Download Introduction to Carbohydrates

03-131 Genes, Drugs, and Disease
Lecture 24
October 27, 2015
Concept Map:
1. Carbohydrates
2. Lipids & Membranes
3. Metabolism - pathways
 Glycolysis
 Electron transport
 ATP synthesis
 Anaerobic metabolism (fermentation)
4. Cholesterol metabolism & cholesterol control
5. Cell Signaling and breast cancer.
Introduction to Carbohydrates:
Monosaccharides: All carbons in monosaccharides are 'hydrated' -hence
the name carbohydrate (general formula (CH2O)N). Each carbon is bound to
one oxygen. The first or the second carbon is a C=O.
1. The simplest monosaccharides contain three carbons
(dihydroxyacetone, glyceraldehydes)
2. When the C=O group is at the 2nd position it's called an ketose,
because the functional group is a ketone, e.g. dihydroxyacetone.
3. When the C=O group is at the very beginning it's an aldose, because
the functional group is an aldehyde, e.g. glyceraldehydes.
4. Additional hydrated carbons (HO-C-H) are added just below the aldehyde
or ketone group to make longer carbohydrates.
5. The added carbon generates a new chiral center. Each aldose differs
from its neighbor by the configuration (orientation of –OH) of at least one
of the carbon.
dihydroxyacetone
(no chiral center)
D-glyceraldehyde
Aldoses
D-Glyceraldehyde
Ribose
Glucose
Ketoses: The addition of three (HO-C-H) units to
dihydroxyacetone gives the 6 carbon ketose - fructose,
an important sugar in metabolism.



Fructose
Aldose – C=O on carbon one.
Ketose – C=O on carbon two
All other carbons have –OH group.
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03-131 Genes, Drugs, and Disease
Lecture 24
October 27, 2015
Ring Formation in Glucose
1. Six membered ring
created by forming a
bond between C1 and
O5. Most stable state.
2. The C1 carbon
becomes chiral and is
called the anomeric
carbon
3. The new OH group (on
C1) can exist in either
the  or  form.
α-down β-up
Ring formation in Ribose Formation of a 5 membered ring
can occur by forming a bond
between C1 and O4.
H
CH2OH
O
CH2OH
O
H
O
H
O
OH
H
OH
H
OH
H
O
OH
OH
OH
CH2OH
H
O
H
OH
C6 Ketose: Fructose - Although this is
a 6-carbon sugar, because it is a ketose a
five membered ring is formed when it
forms a ring.
CH2OH
O
O
CH2OH
OH
OH
H
OH
OH
OH
H
H
O
OH
1
CH2OH
C
C
OH C
2
4
2
C
CH2OH
CH2OH
5
O
3
C
O
CH2OH
O
HO
C
OH
HO
HO
3
H
4
H
5
C
C
OH
H
OH
O
C
O
CH2OH
H
CH2OH
CH2OH
5
C
4
CH2OH
C
OH C
2
O
OH
O
HO
CH2OH
3
C
OH
OH
Disaccharides: Linkage of the anomeric
carbon of one monosaccharide to the OH of
another monosaccharide via a condensation
reaction.


The bond is termed a glycosidic
bond.
At least on anomeric carbon
participates in forming the bond.
glucose
glucose
maltose
Lactose (milk sugar):
Major sugar in mammalian milk.
 Infants produce lactase to hydrolyze the
disaccharide to monosaccharides, the
released glucose and galactose are sued
 Some adults have low levels of lactase.
This leads to lactose intolerance. The
ingested lactose is fermented by bacteria
in the large intestine, producing
uncomfortable volumes of CO2.
CH2OH
O
CH2OH
O
HO
CH2OH
OH
OH
O
OH
OH
glucose
OH
galactose
CH2OH
O
HO
OH
O
O
OH
OH
OH
OH
(alternate drawing)
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03-131 Genes, Drugs, and Disease
Lecture 24
October 27, 2015
Sucrose (table sugar): The anomeric carbon of glucose forms a
glycosidic bond to the anomeric carbon of fructose.
Sucrose
C. Polysaccharides: Many monosaccharides linked by glycosidic
bonds. Most poly-saccharides are polymers of either glucose, or
modified glucose.
Short-hand nomenclature: In the case of homo-polymers, the
short-hand notation is to simply describe the linkage between the
glucose units: both the conformation of the anomeric carbon and the
carbons participating in the glycosidic bond, i.e. (1-4).
Energy Storage Polysaccharides: Glucose is released when
required.
glucose
fructose
1. Starch [plants] (mixture of amylose and amylopectin).
 amylose =  (1-4) glucose. .
2. Amylopectin [plants] = amylose plus  (1-6) branches.
CH2OH
CH2OH
O
O
CH2OH
O
O
O
O
O
O
CH2OH
OH
3. Glycogen [animals] =
 more highly branched than amylopectin.
glycogen
starch
Structural Polysaccharides
1. Cellulose: Structural polysaccharide of plants.
  1-4 glucose, can't be digested by mammalian enzymes.
 Digested by symbiotic microorganisms (such as those in termites)
CH2OH
O
CH2OH
O
(alternative drawings)
CH2OH
O
OH
O
OH
OH
(1-4)
O
OH
OH
O
O
CH2OH
O
O
O
O
CH2OH
CH2OH
CH2OH
OH
O
OH
OH
2. Bacterial Cell Walls (Peptidoglycan)
 Polysaccharide chains of alternating
N-acetylglucose amine (NAG) and Nacetylmuraminc acid (NAM)
 Muramic acid on NAM linked to a
small peptide (L-Ala D-Gln L-Lys DAla).
 NAM peptide chains are crosslinked
with penta(5)glycine bridges that
extend off of terminal Ala and join to
L-Lys sidechain on adjacent chain,
forming a tough crosslinked cell wall.
OH
O
OH
O
(1-4)
OH
O
OH
O
OH
CH2OH
O
OH
OH
OH
CH2OH
O OH
H3C CH2OH
CH2OH
O OH
O
O OH
O
OH
OH
OH
OH
OH
HN
NH2
glucosamine
CH3
O
N-acetyl glucosamine
(NAG)
OH
HN
CH3
O
N-acetylmuramic acid
(NAM)
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03-131 Genes, Drugs, and Disease
Lecture 24
October 27, 2015
NAM
NAG
NAM
NAG
Mechanism of Action of Penicillin:
 Penicillin inhibits enzymes that are responsible for crosslinking
the Gly5 chain to alanine (circled on diagram).
 The crosslinking of the cell wall is broken, making the bacteria
fragile to breakage.
 Inhibition is by formation of a chemical bond between penicillin
and the enzyme (covalent inhibitor). This type of inhibition is not
penicillin
the same as competitive inhibition because: i) the penicillin forms
a covalent bond with the enzyme, ii) penicillin is modified by the reaction, iii) the reaction is
essentially irreversible.
H
H
H
S CH
3
R
O
N
H
CH3
COOH
S CH
3
R
N
O
O H
Serine
H
H
H
CH3
COOH
H
H
S CH
3
R
N
O
O
H
CH3
COOH
N
O
O
H
S CH
3
R
O
R
CH3
COOH
H
Serine
S CH
3
N
O
CH3
COOH
OH H
O
Serine
Serine
H
H
OH
H
Serine
Penicillin Resistance: Bacterial produce a protein that degrades penicillin (β-lactamase). This is a
common antibiotic resistance gene that is used on plasmids. The transformed bacterial are resistant
to penicillin!
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