Download Carbohydrates and Pigments

Carbohydrates
Zachary R. Woydziak, Ph.D.
Chem 377
Carbohydrates
• A carbohydrate is an organic compound with the empirical formula
Cm(H2O)m; or contains 2 hydrogen, and one oxygen for
every carbon.
• Is often thought of as having one water molecule for every carbon, which
is how the name “carbo-hydrate” is derived.
• Structurally however, it is more accurate to view them as polyhydroxy
aldehydes and ketones.
• Some common carbohydrates are starch, sucrose, glucose, cellulose,
fructose and ribose.
Monosaccharide = One Sugar
• Monosaccharides are the simplest form of a sugar, as they can’t be
hydrolyzed (reacted with water) to smaller carbohydrates.
• Are generally used for energy or for building blocks in an organism.
• Can exist in both an open and cyclic form and rapidly interconvert
between the two forms by the mechanism shown below.
(See http://en.wikipedia.org/wiki/File:Glucose_Fisher_to_Haworth.gif#file)
Example of Cyclizations for
Monosaccharides
a and b Hydroxyl Isomers
Glucose
Emil Fischer
Andreas Marggraf
Aleksandr Butlerov
• The “choice” sugar for life, and has likely been consumed since the existence
of life.
• First isolated in 1747 by the German chemist Andreas Sigsmund Marggraf.
Later it was named Glucose by Jean-Baptist Dumas in 1838 after the Greek
term “glycos” which mean “sweet.”
• It was quickly recognized as being important to life, and many attempted
syntheses failed to produce any glucose with one exception: Butlerov
(Russian chemist) who took formaldehyde and treated it with hot limewater
(Ca(OH)2) to produce a sweet syrup!
Butlerov’s reaction which give a
complex mixture of sugars!
Glucose and Emil Fischer
(A rockstar of Ochem)
Emil Fischer
Fischer Projections
• First to synthesize Glucose as
well as Fructose, and many
other sugars … he did so in a
way that produced them
enantiomerically pure … a
150 yrs ago!
• Fischer
was
able
to
accomplish this by using
enzymes, which he also
studied intently.
• Fishers recognized at the
time that glycerol (which was
easy to obtain) had 3
carbons and 3 alcohol group.
He reasoned that if he could
link 2 glycerol molecules
then he could make glucose.
He made more than glucose
this way!
Problem
Using convincing arrow-pushing mechanisms, show how Fischers conversion of
glyceraldehyde to dihydroxyacetone is possible. (Hint: this involves forming an
enol intermediate).
Other Syntheses of Fischer
Theobromine is present in chocolate
Glucose
Ring open and closed forms
(Natural D-form shown above)
• Glucose is the major source of energy for cells, and the only source of energy
for the human brain.
• In cells, Glucose is converted to energy by Glycolysis (in anaerobic respiration)
or by Glycolysis, Krebs cycle and electron transport chain (aerobic
respiration).
• The net reaction of Glycolysis looks like the following:
Glucose + 2ADP + 2P + 2NAD+  2 Pyruvate + 2ATP + 2NADH
• The net reaction of aerobic respiration looks like the following:
Glucose + 36ADP + 36P + 2NAD+  6 CO2 + 6 H2O + 36ATP + 12NADH + heat
Glucose Production
• Glucose is produced in large abundance in plants as a product of
photosynthesis. The plant uses glucose to trap and store light energy.
Without this process complex life of all sorts (as we know it) would not be
possible.
• Animals also can produce glucose through a process called gluconeogenesis
though it is a bit inefficient.
• Deep sea bacteria (which are far from light) produce glucose harboring Energy
from geothermal vents in the ocean through a process called chemosynthesis.
• Commercially, glucose (also known as “Dextrose”) is obtained from starch
(derived from plants) which is broken down into glucose by an enzyme and
water.
Why did Nature Choose Glucose?
• The aldehydes or ketones in the open form of sugars are quite reactive with
amine residues on proteins (i.e. the side chain of lysine for example can form
Schiff bases).
• Glucose spends the majority of time in a cyclized form (open chain of glucose in
water is only around 0.25%, that means 99.75% is in the cyclic form).
• Other sugars have a much higher rate of the open form which can cause havoc on
functioning proteins.
• However, if too much glucose is present, it will damage proteins an effect which
may lead to complications such as diseases like type II diabetes.
Fructose
Almost all soda-pop contains
high fructose corn syrup as
a first ingredient
Ring open and closed forms
(Natural D-form shown above)
Fructose is an high
Abundance in fruits
• Fructose, otherwise known as fruit sugar, is found in many foods and is
quite abundant in tree fruit, honey, berries, melons, and some root
vegetables.
• It is one of the three important dietary monosaccharides along with
glucose and galactose.
• The organic fructose molecule was first discovered by Augustin-Pierre
Dubrunfaut in 1847 and synthesized later by Fischer.
• Fructose is a white solid that dissolves in water – it is the most watersoluble of all the sugars.
• About 240,000 tonnes of crystalline fructose are produced annually.
Fructose Abundance in Common Foods
Food Item
Fruits
Apple
Apricot
Banana
Grapes
Peach
Pineapple
Pear
Vegetables
Beet, Red
Carrot
Corn, Sweet
Red Pepper,
Sweet
Onion, Sweet
Total
Total
Carbohydrate
Sugars
Free
Fructose
Free
Glucose
13.8
11.1
22.8
18.1
9.5
13.1
15.5
10.4
9.2
12.2
15.5
8.4
9.9
9.8
5.9
0.9
4.9
8.1
1.5
2.1
6.2
9.6
9.6
19.0
6.8
4.7
3.2
6.0
7.6
Sweet Potato 20.1
Yam
27.9
Sugar Cane
Sugar Beet
Sucrose
Fructose/
Glucose
Ratio
Sucrose
as a % of
Total Sugars
2.4
2.4
5.0
7.2
2.0
1.7
2.8
2.1
5.9
2.4
0.2
4.8
6.0
0.8
2.0
0.7
1.0
1.1
0.9
1.1
2.1
19.9
63.5
20.0
1.0
56.7
60.8
8.0
0.1
0.6
0.5
0.1
0.6
0.5
6.5
3.6
2.1
1.0
1.0
1.0
96.2
70.0
64.0
4.2
2.3
1.9
0.0
1.2
0.0
5.0
2.0
2.3
0.7
0.9
14.3
4.2
0.5
13 - 18
17 - 18
0.7
tr
0.2 – 1.0
0.1 – 0.5
1.0
tr
0.2 – 1.0
0.1 – 0.5
2.5
tr
11 - 16
16 - 17
0.9
na
1.0
1.0
60.3
tr
100
100
Fructose = Sweet!
Note: HFCS-42% is common high fructose corn syrup (mixture of fructose and glucose)
Fructose Intolerance
• Fructose Intolerence effects about 1 in 20,000 people.
• In consuming Fructose they will become very ill and sick to their
stomach to the point where the body will induce vomiting to rid
itself of fructose.
• This condition is caused by a mutation in the enzyme Fructase
(which breaks down Fructose in the body), the mutation makes
the enzyme inactive.
• People with this genetic disposition can, however, consume
glucose (dextrose) and all other sugars that don’t contain fructose.
Sucrose – A Disaccharide Sugar
• Sucrose is more commonly known as table sugar. Although almost all plants (and
exclusively in plant) produce sucrose, it is routinely extracted and
refined by recrystallization from both sugar cane and sugar beets.
• People used to chew the cane raw to extract its sweetness. Indians discovered
how to crystallize sugar during the Gupta dynasty (of India), around AD 350.
• The Portuguese took sugar to Brazil. Hans Staden, published in 1555, writes that
by 1540 Santa Catarina Island had 800 sugar mills and that the north coast of
Brazil. From South America it soon spread to the Caribbean islands.
• Today about 150,000,000 tonnes (metric tons) are produced annually.
Long Chain Carbohydrates
Amylose is a polymer exclusively of a-Glucose linkages
Amylopectin is a polymer containing all a Glucose
linkages but is also substituted at the 6-position.
Amylose is a linear polymer made up of Dglucose units. This polysaccharide is one of
the two components of starch, making up
approximately 20-30% of the structure. The
other component is amylopectin, which
makes up 70-80% of the structure. Because of
its tightly packed structure, mylose is more
resistant to digestion than other starch
molecules. Amylose is important in plant
energy storage.
Amylopectin is the other components of
starch. Glucose units are linked in a linear
way with α(1→4) glycosidic bonds.
Branching takes place with α(1→6) bonds
occurring every 24 to 30 glucose units.
Plants store starch and when energy is
needed for cell work, the plant hydrolyzes
the starch, releasing the glucose subunits.
Humans use amylase, an enzyme that
assists in breaking down amylopectin.
Long Chain Carbohydrates
Glycogen is a polymer containing all a Glucose
linkages but is also substituted at the 6position.
Cellulose has very stable 1,4-b-b linkages
Glycogen is the molecule that functions as the
secondary long-term energy storage in animal and
fungal cells. It is made primarily by the liver and
the muscles, but can also be made by glycogenesis
within the brain and stomach. Glycogen is the
analogue of starch, a less branched glucose
polymer in plants, and is commonly referred to as,
animal starch. Glycogen forms an energy reserve
that can be quickly mobilized to meet a sudden
need for glucose, but one that is less compact
than the energy reserves of triglycerides (lipids).
Cellulose is a polysaccharide consisting of a linear
chain of several hundred to over ten thousand
β(1→4) linked D-glucose units. Cellulose is the
structural component of the primary cell wall of
green plants and algae. Cellulose is the most
common organic compound on Earth. About 33%
of all plant matter is cellulose (the cellulose
content of cotton is 90% and that of wood is 40–
50%).
Long Chain Carbohydrates
Chitin is a long-chain polymer of a Nacetylglucosamine, a derivative of glucose, and is
found in many places throughout the natural
world. It is the main component of the cell walls
of fungi, the exoskeletons of arthropods such as
crustaceans (e.g., crabs, lobsters and shrimps)
and insects, the radulas of mollusks, and the
beaks of cephalopods, including squid and
octopuses. In terms of structure, chitin may be
compared to the polysaccharide cellulose.