Carbohydrates

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Carbohydrates
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Carbohydrates sugar containing compounds

• Widely distributed in plants, some in animals
• made of Carbon, Hydrogen, and Oxygen
• Abbreviated as CHO
• Made during photosynthesis
• 6CO2 6H20 --gt (CH2O) 6 6O2

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Photosynthesis

• H acceptor H donor --gt Reduced acceptor with O2
  release(from water)
• Some bacteria can use H2S as the H donor

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Size of Carbohydrate Polymer

• Monosaccharide one sugar unit
• Disaccharide two sugar units
• Oligosaccharide three to ten(6) sugar units
• Polysaccharide 10 (6) or more sugar units

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Monosaccharides

• Aldoses aldehyde group is present
• H
• R-- C O
• A sugar containing an aldehyde group is called an
  aldose

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Monosaccharides

• Ketose a sugar that contains a ketone group
• R
• C O
• R
• A sugar that contains a ketone group is called a
  ketose

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Monosaccharides

• Trioses 3 carbons long C3H6O3
• Tetroses 4 carbons long C4H8O4
• Pentoses 5 carbons long C5H10O5
• Hexoses 6 carbons long C6H12O6

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Common Monosaccharides

• Glucose Hexose, aldose
• Fructose Hexose, ketose
• Galactose Hexose, aldose
• Ribose Pentose, aldose

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Common Disaccharides

• Sucrose glucose fructose
• Lactose glucose galactose
• Maltose glucose glucose

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Common methods of showing sugar structure

• stick method
• straight chain
• Haworth thermodynamic model
• boat and chair forms, from x-ray diffraction

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Stereo-isomerization

• Asymmetric carbons make stereoisomers possible
• Carbons attached to 4 different groups
• n number of asymmetric carbons
• 2 n number of stereoisomers possible
• For glucose, how many stereoisomers are possible?

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Isomerization

• Well Discuss three types
• D L
• alpha and beta
• epimers

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D L Isomers

• Based on the orientation of the OH and H adjacent
  to the terminal primary alcohol or carbon
• D dextarotatory rotates polarized light to the
  right(most Glucose is D)
• L Levarotatory rotates polarized light to the
  left
• When D L present in equal amounts no optical
  activity

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Alpha and Beta Anomers

• Ring structure of an aldose is a hemiacetal
• Ring structure of a ketose is a hemiketal
• In D glucose, mutarotation occurs at C1 so OH and
  H rotation occurs
• alpha one with greater rotation

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Epimers

• Important Glucose isomers in nutrition
• alpha, D Galactose at C4
• alpha, D mannose at C2

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Pentoses 5 Carbon Sugars

• Ribose and Deoxyribose RNA DNA
• Adenosine Phosphate ----gt AMP
• Adenosine is also a vasodilator in head
• Fits into a receptor in the cell membrane
• Relationship to caffeine and headaches?

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Hexoses

• D sugars are important in nutrition
• D glucose, D fructose, D galactose, D mannose
• Abnormalities associated with genetic inability
  to metabolize D galactose
• Galactosemia autosomal recessive disorder
• 1/25,000 in US hepatomegaly, cataracts,
  retardation

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Fructose

• Ketohexose
• forms a 5 member ring(a furan Vs a Pyran)
• absorbed by body but metabolized to glucose in
  liver before it is usable by the body
• commonly found in fruit, honey

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Fructosuria Hereditary Intolerance

• Autosomal recessive
• Two potential problems
• A. inactive fructokinase
• alternate pathway to fructose-6 phosphate
• no damage asymptomatic
• B. inactive Fru-1 P aldolase
• build-up of Fru-1-P
• GI problems, liver and kidney dysfunction and
  failure

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Fructosuria Onset and treatment

• Onset After solid foods are introduced
• Treatment Avoid fructose in the diet
• No sucrose, fructose

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Glucose

• Major compound of metabolism
• Used by all tissues for energy
• Some tissues use ONLY glucose
• lens of eye, nervous tissue, RBCs, parts of
  kidney
• Highly regulated in the blood because of its
  importance

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Glucose normal and abnormal

• normal fasting blood glucose 75-105 mg/dl plasma
• Hypoglycemia below that
• fasting hypoglycemia
• reactive hypoglycemia
• too much insulin moves glucose out of blood
• Hyperglycemia above that

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Diabetes Type 1 and Type 2

• Type 1 no insulin produced
• Beta cells in pancreas killed by autoimmune
  activity
• Genetics Vs environment
• 25 of identical twins develop Type 1

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Diabetes Type 2

• Type 2
• non-functional insulin
• insulin receptor site down regulation
• upregulation occurs with weight loss and exercise
• many people can control with diet and exercise
• many people take oral hypoglycemic agent such as
  Diabanese increases insulin secretion
• Some people take insulin

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Sugar Derivatives Alcohols

• Xylitol pentose sugar alcohol
• found naturally in fruits and vegies
• raspberries, strawberries, lettuce, cauliflower
• name comes from adding an alcohol
• used as an alternative sweetener
• available from hemicellulose, a fiber that is
  found in almond shells, hardwood, oat hulls.
• Cariostatic Properties decreases risk of decay

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Sugar Derivatives xylitol

• 2 field studies
• French Polynesia 32 months
• Hungary 36 months
• 2 groups A control brushed with Fluoride
  toothpaste
• B Test A plus 14-20 grams/day of xylitol in
  hard candy
• Test group had 45-50 fewer cavities that
  Control group

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Xylitol mechanism of action

• Bacteria do not ferment xylitol and it may be
  toxic to some oral bacteria
• Stimulates flow of saliva in the mouth
• pH doesnt have the chance to drop too much
• 2.4 to 4 Kcal/ gram not as well absorbed
• sweetness equivalent to fructose, sweeter than
  sucrose

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Other sugar alcohols

• Ribitol not used as a sweetener
• produced by reduction of ribulose, a ketopentose
• component of Riboflavin, a B vitamin
• Sorbitol pentose alcohol
• intermediate in Glycogen to Fructose
• 50 as sweet as sucrose
• poorly absorbed small effect on blood glucose

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Sugar Acids

• Aldonic Acids
• Aldehyde at C1 oxidized to COOH, carboxylic acid
• First step in pentose formation in hexose
  monophosphate shunt
• used to form ribose for RNA and deoxyribose for
  DNA

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Sugar Acids

• Uronic Acids
• in other animals first step in vitamin C
  formation
• Alternate pathway in metabolism of Glucose with
  no ATP produced
• COOH at C6

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Sugar Phosphates

• Metabolically active forms of CHOs
• Intermediates in metabolic pathways
• found in small quantities because they are
  turning over very quickly
• Why phosphorylated?
• they release energy when phosphate is removed to
  drive reactions
• they cant pass through cell membranes so
  metabolically active molecules stay inside cells

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Other sugar derivatives

• Amino sugars
• Hexosamines glucose amines
• constituent of hyaluronic acid found in loose
  connective tissue
• Proteoglycan
• Heparin oligosaccharide attached to a
  polypeptide backbone
• anticlotting properties

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Other sugar derivatives

• Glycoproteins
• MW 15000 to 1 million
• mono or oligosaccharide covalently bound to
  proteins
• structural component of cell walls, collagen,
  elastin, bone matrix, fibrins
• Fibrin is a glycoprotein involved in the clotting
  of blood. It is a fibrillar protein that is
  polymerised to form a "mesh" that forms a
  hemostatic plug or clot (in conjunction with
  platelets) over a wound site.
• lubricant mucins, mucous secretions
• transport molecule for vitamins, lipids
• antifreeze in antarctic fishes

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Other Sugar Derivatives

• Glycolipids (sphingolipids)
• fatty acids with CHO
• structural components of membranes and neural
  tubes
• non-polar lipids embedded in cell membrane while
  polar sugar sticks out into watery environment

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Disaccharides

• Formed from condensation reactions
• monosaccharides form glycosidic bonds
• Glucose aldehyde in ring structure forms a
  hemiacetal which is reactive
• reacts with the OH from another sugar to form a
  1,4 glycosidic bond
• Alpha if sugar is an alpha sugar, beta if beta
  sugar
• 1,6 glycosidic bonds also possible

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Nutritionally important Disaccharides

• Sucrose glucose and fructose
• Maltose glucose and glucose
• Lactose glucose and galactose

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Sucrose Most widely distributed of Disaccharides

• Table sugar sources are sugar cane and sugar
  beets
• Relatively pretty sweet because fructose is in an
  accessible location and fructose is very sweet.
• Non-reducing sugar no free aldehyde or
  hemiacetal to condense with

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Sucrose called invert sugar

• When hydrolyzed optical rotation changes
• sucrose 66.5
• glucose 52.7
• fructose -92.4
• net optical activity -40 therefore inverts from
  positive rotation to negative rotation

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Maltose

• Found at seed stage of plant lifecycle
• Starch in seed is broken down during germination
• provides energy for sprouting
• Found in digestion when starch is digested to
  smaller molecules
• Also found in beer making where starch of grain
  is broken down or malted

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Lactose milk sugar

• Principle CHO of cows milk
• Lactase enzyme that digests Lactose in GI tract
• Lactose-----gt Glucose and Galactose
• Lactose Intolerance or Lactase Deficiency
• Both mean the person is unable to digest Lactose
  because they cant produce Lactase

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Lactose Intolerance

• 3 forms
• Primary means the person has lost the ability to
  produce lactase because of genetics. Production
  ok until weaning and then the person gradually
  loses ability to produce. Common in some
  equatorial populations not as common in northern
  climates
• Secondary due to infection of GI tract clears
  up when infection is dealt with
• Congenital at birth very rare

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Lactose Intolerance Symptoms and Diagnosis
Treatment

• Symptoms GI track distress, diarrhea.
• Dx Intestinal Biopsy and enzyme assay, invasive
  and not often done
• lactose tolerance test
• 50 grams lactose given
• Blood glucose checked at 0, 15, 30, 60 and 120
  minutes
• Plasma Glucose increase of 30 mg/dl normal
• 20-30 questionable lt 20 lactase deficiency
• Treatment

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Polysaccharides

• Homopolysaccharides all the same sugar in the
  molecule
• Starch and Glycogen Cellulose
• Heteropolysaccharides two or more sugars in
  molecule
• Hemicellulose

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Starch Glucose homopolysaccharide

• 2 chief constituents amylose and amylopectin
• Amylose 15-20 of most starch
• molecular wt of up to 500,000(glucose mw180 up
  to 2700 glucose units)
• non-branching helical structure
• Amylopectin 80-85 of most starch
• 1,4 and 1,6 glycosidic bonds branches every 5 to
  8 glucose residues
• mw 500,000 to 500,000,000 (over 2700 glucoses)

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Digestion of Starch Enzymes needed

• Amylose
• Alpha amylase (endoglucosidase)
• clips 1,4 bonds on interior of molecule
• Beta amylase (exoglucosidase)
• clips 1,4 bonds at end of molecule at
  non-reducing end releases Maltoses
• End result maltoses and some maltotrioses
• Maltase breaks down these molecules to glucose
  which is absorbed

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Starch Digestion Enzymes needed

• Amylopectin
• alpha and beta amylase needed for 1,4 bonds to
  produce maltose and maltotriose
• maltase to break these down
• then alpha 1,6 glucosidase to breakdown the 1,6
  bonds

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Summary of Enzymes needed

• 1,4 endoglucosidase(alpha amylase)
• 1,4 exoglucosidase(beta amylase)
• 1,6 glucosidase
• maltase

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Glycogen only homopolysaccharide of animal tissue

• similar to amylopectin in structure but more
  highly branched
• branched every 3 to 4 glucose units
• 6,000 to 30,000 glucose units in a glycogen
  molecule
• muscle glycogen shorter than liver
• size dependent on metabolic state of animal
  glucoses constantly added and removed

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Glycogen

• glycogen used during activity
• slaughtered animal muscle glycogen quickly
  degraded so not much left by the time it is eaten

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Why is glycogen highly branched?

• So energy is quickly available in emergencies.
• fight or flight reaction
• saber toothed tiger
• epinephrine secreted from adrenal glands
• causes a cascade of reactions to release maltoses
  and then glucoses from the end of the chains
• Glucose acts as a source of energy

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Glycogen storage

• We have about a 12 to 24 hour supply of glycogen.
  Why dont we store more?
• It takes up quite a bit of space because it is
  highly branched, it isnt very dense
• Fat is more dense so is used for long term
  storage molecule. We have almost unlimited
  ability to store fat.

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Fiber

• Structural Polysaccharides
• cellulose
• hemicellulose
• pectins
• Structural non-polysaccharides
• lignins
• non-structural polysaccharides
• gums, mucilages algal and seaweed derivatives

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Cellulose

• Chief component of plant framework
• not soluble in ordinary solvents
• long straight chains of beta D glucopyranoside
  units with beta 1,4 bonds
• not digested by digestive enzymes
• MW up to 3000 glucose units
• Most abundant organic compound

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Hemicellulose Branched heteropolysaccharide

• Hexoses and pentoses
• MW smaller than cellulose
• found as part of cell wall

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Pectic Substances

• Found in fresh fruits, used to solidify jelly
• beta 1,4 D galacturonic acid polymers

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Fiber intake

• WHO 27-40 grams/day
• 10 g in 41 cups of corn flakes
• 18 grams in one cup of baked beans
• 13 grams in 1 cup of canned peas
• 4 grams in 1 apple with the skin

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Not all fibers are created equal

• Insoluble Fiber
• cellulose, hemicellulose
• Adds Bulk to the diet laxative
• Decreases risk of cancer by dilution of
  carcinogens
• Limits absorption of minerals
• Soluble Fiber
• Pectic substances oatbran, fruit
• reduces serum cholesterol

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Summary of Fiber Effects

• Increases GI tract motility
• Increases volatile fatty acid production which
  increases motility
• softens stools by absorbing water
• Decrease intraluminal pressure less
  diverticulosis
• Decrease glycemic effect and insulin response
• Decrease risk of cancer and high serum cholesterol

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Dietary Fiber Classification and Definition

• Defn plant components in diet that are resistant
  to digestion in human digestive tract
• Difficult to remove from food because difficult
  to simulate the GI tract