metabolisme karbohidrat

METABOLISME KARBOHIDRAT

Carbohydrate metabolism ICarbohydrate metabolism I

Carbohydrates computing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

Carbohydrates

composed of carbon, hydrogen and oxygen only

in the ratio C6H12O6

Carbohydrates

• Contain carbon, hydrogen, and oxygen• Their major function is to supply a source of

cellular food• Examples:

– Monosaccharides or simple sugars

Figure 2.13a

Carbohydrates

• Disaccharides or double sugars

Figure 2.13b

Carbohydrates

• Polysaccharides or polymers of simple sugars

Figure 2.13c

Nutritionally important disaccharides - 1

computing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

Nutritionally important disaccharides

-1,4-binding -1,4-binding

Figuur 11. De -1,4-binding en de -1,4-binding die in polysacchariden voorkomen.

-1,6-binding

Figuur 12. De -1,6-binding zoals deze in amylopectine voorkomt.

Nutritionally important disaccharides - 2

computing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

Nutritionally important disaccharides

isomaltosemaltose (glucosyl-glucose)

OOH

OH

OH

CH2OHCH2OH

O

OH

OHO

O H

H

CH2OH

O

OH

OHO

O

CH2

O OH

OH

OHO

H

Branched structure of starch and glycogen

computing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

The branched structure of starch and glycogen

1 6 links: branch points inamylopectin and glycogen O

OH

OH

CH2OH

OOH

OH

CH2OH

O O

OOH

OH

CH2OH

OOH

OH

CH2

O O O

O

O

OOH

OH

CH2OH

O

OOH

OH

CH2OH

Hydrolysis of starch by amylase

computing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

Hydrolysis of starch by alpha-amylase in saliva and pancreatic juice results in formation of dextrins, then:

glucose

maltose

isomaltose

1 6 links: branch points inamylopectin and glycogen O

OH

OH

CH2OH

OOH

OH

CH2OH

O O

OOH

OH

CH2OH

OOH

OH

CH2

O O O

O

O

OOH

OH

CH2OH

O

OOH

OH

CH2OH

Major types of non-starch polysaccharides

computing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

cellulose - glucose polymer linked 1 4

O

OH

OH

CH2OH

O

OOH

OH

CH2OH

OOH

OH

CH2OH

OOH

OH

CH2OH

O O O O

chitin - N-acetylglucosamine polymer linked 1 4

O

OH

CH2OH

O

OOH

CH2OH

OOH

CH2OH

OOH

CH2OH

O O O O

HN C CH3

O

HN C CH3

O

HN C CH3

O

HN C CH3

O

pectin - galacturonic acid polymer linked 1 4, partially methylated; some glactose and/or arabinose branches

O

OH

OH

COOH

OOH

OH

COOH

OOH

OH

CO CH3

OOH

OH

COOH

O O O OO

O CH2

OH

OH

O

HOCH2

O CH2

OH

OH

HOCH2

O CH2

OH

OH

HOCH2

O CH2

OH

OH

HOCH2

O

O

O

O

inulin - fructose polymer linked 2 1

The major types of non-starch polysaccharide

Glycaemic and non-glycaemic carbohydrates - 1

computing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

Dietary starches can be classified as:

rapidly digested (hence high glycaemic index) slowly digested (lower glycaemic index)

not all digested in small intestine amylose is hydrolysed more slowly than amylopectin

resistant starch (low glycaemic index) only hydrolysed to a limited extent in small intestine

starch may be resistant because: it is crystalline and resistant to amylases it is enclosed in plant cell walls that are not digested

some resistant starch is fermented by bacteria in the large intestine

Glycaemic and non-glycaemic carbohydrates

Glycaemic indexThe extent to which a test dose of a carbohydrate increases blood glucosecompared with an equivalent amount of glucose

Glucose

Glucose-6-P

Pyruvate

Hexokinase

PentosePhosphateShunt

glycolysis

Carbohydrates• Serve as primary source of energy in the cell• Central to all metabolic processes

Glc-1- phosphate

glycogen

Cytosol - anaerobic

Pyruvatecytosol

Aceytl CoAmitochondria (aerobic)

Krebscycle

Reducingequivalents

OxidativePhosphorylation(ATP)

AMINOACIDS

FATTY ACIDS

Glycogen synthase (active)

OHPGlycogen synthase (inactive)

Glycogen formation

Glycogen synthase kinase (active)

OH

IRinsulin

P

PProtein Kinase B (active)

Protein Kinase B (inactive)

OH

P Glycogen synthase kinase (inactive)

Overview of metabolismcomputing

Presentation copyright © 2002 David A Bender and some images copyright © 2002 Taylor & Francis Ltd

glucose-6-phosphate glucoseglycogen( 6 carbons)

(3 carbons)lactate

acetyl CoA

pyruvate

CO2

(2 carbons)fatty acids

triacylglycerols

ketones

oxaloacetate citrate

CO2

CO2

CITRIC ACID CYCLE

FATTY ACID SYNTHESIS

FATTY ACID OXIDATIONKETOGENESIS

GL

UC

ON

EO

GE

NE

SIS

GLYCOGEN SYNTHESIS

GLYCOGENOLYSIS

LIPASE

GL

YC

OL

YS

IS

Glycolysis pathway

[Tri-carboxylic Acid (TCA) cycle]