Part 2: Fats Prepared by: Dr A. Riasi ( Isfahan University of Technology ) Reference: Lehninger Biochemistry Advance Biochemistry Isfahan University of.

Part 2:

Fats

Prepared by:

Dr A. Riasi ( Isfahan University of Technology)

Reference:

Lehninger Biochemistry

Advance Biochemistry

Isfahan University of Technology

Biological Lipids

Lipids are divides to three original groups:

Fats and oils

Phospholipids and sterols

Other lipids

Storage lipids

Fatty acids are carboxylic acids:

CH3(CH2)n-COOH

Storage lipids

A few contain three-carbon rings, hydroxyl

groups, or methyl group branches.

A simplified nomenclature for these compounds

specifies the chain length and number of double

bonds.

Storage lipids

The positions of any double bonds are specified

by superscript numbers following (Δ).

A 20-carbon fatty acid with one double bond

between C-9 and C-10 and another between C-12

and C-13 is designated as C20:2(Δ9,12).

Storage lipids

The poly unsaturated fatty acid of Arachidonic [20:4

(Δ5,8,11,14)] is an exception to this generalization.

CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH14 11 8 5

Storage lipids

CH3-(CH2)7-CH=CH-(CH2)4-CH2-CH2-CH2-COOHω

n

Δαβγ

Storage lipids

In nearly all naturally occurring unsaturated

fatty acids, the double bonds are in the cis

configuration.

Storage lipids

Storage lipids

11

What are the differences between α Linolenic acid and γ Linolenic acids?

Storage lipids

Comparison of the satutare Stearic acid (left), trans

isomer (middle) Elaidic acid and the cis-isomer (right)

Oleic acid.

Storage lipids

Most naturally occurring triacylglycerols are

mixed.

They contain two or more different fatty acids.

Storage lipids

Storage lipids

Storage lipids

Vegetable oils are converted industrially into

solid fats by catalytic hydrogenation.

Storage lipids

Storage lipids

Biological waxes are esters of:

Long-chain (C14 to C36) saturated

Unsaturated fatty acids with long-chain (C16 to

C30) alcohols.

Storage lipids

Storage lipids

There are different generals types of

membrane lipids:

Glycerophospholipids

Galactolipids and Solpholipds

Archaebacterial tetraether lipids

Sphingolipids

Sterols

Phospholipids and sterols

Phospholipids and sterols

Glycerophospholipids and some sphingolipids

are named phospholipids.

Phospholipids and sterols

Other sphingolipids are

the glycolipids.

Phospholipids and sterols

Phospholipids and sterols

The polar alcohol may have

different charge: Negatively charged:

phosphatidylinositol 4,5-

bisphosphate

Neutral: phosphatidylserine

Positively charged:

phosphatidylcholine or

phosphatidylethanolamine

Phospholipids and sterols

The fatty acids in glycerophospholipids can be

any of a wide variety

A given phospholipid may consist of a number

of molecular species, each with its unique

complement of fatty acids.

Phospholipids and sterols

Some animal tissues are rich in ether lipids.

In ether lipids one of the two acyl chains is

attached to glycerol in ether linkage.

Phospholipids and sterols

Two kind of ether lipids:

Ether-linked chain is saturated

Ether-linked chain is unsaturated

Phospholipids and sterols

The functional significance of ether lipids in

these membranes is unknown.

The ether lipid, platelet-activating factor, is a

potent molecular signal.

It is released from leukocytes called basophils.

Phospholipids and sterols

The galactolipids & Solpholipids are

predominate in plant cells.

Phospholipids and sterols

The archaebacteria, most of which live in

ecological niches with extreme condition:

Low pH

High ionic strength

High temprature

Phospholipids and sterols

Phospholipids and sterols

Sphingolipids, have a polar head group and

two nonpolar tails.

Unlike glycerophospholipids and galactolipids

they contain no glycerol.

Phospholipids and sterols

Sphingolipids are composed of:

one molecule of the long-chain amino alcohol

one molecule of a long-chain fatty acid

a polar head group

Phospholipids and sterols

Carbons C-1, C-2, and C-3 of the sphingosine molecule are structurally analogous to the three carbons of glycerol in glycerophospholipids.

Phospholipids and sterols

There are three subclasses of sphingolipids, all

derivatives of ceramide but differing in their

head groups:

Sphingomyelins,

Neutral (uncharged) glycolipids,

Gangliosides.

Phospholipids and sterols

Phospholipids and sterols

Sterols are structural lipids present in the

membranes of most eukaryotic cells.

Cholesterol is the major sterol in animal

tissues, is amphipathic.

Similar sterols are found in other eukaryotes:

stigmasterol in plants and ergosterol in fungi.

Phospholipids and sterols

The sterols serve as precursors for a variety of

products with specific biological activities.

Steroid hormones

Bile acids to make them more readily accessible to

digestive lipases.

Phospholipids and sterols

Steroids are oxidized derivatives of sterols

Steroid hormones move through the

bloodstream (on protein carriers) from their

site of production to target tissues, where they

enter cells, bind to highly specific receptor

proteins in the nucleus.

Phospholipids and sterols

The major groups of steroid hormones are the

male and female sex hormones and the

hormones produced by the adrenal cortex.

Phospholipids and sterols

Prednisone and prednisolone are steroid drugs

with potent antiinflammatory activities.

They have a variety of medical applications,

including the treatment of asthma and

rheumatoid arthritis.

Phospholipids and sterols

Phospholipids and sterols

Eventually the fat-soluble group was resolved

into the four vitamin groups A, D, E, and K,

all of which are isoprenoid compounds.

Two of these (D and A) serve as hormone

precursors.

Phospholipids and sterols

Vitamin D3, also called cholecalciferol, is

normally formed in the skin from 7-

dehydrocholesterol in a photochemical

reaction driven by the UV component of

sunlight.

Phospholipids and sterols

Vitamin D3 is not itself biologically active, but

it is converted by enzymes in the liver and

kidney to 1,25-dihydroxycholecalciferol.

Vitamin D2 (ergocalciferol) is a commercial

product formed by UV irradiation of the

ergosterol of yeast.

Phospholipids and sterols

Vitamin D2 is structurally similar to D3, with

slight modification to the side chain attached

to the sterol D ring.

Phospholipids and sterols

Like steroid hormones, the product of vitamin

D metabolism, 1,25-dihydroxycholecalciferol,

regulates gene expression—for example,

turning on the synthesis of an intestinal Ca2-

binding protein.

Phospholipids and sterols

Vitamin A (retinol) in its various forms

functions as a hormone.

The vitamin A derivative, retinoic acid,

regulates gene expression in the development

of epithelial tissue, including skin.

Phospholipids and sterols

The vitamin A derivative, retinal, is the

pigment that initiates the response of cells of

the retina to light, producing a neuronal signal

to the brain.

Phospholipids and sterols

In vertebrates, -carotene, the pigment that

gives carrots, sweet potatoes, and other yellow

vegetables their characteristic color, can be

enzymatically converted to vitamin A.

Phospholipids and sterols