Uploaded by Jan Bernabe Sabado


on Earth
• Polyhydroxy aldehydes or ketones, or
substances that yield such compounds on
• Many have the empirical formula (CH2O)n;
some also contain nitrogen, phosphorus, or
Major Size Classes
• Monosaccharides
• Oligosaccharides
• Polysaccharides
“Saccharide” is derived from the Greek
sakcharon, meaning “sugar”
• Simple sugars
• Colorless, crystalline solids that are freely
soluble in water but insoluble in nonpolar
• Most have a sweet taste
• Most abundant in nature: D-glucose
• Consist of a single polyhydroxy aldehyde or ketone
• Backbones are unbranched carbon chains in which
all the carbon atoms are linked by single bonds
• In the open-chain form, one of the carbon atoms is
double-bonded to an oxygen atom to form a
carbonyl group; each of the other carbon atoms
has a hydroxyl group
• According to Functional Group
– Aldose: carbonyl group is at an end of the carbon
– Ketose: carbonyl group is at any other position
• According to Number of C
– Trioses, tetroses, pentoses, hexoses, heptoses, etc.
• Simplest monosaccharides: glyceraldehyde, an
aldotriose, and dihydroxyacetone, a ketotriose
• Most common
in nature: Dglucose and Dfructose
• Components of nucleotides and nucleic acids:
D-ribose and 2-deoxy-D-ribose
• All the monosaccharides contain one or more
asymmetric (chiral) carbon atoms and thus occur
in optically active isomeric forms
• To represent three-dimensional sugar structures
on paper, we often use Fischer projection
• In general, a molecule with n chiral centers can have 2n
• Stereoisomers of each carbon-chain length can be
divided into two groups that differ in the configuration
about the chiral center most distant from the carbonyl
– D isomers: hydroxyl group on the reference carbon is on
the right in the projection formula
– L isomers. hydroxyl group on the reference carbon is on
the right in the projection formula
• Carbons of a sugar are numbered beginning at the
end of the chain nearest the carbonyl group.
• The four- and five-carbon ketoses are designated
by inserting “ul” into the name of a corresponding
• Two sugars that differ only in the configuration
around one carbon atom are called epimers
• In aqueous solution, aldotetroses and all
monosaccharides with five or more carbon
atoms in the backbone occur predominantly
as cyclic (ring) structures in which the carbonyl
group has formed a covalent bond with the
oxygen of a hydroxyl group along the chain.
• Formation of ring structures is the result of a
general reaction between alcohols and
aldehydes or ketones to form derivatives
called hemiacetals or hemiketals, which
contain an additional asymmetric carbon atom
and thus can exist in two stereoisomeric
• Six-membered ring compounds are called pyranoses
• Five-membered ring compound are called furanoses.
• Six-membered aldopyranose ring is much more stable than
the aldofuranose ring and predominates in aldohexose
• Only aldoses having five or more carbon atoms can form
pyranose rings.
• Isomeric forms of monosaccharides that differ only in their
configuration about the hemiacetal or hemiketal carbon
atom (or anomeric carbon) are called anomers.
Monosaccharide Derivatives
Aldonic acid
Uronic acid
Amino sugar
Deoxy sugars
Derivatives of Monosaccharides
Basis of Fehling’s Reaction = Glucose
is Reducing
This is the more sensitive and specific
test for glucose
Formation of Glycosidic
Bond..Polysaccharides Written from
Non-Reducing to Reducing End
• Consist of short chains of monosaccharide units,
or residues, joined by characteristic linkages
called glycosidic bonds
• Most abundant: disaccharides like sucrose or
cane sugar
• Incells, most oligosaccharides consisting of three
or more units are joined to nonsugar molecules
• Consist of two monosaccharides joined
covalently by an O-glycosidic bond
Glycosidic bond
• Formed when a hydroxyl group of one sugar
reacts with the anomeric carbon of the other
• Represents the formation of an acetal from a
hemiacetal and an alcohol (a hydroxyl group of
the second sugar molecule)
• Readily hydrolyzed by acid but resist cleavage by
• Can be hydrolyzed to yield their free
monosaccharide components by boiling with
dilute acid
• Oxidation of a sugar’s anomeric carbon by
cupric or ferric ion occurs only with the linear
form, which exists in equilibrium with the
cyclic form(s)
• When the anomeric carbon is involved in a
glycosidic bond, that sugar residue cannot
take the linear form and therefore becomes a
nonreducing sugar
What Is Sweet?
Tasting Panels: Taste Relative to
Sucrose….dilutions of the test molecules.
Compound Sweetness
Lactose 0.16
Glycerol 0.60
Glucose 0.75
Sucrose 1.0
Fructose 1.75
Aspartame 250
Na-saccharine 510
Sucralose 600
Lugduname 225,000
Because of sucralose intense sweetness, what
is sold in the supermarket is mixed with a filler:
fluffed glucose or fluffed maltodextrin. (Fluffed
by the same process that makes Puffed Wheat
or Puffed Rice).
While sucralose can not be metabolized, the
filler does have calories .. but less than 5
cal/gram. So the FDA allows the claim that
sucralose products have no calories.
What is the nutritional calorie compared to the
biochemical calorie?
What are the safety concerns?
• Sugar polymers containing more than 20 or so
monosaccharide units
• Most common form of carbohydrates in
• Also called glycans
• Do not have definite molecular weights
• Most abundant: cellulose
• Differ from each other in:
– identity of recurring monosaccharide units
– length of their chains
– types of bonds linking the units
– degree of branching
Classification of Polysaccharides
• Homopolysaccharides contain only a single type of
monomer. They usually serve as storage forms of
monosaccharides that are used as fuels or as
structural elements in plant cell walls and animal
• Heteropolysaccharides contain two or more
different kinds of monomers. They usually provide
extracellular support for organisms of all kingdoms.
• Most important storage polysaccharides are
starch in plant cells and glycogen in animal
cells which are both occur intracellularly as
large clusters or granules and heavily
hydrated, because they have many exposed
hydroxyl groups
• Most plant cells have the ability to form starch, but it is
especially abundant in tubers, such as potatoes, and in
• Contains two types of glucose polymer, amylose and
• Amylose is unbranched, with molecular weight from a
few thousand to more than a million.
• Amylopectin is highly branched (occurring every 24 to 30
residues ), with molecular weight up to 100 million.
• Main storage polysaccharide of animal cells
• Like amylopectin, but more extensively branched (on
average, every 8 to 12 residues) and more compact than
• Especially abundant in the liver, where it may constitute
as much as 7% of the wet weight; it is also present in
skeletal muscle
• With an average molecular weight of several million.
• Has as many nonreducing ends as it has branches, but
only one reducing end
• Bacterial and yeast polysaccharides made up
of (α 1→6)-linked poly-D-glucose; all have (α1
→ 3) branches, and some also have (α 1 → 2)
or (α 1 → 4) branches
• Found in dental plaque
• Used in several commercial products for
fractionation of proteins
• Fibrous, tough, water-insoluble substance, found in
the cell walls of plants, particularly in stalks, stems,
trunks, and all the woody portions of the plant
• Constitutes much of the mass of wood and cotton
• Linear, unbranched homopolysaccharide, consisting
of 10,000 to 15,000 D-glucose units, but unlike
amylose, in β configuration
• Linear homopolysaccharide composed of Nacetylglucosamine residues in β linkage
• Forms extended fibers similar to those of cellulose,
and like cellulose cannot be digested by vertebrates
• Principal component of the hard exoskeletons of
arthropods and is probably the second most
abundant polysaccharide, next to cellulose, in
Homopolysaccharide Folding
• Stabilized by weak interactions within or
between molecules
– Hydrogenbond
– Hydrophobic and van der Waals interactions
– Electrostatic interactions
Homopolysacchaide Folding
• Starch and glycogen : tightly coiled helix,
stabilized by interchain hydrogen bonds
• Along the amylose chain forms a 60° angle
with the preceding residue, so the helical
structure has six residues per turn
Homopolysaccharide Folding
• Cellulose: Each chair is turned 180°relative to
its neighbors, yielding a straight, extended
• Several chains lie side by side produces
straight, stable supramolecular fibers of great
tensile strength
• Can be found in bacterial and algal cell walls
• Heteropolymer of alternating (β1→4)-linked Nacetylglucosamine and N-acetylmuramic acid
• Lie side by side in the cell wall, crosslinked by
short peptides which weld the polysaccharide
chains into a strong sheath
• Lysozyme kills bacteria by hydrolyzing
glycosidic bonds
• Present in tears and produced by certain
bacterial viruses
• Produced by certain marine red algae, including some
of the seaweeds
• Mixture of sulfated heteropolysaccharides made up of
D-galactose and an L-galactose derivative ether-linked
between C-3 and C-6
• Contains agarose (unbranched) and agaropectin
• Agarose has gel-forming property
• Forms a double helix when heated then cooled,
trapping water molecules in the central cavity
• Used as inert supports for the electrophoretic
separation of nucleic acids, an essential part of
the DNA sequencing process
• Used to form a surface for the growth of bacterial
• Used for the capsules in which some vitamins and
drugs are packaged
Extracellular Matrix
• Gel-like material found in the extracellular space in
the tissues of multicellular animals
• Holds the cells together and provides a porous
pathway for the diffusion of nutrients and oxygen
to individual cells
• Composed of an interlocking meshwork of fibrous
proteins and glycosaminoglycans, a family of linear
polymers composed of repeating disaccharide units
• One of the two monosaccharides is always either
N-acetylglucosamine or N-acetylgalactosamine;
the other is in most cases a uronic acid
• Has very high density of negative charge
• Assume an extended conformation in solution
• Attached to extracellular proteins to form
Hyaluronic Acid/Hyaluronate
• Have molecular weights greater than 1 million
• Form clear, highly viscous solutions that serve as
lubricants in the synovial fluid of joints and give
the vitreous humor of the vertebrate eye its
jellylike consistency
• Essential component of the extracellular matrix
of cartilage and tendons, to which it contributes
tensile strength and elasticity
Other Glycosaminoglycans
• Much shorter polymers than hyaluronate and they are
covalently linked to specific proteins
• Includes
– Chondroitin sulfate (contributes to the tensile strength of
cartilage, tendons, ligaments, and the walls of the aorta)
– Dermatan sulfate (contributes to the pliability of skin and is
also present in blood vessels and heart valves)
– Keratan sulfates (present in cornea, cartilage, bone, and a
variety of horny structures formed of dead cells)
• Natural anticoagulant made in mast cells (a type of
white blood cell) and released into the blood
• Inhibits blood coagulation by binding to the protein
• Has the highest negative charge density of any
known biological macromolecule
• Routinely added to blood samples obtained for
clinical analysis, and to blood donated for
transfusion, to prevent clotting
• Sugar covalently joined to a protein or a lipid
• Act in cell-cell recognition and adhesion, cell
migration during development, blood clotting,
the immune response, and wound healing
• Macromolecules of the cell surface or
extracellular matrix in which one or more
glycosaminoglycan chains are joined
covalently to a membrane protein or a
secreted protein
• Major components of connective tissue such
as cartilage
• Have one or several oligosaccharides of varying
complexity joined covalently to a protein
• Found on the outer face of the plasma membrane,
in the extracellular matrix, blood, Golgi complexes,
secretory granules, and lysosomes
• Rich in information, forming highly specific sites for
recognition and high-affinity binding by other
• Membrane lipids in which the hydrophilic
head groups are oligosaccharides
glycoproteins, act as specific sites for
recognition by carbohydrate-binding proteins
• glucose provides energy for the brain and ½ of
energy for muscles and tissues
• glycogen is stored glucose
• glucose is immediate energy
• glycogen is reserve energy
• all plant food
• milk
• carbohydrates are not equal
– simple carbohydrates
– complex carbohydrates
Simple Carbohydrates
• sugars
– monosaccharides – single sugars
– disaccharides – 2 monosaccharides
Complex Carbohydrates
• starches and fibers
• polysaccharides
– chains of monosaccharides
Simple Carbs
• monosaccharides
– all are 6 carbon hexes
6 carbons
12 hydrogens
6 oxygens
arrangement differs
– accounts for varying sweetness
– glucose, fructose, galactose
mild sweet flavor
known as blood sugar
essential energy source
found in every
disaccharide and
• sweetest sugar
• found in fruits and honey
• added to soft drinks,
cereals, deserts
• hardly tastes sweet
• rarely found naturally
as a single sugar
• pairs of the monosaccharides
– glucose is always present
– 2nd of the pair could be fructose, galactose or
another glucose
– taken apart by hydrolysis
– put together by condensation
– hydrolysis and condensation occur with all energy
– maltose, sucrose, lactose
• making a disaccharide
– chemical reaction linking 2
• breaking a disaccharide
– water molecule splits
– occurs during digestion
• 2 glucose units
• produced when starch breaks down
• not abundant
• fructose and glucose
• tastes sweet
– fruit, vegetables, grains
• table sugar is refined
sugarcane and sugar
• brown, white,
• glucose and galactose
• main carbohydrate in
– known as milk sugar
Complex Carbohydrates
• polysaccharides
– glycogen and starch
• built entirely of glucose
– fiber
• variety of monosaccharides and other carbohydrate
• limited in meat and not found in plants
– not an important dietary source of carbohydrate
– all glucose is stored as glycogen
– long chains allow for
hydrolysis and release
of energy
• stored in plant cells
• body hydrolyzes plant starch to glucose
• structural parts of plants
– found in all plant derived food
• bonds of fibers cannot be broken down during
the digestive process
– minimal or no energy available
Fiber types
• cellulose
• pectins
• lignins
• resistant starches
– classified as fibers
– escape digestion and absorption
Fiber Characteristics
• soluble fibers, viscous, fermentable
– easily digested by bacteria in colon
– associated with protection against heart disease and
• lower cholesterol and glucose levels
– found in legumes and fruits
• insoluble and not easily fermented
– promote bowel movements
– alleviate constipation
– found in grains and vegetables
DRI and Fiber
• distinguish fibers by source
– dietary fibers: naturally in intact plants
– functional fibers: extracted from plants or
– total fiber: sum of the 2
Carbohydrate Digestion
• break down into glucose
– body is able to absorb and use
• large starch molecules
– extensive breakdown
• disaccharides
– broken once
• monosaccharides
– don’t need to be broken down
Carbohydrate Digestion
• begins in mouth
– chewing releases saliva
– enzyme amylase hydrolyzes starch to
polysaccharides and maltose
• stomach
– no enzymes available to break down starch
– acid does some breakdown
– fibers in starch provide feeling of fullness
• small intestine
– majority of carbohydrate digestion takes place
– pancreatic amylase reduces carbs to glucose
chains or disaccharides
– specific enzymes finish the job
• maltase
– maltose into 2 glucose
• sucrase
– sucrose into glucose and fructose
• lactase
– lactose into glucose and galactose
• large intestine
– 1-4 hours for sugars and starches to
be digested
– only fibers remain
• attract water, which softens stool
– bacteria ferment some fibers
• water, gas, short-chain fatty acids (used
for energy)
Carbohydrate Absorption
• glucose can be absorbed in the mouth
• majority absorbed in small intestine
– active transport
• glucose and galactic
– facilitated diffusion
• fructose
• smaller rise in blood glucose
Lactose Intolerance
• more lactose is consumed than can be digested
– lactose molecules attract water
• cause floating, abdominal discomfort, diarrhea
– intestinal bacteria feed on undigested lactose
• produce acid and gas
Lactose Intolerance
• age, damage, medication, diarrhea, malnutrition
• management requires dietary change
– 6 grams (1/2 cup) usually tolerable
– take in gradually
– hard cheeses & cottage cheese
– enzyme drops or tablets
• lactose free diet is extremely difficult to accomplish
Carbohydrate Metabolism
1/3 of body’s glycogen is stored in liver
released as glucose to bloodstream
eat – intake glucose
liver condenses extra glucose to glycogen
blood glucose falls
liver hydrolyzes glycogen to glucose
Glycogen is bulky, so we store only so much: short
term energy supply
Fat is the long term energy supply.
Glucose for Energy
• enzymes break apart glucose – yielding energy
• inadequate supply of carbohydrates
– ketone bodies (fat fragments) are an alternate
energy source during starvation
– excess ketones can lead to ketosis: imbalance of
acids in body
• minimum of 50 – 100 grams of carbs/day are
needed to avoid ketosis
Glucose Homeostasis
• maintaining an even balance of glucose is
controlled by insulin and glucagon
– insulin
• moves glucose into the blood
– glucagon
• brings glucose out of storage
• maintaining balance
– balanced meals at regular intervals
• fiber and some fat slow the digestive process down
• glucose gets into the blood slow and steady
Blood Glucose
When a person eats,
blood glucose rises.
High blood glucose stimulates
the pancreas to release insulin.
Insulin stimulates the uptake of
glucose into cells and storage
as glycogen in the liver and
muscles. Insulin also stimulates
the conversion of excess
glucose into fat for storage.
Fat cell
As the body's cells use
glucose, blood levels decline.
Low blood glucose stimulates
the pancreas to release
glucagon into the bloodstream.
Glucagon stimulates liver
cells to break down glycogen
and release glucose into the
The stress hormone
epinephrine and other hormones
also bring glucose out of storage.
Blood glucose begins to
• diabetes
– after food intake, blood glucose rises and is not
regulated because insulin is inadequate
• hypoglycemia
– blood glucose drops dramatically
• too much insulin, activity, inadequate food intake, illness
• diet adjustment includes fiber-rich carbs and protein
Glycemic Index
• way of classifying food
according to their
ability to raise blood
• much controversy
• ½ comes from natural sources, ½ from
refined and added
– sucrose, corn syrup, honey
• excess can lead to nutrient deficiencies and
tooth decay
– empty calories
– sugar and starch break down in the mouth
• recommended intake
– added sugar = no more than 10% of energy intake
Starch and Fiber
• diet that includes starch, fiber and natural
– whole grains, vegetables, legumes, fruits
may protect against heart disease and stroke
reduces the risk of type 2 diabetes
enhances the health of the large intestine
can promote weight loss
Starch and Fiber
• starch intake
– 45-65%
– 225 – 325 grams (DV is 300 grams)
– 900-1300 kcal/2000 kcal
– RDA is 130 grams
• fiber intake
– Daily Value is 25 grams/2000 kcal
• grains: 1 serving = 15 grams
• vegetables
– ½ cup starchy = 15 grams
– ½ cup nonstarchy = 5 grams
fruit: 1 serving = 15 grams
milk: 1 cup = 12 grams
meat: none or little
legumes: ½ cup = 15 grams
Artificial Sweeteners
• help keep sugar and energy intake down
• anything we eat has FDA approval
– saccharin
– aspartame
– acesulfame potassium
– sucralose
– neotame
Sugar Replacers
• sugar alcohols
– provide bulk and sweetness
• cookies, gum, candy, jelly
– do contain minimal kcal
– low glycemic response
• absorbed slowly
– do not cause dental caries