Lipids .pdf

7/23/2019 Lipids .pdf

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Lipids

PH 161 BiochemistryGroup 2

Prof. Palaruan


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Objectives

By the end of the class, you should be able:

I. To enumerate the characteristics of Lipids

II. To explain the basic structure of Lipids

III. To classify Lipids based on their structure

IV. To enumerate some of the biomedical

importances of Lipids

V. To explain the process of Lipid digestion


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Chemistry: Definition

Lipids are a class of chemically diversemoleculesthat are generally non-polar!


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Lipids are usually any fatty acidand its derivatives, or anysubstance biosynthetically orfunctionally related to them.


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In general, they are for storage(fatty acids and oils),for use as structural components of biologicalmembranes(phospholipids and steroids), and asenzyme cofactors, electron carriersand pigmentsamong others.


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Chemistry: Characteristics

Lipids are generally insoluble in water, and hence,nonpolar like hydrocarbons.

There are some lipids that exhibit amphipathicity,meaning part of the molecule is hydrophobic andanother, hydrophilic.

Examples: Bile salts, phospholipids, sphingolipids,fatty acids, and some cholesterols


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These amphipathic molecules tend to self orient inoil:water interfaces.


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When a critical concentration of amphipathic lipids ispresent in an aqueous medium, they tend to formmicelles.


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Lipids are important dietary constituents as they havehigh energy value.

1g of fat = 9 kcal

1g of protein = 4 kcal


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In the body.


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As used in transport


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Structure

Lipids generally have both polar and nonpolar ends (although predominantly polar).

For each classification of lipid, theres aspecific structure.


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Structure

FATTY ACIDS-are the precursors to more complex lipids

-consist of a carboxylic acid and a long unbranchedhydrocarbon chain-may be saturated (no double bond C=C present) orunsaturated (double bonds are present)


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Structure

a. Saturated Fatty Acids


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Structure

b. Unsaturated Fatty Acids- may be mono or poly


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Structure

b. Unsaturated Fatty Acids-may also be cis or trans


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Structure

WAXES-esters with long hydrocarbon chains on both ends


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Structure

PHOSPHOLIPIDS-contains a hydrophobic tail and hydrophilic

head-glycerol esterified with two fatty acids andone phosphate group

-hydrophilic: glycerol, phosphate and cholinehydrophobic: the remainder of the molecule


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Structure

PHOSPHOLIPIDS


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Structure

PHOSPHOLIPIDS


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Structure

STEROIDS-exhibits a ring of three adjacent cyclohexanes and a

single cyclopentane


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Structure

TRIACYLGLYCERIDES-fatty acid triesters of glycerol


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Structure

GLYCOLIPID-sugar-containing lipid


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Structure

PROSTAGLANDINS-cyclic fatty acid compounds

-always contain 20 carbons, and a 5-member ring


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Precursors to Lipids

Molecules from where lipids are formed Namely the ff:

Fatty acids Glycerol Hydrocarbons


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a. Fatty acids

building blockscomposed of C, H, Oarranged in chainscarrying terminalcarboxyl (-COOH)

which gives the acidicproperties of themolecule

b. Glycerol

Glycerol (or Glycerine)is a simple polyol withthree hydroxyl (-OH)groups.

It serves as the

backbone of thetriglycerides or fats.


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c. Hydrocarbons

an organiccompoundconsisting entirelyof hydrogen andcarbon

alkanes, alkenes,alkynes


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Classifications

1. Simple Lipids

fatty acid esters with alcohols do not carry any other substances Examples are:

Fats/Trigycerols Waxes


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1.1 Triglycerols

also known as triacylglycerides/triglycerides or

triacylglycerols, more commonly known as fats

esters of fatty acids with the alcohol glycerol usually solid (fats) in room temperature

liquid state of fats (at higher temperature) is

termed as oil


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1.1 Triglycerols

stored as fatdroplets inspecialized

vertebrate fat cellscalled adipocyte

most abundant

lipids in nature


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1.1 Triglycerols

stored in seeds/plant cells Triacylglycerides are either simple (three fatty

acid radicals are identical or similar) or mixed

(three fatty acids are different) many natural fats found in foods are complex

mixtures of simple and mixed triacylglycerols


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1.1 Triglycerols

A. Saturated Fats (no double bond) animal in origin solid at room temperature called saturated because of Hydrogen


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1.1 Triglycerols

B. Unsaturated Fats (with doublebonds)

Plant oils

Lower cholesterol layer two categories

MUFA (monosaturated fatty acid---1 double bond only)

PUFA (polysaturated fatty acid---numerous double bonds) PUFA is healthier


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1.2 Waxes

Are esters of long-chain fatty acidswith long-chain monohydroxyalcohols having higher molecularweight

in solid phase generally higher melting point than

triacylglycerols water repellant, with a firm

consistency used in manufacture of lotions,

ointments, and polishes(shoewaxing)


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Classifications

2. Complex Lipids esters of fatty acids containing groups in addition to fatty acids

and an alcohol, a phosphoric acid residue

usually have nitrogen-containing bases and other constituents


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!4 Pics One Word!


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2.2 Glycolipids

Glyceroglycolipid- glycerol backbone- cerebroside

(galactocerebroside): foundprimarily in the brain and

peripheral nervous tissues

Sphingoglycolipid- glycosphingolipid- sphingosine backbone- found at the outer face of

plasma membranes

- contain a sugar residue (may be mono-, di- or oligosaccharide); nophosphate group

- found in the blood as they act as receptors at the surface of the red

blood cell

Tay-Sachs Disease- occurs when harmful quantities of a

sphingoglycolipids accumulate in thenerve cells of the brain


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2.3 Lipoprotein

- contains both proteins and lipids

- enzymes, transporters, structural proteins, antigens, adhesins

and toxins

- High density (HDL) and low density (LDL) lipoproteins: enablefats to be carried in the blood stream

- High levels of lipoproteins (LDL) can increase the rheart disease: atherosclerosis (stroke and heart attack)


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Classifications

3. Derived Lipids

Derived Lipidsare derived from simple andcompound lipids via hydrolysis

Namely the ff: Steroids and hormones Fatty aldehydes

Ketone Bodies Lipid Soluble vitamins and micronutrients


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!4 Pics One Word!


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Derived Lipids

a. Steroidsand some hormones

Steroids are flat molecules with four interlockingrings with no fatty acid tail. One of the importantsteroids of the body is cholesterol.

Hormones such as sex hormones testosterone,estrogen and progesteroneare also classified

under steroids. Vitamin Dis also a steroid.

H d A b li St id


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How do Anabolic Steroidswork?Anabolic-androgenic steroidspromote growth ofmuscles. Once ingested or injected, steroids travel inthe bloodstream to the skeletal muscles where they

bind with androgen receptors. They react with theDNA of the cells and stimulate protein synthesiswhich leads to increase in cell size or muscle

hypertrophy.

***Warning: There are side-effects!


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Derived Lipids

b. Fatty aldehydes

Aldehydes with fatty aliphatic 8 or morecarbon membered chain attached.


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Derived Lipids

c. Ketone Bodies

Three water-solublemolecules producedby the liver when theglucose level of bodyis low in level (ie.

during low foodintake) as sources ofenergy.

Acetone

Acetoaceticacid

Beta-hydroxybutyric acid


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Excess Ketone Bodies

Ketosis

Presence of ketone bodies inthe blood

Ketonuria Presence of ketone bodies

Ketone bodies are toxic and acidic.Some can be expelled through

urination.Acetone on the other hand can bereleased out of the body viarespiration (your breath will smell

fruity)


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Derived Lipids

d. Lipid-soluble vitaminsand micronutrients

Vitamins are essential

micronutrients neededby the body is smallamount for proper

functioning. Some ofthe fat solublevitamins are A, D, E, Kusually stored in liver

and adipocytes

Homeostatic Imbalance:


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Homeostatic Imbalance:LDLLow Density Lipoprotein

Bad cholesterol Excess of LDL may lead to stroke, heart

attack and high blood pressure


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Functions

1. STORAGE LIPIDS Triacylglycerols or fats

provide stored energy Adipocytes in vertebrates Oils in plant seed


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Functions1. STORAGE LIPIDS

Why triacylglycerols as fuel instead of polysaccharides? Theyproduce more than 2x energy(from oxidation): 9 calories per gram, whereas protein and carbohydrate contain

only 4 calories per gram Carbohydrates = ready source of energy, but fats = easier

and lighter to carry around because they are unhydrated unlike

carbohydrates


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Functions

2. LIPIDS AS INSULATORS

Thermal Insulation-

Subcutaneous tissue: layer of fat

just below your skin helps keep

internal body temperature regular

despite the external temperature E.g. Seals, walruses, penguins and other

warm-blooded polar animals, humans


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Functions

2. LIPIDS AS INSULATORS Electrical Insulation- Nonpolar lipids in

myelinated nerves


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Functions

3. SOURCE OF FAT-SOLUBLE VITAMINS


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Functions

3. SOURCE OF FAT-SOLUBLE VITAMINS

Vitamin A- furnishes the visual pigment of the vertebrate eye

and is a regulator of gene expression during epithelial cellgrowth

Vitamin D - precursor to a hormone that regulates calciummetabolism

Vitamin E - protects the membrane lipids from oxidativedamage

Vitamin K - essential in the blood-clotting process


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Functions

4. PROTECTION Layers of fat surround vital organs to protect them

from injury (Visceral Fat) Waxes found on animal feathers, in human ears and

even on the leaves of plants function mainly inprotection


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Functions

5. STRUCTURAL LIPIDS Phospholipids are important component of cell membrane

structure (membrane permeability) Sphingolipidsat cell surfaces are sites of biological

recognition. e.g. Glycosphingolipids as determinants of blood

groups O, A, B Cholesterol, the major sterol in animals, is both a

structural component of membranes and precursor to awide variety of steroids.


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The oligosaccaride headgroups of the

glycosphingolipidsdetermine if the blood

group is O, A, or B.


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6. LIPIDS AS SIGNALS Cellular metabolic regulators - Control of the bodys homeostasis

Steroid Hormones:estrogen, progesterone, cortisol, aldosterone

Functions


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6. LIPIDS AS SIGNALS

Prostaglandins, Thromboxanes, Leukotrienes

Platelet-activating factor: released by basophilsand stimulates platelet aggregation and therelease of serotonin (a vasoconstrictor) fromplatelets.

Functions


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Spermaceti Organ

A. Spermaceti Organ of sperm whales 1. 90% of headweight is spermaceti organ 2. blubbery masscontaining up to 4 tons of spermaceti oil -

triacylglycerol + waxes mixture - lots of unsaturatedfatty acids - liquid at normal body temp but solidifiesat lower temps 3. buoyancy of whale changes tomatch surrounding waters when diving for food B.Inheritable Human Diseases 1. Hydrolytic enzymes inlysosomes break down lipids 2. When enzyme has adefect, partial breakdown products accumulate in

tissues and cause serious damage


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Biomedical Importance

Inheritable Human Diseases

1. Hydrolytic enzymes in lysosomes break downlipids 2. When enzyme has a defect, partial

breakdown products accumulate in tissues and causeserious damage


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!4 Pics One Word!


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Lipid Digestion

Major lipids in our diet are triacylglycerols and to alesser extent phospholipids.

The fat-soluble vitamins are absorbed dissolved inthe lipid micelles, but this is impaired on a very lowfat diet


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Lipid Digestion

Hydrolysis of Triacylglycerols via gastric &lingual lipases to aid emulsification(Triacylglycerol -> Diacylglycerol + fatty acids)

Pancreatic Lipase is secreted into the

small intestine, aided by colipase(Diacylglycerol -> monoacylglycerol + fatty acids)

Hydrolysis of monoacylglycerol(only 25% of ingested triacylglycerol is completely

hydrolyzed into glycerol & fatty acids)

Bile salts enable emulsification of theproducts of lipid digestion into micelles

and liposomes


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Lipid Digestion

absorbed intothe intestinalepithelium,

mainly of thejejunum

All long-chainfatty acids

absorbed areconverted back

totriacylglycerolin the mucosal

cells

Triacylglyceroland other

products of lipiddigestion are then

secreted aschylomicrons into

the lymphaticsand then enter

the bloodstreamvia the thoracic

duct.


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Lipid Digestion


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THANK

YOU FOR

LISTENING!


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References

http://www.ext.colostate.edu/pubs/foodnut/09315.html

http://biology.tutorvista.com/biomolecules/lipids.html

http://catalog.flatworldknowledge.com/bookhub/reader/2547?e=gob-ch17_s02

Hallare, A. Student Handbook in General Zoology

Harpers Illustrated Biochemistry

http://www.nutriology.com/GLmetab.html

http://courses.washington.edu/conj/membrane/lipids.htm

http://courses.washington.edu/conj/membrane/lipoprotein.htm


http://lipidlibrary.aocs.org/Lipids/whatlip/index.htm

Murray, R. et al. (2003). Harpers Illustrated Biochemistry, 26th Edition. USA: McGraw-Hill Companies, Inc.

NCS, Pearson. Lipids. (2015). Retrieved 11 August 2015 from http://biology.tutorvista.com/biomolecules/lipids.html

http://www.phschool.com/science/biology_place/biocoach/bioprop/lipids.html

Lehninger Principles of Biochemistry

http://www.livescience.com/3349-steroids-work.html

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Lipids .pdf