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9. Carbohydrates
Chapter 16
CARBOHYDRATES
Contain C, H, O only
CXH2YOY = CX(H2O)Y
i.e hydrates of carbon
most common names end in '-----ose'
Carbohydrates
General Structural Features
Usually 5/6 membered rings with C and one O
Many -OH groups
 water soluble (simple ones )
 easily broken down for energy
(already partly 'oxidized')
From Monosaccharides to Polysaccharides
The root sacchar- comes from the
Latin saccharum, "sugar".
A monosaccharide is the smallest molecular
unit of a carbohydrate.
Glucose, the prototypical monosaccharide, is the
most abundant organic molecule on earth.
A disaccharide is a molecule formed from a
combination of two monosaccharides, eg.
sucrose
A polysaccharide is a molecular chain (maybe
branched) of hundreds / thousands of monosaccharides, eg. cellulose
Common Carbohydrates
Carbohydrate
Formula
Monosaccharides, C6(H2O)6
Glucose (blood sugar, grape sugar, dextrose)
Fructose ( levulose )
Galactose
C6H12O6
C6H12O6
C6H12O6
Disaccharides, C12(H2O)11
Sucrose (table sugar,beet sugar, cane sugar)
Maltose (malt sugar)
Cellobiose
Lactose (milk sugar )
C12H22O11
C12H22O11
C12H22O11
C12H22O11
Polysaccharides, Cx(H2O)y
Starch
Cellulose
Glucose – a 2,3,4,5,6-pentahydroxy hexanal
C6H12O6 – a(aldo)hexose
6
HO
5
HO
HO
H
5
O
O
4
1
3
HO
6
HO
4
1
2
3
OH
open chain
O
HO
OH
2
OH
cyclic
(6 mem. ring = pyran)
Glucose – single then soluble
Polysaccharides – the Glycosidic Linkage
+ HO
HO
OH HO
HO
HO
O
O
O
OH
HO
OH
O
+ H2O
OH
monosaccharides
O
*
O
glycosidic linkage
O
O
O
O
O
starch = 1,4 linkages = cellulose
O
n*
STARCHES
Plant :
Amylose -straight chain (~200 -D glucose
units)
 Amylopectin - branched every ~25 units
(1000+ -D glucose units)
 Dextrins -partial breakdown of amylopectin
(food additives , paste , fabric finishes )
Animal :
 Glycogen
-branches every~12 units
-short-term energy in body (liver & muscle).
More Branching = Faster ‘Breakdown’
Amylopectin
Glycogen
Amylose Helical Structure
• Left hand helix (partial)
Iodine test for Starch
• Helical structure of amylose holds the I3ion; linear cellulose does not
Carbohydrates
The Most Common Energy Source
Chemical Breakdown / Reaction = Digestion
H2O
H2O
Complex  Dextrins 
(starch)
H2O
Simple  Mono(glucose)
O2
 acetate(2C) + CO2 + H2O + Energy
NB. can be reversed, ie. glucose   glycogen
Starch Breakdown / Digestion
Complex
Dextrins
Small
Mono-
Energy Sources
Instant
Blood sugar(glucose): ~1g/L or 20Cal or ~30mins.
Short Term
Liver/Muscles(glycogen): ~325g or ~6 hrs.
the more muscle, the more glycogen
any excess is converted into fat
Long Term
Fat(adipose tissue): ~ 20kg or ~35 days
Nutritional / Dietary Carbohydrates
Starch - the digestible carbohydrate(for humans)
Simple - mono-/disaccharides, eg. sugars
Complex -seeds/roots of plants,
eg. grains(pasta), corn, potatoes, rice
Recommended - at least 55% of our Caloric intake
(10% sugar & 45% complex)
N A average
- 20% sugar + 25% complex!
Cellulose - indigestible carbohydrate for humans
Soluble(pectins/gums) - fruits(apples), grain husks
(oat bran)
Insoluble(fiber/bulk/roughage) - potato skins, apple
peels, celery, lettuce
Recommended - ~30g/day
NA average - ~15g/day
What is Dextrose?
Dextrose (Blood sugar) is the form of
glucose that rotates the plane of polarized
light in a clockwise direction.
What is “invert sugar?”
• Hydrolysis of (+)sucrose (table sugar) produces equal
amounts of (+)glucose and (-) fructose (levulose).
• But, fructose optical rotation is larger (negatively) than
glucose rotation is positively. Hence, the resulting solution
is levorotatory (-).
• Thus, start with only (+) then get (-) after hydrolysis-so the
net result of hydrolysis is inversion of the direction of the
optical rotation
• Honey is mostly invert sugar –ie an equal mixture of
glucose and fructose
Sucrose -> Glucose + Fructose (Invert)
O
OH
sucrose(+66)
HO
OH
HO
HO
HO
O
sucrase
(invertase)
HO
O
D-glucose(+52)
(dextrose)
+
D-fructose(-92)
(levulose)
OH
Maltose – the basic unit of Starch
OH
O
(down) - linkage
HO
HO
HO
OH
O
O
HO
requires maltase
(humans > yes)
OH
OH
Cellobiose – the basic unit of Cellulose
(up) - linkage
O
OH
HO
HO
HO
OH
O
HO
requires cellobiase
(humans > no)
HO
O
OH
Why Dietary Fibre? It's Indigestible!
Beneficial statistical correlations for colon cancer,
obesity, diabetes, heart disease.
Acts as a sponge for water and other substances
Functions as a physical 'cleaner'
Soluble - can help lower cholesterol levels
reduces rate of glucose absorption
Insoluble - fills you up eat less fat
'cleans' folds in intestinal walls
no physical damage to intestinal walls
adsorbs/removes many 'nasties'
Human Exploitation of Cellulose
Cellulose is a major component of grass, leaves,
wood, cotton(produced by photosynthesis).
World Biomass Production = 1011 tons annually
Present: Humans benefit indirectly by allowing
ruminants(cows, sheep) to digest cellulose
and convert it into protein which we eat.
Enzyme & Substrate: like a Lock & Key
Enzymes are huge protein molecules with intricate
but well-defined shapes. They are the catalysts that
bring about all the chemical reactions in our bodies.
For effective reactivity the molecule must fit into the
convolutions of the shape of the enzyme.
Much like a key must fit the tumblers of a lock.
Lactose Intolerance
Lactase is the enzyme that specifically breaks the
-1,4- linkage of lactose to produce D-galactose and
D-glucose. Infants have a highly active form but
70% of adults have some lactase deficiency.
If lactose is not cleaved in small intestine it passes to
the colon and 1) absorbs water or 2) is degraded by
bacteria, resulting in cramps, diarrhea, etc.
About 10% of NA adults permanently lose their
lactase compared to 3% of Danes and 97% of Thais.
Lactose (milk sugar) – a disaccharide
OH
OH
HO
O
HO
D-galactose
lactase + H2O
OH
O
HO
O
HO
D-glucose
4-O-(-D-galactopyranosyl)-D-glucopyranose
OH
Solving the problem
• Buy it!
Sweetness Index
Substance
Lactose
Maltose
Glucose
Sucrose
Fructose
Relative Sweet Taste
0.16
0.33
0.74
1.00
1.73
(NB. Glucose + Fructose = Honey or Invert Sugar)
Aspartame
Saccharin
180
300
Sucrose : lots of –OH’s: high
water solubility
-D-glucopyranosyl- -D-fructofuranoside
Refined Sugar
NA sugar consumption:
(annually/person)
~1kg (1750)
~50 kg(1990)
Per day: 50, 000/365= 136 grams per person/day
world-wide production = >80 million tons
(60% from cane; 40% from beets)
Dangers:
 dumps too much glucose into blood too quickly
 all other nutrients(vitamins, minerals) are removed
Everybody’s Comfort Food !
Wow !
An Informative Label ?! …..Not Likely
Refined Sugar in some Processed Foods
Food
Jello
Coffeemate
Shake’N Bake
Salad Dressing
Ketchup
Ice cream
Peaches(in syrup)
Peanut butter
Coca Cola
% Sugar
~83
~65
~50
~30
~29
~21
~18
~9
~9
Sugar in human blood
• Blood sugar is glucose (dextrose)
• It is the only fuel for the brain and the
Central nervous system (CNS) and supplies
the E for basal metabolism
• For continuous supply, a concentration of
0.06 to 0.11 weight % is maintained
Control of Blood Sugar (normal ~100mg/dL)
Too Low
(<75mg/dL) = hypoglycemia(fainting)
Too High
(>150mg/dL) = hyperglycemia/diabetes
Urine test for diabetes
• Above 0.16 weight % in blood , glucose
seeps through the kidneys into the urine
Diabetes Mellitus
Type I (insulin dependent): ~10% of all diabetics
(juvenile onset)
Type II (non-insulin dependent; insulin receptors in
cells have become inactivated by excess use of
sugar): ~90% of all diabetics (formerly called
adult onset but now found in 10-12 year olds!)
NB. Diabetes is:
1) second only to trauma for leg amputation
2) leading cause of blindness in adults over 20
3) leading cause of kidney failure
4) almost triples risk of heart attack or stroke
Type 1 Diabetes
• Body produces virtually no insulin
• Thus insulin needed for treatment
• Absence of insulin causes uncontrolled
lipolysis of fat and severe wasting of body
tissues, eventually resulting in death
Living with Type 2 Diabetes
• Body makes too little insulin or its effect is
resisted
• In some cases insulin is needed
• sometimes controlled with a reduced sugar
diet
• Loss of weight will cause an increase in the
number of insulin receptors, hence
improved condition
Canadians Discover Insulin (1921)
• Frederick Banting and his assistant Charles Best isolated
insulin from the pancreas of dogs (canine insulin) and
administered it to Type 1 patients
• Nobel Prize awarded to Banting and McLeod for this work
Structural Differences
• Porcine & canine insulin are identical and
have 50/51 amino acids in common with
human insulin
• Bovine insulin and human insulin have
48/51 amino acids in common
• Thus porcine insulin most often used
Source of Human Insulin
• Patients who are allergic to these can now
get cloned Insulin marketed as the Drug
Humulin
Synthesis of Human Insulin
•
•
•
•
•
•
•
Saran Narang (NRC Ottawa) 1930-2007
Synthesised the proinsulin gene
Enabled mass production of Humulin
Via recombinant DNA
Insulin is a protein
51 amino acids
DNA>RNA>protein
Other molecules with sugar type
structures
Fake Fats
•
Simplesse - from egg white or milk proteins
 Emulsified starch - in Hellman’s light mayonaisse
 Emulsified protein - gelatin + water
 Olestra* ($200 million, by Proctor&Gamble) may cause cramps/diarrhea(dehydration)
reduces absorption of vit. A, D, E, K (fatsoluble vitamins) into body
* not digested; available in USA since 1996;
must carry warning label; not legal in Canada
Olestra = Sucrose Octa Palmitate
OH
O
HO
OH
HO
HO
HO
O
OH
HO
O
Not OH but OR (R = O=C-C16 (sat. = palmitate)
NB. At least 6OHs esterified to be non-metabolized
Olestra – Indigestible !
Olestra
a Triglyceride
Chitin (an exoskeleton polymer)
O
OH
(D)-glucosamine
HO
HO
O
OH
*
OH
NH2
O
O
OH
O
HO
NH
O
HO
O
CH3
NH
O
CH3
n*
Glucosamine
• A simple amino sugar C6H13NO5.
• Produced commercially by hydrolysis of
crustacean exoskeletons
• Used in treatment of osteoarthritis
• Sold as a salt-either HCl or sulfate
• Typical dose up to 1.5gr/day
Glucosamine (3-aminoglucose)
Blood Typing by Glycoprotein Antigens
Type A:
acetylgalactosamine-galactose-acetylglucosamine-PRO
fucose
Type B: lactose-galactose-acetylglucosamine-PRO
fucose
Type O:
galactose-acetylglucosamine-PRO
fucose
Chocolate - Covered Cherries
Cherries are first coated with
sugar paste(sucrose) +
sucrase(enzyme). After
hardening they are dipped in
chocolate and stored. After 12 weeks the sucrose is
hydrolyzed/split by the
sucrase into glucose +
fructose which dissolves
easily in the cherry juice.
Chemistry is Everywhere !
3 Cherry Blossom Questions
• One ingredient is called “invertase” .What
is another name for this?
• Another ingredient is soy lecithin. What
function does it serve?
• Another ingredient is “modified vegetable
oil” How has it been modified?
Problem set #3
• Chapt 13 #1
• Chapt 15#1,8,9,10,11,25,29
• Chapt 16#1,9,11,12,18