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 mono-

saccharides, eg. cellulose

Common Carbohydrates

Carbohydrate Monosaccharides, C6(H2O)6 Glucose (blood sugar, grape sugar, dextrose) C6H12O6 Fructose ( levulose ) C6H12O6

Galactose C6H12O6

Disaccharides, C12(H2O)11 Sucrose (table sugar,beet sugar, cane sugar) C12H22O11

Maltose (malt sugar) C12H22O11

Cellobiose C12H22O11

Lactose (milk sugar ) C12H22O11

Polysaccharides, Cx(H2O)y

Starch Cellulose

Formula

OH

OH

OOH

OH OH

OH

O

OH OH

OH OH

1

23

4

5

6

1

23

4

5

6

Glucose – a 2,3,4,5,6-pentahydroxy hexanal

C6H12O6 – a(aldo)hexose

open chain cyclic (6 mem. ring = pyran)

Glucose – single then soluble

OOHOH

OHOH

OHO

OHOH

OHOH

OHOO

O

+

+ H2O

OOOOO O O* *n

Polysaccharides – the Glycosidic Linkage

monosaccharides glycosidic linkage

starch = 1,4 linkages = cellulose

STARCHESPlant :

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 I3- ion; linear cellulose does not

Carbohydrates The Most Common Energy Source

Chemical Breakdown / Reaction = Digestion

Complex Dextrins Simple Mono-

acetate(2C) + CO2 + H2O + Energy

NB. can be reversed, ie. glucose glycogen

(glucose)(starch)

H2O H2O H2O

O2

Complex Dextrins Small Mono-

Starch Breakdown / Digestion

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 glycogenany 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/dayNA 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

O

OHOH

OH

O

O

OH

OH

OH

OH

OH

Sucrose -> Glucose + Fructose (Invert)

sucrose(+66)

D-glucose(+52) (dextrose)

D-fructose(-92)

(levulose)

sucrase (invertase)

+

OO

OH

OH

OHOH

OOH

OH

OHOH

Maltose – the basic unit of Starch

(down) - linkage

requires maltase (humans > yes)

O

OH

OH

OHOH

OOH

O

OH

OHOH

Cellobiose – the basic unit of Cellulose

(up) - linkage

requires cellobiase (humans > no)

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'

Why Dietary Fibre? It's Indigestible!

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.

Human Exploitation of Cellulose

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.

O

OH

OH

OHOH

OOH

O

OH

OHOH

Lactose (milk sugar) – a disaccharide

lactase + H2O

D-galactose

D-glucose

4-O-(-D-galactopyranosyl)-D-glucopyranose

Solving the problem• Buy it!

Sweetness Index

Substance Relative Sweet Taste

Lactose 0.16 Maltose 0.33 Glucose 0.74 Sucrose 1.00 Fructose 1.73

(NB. Glucose + Fructose = Honey or Invert Sugar)

Aspartame 180 Saccharin 300

Sucrose : lots of –OH’s: high water solubility

-D-glucopyranosyl- -D-fructofuranoside

Refined Sugar

NA sugar consumption: ~1kg (1750) (annually/person) ~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 % Sugar Jello ~83 Coffeemate ~65 Shake’N Bake

~50 Salad Dressing ~30 Ketchup ~29 Ice cream ~21 Peaches(in syrup) ~18 Peanut butter ~9 Coca Cola ~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

Too High

(<75mg/dL) = hypoglycemia(fainting)

(>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 (fat- soluble vitamins) into body

* not digested; available in USA since 1996;

must carry warning label; not legal in Canada

O

OHOH

OH

O

O

OH

OH

OH

OH

OH

Olestra = Sucrose Octa Palmitate

Not OH but OR (R = O=C-C16 (sat. = palmitate)

NB. At least 6OHs esterified to be non-metabolized

Olestra a Triglyceride

Olestra – Indigestible !

Chitin (an exoskeleton polymer)

NH

CH3

O

NH

CH3

O

OO

O

OH

OH

OO

OH

OH

*

*n

O

OH

OH

OH

NH2OH

(D)-glucosamine

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

Type B: lactose-galactose-acetylglucosamine-PRO

Type O: galactose-acetylglucosamine-PRO

fucose

fucose

fucose

Chocolate - Covered Cherries

Chemistry is Everywhere !

Cherries are first coated with sugar paste(sucrose) + sucrase(enzyme). After hardening they are dipped in chocolate and stored. After 1-2 weeks the sucrose is hydrolyzed/split by the sucrase into glucose + fructose which dissolves easily in the cherry juice.

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