carbohydrate and lipid biochemistry

BIOCHEMISTRYBY: KAREEM HUSSIEN

CARBOHYDRATESAND

LIPIDS

I. CARBOHYDRATES Organic substances composed of carbon, hydrogen and oxygen Soluble in water CLASSIFICATION

1. Monosaccharides (simple sugars)2. disaccharides3. Oligosaccharides4. Polysaccharides (glycans)

1. MONOSACCHARIDES The simplest units and can’t be hydrolyzed into simpler forms CLASSIFICATION

Acc to no. of carbon atoms > triose, tetrose, pentose,hexose… Acc to the “carbonyl” group

A. Aldo sugar : having an aldehyde group ex. Glucose or riboseB. Keto sugar : having a ketone group ex. Fructose

Carbonyl group is C-1 in aldoses and C-2 in ketoses

• RING FORM Monosaccharides of 5 or more carbon atoms are present in ring form

In “Howorth” configuration of the ring form, all groups to the right of the carbon atom will be directed downward and all groups to its left will be directed upward, except around C-5 where the reverse occurs

Condensation of the carbonyl group with one of the alcohol groups of the same sugar forms closed ring structure “pyran or furan”

Carbonyl group will be called “Anomeric” group in ring form and can exist in two forms α form with hydroxyl group to the right (down) β form with hydroxyl group to the left (up)

• ASYMMETRIC CARBON ATOM A carbon atom attached to 4 different atoms or groups Compounds having one of those will have

1. Isomers : compounds having the same molecular weight and composition but differ in their physical and chemical properties

2. Optical activity : when a beam of light passes in their solution it will be either rotated to the right “dextrorotatory” or the left “levorotatory” D & L

Epimers : differ only around one carbon “not anomeric”1. Glucose & mannose at C-22. Glucose & galactose at C-4

α & β anomers : differ around anomeric (ring form) Aldo & keto isomers : differ in functional group “aldehyde & ketone”

1. Glucose and fructose

• TYPES OF ISOMERS

• DERIVATIVES OF MONO..1. Sugar acids : oxidation product of monosaccharides

“adding O” Uronic acid > glucose gives glocuronic by oxidation of last carbon

2. Sugar alcohols (-itols) : reduction product of monosaccharides “adding H2”

Glucose gives sorbitol by reduction of first carbon3. Deoxy sugar : a hydroxyl group (OH) is replaced by a

hydrogen atom 2-Deoxy-ribose > component of DNA

4. Amino sugar : a hydroxyl group at C-2 is replaced by an amino group (NH2)

Glucose gives glucosamine

2. DISACCHARIDES Compounds formed of 2 monosaccharides (same or different) linked by

glycosidic bonds1. Maltose : 2 D-glucose linked by α-1-4 glucosidic bond2. Lactose : D-glucose & β-D-galactose linked by β-1,4-galactosidic bond3. Sucrose : D-glucose & β-D-fructose linked by β-2,1-fructosidic = α-1-2 glucosidic bond

3. POLYSACCHARIDES (GLYCANS) Polymers of 10 or more mono Or their derivatives linked by glycosidic bonds.

CLASSIFICATION1. Homopolysaccharides (simple) : contain only one type of mono

ex. Glucosans > starch , glycogen , cellulose fructosans > inulin galactosans > agar agar

2. Heteropolysaccharides (mixed) : more than one type of monoThey mey be acidic (contain acid sugars) or neutral (contain sugars and amio sugars)

• SIMPLE POLYSACCHARIDES1. Starch

storage form of carbs in plants and major source of it for animals Each molecule is formed of 2 types of glucosans

Complete hydrolysis with 1. Acids : gives rise to free glucose units 2. Amylase : gives maltose as end product

Partial hydrolysis give rise to forms of dextrins ex. Erythro & amylodextrin

Amylose amylopectinInner part OuterStraight chain of D-glucose linked by α-1,4

Branched chain linked by α-1,4 except at branching point α-1,6

Gives blue color with iodine Red with iodine

2. Glycogen Storage form of carbohydrates in animals .. Stored mainly in liver and

muscles Similar to amylopectin but more branched and compact Pink with iodine

3. Cellulose Structural polysaccharide present in plants Linear polymer of D-glucose linked by β-1,4-glucosidic bond Not digested in man d.t absence of cellulose enzymes

II. LIPIDS They are compounds that relate directly or indirectly to fatty acids They contain C, H, O ± P, N & S They have common properties of being

1. Insoluble in water2. Soluble in nonpolar solvents as ether and benzene3. Associated with fatty acids and utilized by living organisms

IMPORTANCE1. High caloric value= 9.3 Kcal/g2. Organ coating3. Thermal insulator4. Cell membrane

LIPIDS

SIMPLE(ALCOHOL+F.A)

TRUE FATS(GLYCEROL+F.A)

WAXES(MONOHYDRIC ALCOHOL+F.A)

COMPOUND(ALCOHOL+F.A+OTHER

GROUPS)

GLYCOLIPIDS

PHOSPHOLIPIDS

DERIVED

HYDROLYSIS OF COMPOUND LIPIDS

F.As

ALCOHOLS

ASSOCIATED WITH LIPIDS

STEROIDS

FAT SOLUBLE VITAMINS

CAROTINOIDS• CLASSIFICATION

1. SIMPLE LIPIDS (TRUE FATS) They are esters of glycerol with various fatty acids CLASSIFICATION OF FATTY ACIDS

1. Chain length Short chain (low F.A) (2-10 F.A) ex. Acetic acid 2C ,butyric acid 4C Long chain (high F.A) (>10 F.A) ex. Palmetic 16C ,stearic 18C

2. Saturation Saturated (no double bonds) ex. butyric ,stearic Unsaturated (double bonds)

Mono (one db) ex. Oleic acid 18:1;9 nervonic acid 24:1;15Poly (>1 db) ex.leinoleic 18:2;9,12 arachidonic 20:4;,5,8,11,14

3. Biological importance1. Essential F.A (polyunsaturated) : cant be synthesized in body2. Non essential F.A (saturated or monounsaturated) synthesized in body from

other precursor3. Relatively essential F.A (arachidonic) : synthesized n body only in presence of

linoleic

• WHAT IS .. ? Alcohol ?

organic compound in which the hydroxyl functional group (-OH) is bound to a carbon atom (R3COH) , it is colorless and sweet

Ex. Glycerol sphignosine & cholesterol Glycerol ?

a trihydric alcohol with 3 OH groups Fatty acids ?

organic acids originating from hydrolysis of natural fats and oils

Aliphatic Monocarboxylic Even no. of C atoms

LIPIDS

SIMPLE(ALCOHOL+F.A)




GROUPS)

GLYCOLIPIDS

PHOSPHOLIPIDS

DERIVED


F.As

ALCOHOLS


STEROIDS

FAT SOLUBLE VITAMINS


1. PHOSPHOLIPIDS They are membrane components amphipathic and ionic in natureA. GLYCERO-P.L (having glycerol as their alcohol backbone)

The precursor is (glycerol-3-phosphate) The fatty acids present are mostly saturated at R1 unsaturated at R2

ex. Phosohatidic acid : simplest form and precursor for others with no base

Phosphatydyl choline : most abundant present in cell membrane with choline base

2. COMPOUND LIPIDS

B. SPHIGNO-P.L (having sphignosine as their alcohol backbone) Contain sphignosine instead of glycerol, a higher fatty acid, phosphoric acid and a base

Important membrane component for animals and plants, they are present in large amounts in brain and myelin of nerves

Sphignosine + saturated or unsaturated F.A = CERAMIDE (the characteristic parent structure for sphignolipids)

2. GLYCOLIPIDS (glyco-sphigno-lipids) They are in every tissue of the body especially nervous .. They also occur at outer leaflet of plasma membraneA. NEUTRAL G.L (cerebrosides) :

They contain one or more neutral sugar molecules as their polar head group .. The monosaccharide is bound to the OH of ceramide Ex. Galactocerebroside glucocerebroside

They are concerned with Cell communication and recognition Tissue immunity Species specificity Bloog group antigens

B. ACIDIC G.L :Ex. Cerebroside sulphate (sulphatides) : sulphate ester of galactocerebroside gangliosides : neuraminoc acid in addition to glycosyl ceramide

LIPIDS

SIMPLE(ALCOHOL+F.A)




GROUPS)

GLYCOLIPIDS

PHOSPHOLIPIDS

DERIVED


F.As

ALCOHOLS


STEROIDS

FAT SOLUBLE VITAMINSK E D A


• DERIVER LIPIDSSTEROIDS They have in common a cyclic ring called “steroid nucleus” It is composed of 17 C with 2 methyl groups at C10 & C13 Steroids include

A. SterolsB. Bile acids and saltsC. Steroid hormonesD. Vitamin D

A. STEROLS It has a hydroxyl group (OH) at C3 and an aliphatic side chain at C17 (Alcohol)

TYPES1. Animal sterols :cholesterol and its derivatives (vit D3)2. Plant sterols : ergosterol (pro vit D2) and its derivatives

B. BILE ACIDS AND SALTSI. Bile acids are hydroxyl derivatives of cholanic acid

It is obtained in the liver by oxidation of cholesterol at C24 with removal of the last 3C

They are the end products of cholesterol catabolism in the body as it can not break down steroid nucleus

II. Bile salts are products of conjugation of bile acids with amino acids “glycine and taurine” in their sodium or potassium salts

carbohydrate and lipid biochemistry

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