form carbohydrates, new fats & cholesterol
* cholesterol - precursor of hormones, bile salts, vitamin D
what are fatty acids
Building blocks of lipids, usually derived from triglycerides or phospholipids
* Hydrocarbon chain with - terminal Carboxyl group (-COOH)
and on other side Methyl group (-CH3)
-have EVEN number of carbons
- 4-6 carbons: short-chain
- 8-12 carbons: medium chain
- >12 carbons: long chain (dietary) – most abundant
how are fatty acids classified and labelled
-degree of saturation
- saturated - no double bonds between CARBONS,
-monoUNSAT - 1 double bond between carbon
-polyUNSAT - 2 double bond between carbons
labelling fatty acids
-start from the carboxyl end O=C-OH
* show number of carbon atoms
* show number of double bonds
* show position of double bonds
what are saturated fatty acids
-General formula CnH2n+1COOH
- n will be the Carbon number Cn
-No double bonds between carbon atoms
* chain is extended and flexible (free rotation)
butyric acid C3H7COOH 4:0
there is no double bond because it has to be between two carbons
what are unsaturated fatty acids
- general formula CnH2n-1COOH (for one double bond) * NOTE THE N-1
- one or more double bonds between carbon atoms
- double bonds introduce a bend in the molecule- cis and trans configuration
CIS - naturally occurring where the H are on the same side both on top or both on the bottom on either side of the C=C
trans - formed from catalytic hydrogenation
* do not bend
* have physical properties similar to saturated fatty acids
* more risk to cardiovascular health
occurs when the H on either side of the C=C is on the opposite side like one H axial and the other equatorial
what are monoUNSAT and poly UNSAT fatty acids like
monounsaturated
one double bond
usually found at the 9th carbon
known as OMEGA 9 - from oils, soy, sunflower, pistachios, avocados good for heart health, blood sugar control
polyunsaturated
* two or more double bonds
* usually, three carbon atoms apart like linoleic acid - ESSENTAIL AMINO ACID
-known as Omega 3 - from oils like canola, flax, soybean Can be eaten from fishes and eggs . it helps with brain development , heart health and mood
also known as OMEGA 6 - which comes from buts and eggs
what are Physical properties of fatty acids
-Affected by chain length, degree of saturation, and cis/trans
configuration
so the longer the chain length and higher the saturation and increased trans bonds = the higher the melting point, viscosity, and lower solubility in water
-the higher the double bond means lower saturation and higher reactivity causing a lower melting point
-
fatty acid catabolism
Beta-oxidation occurs in the mitochondria
* cyclical series of reactions that shorten the fatty acid chain from the –COOH end by 2 carbons at a time
-Fatty acids (in form of acyl-CoA) broken down in the mitochondria in Krebs cycle/TCA to generate ATP
- Triglycerides are an efficient storage form of reserve energy (adipose tissue) and Can produce more energy that the same amount of glucose
Lipid classification
simple
complex
sterol
derived
-Simple lipids
* esters of fatty acids & alcohols
* fats, oils, waxes
Complex lipids
* esters of fatty acids with other groups in addition to an alcohol and fatty acids
* phospholipids, glycolipids, lipoproteins
Sterol derivatives
* cholesterol, Vitamin D, hormones, bile acids
Derived lipids
* substances derived from lipids by hydrolysis
* fatty acids, glycerol, ketones
What are simple lipids
fat
oil
waxes
Ester of fatty acids + alcohol simple lipid + H2O undergo HYDROLYSIS to form fatty acid +alcohol
Fats
* solid at room temperature
* derived from animal sources
* saturated: butter, lard
Oils
* liquid at room temperature
* Derived from plant sources
* unsaturated & polyunsaturated: olive oil, canola oil
Waxes
* alcohol is a long chain alcohol other than glycerol
* Solid at room temperature
* bees wax
what are trig
- neutral fat
- no net electrical charge
- Most abundant lipid found in nature
- Chief lipid constituent in the diet
- Main storage form of lipids
- when pure they are colourless, odourless, tasteless
-Insulation
* poor conductors of heat & electricity
- Solubility
- non-polar - no ionizable groups
- water-insoluble
- must be sequestered during transport in plasma
- Chronically elevated blood levels associated with dyslipidemias and cardiovascular disease
-formed from a condensation reaction (dehydration) with ester (RCOOR’)
- glycerol + three fatty acids ↔ triacylglycerol with 3 H20 removed
An ester bond is formed when -OH group joins to –COOH group
how does hydrolysis happen
what is hydrogenation
Breakdown of a molecule by adding H2O
* triglycerides can be hydrolyzed
* enzymatically by pancreatic and intestinal lipases
* chemically by alkaline reagent: saponification
Saponification -hydrolysis of fat with an alkali to produce soap
* A mixture of Na+ (hard soap) or K+ (soft soap) salts of long-chain fatty acids
- Non-polar hydrocarbon chain –hydrophobic
- Polar carboxylate salt –hydrophilic
- Soaps not H2O soluble –don’t form true solutions rather spherical clusters called micelles which have hydrophilic heads outside and tails inside in a sphere
hydrogenation is the process of saturating a fatty acid
what are compound lipids
Fatty acids + alcohol + another group
* The other group may be a simple compound (e.g. Phos)
May be complex compound e.g. protein, sugar
* Phospholipids (Ex: structure of cell membrane)
* Glycolipids (ex: red cell antigens)
* Lipoproteins (ex: chylomicrons, VLDL, HDL, LDL)
what is a phospolipid -compound lipids
Similar structure to triglycerides but only 2 FA, 3rd is a phosphate “head” E.g. choline, inositol, serine
* hydrophilic “head”
component of cell membranes & lipoproteins
* Polar and non-polar groups have role in membrane transport system
* Readily form liposomes
* Example: lecithin –a common phospholipid (egg yolk, soy beans)
what is a Glycolipid -compound lipids
2 FA, 3 rd is a carbohydrate (sugar)
- Found primarily in brain and myelin sheath of nerves
- also red cell antigens
the hydrophilic head will have the sugar on it
what are Lipoproteins -compound lipids
Spherical lipid-protein complex
* transport vehicle for plasma lipid
-transporting insoluble lipids throughout the body
4 classes:
* Chylomicrons (milky appearance in plasma)
* Very Low Density Lipoproteins (VLDL)
* Low Density Lipoproteins (LDL) BAD small - macro eats them causing build up in the artery
* High Density Lipoproteins (HDL) GOOD - smallest densest takes away bad chol
-you can see the difference in density if you separate with ultracentrifugation
what are derived lipids
-products obtained on hydrolysis of lipids (so lipid is broken back down into its building blocks fatty acids, glycerol, ketone bodies)
-ketone bodies are by products of B oxidation of fatty acids in the liver
still biochemically related to lipids
Sterol derivatives (steroids)
Lipids that contain a specific organic structure: the steroid nucleus
Cholesterol
* Bile acids
* Vitamin D
* ring B opens up
* Hormones
steroids are found in plant & animal tissue
-the ring may not be intact
* may or may not be an aliphatic side chain
* the ring may contain double bonds and other substituents
what is cholesterol
Unsaturated steroid alcohol
* Most biologically important sterol
* almost exclusively synthesized by animals
-Steroid nucleus (4 rings : ABCD with a single side chain tail
* Only hydrophilic part is the –OH on the A ring
* Amphipathic lipid (having a hydrophilic -polar or hydrophobic - non polar end)
* Found on surface of lipid layers along with phospholipids
what are Cholesterol characteristics
- polar
- Cholesterol ester is not polar because the –OH has been used up
- Cannot be saponified
- Present in plasma as free cholesterol but mostly as cholesterol esters - 70% (joined to a fatty acid) but both packaged in a lipoprotein particle
- Cholesterol is esterified in the liver
- all cholesterol in intestinal tract is present in the free form
Dietary cholesterol
Exogenous (obtained from diet)
-esterified
-After absorption, cholesterol turns into chylomicron particle with apoliproteins
-Travels through lymphatics → thoracic duct → venous circulation Causing lipemia
-lower dietary cholesterol = modest lower in plasma levels
Cholesterol synthesis
Endogenous (synthesis by the body)
synthesized in liver from acetyl-CoA
* Cholesterol is carried within lipoprotein molecules
* released into the circulation in VLDL
* carried to the tissues in LDL
* returns in HDL
