Chem 45 Biochemistry: Carbohydrates

Chapter 2
Carbohydrates –
Structure and
Function

Chapter 18
Table of Contents
Copyright © Cengage Learning. All rights reserved 2
18.1 Occurrence and Functions of Carbohydrates
18.3 Classification of Carbohydrates
18.4 Classification of Monosaccharides
18.5 Biochemically Important Monosaccharides
18.6 Cyclic Forms of Monosaccharides
18.7 Haworth Projection Formulas
18.8 Reactions of Monosaccharides
18.9 Disaccharides
18.10 Oligosaccharides
18.11 General Characteristics of Polysaccharides
18.12 Storage Polysaccharides
18.13 Structural Polysaccharides
18.14 Acidic Polysaccharides
18.15 Dietary Considerations and Carbohydrates
18.16 Glycolipids and Glycoproteins: Cell Recognition
18.17 Unavailable Carbohydrates

Section 18.2
Occurrence and Functions of Carbohydrates
Carbohydrates
• The most abundant class of
bioorganic molecules on earth
• produced by the
photosynthetic activity of the
green plants
• also referred to as saccharides
because of the sweet taste of
many carbohydrates
• (Latin, saccharum, meaning
sugar)
• storehouse of chemical energy
(glucose, starch, glycogen)
– a gram of digested
carbohydrate gives about 4
kcal of energy
– complex carbohydrates are
best for diet
• supportive structural components
in plants and some animals
(cellulose, chitin)
• form part of the structural
framework of DNA & RNA
• carbohydrate “markers” on cell
surfaces play key roles in cell-cell
recognition processes.

Section 18.3
Classification of Carbohydrates
• Simpler Formula:
– CnH2nOn or Cn(H2O)n
(hydrates of C)
– n= number of atoms
• polyhydroxy aldehydes or
polyhydroxy ketones or
compounds that produce such
substances upon hydrolysis.
• Classification based on
products of acid hydrolysis:
• Monosaccharides
– the simple sugars
– contain a single polyhydroxy
aldehyde or polyhydroxy ketone
unit
– cannot be degraded into simpler
products by hydrolysis reactions
– pure monosaccharides are water-
soluble, white, crystalline solids
• Disaccharides
– contains 2 monosaccharide units
covalently bonded to each other
– crystalline and water soluble
substances
– upon hydrolysis they produce
monosaccharides

Section 18.3
Classification of Carbohydrates
• Oligosaccharides
– contains 2-10 monosaccharide
units - covalently bonded
– disaccharides are the most
common type
– trisaccharides (raffinose)
– tetrasaccharides (stachyose)
– free oligosaccharides, other than
disaccharides, are less common
in nature
– usually found associated with
proteins and lipids in complex
molecules that serve structural
and regulatory functions
• Polysaccharides
– consist of tens of thousands of
monosaccharide units covalently
bonded
– homopolysacchrides – polymers
of a single monosaccharide
(glycogen, cellulose, starch)
– heteropolysaccharides – contain
more than one kind of
monosaccharide (hyaluronic acid,
heparin, chondroitin sulfate)
• Derived carbohydrates
– those where carbohydrate
moieties have undergone some
reactions converting them into
other products
– sugar acids, sugar alcohols,
deoxysugars, and sugar amines

Section 18.8
Classification of Monosaccharides
• carbohydrates that have the
general formula CnH2nOn
– n varies from 3 – 8.
• grouped together according to
the number of carbons they
contain
– C3H6O3 triose
– C4H8O4 tetrose
– C5H10O5 pentose
– C6H12O6 hexose
– C7H14O7 heptose
– C8H16O8 octose
• may either be:
– an aldose – contains aldehyde
group
– a ketose – contains ketone group
-presence of a ketone group is
usually indicated by using the
ending “___ulose” in naming the
sugar
- e.g., levulose

Section 18.8
Exercise
Classify each of the following monosaccharides according
to both the number of carbon atoms and the type of
carbonyl group present.

Section 18.8
Exercise
Classify each of the following monosaccharides according
to both the number of carbon atoms and the type of
carbonyl group present.
Answers:
a. aldopentose; b. ketohexose;
c. aldohexose; d. ketopentose

Section 18.8
• Trioses
• the parent member of the
family of monosaccharides
• from them emanates the other
members of the
monosaccharide family.
• the final form of carbohydrate
into which all carbohydrates,
regardless of their complexity,
are degraded in the body
during carbohydrate
metabolism.
• D(+)- glyceraldehyde
– an aldotriose
• Dihydroxyacetone
– a ketotriose
• Pentoses
• aldopentoses
– D-(-)-lyxose
• a constituent of the heart
muscle
– D-(-)-ribose
• ribose and 2-deoxyribose –
present as intermediates in
metabolic pathways and are
important building blocks
of RNA and DNA
• ketopentoses
– D-ribulose
– D-xylulose

Section 18.8
• Hexoses
• the most common of all the
monosaccharides
• aldohexoses
– D-(+)-mannose
– D-(+)-glucose
• A 5% (m/v) glucose solution
is often used in hospitals as
an intravenous source of
nourishment for patients who
cannot take food by mouth.
– D-(+)-galactose
• ketohexose
– D-(-)-fructose
• D-mannose
– found in certain bacteria, fungi,
and plants
– converted to usable glucose in the
body, but has no real
physiological significance

Section 18.8
• Monosaccharides can be
classified based on their spatial
orientation (stereochemistry).
• A monosaccharide can be
classified as a D or L isomer,
depending on the spatial
orientation of the –H and –OH
groups attached to the carbon
atom adjacent to the terminal
primary alcohol group.
• The D isomer is represented when
the –OH is written to the right of
this carbon in the Fischer
projection formula. The L isomer is
represented when this –OH is
written to the left.

Section 18.9
Biochemically Important Monosaccharides
Glucose and Fructose
1. Most abundant in nature
2. Nutritionally most important
3. Grape fruit good source of glucose (20 -
30% by mass) -- also named grape
sugar, dextrose and blood sugar (70 -
100 mg/100 mL of blood)
4. Six membered cyclic form
1. Ketohexose
2. Sweetest of all sugars; the fruit sugar
3. Found in many fruits and in honey
4. Good dietary sugar-- due to higher
sweetness
5. Five membered cyclic form

Section 18.9
Biochemically Important Monosaccharides
Galactose and Ribose
1. A component of milk sugar
2. Synthesized in human
3. Also called brain sugar-- part of brain and
nerve tissue
4. Used to differentiate between blood types
5. Six membered cyclic form
6. Galactosemia
- a result of genetic deficiency in the infant – the gene responsible for
the enzyme that converts D-galactose to D-glucose. Such infants cannot
metabolize galactose and it builds up in the blood and tissue.
1. Part of RNA
2. Part of ATP
3. Part of DNA
4. Five membered cyclic form

Section 18.10
Cyclic Forms of Monosaccharides
Hemiacetals and Hemiketals
• The dominant form of
monosaccharides with 5 or more
C atoms is cyclic
• Hemiacetals and hemiketals are
formed from the reaction between
two functional groups: aldehyde or
ketone and alcohol
– may take place either
intermolecularly or
intramolecularly as in the case of
sugars, provided there are
sufficient number of carbons
between the aldehyde or ketone
and the alcohol group to permit a
stable ring formation
– five- or six-membered hemiacetal
rings are stable
• Two types of ring structures are
possible:
– five-membered ring, or furanose ring,
derived from parent compound furan
– six-membered ring, or pyranose ring,
derived from parent compound pyran

Section 18.10
Cyclic Hemiacetal Forms of D-Glucose
• In the cyclic hemiacetals of
glucose, C1
*, is now a chiral
center (an anomeric carbon)
– two anomers of D-glucose: -D-
glucose & -D-glucose
• The cyclic hemiacetals are
readily interconvertible in
aqueous solution
– this intercoversion of - and -
anomers in solution is
accompanied by a change in
specific rotation called
MUTAROTATION.
– only sugars that form hemiacetal
or hemiketal structure mutarotate.

Section 18.10
• 2 anomeric forms of D-
glucose:
– Alpha-form: -OH of C1 and
CH2OH of C5 are on
opposite sides
– Beta-form: -OH of C1 and
CH2OH of C5 are on same
sides
• Anomers: Cyclic
monosaccharides that differ
only in the position of the
substituents on the anomeric
carbon atom.
• Any —OH group at a chiral center
that is to the right in a Fischer
projection formula points down in
the Haworth projection formula
and any —OH group to the left in
a Fischer projection formula points
up in the Haworth projection
formula.
O
OH OH
OH
OH
CH2OH
O
OH
OH
OH
OH
CH2OH
a-D-Glucose b-D-Glucose
1
2
3
4
5
6
1
2
3
4
5
6
Anomeric
Carbon
Anomeric
Carbon

Section 18.10
• All aldoses with five or more
carbon atoms establish similar
equilibria, but with different
percentages of the alpha, beta,
and open-chain forms
• Fructose and other ketoses
with a sufficient number of
carbon atoms also cyclize

Section 18.11
Haworth Projection Formulas
Practice Exercise
• Which of the monosaccharides glucose, fructose, galactose, and
ribose has each of the following structural characteristics? (There
may be more than one correct answer for a given characteristic)
a. It is a pentose.
b. It is a ketose.
c. Its cyclic form has a 6-membered ring.
d. Its cyclic form has two carbon atoms outside the ring.

Section 18.11
Haworth Projection Formulas
Practice Exercise
• Which of the monosaccharides glucose, fructose, galactose, and
ribose has each of the following structural characteristics? (There
may be more than one correct answer for a given characteristic)
a. It is a pentose.
b. It is a ketose.
c. Its cyclic form has a 6-membered ring.
d. Its cyclic form has two carbon atoms outside the ring.
Answers:
a. Ribose
b. Fructose
c. Glucose, galactose
d. Fructose

Section 18.12
Reactions of Monosaccharides
• Five important reactions of monosaccharides:
– Oxidation to acidic sugars
– Reduction to sugar alcohols
– Phosphate ester formation
– Amino sugar formation
– Glycoside formation
• These reactions will be considered with respect to
glucose; other aldoses, as well as ketoses, undergo
similar reactions.

Section 18.12
Oxidation
• Gives three different types of
acidic sugars depending on the
type of oxidizing agent used:
– Weak oxidizing agents like
Tollens and Benedict’s solutions
oxidize the aldehyde end to give
an aldonic acid.
– Strong oxidizing agents can
oxidize both ends of a
monosaccharide at the same time
to produce aldaric acid.
– In biochemical systems enzymes
can oxidize the primary alcohol
end of an aldose such as
glucose, without oxidation of the
aldehyde group, to produce an
alduronic acid.

Section 18.12
Reduction
• The carbonyl group in a
monosaccharide (either an
aldose or a ketose) is reduced
to a hydroxyl group using
hydrogen as the reducing
agent.
– product is the
corresponding polyhydroxy
alcohol, sugar alcohol
– e.g., Sorbitol (glucitol) -
used as moisturizing
agents in foods and
cosmetics and as a
sweetening agent in
chewing gum

Section 18.12
Redox Reactions of Monosaccharides

Section 18.12
Redox Reactions of Monosaccharides
• Under prescribed conditions,
some sugars reduce silver ions
to free silver and copper(II)
ions to copper(I) ions. Such
sugars are called reducing
sugars.
• A reducing sugar will have one
of the following groups.
• an aldehyde group (as in
glyceraldehyde)
• a hydroxyketone (as in fructose)
• a cyclic hemiacetal group (as in
glucose and maltose)
• The Benedict, Barfoed, and
Fehling tests are based on the
formation of a brick red copper(I)
oxide precipitate as a positive
result while the Tollens test is
based on the formation of a silver
mirror.
• The Barfoed test is more sensitive
in that it can distinguish a reducing
monosaccharide from a reducing
disaccharide.
• The sugars are oxidized to
carboxylic acids and the metal
ions are reduced

Section 18.12

Section 18.12
Reducing sugars
• Many clinical tests that monitor
color change are based on the
oxidation reaction shown here.
• Sugars with the hemiacetal
structure can be reducing sugars
under alkaline conditions because
the ring opens forming an
aldehyde group.

Section 18.12
Phosphate Ester Formation
• The hydroxyl groups of a
monosaccharide can
react with inorganic
oxyacids to form
inorganic esters.
• Phosphate esters of
various monosaccharides
are stable in aqueous
solution and play
important roles in the
metabolism of
carbohydrates.

Section 18.12
Amino Sugar Formation
• One of the hydroxyl groups of
a monosaccharide is replaced
with an amino group
• In naturally occurring amino
sugars the carbon 2 hydroxyl
group is replaced by an amino
group
• Amino sugars and their N-
acetyl derivatives are important
building blocks of
polysaccharides such as chitin
and hyaluronic acid

Section 18.12
Glycoside Formation
• The cyclic forms of
monosaccharides, the
hemiacetals, react with
alcohols to form acetals (also
called glycosides)
• A glycoside is an acetal
formed from a cyclic
monosaccharide by
replacement of the hemiacetal
carbon —OH group with an —
OR group to form a double
ether
• A glycoside produced from
glucose - glucoside
• from galactose – galactoside

Section 18.12
p622

Section 18.13
Disaccharides
• The two monosaccharides are
linked together by acetal
formation to form disaccharide
• One monosaccharide act as a
hemiacetal and other as
alcohol and the resulting ether
bond is a glycosidic linkage.
• Condensation of the hydroxyl
function of the hemiacetal
group of one monosaccharide
with the hydroxyl group of
another monosaccharide forms
the bond, called a glycosidic
bond, joining the 2 saccharide
units.

Section 18.13
Disaccharides
Maltose (reducing sugar)
• Malt sugar, found in corn syrup,
malt, and germinating seeds
• consists of two molecules of
glucose joined by -1,4-glycosidic
bond
– -1,4-glycosidic bond means that
the first sugar is in -configuration
and its C#1 is linked to C#4 of the
second sugar component
– the second sugar may be either
an α- or a β-anomer.

Section 18.13
Disaccharides
Maltose (reducing sugar)

Section 18.13
Disaccharides
Cellobiose (reducing disaccharide)
• one of the major fragments
isolated after extensive
hydrolysis of cellulose
• Maltose is digested easily by
humans because we have
enzymes that can break α-
(14) linkages but not β-
(14) linkages of cellobiose
• the 2 glucose units are joined
by a -1,4-glycosidic linkage

Section 18.13
Disaccharides
Lactose (reducing disaccharide)
• Milk sugar
– human - 7%–8% lactose
– cow’s milk - 4%–5% lactose
• consists of -galactose with a
-1,4-glycosidic linkage to -
glucose (or -glucose)
• Lactose intolerance: a condition in
which people lack the enzyme
lactase needed to hydrolyze
lactose to galactose and glucose.
• Lactose intolerance is unpleasant,
but its effects can be avoided by a
diet that rigorously excluded milk
and milk products.

Section 18.13
Disaccharides
Lactose intolerance
vs Galactosemia
• When undigested, lactose attracts
water causing fullness, discomfort,
cramping, nausea, and diarrhea.
• Bacterial fermentation of lactose
along the intestinal tract produces
acid (lactic acid) and gas, adding
to the discomfort.
• Galactosemia: the genetic disease
caused by the absence of the
enzymes needed for conversion of
galactose to glucose.
• A reduced form of galactose,
called dulcitol (galactitol), a toxic
metabolite, is produced and
accumulates.
• If galactosemia is not treated, it
leads to severe mental
retardation, cataracts, and early
deaths

Section 18.13
Disaccharides
Sucrose (nonreducing disaccharide)
• the common table sugar & the
most abundant of all
disaccharides found in plants.
• produced commercially from
the juice of sugar cane and
sugar beets.
• the -anomeric carbon 1 of
glucose joins the -anomeric
carbon 2 of fructose (-1,2-
glycosidic bond)

Section 18.13
Disaccharides
Invert sugar
• Optical activities:
– Sucrose : +66.5
– Glucose : +53
– Fructose : -92
– Invert sugar : -39
• invert sugar has a much greater
tendency to remain in solution.
• In the manufacture of jelly and
candy and in the canning of fruit,
crystallization of the sugar is
undesirable, therefore conditions
leading to the hydrolysis of
sucrose are employed in these
processes; in addition, fructose is
sweeter than sucrose
• Honeybees and many other
insects possess an enzyme called
invertase that hydrolyzes sucrose
to invert sugar.
• Thus honey is predominantly a
mixture of D-glucose and D-
fructose with some unhydrolyzed
sucrose.

Section 18.13
Disaccharides
Practice Exercise
• Which of these disaccharides, i.e., maltose, cellobiose, lactose, and
sucrose, have the following structural or reaction characteristics?
(There may be more than one correct answer for a given
characteristic)
a. Two different monosaccharide units are present.
b. Hydrolysis produces only monosaccharides.
c. Its glycosidic linkage is a “head-to-head” linkage.
d. It is not a reducing sugar.

Section 18.13
Disaccharides
Practice Exercise
• Which of these disaccharides, i.e., maltose, cellobiose, lactose, and
sucrose, have the following structural or reaction characteristics?
(There may be more than one correct answer for a given
characteristic)
a. Two different monosaccharide units are present.
b. Hydrolysis produces only monosaccharides.
c. Its glycosidic linkage is a “head-to-head” linkage.
d. It is not a reducing sugar.
Answers:
a. Lactose, sucrose
b. Maltose, cellobiose, lactose, sucrose
c. Sucrose
d. Sucrose

Section 18.13
Disaccharides
Artificial sweeteners

Section 18.14
Oligosaccharides
• Commonly found in onions, cabbage, broccoli and wheat
• In humans, intestinal bacteria action on the undigestable raffinose
and stachyose present in beans produces gaseous products that
can cause discomfort and flatulence.

Section 18.14
Oligosaccharides
• Solanin - a potato toxin, is a oligosaccharide found in association
with an alkaloid
• bitter taste of potatoes is due to relatively higher levels of solanin.

Section 18.12
Antigens used in the ABO blood group classification

Section 18.15
General Characteristics of Polysaccharides
The Polymer Chain
• many monosaccharide
units bonded with
glycosidic linkages
• branched or unbranched
• homopolysaccharide or
heteropolysaccharides

Section 18.15
General Characteristics of Polysaccharides
• alternate name is glycan
• not sweet and don’t show
positive tests with Tollen’s and
Benedict’s solutions
• limited water solubility
• Storage polysaccharides
– starch
– glycogen
• Structural polysaccharides
– cellulose
– chitin
• Acidic polysaccharides
– heparin
– hyaluronic acid
• Homopolysaccharides
– starch
– glycogen
– cellulose
– chitin
– carageenan
• Heteropolysaccharides
– hyaluronic acid
– heparin
– chondroitin sulfate
– alginic acid

Section 18.16
Storage Polysaccharides
Starch
• the chief caloric distributor in the diet; the reserve carbohydrates for plants
• Amylose - straight chain polymer; 15 - 20% of the starch; water-soluble fraction; 60
– 300 glucose units joined by -1,4-glycosidic bonds
• experimental evidence indicates that the molecule is actually coiled like a spring and
is not a straight chain of glucose units.
• When coiled in this fashion the molecule has just enough room in its core to
accommodate an iodine molecule.
• The characteristic blue color that starch gives when treated with iodine is due to the
formation of the amylose-I2 complex.

Section 18.16
Starch
• Amylopectin
– branched chain polymer
– 80 - 85 % of the starch
– the water-insoluble fraction
– composed of 300 – 6000
glucose units joined
primarily by -1,4-
glucosidic bonds and
occasionally by -1,6-
glucosidic bonds
– -1,6 bonds are
responsible for branching
which occurs about once
every 25-30 units.

Section 18.16
Glycogen
• the animal starch
• glucose storage molecule of
animals
• stored in granules in liver and
muscle cells
• like amylopectin, is a nonlinear
polymer of glucose units joined
by -1,4- and -1,6-glycosidic
bonds but has lower molecular
weight
• more highly branched structure
• its branches are shorter
• gives red-brown color with I2

Section 18.17
Structural Polysaccharides
Cellulose
• a fibrous carbohydrate found in all
plants where it serves as the
structural component of the plant’s
cell wall
• a linear polymer of glucose units
joined by -1,4-glucosidic bonds
• linear nature of chains allows
close packing into fibers, making it
difficult for solvent molecules to
pull the chains apart, thus
cellulose is inert towards most
solvents
• Cotton ~95% cellulose and wood
~50% cellulose
• It serves as dietary fiber in food--
readily absorbs water and results
in softer stools
• 20 - 35 g of dietary fiber is desired
everyday

Section 18.17
Cellulose
• yields D-glucose upon hydrolysis
yet man & the carnivorous animals
can’t utilize cellulose as a source
of glucose.
• human‘s digestive juices lack the
enzyme cellulase that hydrolyze -
1,4-glucosidic linkages.
• ruminants (cows, goats) and
termites have, within their
digestive tracts, microorganisms
that produce cellulase

Section 18.17
Chitin
• Similar to cellulose in both
function and structure
• polymer of N-acetyl-D-
glucosamine bound by β-1  4
glycosidic linkages (has a linear
extended structure like cellulose)
• Function is to give rigidity to the
exoskeletons of crabs, lobsters,
shrimp, insects, and other
arthropods
• itself is inert and practically
insoluble in most solvents. Its
derivative, chitosan, can be
prepared by simple alkali-
catalyzed deacylation. Chitosan
derivatives are commercially used
as films, fibers, surface coatings
and ultrafiltration membranes

Section 18.17
Carageenan
• occurs as hydrocolloid extracted
from selected species of red algae
• locally obtained from Eucheuma
• striatum, Eucheuma spinosum
and Acanthapora
• sulphated polysaccharides,
consisting of polymers of
sulphated D-galactopyranose
bonded through alternating α-
13 and β-14 glycosidic
linkages
• widely used in food industry
• its gelling property is used in
enhancing the texture of various
dairy products and in preventing
oiling off in caramel and toffee
during hot weather
• also serve as coating to retard
moisture loss from foods and fresh
produce like fruits and vegetables

Section 18.18
Acidic Polysaccharides
Hyaluronic acid
• repeating unit is a disaccharide
composed of -D-glucuronic acid
and N-acetyl-D-glucosamine in a
-(13)-linkage.
• each disaccharide is attached to
the next by -(14)-linkage
• alternating -(13) and -(14)-
linkages
• highly viscous - serve as
lubricants in the fluid of joints and
part of vitreous humor of the eye
• when some insects sting, they
inject an enzyme called
hyaluronidase, which breaks
hyaluronic acid linkages and
facilitates the spread of the venom

Section 18.18
Heparin Alginic acid
• consists of repeating units of D-
glucuronic acid and D-
glucosamine
• an anticoagulant in blood that
inhibits blood clot formation
• used in open-heart surgery
• locally extracted from Sargassum
seaweeds
• consist of repeating units of β-
14 bonded mannuronic and α-
14 bonded L-guluronic acid; cell
wall material
• serves as base coatings in meats
and fish which reduces moisture
loss and fat absorption

Section 18.18
Chondroitin sulfate
• consists of repeating units of D-
glucuronic acid-D-glucosamine
sulfate
• structural role in cartilage, bone,
and cornea of the eye

Section 18.19
Dietary Considerations and Carbohydrates
Glycemic Foods
• A developing concern about intake of carbohydrates
involves how fast the given dietary carbohydrates are
broken down to glucose within the human body
• Glycemic index refers to:
– how quickly carbohydrates are digested
– how high blood glucose rises
– how quickly blood glucose levels return to normal
• Glycemic index (GI) has been developed for rating foods
• Low-GI foods are desirable

Section 18.20
Glycolipids and Glycoproteins: Cell Recognition
• A glycolipid is a lipid molecule that has one or more
carbohydrate (or carbohydrate derivative) units
covalently bonded to it.
• A glycoprotein is a protein molecule that has one or
more carbohydrate (or carbohydrate derivative) units
covalently bonded to it.
• Such carbohydrate complexes are very important in
cellular functions such as cell-cell recognition, cell
adhesion and cellular communication.

Section 18.19
Unavailable carbohydrates
• those not hydrolyzed by digestive
enzymes
• they constitute the dietary fiber
• Fiber in the diet aids in the formation
of bulk in the intestinal tract, which
increases the absorption of water
along the tract.
• Dietary fiber, as it reaches the gut, is
intact in structure where they form a
meshwork
• The meshwork has spaces where fecal
matter and water are trapped
• The effect is soft fecal matter which
can be easily removed.
• If absent fecal matter is hard, and has
a long transit time.
• Long sojourn will dehydrate it and will
make it harder to remove.
• It also increases the rate at which
digestive wastes move through the
intestinal tract, which lessens the time
the intestine comes in contact with any
ingested carcinogens.
• Some forms of diverticulitis
(inflammation of the colon) have been
relieved by increasing the quantity of
fiber in the diet.
• Straining at stool because of lack of
dietary fiber can lead to
hemorrhoidsand nervous disorders.

Section 18.19
Dietary fiber
• Lack of dietary fiber may also lead to
overnutrition.
• When one does not masticate, the
secretion of digestive hormones (such
as gastrin and cholecystokinin) is not
induced.
• Without these hormones, it takes
longer to reach the feeling of satiety.
• Dietary fiber may also be beneficial in
weight maintenance.
• Fiber increases the bulk in the
stomach and intestines without
contributing to the caloric intake.
• There is also a correlation between
ischaemic heart disease and gallstone
formation with the lack of dietary fiber.
• Cholesterol can be trapped in the
meshwork reducing the concentration
of blood cholesterol.
• With dietary fiber, bile will not be
supersaturated with cholesterol.
• In its absence, bile will be
supersaturated with cholesterol and
gallstone formation results.
• When cholesterol is trapped plaque
formation will be reduced.
• In the absence of dietary fiber, excess
cholesterol can lead to plaque
formation leading to ischaemic heart
disorders.
• About 20-35 grams of dietary fiber
daily is a desirable intake.

Section 18.19

Chem 45 Biochemistry: Carbohydrates

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Chem 45 Biochemistry: Carbohydrates