Kaplan MCAT - Biochemistry - Ch 5 Lipid Structure and Function

amphipathic

having both a hydrophilic region and a hydrophobic region

phospholipids

A molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.

glycerol

A three-carbon alcohol to which fatty acids are covalently bonded to make fats and oils.

saturation

the state or process that occurs when no more of something can be absorbed, combined with, or added.

saturated fatty acid

molecule in lipids in which carbon atoms are bonded to as many hydrogen atoms as possible

unsaturated fatty acid

a fatty acid whose hydrocarbon chain contains one or more double bonds

Glycerophospholipids (phosphoglycerides)

-have a glycerol backbone bonded by ester linkages to 2 fatty acids & by a phosphodiester linkage to a highly polar head group

-named according to the polar head group b/c the head group determines the membrane surface properties

-Has FA group at positions 1 and 2 & polar or charged head group in a phosphodiester linkage to position 3

Phosphatidylcholine

glycerophospholipid w/ a choline head group

Phosphatidylethanolamine

glycerophospholipid w/ an ethanolamine head group

Sphingolipids

Lipids with a sphingosine backbone, 4 classes: ceramide, sphingomyelins, glycosphingolipids, gangliosides. Can be phospholipids or glycolipids

ceramide

sphingosine + fatty acid

The simplest sphingolipid, with a single hydrogen as its head group.

sphingomyelins

- major class of sphingophospholipids

- contain phosphatidylcholine or phosphatidylethanolamine head group

- major component of myelin sheath

glycosphingolipids

• sphingolipids w/ head groups composed of sugars bonded by glycosidic linkages

-not phospholipids b/c they have no phosphodiester linkage

- found on the outer surface of the plasma membrane

cerebrosides

Glycosphingolipids with one sugar

globosides

glycosphingolipids with two or more sugars

gangliosides

Glycolipids with a head group composed of oligosaccharides with a terminal sialic acid (NANA) molecule.

N-acetylneuraminic acid

sialic acid

waxes

-esters of long-chain fatty acids w/ long chain alcohols

- form pliable solids at room temp.

- function as protection for plants and animals

Terpenes

class of lipids built from isoprene moieties and share a common structural pattern with carbons grouped in multiples of five

1) One terpene (monoterpene) contains two isoprene units.

Generally strongly scented

Produced mainly by plants and insects

(Turpentine)

grouped according to number of isoprene units present

monoterpenes

C10H6

two isoprene units

abundant in essential oils and turpentine

sesquiterpenes

* sesqui means ½

*contain 3 isoprene units

diterpenes

four isoprene units

ex. vitamin A --> makes retinal (pigment necessary for sight)

Carotenoids

tetraterpenes - have eight isoprene units

ex. beta carotene and lutein

triterpenes

-have 6 isoprene units

-can be converted to cholesterol & various steroids

steroids

lipids characterized by a carbon skeleton consisting of four fused rings, 3 cyclohexane and one cyclopentane

steroid hormones

-steroids that act as hormones

-secreted by endocrine glands into the bloodstream & then travel to protein carriers to distant sites where they bind to specific high-affinity receptors & alter gene expression

cholesterol

A steroid that is an important component of animal cell membranes and that acts as a precursor molecule for the synthesis of other steroids such as hormones.

Prostaglandins

* 20 carbon molecules

*unsaturated carboxylic acids derived from arachidonic acid

*contain 1 five carbon ring

* act as paracrine or autocrine signaling molecules

*regulate synthesis of cAMP (intracellular messenger that regulates action of other hormones)

*influence sleep-wake cycles, have effects on smooth muscle, involved in elevation of body temp due to fever

arachidonic acid

an omega-6 polyunsaturated fatty acid with 20 carbons and four double bonds; present in small amounts in meat and other animal products and synthesized in the body from linoleic acid.

vitamin

An essential organic (carbon-containing) compound needed in small amounts in the diet to help regulate and support chemical reactions and processes in the body. Cannot be synthesized by the body

Vitamin A

-carotene

-unsaturated

- important in vision, growth, development, & immune function

-Important metabolite of vitamin A is retinal: component of light sensing molecular system in the human eye

-Retinol (the storage form of vitamin A) is oxidized to retinoic acid --> hormone that regulates gene expression during epithelial development

Vitamin D

-cholecalciferol

-consumed or formed in a UV light driven reaction in the skin

-vitamin D is converted to calcitriol which increases calcium and phosphate intake in intestines (promotes bone production)

-Regulates calcium so it is added to milk to aid in absorption of calcium

Vitamin E

Tocopherols, tocotrienols. Involved as biological antioxidants.

tocopherols

members of the vitamin E family having the chemical structure of a complex ring structure with a long saturated side chain

tocotrienols

members of the vitamin E family having the chemical structure of a complex ring structure with a long unsaturated side chain

Vitamin K

- phylloquinone and menaquinones

- important for formation of prothrombin (clotting factor)

- performs post-translational modifications on a number of proteins, creating calcium binding sites

Phylloquinone (K1)

plant form of vitamin K

Menaquinone (K2)

the form of vitamin K produced by bacteria in the colon

Triacylglycerols (triglycerides)

-composed of three fatty acids bonded by ester linkages to glycerol

-nonpolar and hydrophobic

-insoluble in water

-the preferred method of storing energy for long-term use

-the carbon atoms in lipids are more reduced than carbohydrates, giving twice as much energy per gram during oxidation

-very hydrophobic, so they are not hydrated by body water and do not carry additional water weight

adipocytes

store triglycerides

Saponification

the reaction between a fat and a strong base to produce glycerol and the salt of a fatty acid (soap) - the ester hydrolysis of triacylglycerols using a strong base. Traditional base is lye (sodium or potassium hydroxide)

surfactant

lowers the surface tension at the surface of a liquid, serving as a detergent or emulsifier

colloid

A mixture containing small, undissolved particles that do not settle out.

micelles

tiny aggregates of soap with the hydrophobic tails turned inward and the hydrophilic heads turned outward, thereby shielding the hydrophobic lipid tails and allowing for overall solvation