Download - Chem 1152: Ch. 18 Lipids. Lipids Biomolecules defined in terms of solubility: – Insoluble in water but soluble in nonpolar solvents. – Waxy, greasy or.

Chem 1152: Ch. 18

Lipids

LipidsLipids• Biomolecules defined in terms of solubility:

– Insoluble in water but soluble in nonpolar solvents.– Waxy, greasy or oily compounds.

• Biological Functions:– Energy Storage– Structural component of cell membranes– Signaling molecules

Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011

Two major classes

Saponifiable LipidsSaponifiable LipidsSaponification: base hydrolysis of esters to produce carboxylic acid salt and alcohol


• Simple Lipids:– Contain fatty acids and alcohols

• Complex Lipids:– Contain multiple fatty acids,

alcohol, something else

Fatty AcidsFatty Acids• Building blocks of many lipids• Long chain carboxylic acids• Carboxyl group hydrophilic at physiological pH (7.4)


MicellesMicelles

• In aqueous solutions, ionized fatty acids form spherical clusters– Polar head is facing out towards water (hydrophilic)– Long alkane chains associate in interior (hydrophobic) through weak dispersion forces


Characteristics of Fatty AcidsCharacteristics of Fatty Acids

1. Straight chain (unbranched) carboxylic acids2. Comprised of 10-20 carbons3. Usually have even number of carbons4. Can be saturated or unsaturated5. Usually no other functional groups

• Unsaturated fatty acids usually contain double bonds in the cis configuration

• This creates kink or bend in chain that prevents unsaturated fatty acids from packing together closely unlike saturated fatty acids– Results in weaker intermolecular forces, lower MP’s – Usually liquid at room temp

O

O-

CH3

CH3

O

O-

unsaturated

saturated


Properties of Unsaturated Fatty AcidsProperties of Unsaturated Fatty Acids


• The kink or bend in chain of unsaturated fatty acids prevents from packing together closely unlike saturated fatty acids– Results in weaker intermolecular forces, lower MP’s – Increases fluidity of biological membranes

Properties of Unsaturated Fatty AcidsProperties of Unsaturated Fatty Acids


• Phospholipids form bilayer in cell membrane

Essential Fatty AcidsEssential Fatty Acids


• The human body can synthesize all but two of the necessary fatty acids• Linoleic acid (omega-6 fatty acid)• Linolenic acid (omega-3 fatty acid)

• Must be obtained from diet (plant and fish oils)• Polyunsaturated (multiple double bonds) • 18 Carbons in chain

Diets rich in omega-3 fatty acids may:decrease serum cholesterol, triglycerides reduce risk of heart disease

Fish Nuts Kidney Beans

Sources of omega-3 fatty acids: Spinach Broccoli and cauliflower Oils

Structures of Fats and OilsStructures of Fats and Oils


• Fats: Triglycerides from animal (saturated)• Oils: Triglycerides from vegetables

(unsaturated)• These are esters (alcohol + acid)• Alcohol derived from glycerol• Acid from fatty acids

Most common

lipids

triglyceride

Reactions of TriglyceridesReactions of Triglycerides


hydrolysis

saponification

hydrogenation

triglyceride

Ester of 3 alcohols, 3

acids

Chemical Properties of Fats and OilsChemical Properties of Fats and Oils


• Triglycerides exhibit chemical properties of esters and alkenes

Rxn: Hydrolysis

Breakdown of cellular fats to supply energy begins with lipase catalyzed hydrolysis reaction



Rxn: Saponification

Soapmaking (up to AD 500), by adding base (lye or aqueous extract of wood ash) to animal fat



Rxn: Hydrogenation

Results in partial hydrogenation (partially-hydrogenated vegetable oils) Semi-solids that don’t separate Crisco

WaxesWaxes


• Simple, saponifiable lipids (long chain fatty acid + alcohol = ester)• Alcohol derived from long chain alcohols (12-32 carbons) not glycerols• Water insoluble• Occur in nature as protective coatings on:

• Feathers• Fur• Skin• Leaves• Fruits

Beeswax

PhosphoglyceridesPhosphoglycerides


• Complex lipids• Serve as major components of cell membranes• Also known as phospholipids• Structure similar to triglycerides

triglyceride

phosphoglyceride



• The most common phosphoglycerides have choline, ehanolamine, or serine attached to the phosphate group.



Lecithins•Phospholglycerides that contain choline•Soy lecithin used to provide smooth texture to margarine, chocolate

Cephalins•Phospholglycerides that contain ethanolamine or serine

Functions: •structural components of cell membranes •micelle forming agents

Functions:•Cell membranes•Blood-clotting

Phosphatidylcholine (lecithin) Cephalin

SphingolipidsSphingolipids


• Complex lipid found in cell membrane• Contain sphingosine instead of glycerol• These are found in brain and nerve tissue, and in myelin sheath that

surrounds nerves

GlycolipidsGlycolipids


• Another type sphingolipid• Contain carbohydrates• AKA cerebrosides due to abundance in brain tissue• No phosphate linkage

Related DiseasesRelated Diseases


• Some human diseases are related to abnormal accumulation of sphingomyelins and glycolipids

Fluid-mosaic Model of Biological MembranesFluid-mosaic Model of Biological Membranes


• Cell membranes for both prokaryotic and eukaryotic cells comprised of lipids organized in a bilayer

SteroidsSteroids


Exhibit feature of other lipids (e.g., soluble in non-polar solvents) Cholesterol is most abundant steroid in human body

Essential component of cell membranes Precursor for other steroids:

Bile salts Sex hormones Vitamin D Adrenocorticoid hormones

Synthesized in liver or obtained from food May contribute to atherosclerosis

CH3

CH3

CH3

CH3

OH

CH3

Steroid Cholesterol

Bile SaltsBile Salts

Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://www.medicinenet.com/gallstones/article.htm

Yellow-brown or green liver secretion stored in gallbladder

Bile salts are released into intestine to separate large globules of lipids into smaller droplets

Bile salts also emulsify (mix immiscibles) cholesterol found in the bile for excretion

Gallstones may occur if cholesterol too high and/or bile salts too low

Steroid HormonesSteroid Hormones

http://schoolworkhelper.net/2010/07/the-endocrine-system-function-and-structure/

Hormone: Chemical produced in the cell or gland that delivers a message affecting cells in another part of the organism

Steroid hormones derived from cholesterol Two Major Steroid Hormones:

Adrenocorticoid Hormones Male and Female Sex Hormones

Steroid hormones diffuse through the cell membrane and combine with receptor proteins in the cytoplasmHormone-receptor complex cause cell to respond to hormone by interacting with cell DNA and stimulating protein synthesis

CH3

CH3

CH3

CH3

OH

CH3

Adrenocorticoid HormonesAdrenocorticoid Hormones


Produced in adrenal glands located at top of kidneys Classified into 2 functional groups: Mineralocorticoids: Regulate concentration of ions (Na+) in body fluids

Aldosterone: most important mineralocorticoidPromotes absorption of Na+ and Cl- in kidney tubules

Glucorticoids: Enhance carbohydrate metabolism Cortisol is major glucocorticoid in human body Increases glucose and glycogen concentration in body Cortisol, cortisone and prednisolone exert anti-inflammatory effects

Used to treat rheumatoid arthritis, bronchial asthma

Male Sex HormonesMale Sex Hormones

Seager SL, Slabaugh MR, Chemistry for Today: General, Organic and Biochemistry, 7th Edition, 2011; http://artofamandanelson.blogspot.com/2011/09/generating-topics-steroids.html

Male sex hormones (androgens) produced in testes Testosterone: Most important

Promotes normal growth of male genitalia and aids in development of secondary sex characteristics

Anabolic steroids banned for use by athletes include testosterone and derivatives

Use of these can lead to:Liver tumorsTesticular atrophyDecreased sperm count

Female Sex HormonesFemale Sex Hormones


Female sex hormones promote development of secondary sex characteristics Increase in voice pitch Increased breast size Inhibition of facial hair

Estrogens: Primary female sex hormones, play important roles in reproduction:

Estradiol Estrone Progesterone

ProstaglandinsProstaglandins


First identified in secretions from male prostate gland Currently about 20 known prostaglandins in both men and women Cyclic compounds derived from arachidonic acid Hormone-like

Functions:Regulate menstruationPrevent conceptionInduce uterine contractions during childbirth

Therapeutic applications:Induce laborTreat asthmaTreat peptic ulcers