Transcript Carbohydrates B3

Carbohydrates
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Carbohydrate – (hydrated carbon)
Carbohydrates have empirical formula Cx(H2O)y.
Most abundant carbohydrate is glucose, C6H12O6.
Two types of Carbohydrates – monosaccharides (simple
sugars and polysaccharides.
Monosaccharides – 1st type
Simplest form of carbohydrates
Classified according to number of carbons
Triose – 3C’s
Pentose – 5C’s
Hexose – 6C’s
All have 2 or more alcohols and a carbonyl group
General Formula – CH2O
These simple sugars that cannot be broken down
by hydrolysis with aqueous acids.
Examples - Glucose and Fructose are the main substrate for respiration, releasing
energy for all cell processes.
2 Common Monosaccharides – both
isomers
C6H12O6
Each contain
many OH groups
which make these
molecules soluble
in water.
This are the straight
chain form of
these sugars.
Aldose sugar
Ketose sugar
Monosaccharides
When these sugars are put in an (aq) solution,
they undergo and internal reaction which results in
the more familiar ring structure
• Most glucose molecules are in the ring form.
• Note the six-membered rings are not planar.
• Focus on carbon atoms 1 and 5: if the OH groups are on
opposite sides of the ring, then we have -glucose; if
they are on the same side of the ring, then we have glucose.
• The - and - forms of glucose form very different
compounds.
The ring form of sugars make it possible for another type
of isomer.
This OH is above the plane of the ring
This OH is below the plane of the ring
Disaccharides
• Disaccharides are sugars formed by the condensation of
two monosaccharides.
• Examples: sucrose (table sugar) and lactose (milk
sugar).
• Glycoside linkage – “ether” bond formed when
monosaccharides combine to form disaccharides or
polysaccharides (C-O-C).
• Disaccharides can be converted into monosaccharides by
treatment with acid in aqueous solution.
Disaccharides
Lactose – glucose + galactose – found in milk
Maltose – glucose + glucose – product from starch digestion
Sucrose – glucose + fructose – table sugar
All have same molecular formula – C12H12O11
glycosidic linkage (known as 1,4 b/c of C’s involved
Polysaccharides
• Polysaccharides are formed by condensation of several
monosaccharide units.
• All polysaccharides are insoluble so they are ideal for
storage.
• 3 common glucose based polysacch. = starch, glycogen,
and cellulose
1. Starch
• Main storage carbohydrate in plants – this is why food
from plants are rich sources of starch – Ex. potatoes,
rice, flour…
• Starch is a polymer of -glucose.
• Made from two polysaccharides – amylose (straight
chain) and amylopectin (branched)
• Starch contains 1,4 and 1,6 linkages.
Starch
Amylose – 1,4 linkage of -glucose monomers
Amylopectin – 1,4 and 1,6 linkage
of -glucose monomers
2. Glycogen
• Also a polymer of -glucose.
• Sometimes called “animal starch” as it is the main storage carb
in animals – found in the liver and muscles
• Contains many 1,6 branches
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3. Cellulose
Cellulose is a structural material in plant cell walls.
Cellulose is a polymer of -glucose. It is linear.
Every other monomer is upside down – enables to
hydroxyl groups to form hydrogen bonds –gives support
The 1,4 linkage can be hydrolyzed by cellulase which is
absent in most animals, including mammals. (humans
have some from bacteria in our gut, but not much)
Major Functions of Carbohydrates
1. Energy sources – (glucose)
2. Energy reserves (glycogen)
3. Structure (cellulose)
Dietary Fiber – mainly plant material (lots of veggies and salad)
that is not hydrolyzed by enzymes secreted in the human
digestive tract. (may be digested by microflora in the gut)
Most is excreted intact by the body. Ex. Cellulose,
hemicellulose, lignin and pectin
Starch and glycogen are easily broken down and absorbed in
the body.
Importance –as fiber passes through the digestive system it
helps stimulate the lining to produce mucus which helps
smooth passage of undigested foods. May help prevent
diverticulitis, IBS, colorectal cancer, constipation, obesity,
Crohn’s disease, hemorrhoids, and diabetes mellitus.