Lecture 5 Lipids Flashcards Preview

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Flashcards in Lecture 5 Lipids Deck (76):
1

Lipids

Small hydrophobic or amphiphilic molecules

Extractable by nonpolar solvents (e.g., chloroform:methanol)

Include fats, waxes, sterols, mono/diglycerides, phospholipids, etc.

Originate from ketoacyl and isoprene groups

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Fatty Acids

Simplest form of lipids, found primarily in plasma
-Esterified to glycerol to form triacylglycerol (triglyceride)

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Triglycerides

solid storage form of lipids, found primarily in adipose tissue (also mono and di forms)

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Phospholipids

major class of membrane lipids in all cells

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Sterol-containing

(cholesterol) compounds and (glyco)sphingolipids linked with biological membranes

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Lipid functions

Energy storage, structural elements of cells and organelles, signal transduction.

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Energy Storage

Triglycerides (fats) degrade to glycerol and free fatty acids in response to hormonal signals
Released into plasma for metabolism primarily in muscle and liver

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Saponification

ex vivo hydrolysis by a strong base (e.g., NaOH)
One of the products, sodium salt of the fatty acid = soap

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Structural elements of cells and organelles

Vesicles, liposomes, or membranes (plasma) in aqueous environments

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Signal transduction

hormone precursors.

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Fatty acids

Carboxylic acids with long aliphatic chain. Usually with an even number of carbons, usually unbranched. Saturated or unsaturated. Numbered from carboxyl end.

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Common fatty acids

Short, medium, long chain. Essential and non-essential.

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Short chain

2-4 carbon atoms. n = 4, butyric acid

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Medium chain

6-10 carbons atoms, n= 8, caprylic acid

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Long chain

between 12 and 26 carbons, n=16 palimitic acid.

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Essential and nonessential

Cannot and can be synthed in body. Linoleic and linolenic are two essentials.

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Acetyl-CoA

Central to carb and fat metabolism.

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Monounsaturated

Single double bond (cis)
Oleic acid

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Polyunsaturated

Two or more double bonds
Not conjugated, separated by methylene groups
Linoleic acid

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Polyunsaturated FAs are classified into two groups:

ω-3: first double bond appears three carbons from the terminal methyl group
ω-6: first double bond appears six carbons from the terminal methyl group

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Physical properties of fatty acids

Physical properties largely determined by the length and degree of unsaturation of the hydrocarbon chain

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Chain length

The longer the fatty acid chain length, the poorer the solubility in water.
Carboxylic acid end is polar, imparting moderate solubility of short-chains (

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Fewer double bonds in fatty acid

Lower solubility in water.

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Melting point decreases with

number of double bonds - Cis-double bonds place a kink in the linear structure, interfering with close packing, therefore requiring a lower temperature for freezing (i.e., lower melting point; e.g., oils)

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Saturated lipids

Saturated lipids - the most stable arrangement is very close packing of the side chains

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Most fatty acid double bonds

cis

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Trans fats

Associated with heart disease. Caused by hydrogenation of unsaturated fatty acids. Raises melting point of oils -solid at RT - margarine.

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Oils can go bad

oxidations of double bonds can result in cleavage to aldehydes and carboxylic acids
Rancidity of oils

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Fatty acids formed in

Liver and adipose tissues, mammary glands during lactation. Unsaturated fatty acids account for 2/3 of all fatty acids in body. Oleate accounts for 1/2 of total
Palmitate (saturated) accounts for about one quarter of total

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Glycerides

Fatty acids are rarely found floating free in solution- can be complex.

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Carboxylate

Carboxylates (salt or ester) no longer bear a negative charge
Very nonpolar - insoluble in water

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Triacylglycerides

Advantage - storage fuel instead of polysaccharides. More energy present, more reduced than carbs. nonpolar and not hydrated by water - stored in insoluble fat molecules.

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Lipases

catalyze hydrolysis of ester bonds to glycerol and fatty acids for fuel or other purposes.

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Glycerides+sodium hydroxide =

glycerol + fatty acids (soap- salt derivatives)

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Saponification

Forming soap - fatty acids emulsify oils in dirt – allows for removal of oily dirt with water – detergents; micelles, liposomes

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Phospholipids

Major component of cell membranes. Polar lipids derived from phosphatidic acid. sn-3 position occupied by phosphate esterified to amino compound - choline, serine, etc.

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Sphingolipids

Second largest phospholipid class. Backbone is not glycerol, but sphingosine. Fatty acid is joined to sphingosine via an amide linkage rather than an ester linkage with glycerol
Contain various head groups, including sugars (glycolipids)
Found largely in the outer face of plasma membranes
Involved as cell surface recognition sites (e.g., red blood cells)

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Sphingosine

Long chain amino alcohol.

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Blood groups

Sphingolipids determine this - terminal sugars on sphingolipid determine blood type. Galactose - B, N-acetylgalactosamine = A, N-acetylgalactosamine + galactose = AB, no NAG or GAL = O.

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Lipopolysaccharide

LPS. Bacterial endotoxin, core oligosaccharide - Bacterial internalization,
initiation of immune resistance

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Long O-antigen side chains - LPS


Responsible for resistance to human serum, antibiotics, detergents

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Lipid A: hydrophobic anchor

Interacts with host TLR4 to initiate inflammatory response
Fever, hypotension, Gram-negative sepsis

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Cerebroside examples

One sugar molecule
Galactocerebroside – in neuronal membranes
Glucocerebrosides – elsewhere in the body

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Sulfatides or sulfogalactocerebrosides
examples

Sulfuric acid ester of galactocerebroside
Brain lipids, but present in low levels in liver, lung, kidney, spleen, skeletal muscle and heart

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Globosides

Ceramide oligosaccharides
Lactosylceramide

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Gangliosides

Complex glycosphingolipid
Cell-cell recognition,
hormone receptors

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Sterols

Structural lipids that are present in the membranes of most eukaryotic cells. Plants (phytosterols)
Fungi (ergosterol)
Animals (cholesterol)
Four fused rings
Three = six-membered
One = five-membered
Planar main body
Lipid-soluble
Diffuse freely from the blood through the cell membrane into the cytoplasm of target cells

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Cholesterol

Only found in animal fat
Primarily synthesized (and only degraded) in the liver
Phytosterols block cholesterol absorption sites in the human intestine
Serves as a component of membranes of cells (increases or moderates membrane fluidity)
Precursor to steroid hormones and bile acids
Storage and transport –cholesterol esters

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Steroid Hormones

Oxidized derivatives of sterols
Do not have the alkyl chain found in cholesterol
Increased polarity compared to cholesterol
Move through the blood stream attached to protein carriers
Five groups based on binding receptors:
Glucocorticoids
Mineralocorticoids
Androgens
Estrogens
Progestagens
Vitamin D closely related receptors, but it is technically a sterol

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Terpenes

Simple lipids that lack fatty acid component. Formed by the combination of 2 or more molecules of 2-methyl-1,3-butadiene (isoprene)

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Monoterpene

2 isoprenes c-10
Flavors and odors
Limonene (lemons), citronellal (roses/geraniums), pinene (turpentine), menthol (peppermint)

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Sesquiterpene

(C-15) – 3 isoprenes

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Diterpene

(C-20) – 4 isoprenes

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Triterpenes

2 sesquiterpenes C-30
Precursors of cholesterol and other steroids

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Tetraterpenes (C-40)


Not as common as mono, di, and triterpenes
Includes carotenoids (beta-carotene (precursor of vitamin A) and lycopene (tomatoes))
Colorful compounds

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Polyisoprenoids or polyprenols


Consist of numerous isoprene adducts (8 – 22)
Side chains of vitamins K, vitamin E and coenzyme Q

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Prostaglandins and Eicosanoids

Local hormones
Key mediators of inflammation
Derivatives of prostanoic acid
Prostaglandins (e.g., PGE1)

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PGE1

Blocks gastric production (gastric protection agents)
Vasodilator effects
Used to treat infants with congenital heart defects
PGF2a – causes constriction of the uterus

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Leukotrienes

Synthesized in neutrophils, monocytes, macrophages, mast cells and keratinocytes
Also found in lung, spleen, brain and heart
Responsible for inflammation in asthma and bronchitis and anaphylaxis

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Lipoproteins

Particles found in plasma that transport lipids including cholesterol
Liver repackages cholesterol (and triglycerides) into lipoproteins

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Lipoprotein classes

Chylomicrons: take lipids from small intestine through lymph cells
Very low density lipoproteins (VLDL)
Intermediate density lipoproteins (IDL)
Low density lipoproteins (LDL)
High density lipoproteins (HDL)

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Lipid-linked Proteins

Different from lipoproteins - proteins with covalently attached lipids - Peripheral membrane proteins. 3 types: Prenylated proteins, Fatty acylated proteins
, Glycosylphosphatidylinositol-linked proteins (GPI-linked proteins).

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Glycosylphosphatidylinositol-linked proteins (GPI-linked proteins)

Occur in all eukaryotes, but are particularly abundant in parasitic protozoa

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Fatty acylated proteins


Myristoylated and palmitoylated proteins (C14/C16)

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Prenylated proteins

Farnesylated and geranylgeranylated proteins (C15/C20 isoprene units)

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Waxes

Esters of long-chain saturated and unsaturated fatty acids with long-chain alcohols
Typically have fairly high melting points
Skin glands secrete waxes to protect hair and skin to keep it pliable, lubricated, and waterproof

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Spermaceti – cetyl palmitate

Wax (from whale oil) –useful for pharmaceuticals (creams, ointments, tableting and granulation)

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Carnauba wax

Brazilian palm tree – a hard wax used on cars and boats

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Oils

Melting/boiling points are not usually sharp (most fats/oils are mixtures) - liquid. If shaken with water, oils emulsify.
Pure fats and oils are colorless and odorless (color and odor result of contaminants)
Butter - bacteria give flavor, carotene gives color

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Calcium and magnesium soaps

Very poorly water soluble (hard water contains calcium and magnesium salts that insolubilize soaps)

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Floating soap

contains air

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Transparent soap

(contains sucrose)

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Green soap

mixture of sodium and potassium linseed oil

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Castile

Sodium soap of olive oil

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Potassium

soft soap- shaving soaps are potassium soaps of coconut and palm oils

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Sodium

Sodium