Lipids pdf - غير معروف

LIPID

Aim : Introduction and

Definition

Lipid are compounds that are

soluble in organic solvents, such as

ether and relatively insoluble in

water or aqeous media e.g.human

body fluid; blood,…. .The principal

unit of different forms of lipid is

fatty acid with general formula

RCOOH; R

is alphatic carbon chain

structure:

CH3(CH2)nCH2; n

is the

number of carbon. In nature, fatty

acid may be:

1.Saturated;

CH3CH2…….,

the

common one in human body is

Palmitic acid(C16)

2.Monounsaturated

CH3CH2CH=CH……(

one double

bond), and 3.Polyunsaturated(2 or

more double bonds). The EFAs are

those fatty acids that are required

in human body but cannot be

synthesized in it, so must be

supplied in the diet to support the

growth and include:

Linoleic acid C18, 2 double bonds

Linolenic acid C18, 3 double bonds

Arachidonic acid C20, 4 double

bonds. These EFAs are important

components of phospholipids of

cell membrane and mitochondrial

membrane and their deficiencies

result in defect in growth and

development.

Even the incidence of EFAs

deficiencies is rare, it can lead to

scaly dermatitis, visual and

neurologic defects. The absolute

EFAs are the linoleic acid, the

precursor of arachidonic acid that

is a substrate for Prostaglandins

synthesis and the Linolenic acid,

the precursor for other ω-3 fatty

acids

formula important for growth and

development and used

antihypertriglyceridemic drug.

Fatty acids also may be:

Short : C2-C4

Medium: C6-C10

Long: C12 and more.

The saturated fatty acids are

naturally found in Zigzag form,

while the unsaturated ones are in

kink form. The degree of

unsaturation(number of double

bonds) and

the carbon chain length are

important in determining of

melting point of fatty acids and so

of biological membrane fluidity

(permeability to lipid soluble

substances).

The important structures of lipid

materials are:

1. Triglycerides; Simple lipid

2. Phospholipids; Complex lipid

3. Sphingolipids and Glycolipids;

Complex lipid.

4.Cholesterol(Cyclolipid)

5. Lipoproteins, Male and Female Sex

Hs, Adrenal Cortical Hs(cortisol and

aldosterone), Vitamin D, and other.

Definitions:Triglyceride; TG. It is fatty

acid ester of glycerol.

(Triacylglycerol):

CH2OCOR1

glycerol CHOCOR2fatty

CH2OCOR3acids

R1,R2,R3 are different fatty

acids.TG is considered as nonpolar

structure and so not implied in CM

formation.

Glycerol+R1=Monoglycerol

Glycerol+R1+R2+Diacylglycrol

Glycerol+|R1+R2+R3=Triacylglycer-

TG represents(its function) the
principal storage form of energy in
adipose

tissues

that

needed

physiologically in prolonged fasting
and starvation and pathologically,
for

example

uncontrolled

diabetes mellitus. It is also the
preferred form of nutrient that is
used by muscle in producing of
chemical

energy

ATP

under

normaons.

Physiolog. and pathologic

conditions. TG forms about 95 %

of dietary fat.

Phospholipids;PL(

Phosphoglycerolipids):

CH2OCOR1

CHOCOR2

CH2O

PO3-b

b: is Nitrogen base

Base

Choline Lecithin

Ethanol amine Cephalin

Serine Phosphatidylserine

Inositol Phosphatidyl inositol

triphosphate

And Cardiolipin phospholipid;

Diphosphatidyl glycerol.

PLs are considered amphipathic

compounds because of their

formation from polar(PO4 and

nitrogen base) and nonpolar(fatty

acids) structures.

Lecithin PL is:

1.the predominant type of PL in

2.the source of choline component

of the neurotransmitter, the

Acetylcholine

3.the principal lipid component of

Lung surfactant(90 % lipid and 10

% protein), its

deficiency in preterm infants is

is associated with inadequate

production or secretion of

surfactant causes Respiratory

Distress Syndrome(RDS), the

significant cause of death.

Lecithin is made and secreted by

pneumocytes to act as surfactant,

decrease the surface tension of

fluid lining the alveoli so reducing

the pressure needed to reinflate

alveoli, thereby preventing alveolar

collapse(atelectasis)

4. involved in emulsification of fat

diet in small Intestine along with

Bile salt. Cardiolipin PL is the

principal type of PL that involved in

inner mitochondrial

membrane structure(important for

maintenance of certain respiratory

complexes).

Anti-cardiolipin ACL is used in

investigation of abortion or dead

infant delivery, because this PL

cardiolipin is recognized by

antibodies that raised against

Treponema Pallidum the bacterium

that causes Syphilis. Phosphatidyl

inositol triphosphate in CM act as

a second messenger(internal

messanger) for protein hormones

action

action. Platelet activating factor

PAF and Plasmalogensare

compounds that belong to PL

structure but differ in containing

ether linkage ROR instead of ester

linkage ROCOR at C1 of PL. PAF is

synthesized and released by a

variety of cell types, binds to

surface receptors with triggering

potent thrombotic and acute

inflammatory processes. It causes

platelets to aggregate and

degranulate, and neutrophiles and

macrophages to produce

superoxide radicals, the killing

substance of infected bacterium.

Sphingolipids(Phosphoshingolipids

: Sphingomyelin):

These are also PL but differ from

phosphoglycerolipids(previous

types) in their structure: They are
composed of Sphingosine alcohol

instead of Glycerol. Sphingosine is

C18 monoalcoholamine:

CH3(CH2)12CH=CHCHOHCHNH2CH2OH

Sphingosine+fatty acid=Ceramide

Ceramide+Nitrogen base=

sphingolipid. Of the most

significant type of these PL in

humans is sphingomyelin in which

the base is choline. It is an

important component

of myelin sheath of nerve fibers,

insulates and protects neuronal

fibers of the central nervous

system(preventing the short

circulation of nerve electrical pulse

transmission).

Glycolipids:

These are another type of lipid.

Their structures are relatively

similar to sphingolipid;

Ceramide+ carbohydrate moity(or

moities)=Glycolipids. Of which :

the simple forms are

glucosylsphingolipid and

galactosylsphingolipid(only one

unit of

CHO).The complex forms are

Globoside and Ganglioside(2-9

units of CHO).They are found in

outer leaflet of plasma membrane

and contribute to cell surface

In summary

1.Lipids are water insoluble

substances(insoluble in systemic

circulation). 2. TG is the major

dietary lipid and functions as

stored metabolic energy, the major

component that act as source of

energy is fatty acids, particulary

the saturated one.

3.EFAs; are polyunsaturated fatty

acids; particulary Linoleic acid and

Linolenic acid which are precursors

of ω-

drug(antihypertriglyceridemia).

EFAs are essential for growth and

development.4. Phospholipids are

amphipathic and so involved in CM

and mitochondrial membrane

Structure. The most important one

is lecithin. RDS, ACL and APL.
Sphingomyelin is also PL, but

contains sphingomyelin instead of
glycerol alcohol. It is an important

CM component of CNS and myelin

sheath.