l. noha soliman carbohydrates objectives introduction.. functions of carbohydrates. types of...
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L. Noha Soliman
Carbohydrates
Biochemistry(BMS 233)
Carbohydrates
Objectives
Introduction. Functions Of Carbohydrates. Types Of Carbohydrates.Classification Of Carbohydrates.MONOSACCHARIDES
• Monosaccharide Classification. • Some important monosaccharides and their
structures.• Sugars exhibit various forms of isomerism
DISACCHARIDESPOLYSACCHARIDES
Introduction
Also called saccharides , which means “sugars.”
They composed of carbon, hydrogen, and oxygen in a 1:2:1 empirical ratio.
The general empirical formula for a carbohydrate is CH2O. If a carbohydrate has 5 carbons atoms, what would be its empirical formula? If a carbohydrate has 12 hydrogen atoms present, what would be its empirical formula?
All carbohydrates have this empirical formula except deoxy sugars, amino sugars.
Most carbohydrates end with the suffix –ose.
C5H10O5
C6H12O6
Are produced by photosynthesis in plants.
Such as glucose are synthesized in plants from CO2, H2O, and light energy from the sun.
Are oxidized in living cells (respiration) to produce CO2, H2O, and energy.
Introduction
Functions of Carbohydrates
Provide energy source:• Living things use carbohydrates as their main source of energy.
• The breakdown of sugar supplies immediate energy for all cell activities.
Provide energy storage:• Plants store energy in a complex carbohydrate form called starch.
• Animals store energy in a complex carbohydrate in their muscle tissue and liver in the called glycogen.
Functions of Carbohydrates
Structural Building Material:
• Plants and some animals also use carbohydrates for structural purposes.
• Plants build their cell walls of a complex carbohydrate called cellulose.
• Animals such as arthropods build their exoskeletons of a complex carbohydrate called chitin.
• Chitin is also found in the cell walls of Fungi.
Carbohydrates are chains (polymers) made of monomers.
The most common monomer of carbohydrates is…
There are
2 types
of
carbohydrates
Simple Complex
Simple Sugars are carbohydrates made up of 1 or 2 monomers.
They taste sweet.
Complex Cabohydrates are polymers made up of many monomers.
Most taste starchy.
Classes of Carbohydrates
Classifications based on number of sugar units in
total chain:
Monosaccharides - single sugar unit
Disaccharides - two sugar units
Oligosaccharides- 3 to 10 sugar units
Polysaccharides- more than 10 units
Classes of Carbohydrates
MONOSACCHARIDES
The basic building blocks (monomers) of carbohydrates. (cannot be further hydrolyzed into smaller units).
Known as simple sugars.
Readily soluble in water.
Same no. of C as O atoms. e.g. Glucose is C6H12O6
Have the general formula (CH2O)n They contain:
– a carbonyl group (C=O) – either at 1C atom or at the 2C atom – multiple hydroxyl groups (-OH)
White crystalline solids.
Structural representation of sugars
Fisher projection: straight chain form. Haworth projection: simple ring. Chair form.
D-Glucose
α- D-Glucose
α- D-Glucose
Monosaccharide Classification
MONOSACCHARIDE
FUNCTIONAL GROUP
ALDOSE KETOSE
NUMBER OF CARBONS IN THE BACKBONE
TRIOSE PENTOSE HEXOSE
Monosaccharide Classification
OH
OH
H
H
HO
CH2OH
HH
H
OH
O
Glucose
H
OH
HO
O H
HHO
H
Ribose
CH2OH
Glyceraldehyde
H
H
H
H
OH
OH
O
C
C
C
65 3
Classified by number of carbons:3C = triose (glyceraldehyde)5C = pentose (ribose)6C = hexose (glucose)
TRIOSES PENTOSES HEXOSES
contains 3 carbon atoms contains 5 carbon atoms contains 6 carbon atoms
C3H6O3 C5H10O5 C6H12O6
glyceraldehydes dihydroxyacetone
ribose deoxyribose
glucose immediate source of energy for cellular
respiration
building blocks to form larger molecules
components of nucleic acids
galactose sugar found in milk and
yogurt
fructose sugar found in honey
Monosaccharide Classification
Monosaccharide Classification
It can be classified based on functional group(According to where the carbonyl group is located): • Aldose - polyhydroxyl aldehyde (aldehyde sugar):
with the carbonyl group (C=O) at the first carbon position, which forms an aldehyde group (CHO).
• Ketose - polyhydroxyl ketone (ketone sugar):Carbonyl group is at C2 position.
1
2
1
2
Monosaccharide Classification
Both functional group have reducing properties ~ reducing sugars
ALDOSES KETOSES
carbonyl group (C=O) at 1C is the aldehyde group
carbonyl group (C=O) at 2C is the ketone group
sugar is known as aldose (aldehyde sugar)
sugar is known as ketose (ketone sugar)
glucose fructose
Monosaccharide Classification
Learning check
Identify each as aldo- or keto- and as tetrose, pentose, or hexose:
H
CH2OH
OHC
H
H
H
OH
OH
OH
C
C
C
HC
O
CH2OH
HHO
CH2OH
O
H OHC
C
C
Aldohexose Ketopentose
Some important monosaccharides
Glucose:• In plants and fruits.• Mild sweet flavor.• known as blood sugar.• Essential energy source.Fructose:• Sweetest sugar• Found in fruits and honey.• Added to soft drinks, cereals, deserts.
Galactose:• Part of milk sugar.• Hardly tastes sweet.• Rarely found naturally as a single sugar.
Some important monosaccharides
Glyceraldehyde Simplest sugar
Ribose Found in RNA
Deoxyribose Found in DNA
Glyceraldehyde
SUGARS EXHIBIT
VARIOUS FORMS
OF ISOMERISM
SUGARS ISOMERISM
They are molecules which have the same molecular formula but have different structures.
Glucose and fructose both have the empirical formula C6H12O6
but they have different structural formulas or shapes.
1. Aldose – Ketose Isomerism: (Isomers)
•Asymmetric carbon: Cl
4 different things are attached to it. |•You must have at least one asymmetric I - C - F carbon to have stereoisomers. |
Br
Chiral center H
| C=O | H-C-OH |
CH2OH Chiral centerGlyceraldehyde
Chiral center
Physical properties
• Optical activityability to rotate plane polarized light.
• Dextrorotatory - rotate to right
- use + symbol
- usually D isomers• Levorotatory - rotate to left
- use - symbol
- usually L isomers
Light is passed through a polarized filter.
A solution of an optical isomer will rotate the light one direction.
2. D and L Isomerism: (Enantiomers)
• Pairs of structures that are mirror images of each other and CANNOT be superimposed on each other.
• Designated by D- or L- at the start of the name.
O H O H C C H – C – OH HO – C – H
HO – C – H H – C – OH
H – C – OH HO – C – H
H – C – OH HO – C – H
CH2OH CH2OH
D-glucose L-glucose
2. D and L Isomerism: (Enantiomers)
3. Epimers:
• Two sugars that differ in configuration at only one chiral center.
• The most important epimers of glucose are:
Mannose epimerization at C2
Galactose epimerization at C4
Hemiacetal & hemiketal formation:
An aldehyde can react with an alcohol to form a hemiacetal.
A ketone can react with an alcohol to form a hemiketal.
O C
H
R
OH
O C
R
R'
OHC
R
R'
O
aldehyde alcohol hemiacetal
ketone alcohol hemiketal
C
H
R
O R'R' OH
"R OH "R
+
+
4. Pyranose and Furanose ring structures:
Pentoses and hexoses can cyclize as the ketone or aldehyde reacts with a distal OH.
Glucose forms an intra-molecular hemiacetal, as the C1 aldehyde & C5 OH react, to form a 6-member pyranose ring.
H O
OH
H
OHH
OH
CH2OH
H
OH
H H O
OH
H
OHH
OH
CH2OH
H
H
OH
-D-glucose -D-glucose
23
4
5
6
1 1
6
5
4
3 2
H
CHO
C OH
C HHO
C OHH
C OHH
CH2OH
1
5
2
3
4
6
D-glucose (linear form)
4. Pyranose and Furanose ring structures:
Fructose forms either• A 6-member pyranose ring, by reaction of the C2 keto group with
the OH on C6, or• A 5-member furanose ring, by reaction of the C2 keto group with
the OH on C5. CH2OH
C O
C HHO
C OHH
C OHH
CH2OH
HOH2C
OH
CH2OH
HOH H
H HO
O
1
6
5
4
3
2
6
5
4 3
2
1
D-fructose (linear) -D-fructofuranose
5. Alpha and beta anomers:
Cyclization of glucose produces a new asymmetric center at C1.
The 2 stereoisomers are called anomers, a & b. GLUCOSE
primary source of energy
- glucose - glucose
hydroxyl (-OH) group of the 1C projects below the
plane of the ring
hydroxyl (-OH) group of the 1C projects upward the
plane of the ring
DISACCHARIDES
These are formed when two monosaccharide molecules join together with the elimination of one molecule of water.
They have the general formula C12H22O11.
Sweet tasting.
Water soluble.
EXAMPLE: Maltose
Sucrose
Lactose
C6H12O6 + C6H12O6 = C12H22O11 + H2OGlucose + Glucose = Maltose + Water
CH2OH
H O H
OH OH
CH2OH
H O H
HO OH
+H20
CH2OH
H O H
OH
CH2OH
H O H
OHO
α- GLUCOSE α- GLUCOSE MALTOSE
Disaccharide Formation
Disaccharides are formed when two monosaccharides are joined by dehydration synthesis reaction.
GLUCOSE + GLUCOSE -> Maltose (malt sugar)GLUCOSE + FRUCTOSE -> Sucrose (cane sugar)GLUCOSE + GALACTOSE -> Lactose (milk sugar)
Dehydration Synthesis
• Building reaction.
• H2O is removed in order to form a new bond.
Hydrolysis Reaction
• Breaking reaction.
• H2O is required to break a bond.
Glycosidic linkage
• The bond between monosaccharides.• What type of reaction would form this bond?
– Dehydration synthesis reaction.• What kind of bond is a glycosidic linkage?
– Polar covalent bond.O
H2C
OH
CHO
HO
OH
OH
OH2C
OH
HOHO
OHOH
OH2C
OH
CHO
HO
OHO
H2C
OH
O
HO
OHOH
+ H2O
Disaccharide Formation
Some important disaccharides
• Sucrose: Saccharose or table sugar• It is fructose and glucose combined.
• Source of sucrose is sugar beets and sugar cane.
• Tastes sweet, and is readily available.
• brown, white, powdered.
Some important disaccharides
• Maltose: Malt sugar• Consists of two glucose units. • Produced when starch breaks down.• Not abundant.• Present in germinating seeds.
Lactose: milk sugar• Glucose and galactose.• Main carbohydrate in milk.
Some important disaccharides
OLIGOSACCHARIDES
• Oligosaccharide is a few linked monosaccharides and are at time associated with proteins (glycoproteins) or lipids (glycolipids).
POLYSACCHARIDES
Polysaccharides are chains of monosaccharides that have been joined by many dehydration synthesis reactions.
Do not taste sweet and do not crystallize.
Insoluble in water.
Form colloidal solutions when added to water.
Polysaccharide diversity
Molecular structure determines function.
The function of the polysaccharide depends on what type of isomer of glucose the polysaccharide is made.
Storage PolysaccharidesEnergy storage - starch and glycogen.
Structural PolysaccharidesUsed to provide protective walls to cells – cellulose and chitin.
In starch In cellulose
STORAGE POLYSACCHARIDES
STARCH AND
GLYCOGEN
Some important polysaccharides
Starch
Energy storage used by plants.– Storage form of glucose in plants.– Found in grains, tubers, and legumes.
Body hydrolyzes plant starch to glucose.
Long repeating chain of α-D-glucose.
Chains up to 4000 units.
Starch Starch consists of two compounds:
– Amylose: straight chain of α-D- glucose, major form of starch.
– Amylopectin: branched chains of α-D-glucose.
Glycogen
Energy storage of animals:– Storage form of glucose in the body.– Provides a rapid release of energy when needed.
Structure is similar to amylopectin but more branches.
Made from α-glucose.
Glycogen
Found mainly in liver and muscle cells.
When the level of glucose in your blood runs low, glycogen is released from your liver.
The glycogen stored in your muscles supplies the energy for muscle contraction and thus, for movement.
more branching
carbon and energy (glucose) storage molecules
STRUCTURAL POLYSACCHARIDES CELLULOSE
AND CHITIN
Some important polysaccharides
Cellulose
Most abundant organic compound on Earth.
It forms the main part of the cell wall in plants cells.
Cellulose is the major component of cotton , wood and paper.
Cellulose
It is a polysaccharide of β glucose units in unbranched chains.
Linked by β-1,4 glycosidic bonds.
Each β-glucose related to the next by a rotation of 180°.
14
3 2
5
6
1 4 1 4 1 4
Cellulose
Every other glucose is flipped over, due to β linkages. This promotes intra-chain and inter-chain H-bonds and van der Waals interactions, that cause cellulose chains to be straight & rigid, and pack with a crystalline arrangement in thick bundles - microfibrils.
Digesting starch vs. cellulose
starcheasy todigest
starcheasy todigest enzyme
enzyme
cellulosehard todigest
cellulosehard todigest
Cowcan digest cellulose well; no need to eat other sugars
Gorillacan’t digest cellulose well; must add another sugar source, like fruit to diet
Digesting starch vs. cellulose
Amino derivatives
The replacement of a hydroxyl group on a carbohydrate results in an amino sugar.
•Uses for amino sugars.•Structural components of bacterial cell walls.•As a component of chitin.•A major structural unit of chondroitin sulfate - a component of cartilage.•Component of glycoprotein and glycolipids.
H O
OH
OH
H
H
OHH
OH
CH2OH
HH O
OH
OH
H
H
NH2H
OH
CH2OH
H
-D-glucose -D-2-aminoglucose (glucosamine)
Chitin
It is the “plastic-like” material that composes the exoskeletons of arthropods (insects, arachnids, and crustaceans).Most fungi (mushrooms) have chitin present within their cell walls.
Chitin
Similar to cellulose but the hydroxyl group on each monomer substituted with an acetyl amine group.
Cellulose strands are parallel, chitins can be parallel or antiparallel.
Above is a structural monomer of chitin.