Introduction to Organic and
Biochemistry
(CHE 124)
Reading Assignment
General, Organic, and Biological Chemistry: An Integrated Approach
3rd. Ed. Ramond
Chapter 10
Carbohydrates
Work Problems
10.
Functions of Carbohydrates
• energy source (e.g. glucose or sucrose)
• energy storage molecules (e.g. starch in
plants; glycogen in animals)
• structural components (e.g. DNA and RNA)
• cell signaling molecules
• cell to cell recognition (e.g. glycosolation of
proteins and other biomolecules).
Carbohydrates
• hydrate of carbon
– (CH2O)n.
• an aldehyde or ketone
derivative of a polyhydroxyl
compound
• Sugars (saccharides)
–
–
–
–
–
–
Glyceraldyde
3 carbons = trios
4 C = tetrose
5 C = pentose
6 C = hexose
7 C = heptose
8 C = octose
• Saccharide derived from
Greek sakchoron
Glucose
Dihydroxyacetone
Carbohydrate Structures
Linear
Structure
Glucose
Fisher
Projection
Diagram
Glucose
Cyclic
Structure
Glucose
Classification of Carbohydrates
• Classified by repeating
structural element
– Monosaccharide (one)
– Disaccharides (two)
– Oligosaccharides (a
few)
– Polysaccharides (many)
Cyclized Monosaccharides
are classified as alpha or beta
• >5 carbons cyclize into
ring form.
– In vivo <1% exist in linear
form.
• Cyclization produces
anomeric carbon
α–D-Glucose
(α–D-Glucopyranose)
– a new chiral carbon
• REMEMBER:
– Alpha HYDROGEN above
– Beta HYDROGEN below
Linear
Glucose
β–D-Glucose
(β–D-Glucopyranose)
Monosaccharides are classified
as Aldose OR Ketose
Aldehyde
group
Keto
Group
Glyceraldehyde
Dihydroxyacetone
Hemiacetal
Hemiacetal is formed by reacting an aldehyde
with an alcohol
Hemiketal
Hemiketal is formed by reacting an ketone
with an alcohol
Monosaccharides are Classified
as Furanose or Pyranose
Furan
α-D-fructofuranose
Pyran
α-D-glucopyranose
Reducing vs NonReducing
Sugars
• Reducing sugars have a free aldehyde group or are capable
of forming an aldehyde through ring opening, isomerization,
or tautomerization.
– Some ketone groups may, through tautomerization, be reducing.
• Test for reducing sugars.
– Benedicts reagent (CuSO4 / citrate)
– Fehling’s solution (CuSO4 / tartrate)
• Reducing sugars reduce copper (II) to copper (I). The product, copper (I) oxide,
forms a red precipitate.
– Tolllen’s test (silver mirror test)
• Tollen’s reagent precipitates silver metal when exposed to free aldehydes.
Connecting Monosaccharides by
Glycosidic bonds
• Glycosidic Bond
– connects
monosaccharides into:
• dimers, trimers,
oligosaccaharides or
polysaccharides
Condensation
(dehydration)
reaction.
• Two orientations
– alpha (α)
– beta (β)
Polysaccharides
Name
Function
 glycogen
Monomer/bond
glucose
animal
connected α-1,4 energy
with α-1,6 branches
storage
 starch
storage
 cellulose
glucose
plant
connected α-1,4
energy
with α-1,6 branches
glucose
connected β-1,4
linear
plant
structural
fiber
Disaccharides
Maltose
(α-D-glucopyranosyl-1,4-α-D-glucopyranose)
Glucose α -1,4-Glucose
Break down product of glycogen / starch
Lactose
(β-D-galactopyranosyl-1,4-α-D-glucopyranose)
Galactose β-1,4-Glucose
Mammals milk sugar
Sucrose
(α-D-Glucopyranosyl-1,2-β-Dfructofuranoside)
Glucose α 1,2 fructose
Table Sugar
Structure
of
Glycogen
and Starch
• Glycogen and starch are branched polymers of
glucose connected by α-1,4 glycosidic bonds
with α-1,6 branches
– Glycogen is glucose storage molecule in animals.
• Glycogen has more branches than starch.
• Stored in liver and muscle.
– Starch is glucose storage molecule in plants.
Cellulose
• Cellulose is a linear polymer of glucose
connected by β
A B O Blood Types are due to
different Carbohydrates on the
surface of RCBs
•
O antigen group is
foundation.
– Contain four
carbohydrates
– Modified to form A
and B antigens
• A has added
N-acetylgalactosamine
• B has added galactose
• The genes for the
specific
glycosyltransferases are
inherited in a Mendelian
patten.
Proteins Are Modified by
Attachment of Carbohydrates
• N-linked
carbohydrates are
attached to R group of
asparagine
– Glycosylation sites
identified by consenses
sequences
• Asn-X-Ser
• Asn-X-Thr
– X may not be pro.
• O linked
carbohydrates are
attached to R group of
serine or threonine.
N-linked
Oligosaccharides
• Extensive
modification leads to
vast array of
molecular shapes.
Erythropoietin (EPO)
• Function
– Stimulates the
production RBCs
• Glycoprotein hormone
• Secreted kidney
• Structure
– 165 amino acid protein
– Three N-linked groups
– One O- linked
• Uses
– Treats anemia cancer
patients
– Performance
enhancement by
athletes
Digestion of Carbohydrates
• Mouth
– mastication mixes salivary alpha amylase with dietary
starch
• Stomach
– digestion halts due to low pH.
• Small Intestine
– acid neutalized by bicarbonate (from pancreas)
– alpha amylase (from pancreas)
• Mucosal lining of upper jejunum
– disaccharidases, oligosaccharidases
• isomaltase, maltase, sucrase
– secreated by luminal side of the brush border of intestinal mucosal cells.
Digestion of Carbohydrates ( cont’)