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Lipids Function and Structure

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I. THE MOLECULAR STRUCTURE OF LIPIDS

Unlike the proteins, nucleic acids, and polysaccharides, lipids are not polymers

They are quite small molecules. The predominance of hydrocarbon chains (-

CH2-CH2-CH2--) in their structure, lipids have a hydrophobic, which explain why they are insoluble or only poorly soluble in water

They are readily solible in non polar solvent solvent such as ether, chloroform, and benzene

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cis

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DEFINISI

composed of carbon, hydrogen, and oxygen but have many more hydrogens than oxygens. Different types of lipids include the neutral lipids ( fats and oils ), the phospholipids, steroids, and waxes.

Kelompok heterogen senyawa yang memiliki sifat tidak larut dalam air; larut dalam senyawa non polar (eter, kloroform, benzene)

lemak, minyak, wax, dll

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Berdasarkan muatan

Neutral LipidTGKolesterol/ester

Polar lipid

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A. CLASSIFICATION There are many different methods of classifying

lipids. In this chapter used classification of lipids and

the biologic functions FATTY ACIDS TRIACYLGLYCEROL (triglyceride) KETONE BODIES PHOSPHOGLYCERIDES (Phospholipid) SPHINGOLIPIDS EIOCOSANOID (Prostaglandins,Thromboxanes,

Leucotrienes) CHOLESTEROL STEROID HORMONES

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FATTY ACIDS

A. Nature and Nomenclature Fatty acids are water-insoluble long-chain hydrocarbon with one carboxyl group at the end/beginning of the chain, which may be saturated or unsaturated (Table 10.1 list some biologically important fatty acids)

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1. Saturated fatty acids (SFA) do not have double bonds in the chain Nomenclature.

The systematic name gives the number of carbons, with the suffix –anoic (IND=ANOAT).Palmitic acid, for example, has 16 carbons and has the systematic name hexadecanoic acid

Structure

The general formula of saturated fatty acids is CH3-(CH2)n-COOH Where n specifies the number of methylene groups between the methyl and carboxyl carbons

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2. Unsaturated Fatty acids have one or more double bonds

Nomenclature. The most commonly used system for designating the position of double bonds in an unsaturated fatty acid is the delta (Δ) numbering system.(1). The terminal carboxyl carbon is designated carbon number 1, and the double bond is given the number of the carbon atom on the carboxyl side of the double bond.For example:Palmitoleic acid has 16 carbons and has a double bond between carbons 9 and 10. It is designated as 16:1 Δ 9 or 16 : 1 :9

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(2) The systematic name gives the number of carbon atoms,the number of double bonds, and bears thesuffic –enoic

Palmitoleic acid is cis- Δ9-hexadecenoic acid; linoleic acid, which has 18 carbons and two double bonds, is (i.e, all double bond are cis) cis- Δ9- Δ12

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Structure.

Double bonds in naturally occurring Fatty acids are always in a cis

CH2 C C CH2

H H

cis

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B. SOURCES Non essential Fatty acids Essential fatty acids

The melting point of fatty acids is related to chain length and degree of unsaturation. The longer the chain length, the higher the melting point, and the greater the number of double bonds the lower the

melting point

C. PHYSICAL PROPERTIES

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TRIACYLGLYCEROLS : FATS Structure

Triglycerides or triacylglycerols are triesters of glycerol and three fatty acids.The general formula is shown here

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FunctionThe long hydrocarbon chains of fatty acids are extraordinarily efficient for energy storage. In fact, storage of fatty acids in organism is largely in the form of triacylglycerols, or fats.

Fatty acids are converted to triglycerides for transport between tissues and for storage of metabolic fuel.

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a. The main stores are the fat deposit in fats cells (adipocytes)

b. Triglycerides have several advantages (1) Triglycerides are light (less than water). They

complete combustion to CO2 and water release 9 kcal/g as opposed to 4 kcal/g for carbohydrate.

(2)Triglycerides present no osmotic problems to the cell even when stored in large amounts, because they are water insoluble.

c.Utilization of fatty acids. The fatty acids are used by most tissues, with the exeption of the brain .

Utilization of glycerol. The glycerol, which cannot be used by adipose tissue cells, is picked up by the liver as a substrate for gluconeogenesis.

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KETONE BODIES

Keton bodies are small, water soluble, potential units of acetate: acetone, acetoacetate and β-Hydroxybutirate, all of which are formed from fatty acids (and amino acid catabolism): 

1. Synthesis of ketone bodies are limited, for example, in fasting and in

starvation

2. During starvation, keton bodies are the source of fuel

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PHOSPHOLIPIDS

A. FUNCTION Phospholipids are the major lipid constituent of cellular membranes and occur in high concentration in the lipids of glandular organs, blood plasma, egg yolk.40 % of the lipids in the erythrocyte membraneover 95 % of the lipids in the inner mitochondrial membrane, only about 20% the inner mitochondrial membrane are cardiolipin, a phosphoglyceride

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B. STRUCTURE OF PHOSPHOGLYCERIDE

Phosphoglycerides are triesters of glycerol 3-phosphate

O CH2 – O – C – R1

OR2 – C – O – CH

O CH2 – O – C – R3

O

CH2 – O – C – R1

O

R2 – C – CH O

CH2 – O – P – OH

OH

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O

CH2 – O – C – R1

O

CH – O – C – R2 O

R3 – O – P – O – CH2

OH

Glycerophospholipid Structure

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C CLASSIFICATION OF PHOSPHOGLYCERIDE

1. Phosphatidylcholine (lecithin)

2. Phosphatidylethanolamine (a cephalin)

3. Phosphatidylserine

4. Phosphatidylinositol5. Cardiolipin

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D. PROPERTIES OF PHOSPHOGLYCERIDES

1. Amphipatic

Phosphoglycerides possessing both hydrophilic and hydrophobic groups

2. Amphoteric

Phosphoglycerides bering both negatively charged and positively charged groups

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SPHINGOLIPIDS

The greatest concentration of sphingolipids is found in the CNS, particularly in white matter

Types of sphingolipids: sphingomyelin and the glycosphingolipids.

All sphingolipids are derived from sphingosine.

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A. SPHINGOMYELIN

Function. Sphingomyelin are the major phospholipid component of membranes in neural tissue

Structure. Sphingomyelin are the only sphingolipids that contain phosphate and have no sugar moiety

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OH O

CH3 – (CH2)12 – CH = CH – C – CH – NH – C – R

CH2

O

O = P – OH

O – CH2 – CH2 – N(CH3)3

+

Fatty acid

Phosphic acid

Cholin

Sphingosin

Sphingomyelin

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B. GLYCOSPHINGOLIPID Sphingolipids that contain carbohydrate

moieties are known as glycosphingolipids have been distinguished : cerebrosides and Ganglioside

1. Cerebrosides are ceramides monohexosides, the most important being galactocerebroside and glucocerebroside. Cerebrosides are found in neural tissue membrane, particularly the myelin sheath . 2. Gangliosides are ceramide oligosaccharides, they contain one or more neuraminic residue

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Sia

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C. SPHINGOLIPIDOSES

There are a number of inherited genetic disorders referred to as lipid storage diseases in which there is a deficiency of an enzyme.

For example : Gaucher’s disease, Niemann-Pick disease and Tay-Sachs

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EICOSANOIDS

Eicosanoids are products of the metabolism of the 20-carbon-poliunsaturated fatty acid arachidonic acid

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A. PROSTAGLANDINS

1.Structure .

Prostaglandins are analogs of prostanoic acids

Prostaglandin E1

COOH

OH

O

OH

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2. Functiona. Prostaglandins are widely distributed in tissues, but their role is not yet fully understood .

At very low concentrations prostaglandins have been shown biologic activies, including:

(1)   Smooth muscle contraction and relaction(2)   Gastric secretion(3)   Platelet aggregation(4)   Inflamatory response(5)   Response to trophic hormone (FSH & LH)(6)   Sodium and water retention by kidney tubules

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B THROMBOXANES

1. Structure.

Thromboxanes are also analogs of prostanoic acids, but they possess a six-membered, oxygen containing ring

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2. Function

Thromboxane A2 (TX2) is produced by

platelets; it causes contraction of arteries and platelet aggregation.

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STEROIDS

Steroids are lipids that contain four fused carbon rings that form the steroid nucleus cyclopentanoperhydrophenantrene

A. Sterol are a class of steroid in the human body

1. A hydroxyl group at carbon 3 (C-3)

2. An aliphatic chain of at least eight carbons at C-17

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B. Cholesterol is the mayor sterol in the human body.

1. It is a structural component of cell membranes and plasma lipoprotein

2. It is precursor from wich steroid hormones and bile acids are synthesized

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a. Steroid hormones

(1)   The steroid hormones produced in humans are formed and secreted by the adrenal cortex, the testis, the ovary, and the placenta.

In addition, the steroid compound, 1,25-dihydroxycholecalciferol is form in the kidney.

The structures are………

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(2)   The adrenal cortex produces hormones with two kind of physiologic activities.

(a)    The zona fasciculate of the adrenal cortex primarily produces cortisol in humans, they are glucocorticoid and cortisol

(b)   The zona glomerulosa produces mineralocorticoid, that is aldosteron, which controls the reabsorption of Na+ in the kidney.

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(3). Gonadal steroids

(a)Testis produced testosterone

O

CH3

CH3

OH

Testosterone

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b. Bile acids

The predominant bile acids in humans are cholic, chenodeoxycholic, deoxycholic, and lithocholic acids (Figure 8-5)

1. Structure a) The bile acids are C-24 steroids and are

derived from cholesterol (a C-27 steroid) by scissor of the side chain, which leaves:

(i)  A C-24 carboxyl group with the loss of

three carbons

(ii) Saturation on Δ5 double bond of cholesterol

(iii) Hydroxylation of the steroid nucleus

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b) Cholic and chenodeoxycholic acids are formed in the liver from cholesterol and are the primary bile acids.

Deoxycholic acids and lithocholic acids are known as the secondary bile acids because they are formed from the primary bile acids

c). The bile acids are conjugated to glycine or taurine in the liver to form glycol or taurocholate

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2. Function.

Continuos conversion of cholesterol to bile acids prevents the excessive accumulation of cholesterol in tissues.

Bile acids are secreted with faeces

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1. storage form of metabolic fuel

2. transport form of metabolic fuel3. part of the outer coat between the body of

the organism and the environment, providing protection in bacteria, plants, insects and vertebrates

4. structural components of membranes n neural system

5. Precursor of vitamins, hormons6. Cell cignaling

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SELESAI