Transcript Unit 7 Carbohydrates

Unit 7 Carbohydrates
Chapter 16
What are Carbohydrates?
Sugars and starches that are found in such
foods as bread, pasta and rice.
 The term “carbohydrate” comes from the
observation that when you heat sugar, you
get carbon and water.
 Comes from the word “saccharides”
(saccharo is Greek for “sugar”)
 Formed from aldehydes and ketones.
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Formation of Carbohydrates
Form from the reaction of alcohols with
aldehydes or ketones.
 They form hemiacetals (if aldehyde) or
hemiketal (if ketone)
 These are called polyhydroxy because they
have multiple hydroxyl groups
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3 Categories of Carbs
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1. Monosaccharides contain a single
polyhydroxy aldehyde or ketone unit (e.g.,
glucose, fructose).
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2. Disaccharides consist of two
monosaccharide units linked together by
a covalent bond (e.g., sucrose).
3 Categories of Carbs
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Polysaccharides contain very long
chains of hundreds or thousands of
monosaccharide units, which may be
either in straight or branched chains
(e.g., cellulose, glycogen, starch).
Simple Carbs: Monosaccharides
Composed of carbon, hydrogen and
oxygen
 Have the general formula (CH2O)n, where
n is any number between 3 & 7. Not all
follow this formula.
 Can be named by the functional groups
attached (aldehyde or ketone) OR by the
number of carbons in the main skeleton.
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Isomers
Monosaccharides can exist in many
isomeric forms.
 D- and L- are used as prefixes in the
name to identify that it is one of 2
possible stereoisomers.
 Stereoisomers have the same formula
and the same bonding, but differ in spatial
arrangement.
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Isomers
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Stereoisomers are mirror images of one
another, but means if you superimpose
one onto the other, they will not match
up.
Isomers
2 stereoisomers that are
nonsuperimposable mirror images are
called enantiomers.
 Molecules that can exist in enantiomeric
forms are called chiral molecules.
 A carbon that has four different groups
bonded to it is called a chiral carbon.
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Cyclic vs. Straight Chained
The straight chain form of
monosaccharides are less common than
cyclic forms.
 Cyclic forms exist under specific
physiological conditions.
 In the case of glucose the C-1 would
react with the OH group on the C-5
creating a ring.
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Cyclic vs. Straight Chained
In slide #3 of this ppt, we learned that
when aldehydes react with alcohols you
get a hemiacetal.
 In this case, when the aldehyde portion of
glucose reacts with the OH group it
creates an intermolecular hemiacetal.
 These create alpha and beta isomers.
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Chirality: Alpha vs. Beta Glucose
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Both are chair formations
The Beta position is defined as the -OH
being on the same side of the ring as the C
# 6. In the chair structure this results in
a horizontal projection.
The Alpha position is defined as the -OH
being on the opposite side of the ring as the
C # 6. In the chair structure this results in
a downward projection.
Alpha vs. Beta Glucose
The alpha and beta label is not applied to
any other carbon - only the anomeric
carbon.
 The anomeric carbon is the center of a
hemiacetal functional group. A carbon that
has both an ether oxygen and an alcohol
group is a hemiacetal.
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How do complex sugars form from
simple sugars?
A dehydration synthesis reaction occurs.
(Water is removed)
 A glycosidic bond is formed between each
single sugar unit connecting the oxygen
atoms.
 http://www.youtube.com/watch?v=b7Td
WLNhMtM
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Properties & Functions of
Monosaccharides
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Glucose: Common names (dextrose, grape
sugar and blood sugar)
Broken down by the body through glycolysis to
produce energy.
Glucose levels in the body are important for
normal function. (should be 100-120mg/100mL)
Glucose levels rise after eating and return to
normal after a couple of hours.
When levels get too low lightheadedness and
shakiness occurs.
Properties & Functions of
Monosaccharides
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Fructose: Also called levulose and fruit sugar. It
is the sweetest of all sugars.
Naturally found in honey, fruits, berries and root
vegetables.
Commercially added to foods and drinks for
enhancing taste. The form of fructose comes
from corn, sugar beets and sugar cane.
Ketone sugar, meaning it has a ketone group
instead of an aldehyde.
Has 6 carbons.
Properties & Functions of
Monosaccharides
Galactose: Part of biological systems as a
component of lactose (milk sugar)
 Found in the milk of most mammals.
 Beta-D-Galactose and Beta-D-Nacetylgalactosamine are part of the blood
group antigens.
 Contains an aldehyde group.
 A small amount creates a lot of energy.
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Properties & Functions of
Monosaccharides
Ribose: A component of RNA
 5 carbon atoms
 Used to transfer energy rather that
create it
 Helps translate genes into proteins
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Properties & Functions of
Polysaccharides
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Starch: Composed of the 2 glucose
polymers amylose and amylopectin
Produced by green plants as an energy
source
Pure starch is white, tasteless and odorless
The most common carb in the human diet
Found in potatoes, wheat, corn and rice
The largest non-food use of starch is as an
adhesive in the papermaking process
Properties & Functions of
Polysaccharides
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Glycogen: Major glucose storage molecule in
animals
Stored in the liver and skeletal muscle
Similar structure to starch, but more branched
& compact
Used as an energy reserve
Only the glycogen stored in the liver is
accessible to other organs
Glycogen is stored in the uterus during
pregnancy to give nourishment to the embryo
Properties & Functions of
Polysaccharides
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Cellulose: The most abundant
polysaccharide
Contains about 3000 glucose units (the
largest cellulose molecule contains 26,000
glucose units)
Structural component of the plant cell wall
Cannot be digested by the body (because we
cannot synthesize the enzyme cellulase
which can break up the bonds of the
polymer
Starch vs. Cellulose
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Starches can be digested by animals but
cellulose cannot. Most animals that ingest
grass or wood have special
microorganisms living in their gut that
digest the cellulose and the animals in
turn absorb the breakdown product that
is produced.
CORN IN YOUR POOP!!