lipids
1. organic compound found in living organisms that is insoluble (or sparingly soluble) in H₂O but soluble in non-polar organic solvents
2. fats
3. major way of storing chemical energy
4. fats surround & insulate organs
5. don't have common structural features
6. classification = basis of solubility, not funct. group
5 categories of lipids
1. energy-storage lipids: triaclglycerols
2. membrane lipids: phospholipids, sphingoglycolipids, & cholesterol
3. emulsification lipids: bile acids
4. chemical messenger lipids: steroid hormones & eicosanoids
5. protective-coating lipids: biological waxes
structural formulas of lipids
1. structural diversity
2. esters, amides, alcohols (acyclic & cyclic) & polycyclic
fatty acids
1. naturally occurring monocarboxylic acid
a. carboxylic acids w/linear carbon chain
b. contain even number of carbon atoms
long chain = C₁₂-C₂₆
medium chain = C₈-C₁₀
short chain = C₄-C₆
fatty acids: 2 types
1. saturated: all C-C bonds, SB
2. unsaturated
a. monounsaturated (MUFA): 1 C=C bond
b. polyunsaturated (PUFA): 2 or more C=C bonds, up to 6
saturated fatty acids (SFA)
1. numbering starts from end of -COOH
2. structural notation: indicated # of carbon atoms
ex. lauric acid has 12 carbons & no DB →12:0
polyunsaturated fatty acid (PUFA)
1. usually referred by common name
2. Two numbers separated by colon, 1st designates the # of carbon, 2nd is the # of DB
Ex. 18:2 = 18 carbons, with 2 DBs
3. location of DBs use Δ. delta notation always has carboxyl carbon as C₁
ex. 18:3(Δ⁹'¹²'¹⁵) = 18 carbons, 3 DBs, located btw 9-10, 12-13 & 15-16 carbons
4. MUFA;s are usually Δ⁹ acids
5. polyunsaturated are usually at the Δ¹² & Δ¹⁵
biologically important UFAs: define & 2 types
1. several different families, characterized by location of DB relative to methyl end of fatty acid
2. Omega-3 fatty acid: endmost DB is 3 carbons from methyl group
3. Omega-6 fatty acid: endmost DB is 6 carbons from methyl group
physical properties of fatty acids
1. water solubility: short chains have some solubility (b/c of carboxylic acid polar group), long chains are insoluble
2. MP depends on # of C atoms & degree of saturation
a. DB (usually "cis") put a bend in chain, & bend keep unsaturated FA from packing as tightly as saturated & have fewer intermolecular attractions = ↓ MP
energy storage materials: general
1. cells store energy material for when energy demand is high
2. most storage material is carbohydrate glycogen
3. lipid storage=triacylglycerols
energy storage materials: triacylglycerols
a lipid formed by esterification of 3 fatty acids + glycerol
1. most abundant, concentrated in adipocytes (adipose tissue) which are located in various parts of body
2. more efficient than glycogen: large quantities packed in small volumes
3. three ester functional groups
4. alcohol is always glycerin
5. non-polar
2 types of triacylglycerols
1. simple = 3 identical fatty acids (these are rare)
2. mixed = more than 1 kind of fatty acid. includes most biochemically important triacylglycerols. different mixed depend on climate & feed source
fats
1. naturally occurring mixtures of triacylglycerols
2. difference btw fats & oils is physical state
3. predominantly saturated
4. solids or semi-solids at room temp.
5. obtained from animals
6. pure fats & oils are colorless, odorless & tasteless
oils
1. naturally occurring mixtures of triacylglycerols
2. difference btw fats & oils is physical state
3. predominantly unsaturated
4. liquids at room temp.
5. obtained from plants & fish oils
6. pure fats & oils are colorless, odorless & tasteless
"good fats" vs "bad fats"
1. saturated fats are bad fats
2. monounsaturated fats are good fats
3. trans-monoumsaturated fats are bad fats
4. polyunsaturated fats can be both good & bad
5. omega 6 & omega 3 good fats
essential fatty acid
1. a fatty acid needed in human body that must be obtained from dietary sources, b/c not enough can be synthesized in body.
essential fatty acid: 2 types
1. linoleic acid (18:2) omega 6
2. linolenic acid (18:3) omega 3
both needed for
a. proper membrane structure
b. starting point for longer chain omega 3 & 6 fatty acids
chemical reactions: types
due to 2 functional groups: esters & alkenes
1. hydrolysis
2. saponification
3. hydrogenation
4. oxidation
chemical reactions: hydrolysis
1. reverse of esterification
2. in lab = complete hydrolysis
3. in body = partial hydrolysis
a. occurs during digestion
b. break 1-2 ester bonds→mono- or diacylglycerol & fatty acids
c. carried out by enzymes from pancreas
chemical reactions: saponification
1. hydrolysis in basic solution→salt of fatty acid + glycerol
2. it is the process that turns animal fat into soap
chemical reactions: hydrogenation
1. addition of hydrogen across a DB
2. changes from unsaturated into saturated fatty acids
3. many foods produced by partial hydrogenation. ex. peanut butter
chemical reactions: oxidation
1. DB in triacylglycerols subject to oxidation from oxygen in air → breaking C=C bond
2. oxidation of alkenes may result in 2 short chains that can be aldehydes or carboxylic acids.
- when produced these can have bad odors (fats/oils said to be rancid.
- to avoid, antioxidants are added
membrane lipids: general & 3 types
- cells surrounded by membrane to confine contents
- up to 80% of mass of cell membrane can be lipids
3 types
1. phospholipids
2. sphingolycolipids
3. cholesterol
membrane lipids: phospholipids definition
a lipids that contains 1 or more fatty acids, a phosphate group, a platform molecule (glycerol or sphingosine) to which the fatty acids & phosphate group are attached, and an alcohol attached to phosphate group
membrane lipids: glycerophospholipids
1. a lipid with glycerol platform, 2 fatty acids & a phosphate (with an attached alcohol)
2. 4 ester linkages
3. undergo hydrolysis & saponification
4. alcohol attached to phosphate usually 1 of 3 amino alcohols: choline, ethanolamine, serine
5. structurally similar to triacylglycerols but they are components of membrance vs. energy storage
6. structural characteristic is that it contains a polar and non-polar end
membrane lipids: sphingophospholipids
1. lipid that contains 1 fatty acid, 1 phosphate group (with an attached alcohol) attached to a sphingosine.
2. fatty acid attached to the -NH (amide linkage) & phosphate attached to the terminal -OH (ester linkage)
3. head and two tail structure
membrane lipids: sphingoglycolipids
1. lipid that contains a fatty acid (amide linkage) & a carbohydrate (Mono or poly - glycosidic linkage) attached to a sphingosine molecule
2. simple ones called cerebrosides - contain single mono (either glucose or galactose). primarily in brain
membrane lipids: cholesterol
1. much different that other membrane lipids
2. C₂₇ steroid molecule is component of cell membrane & precursor for other steroid lipids
3. most abundant steroid in human body
4. important in human cell membranes, nerve & brain tissue
5. does not have head & two tails
6. lack of large polar ends = limited water solubility
steroid
lipid whose structure is based on a fused ring system that involves three 6 carbons rings & one 5 carbon ring
cholesterol in food
1. liver synthesizes cholesterol, so not necessary to consume
2. synthesis ↓ if cholesterol ingested, but not enough
3. leads to heart disease
4. animal products = lots of cholesterol/plant products= little cholesterol
cells: general
1. surrounded by plasma membrane. 80% are lipids
2. membranes are lipids bilayers (polar heads, non-polar tails)
3. membrane is liquid like structure due to unsaturation in lipid tails
cells: cholesterol
1. cholesterol component of plasma membrane
2. helps regulate membrane fluidity
3. fits btw fatty acid chains of lipid bilayer=rigidity
cells: protein
1. plasma membrane contains proteins
2. responsible for moving substances across membrane
3. receptors for hormones & neurotransmitters
4. proteins and some lipids are further reacted w/carbohydrate molecules. serve as markers
transport across cell membrane: Passive
1. substance moves across membrane by diffusion, from high to low concentration, without energy
2. only a few can. ex. O₂,N₂,H₂O, urea & ethanol
transport across cell membrane: facilitated
1. substance moves across membrane by with the aid of a membrane protein, from high to low concentration, without energy
2. specific proteins are called carriers or transporters
3. glucose, chloride ion & bicarbonate ion use this method
transport across cell membrane: active transport
1. substance moves across membrane by with the aid of a membrane protein, from against (low to high) concentration, expending energy
2. proteins are called pumps b/c they need energy
3. energy supplied by molecules such as ATP
4. sodium, potassium & hydronium ions use this method
emulsifier
1. substance that can disperse & stabilize water-insoluble substances as colloidal particles in an aqueous solution. (similar to soap during washing)
bile acid
1. a cholesterol derivative (tri-or dihydroxy cholesterol derivatives) that functions as a lipid emulsifying agents in the aqueous environment of digestion.
2. the C₁₇ side chain of cholesterol has been oxidized to carboxylic acid. & then bonded to an amino acid thru amide linkage
3. makes dietary lipids soluble
4. approx. 1/3 of cholesterol produced by liver is converted to bile (by oxidation)
bile
1. fluid containing emulsifying agents (bile acids) secreted by the liver, stored in gallbladder, & released into small intestine during digestion
2. gallstones=crystallized cholesterol
hormone
1. biochemical substance, produced by a ductless gland, that has a messenger function
2. hormones communicate btw various tissues
3. some are lipids
4. lipids that are chemical messengers=steroid hormones & eicosanoid
Lipid chemical messenger: steroid - define & 2 classes
1. hormone that is a cholesterol derivative
2. two classes
a. sex hormones: reproduction & sex characteristics
1. estrogen: female sex hormone
2. androgens: male sex hormone
3. progestins: pregnancy hormone
b. adrenocorticoid hormones: produced by adrenal glands, 28 different hormones
a. mineralocorticoids=controls Na & K balances in cell
b. glucocorticoids=controls glucose metabolism & counteract inflammation
Lipid chemical messenger: steroid/adrenocorticoid/mineralcorticoid
control the balance of Na and K ions in cells
Lipid chemical messenger: steroid/adrenocorticoid/glucocorticoids
controls glucose metabolism & counteracts inflammation
Lipid chemical messenger: eicosanoid
1. oxygenated C₂₀ fatty acid derivative that functions as a chemical messenger
2. precursor for eicosanoid is arachidonic acid (20:4)
3. profound physiological effects at low concentrations
4. hormone-like molecules
5. effects at tissues where synthesized
6. very short life
Lipid chemical messenger: eicosanoid physiological effects (6)
1. inflammatory response
2. production of pain & fever
3. regulation of blood pressure
4. induction of blood clotting
5. control of reproductive functions: labor
6. regulation of sleep/wake cycle
Lipid chemical messenger: eicosanoid-prostaglandins
1. messenger lipid that is a C₂₀ fatty acid derivative that contains a cyclopentane ring & oxygen-containing functional groups
2. >20 discovered
involved with
a. raising body temp
b. inhibiting secretion of gastric juices
c. ↑ secretion of protective mucus layer into stomach
d. relaxing & contracting smooth muscle
e. directing water & electrolyte balance
f. intensifying pain
g. enhance inflammation responses
Lipid chemical messenger: eicosanoid-thromboxanes
1. messenger lipid that is a C₂₀ fatty acid derivative that contains a cyclic ether ring & oxygen-containing functional groups
2. promote formation of blood clots
3. produced by blood platelets & promote platelet aggregation
Lipid chemical messenger: eicosanoid-leukotrienes
1. messenger lipid that is a C₂₀ fatty acid derivative that contains a three conjugated DBs & hydroxy groups
2. promote inflammatory & hypersensitivity (allergy) responses
biological wax - define
1. lipid that is a monoester of a long chain fatty acid + a long chain alcohol
biological wax - 2 types
1. fatty acids:
a. generally saturated fatty acids
b. 14-36 carbon atoms
2. alcohols:
a. may be saturated or unsaturated
b. 16-30 carbon atoms
biological wax - properties
1. water insoluble & water repellent b/c of long non-polar hydrocarbons
2. humans & animals secrete biological waxes from skin glands