Chemistry of nutrientsVladimíra Kvasnicová

Energy in a diet

SACCHARIDES / LIPIDS / PROTEINS

60 : 30 : 10

17 kJ/g 37 kJ/g 17 kJ/g

4 kCal/g 9 kCal/g 4 kCal/g

-CH(OH)- -CH2- -CH(NH2)-

CO2, H2O CO2, H2O CO2, H2O, NH3

Oxidation of a hydrocarbon skeleton- individual steps

alkane

alkene

alcohol

aldehyde

carboxylic acid

CO2 + H2O

CH3-CH3

CH2=CH2

CH3-CH2-OH

CH3-CHO

CH3-COOH

2 CO2 + 2 H2O

•monosaccharides

•oligosaccharides

•polysaccharides

17 kJ/g

Saccharides in a diet

• starch predominates (75% of a dry mass of cereals, 65% in potatoes)

� 20% amylose (non-branched, spiral, 200 – 300 glc)

� 80% amylopectine (up to 1000 glc, branched at every 20-25 glucose unit)

• glycogen in meat (branched at every 8-10 glc unit)

• „sugar“ = disaccharide sucrose (Glc-Fru)

• milk sugar = disaccharide lactose (Gal-Glc)

• fiber = indigestible polysaccharides (cellulose, pectin)

MONOSACCHARIDES

Monosaccharides

Glucose Galactose Fructose

RiboseGlucuronic acid

DISACCHARIDES

SALAME

• SAcharose (= sucrose)

• LActose

• MaltosE

saccharose has not reducing properties

The figure has been adopted from J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005

α-Glc(1→4)Glc β-Gal(1→4)Glc α-Glc(1→2)β- Fru

free anomeric (= hemiacetal) hydroxyl ⇒ reducing properties

POLYSACCHARIDES

• homopolysaccharidesstarch, glycogen, cellulose, inuline

• heteropolysaccharidesglycoproteins, proteoglycans

• branched

• unbranched

• storagestarch, glycogen,inuline

• structuralcellulose, proteoglycans

amylose (maltose)n amylopectine

STARCH (Glc)n

The figures have been adopted from Harper´s Biochemistry

α(1→4) glycosidic bonds α(1→4) glycosidic bonds

α(1→6) glycosidic bonds

GLYCOGEN (Glc)n

The figure is found at http://students.ou.edu/R/Ben.A.Rodriguez-1/glycogen.gif (October 2007)

nonreducing end reducing end

OH

CELLULOSE

ββββ-Glc(1→4)Glc

The figures are found at http://web.chemistry.gatech.edu/~williams/bCourse_Information/6521/carbo/glu/cellulose_int_2.jpghttp://www.kjemi.uio.no/14_skole/modul/Evina_organisk/Org_K3fig14_cellulose.JPG (October 2007)

Monosaccharides

• form phosphoric acid esters („phosphates“) in cells

• their carbon skeleton is partially oxidized : -CH(OH)-(less energy produced when it is oxidized in metabolism)

• energy source – Glc, Fru, Gal / energy storage - glycogen

• conversion to other saccharides(components of nucleotides, glycoproteins)or saccharide derivatives(aminosugars, uronic acids – in proteoglycans)

• conversion to fat (energy storage)

• important intermediates of their metabolism:� glyceraldehyde-3-phosphate� dihydroxyacetone phosphate (DHAP)� 1,3-bisphosphoglycerate

anhydride bond

Monosaccharides

glucose

� energy production (glycolysis)

� energy storage (glycogen or conversion to fat)

� conversion to other saccharides, e.g. ribose (pentose phosphate cycle)

� conversion to glucuronic acid (oxidation of glucose)

fructose

� conversion to glucose� energy production (glycolysis)

� energy storage (conversion to fat)

galactose

� conversion to glucose and lactose� synthesis of glycoproteins and proteoglycans

ribose

� nucleotide synthesis

http://www.medicographia.com/2010/01/advanced-glycation-end-products-ages-and-their-receptors-rages-in-diabetic-vascular-disease/

Glycated hemoglobin

fructose

Adopted from Trends in Biochemical Sciences, reference edition, volume 6, page 209.Elsevier/North-Holland Biomedical Press, 1981.

http://www.gisymbol.com/about/glycemic-index/

Glycemic index (GI) of carbohydrate foods

Adopted from the texbook by Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2

sources of blood glucose after a meal and during fasting

and starvation

Content of liver glycogen during a day

Adopted from the textbook by Devlin, T. M. (editor): Textbook of Biochemistry with Clinical Correlations, 4th ed. Wiley-Liss, Inc., New York, 1997. ISBN 0-471-15451-2

37 kJ/glipids

18:3 <0,5%18:3 <0,5%18:3 10%18:3 1%18:3 1%18:3 1,5%PUFA

ωωωω-3

18:2 1,5%18:2 63%18:2 20%18:2 8%18:2 9%18:2 2,5%PUFA

ωωωω-6

18:1 7%18:1 21%18:1 59%18:1 72%18:1 42%18:1 25%MUFA

12:0 45%

14:0 17%

16:0 9%

16:0 6%

18:0 4%

16:0 4%

18:0 1,5%

16:0 11%

18:0 2,5%

14:0 1%16:0 24%18:0 14%

14:0 10%16:0 26%18:0 12%

SFA

coco-nut

oilsunflower

oilrapeseed

oilolive

oillardbutter

Composition of sample fats

adopted from http://www.internimedicina.cz/pdfs/int/2009/12/05.pdf

Free fatty acids(FFA)

Esterified fatty acids

= triacylglycerol(TAG)

or triglyceride

ωωωω-9

ωωωω-6

ωωωω-3

oleic acid

linoleic acid

alpha - linolenic acid

gamma - linolenic acid

eicosapentenoic acid (EPA)

arachidonic acid

docosahexenoic acid (DHA)

18

18

9

9 12

18

18

The figure is found at http://courses.cm.utexas.edu/archive/Spring2002/CH339K/Robertus/overheads-2/ch11_cholesterol.jpg (Jan 2007)

Fatty acids (FA)

• saturated fat contains saturated FA(more energy: -CH2-CH2-)

• monounsaturated fat / polyunsaturated fat(less energy – partially oxidized: -CH=CH-)

• even number of carbons (synthesized from C-2 precursor)

• separated cis double bonds: -CH=CH-CH2-CH=CH-

• short chain fatty acids (SCFA): less than 6 carbons

• medium chain fatty acids (MCFA): 6 – 12 carbons

• long chain fatty acids (LCFA): more than 12 carbons

• very long chain fatty acids (VLCFA): more than 22 carbons

The figure was adopted from: J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005

Fat in a diet

fat (triacylglycerols) and phospholipids contain:

• saturated fatty acids (SFA)

• monounsaturated fatty acids (MUFA)

• polyunsaturated fatty acids (PUFA) = essential FA

� omega-6 (ω-6, n-6)

� omega-3 (ω-3, n-3) - in fish oil: EPA, DHA

• trans fatty acids (TFA)

cholesterol

• found in animal fat

Fatty acids (FA)

• in cells they are bound to Coenzyme A → „acyl-CoA“

binding place

• more reduced carbon skeletonthan saccharides: -CH2-

• FA are components of triacylglycerols, phospholipids, cholesterol esters (= hydrolyzable lipids)

• FA are used for energy production (β-oxidation) or

energy storage in a form of triacylglycerols = neutral fat

• FA can be converted to ketone bodies, eicosanoids

The figure was accepted from the book: Grundy, S.M.: Atlas of lipid disorders, unit 1. Gower Medical Publishing, New York, 1990.

blood lipids

17 kJ/g

N →→→→ NH3 →→→→ urea, S → H2SO4 → sulfates

proteins

Proteins in a diet

• animal proteins (all amino acids)

• plant proteins (less common: Met, Lys, Trp)

• essential amino acids:

� branched chain - Val, Leu, Ile

� aromatic - Phe, Trp

� basic - His, Arg, Lys

� secondary alcohol group containing - Thr

� sulfide group containing - Met

Amino acids (AA)• contain other elements: nitrogen (all AA), sulfur (Cys, Met)

� when AA are degraded ammonia NH3 (and H2SO4) are produced

� NH3 is toxic ⇒ it must be converted to urea→ excreted with urine

• AA are primarily used for proteosynthesis

• other use:

� synthesis of N-containing compounds (heme, nucleotides, signal molecules – hormones, neurotransmitters)

� direct energy production (Krebs cycle) or indirec energy production during fasting: after conversion to glucose(gluconeogenesis)

� energy storage after conversion to fat

• the use of AA as energy substrates consumes energybecause ammonia must be detoxified !

Amino acids