Download Carbohydrates

Carbohydrates
Outline
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Nature of carbohydrates
Classes of carbohydrates
Functions of carbohydrates
Food sources of carbohydrates
Body needs for carbohydrates
Nature of carbohydrates
• Energy production system:
- 3 steps to produce energy from a basic fuel supply:
(1) In human body, the body digests its basic fuel,
carbohydrates, changing it to glucose.
(2) The body then absorb & through blood circulation,
carries this refined fuel to cells that need glucose.
(3) Glucose is burned in these cells, & energy produced
through the process of metabolism.
Nature of carbohydrates
• The carbohydrates are a group of naturally
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occurring carbonyl compounds (aldehydes or
ketones) that also contain several hydroxyl
groups.
A carbohydrates is composed of carbon (C),
hydrogen (H), and oxygen (O).
(CH2O)n when n = 5 then C5H10O5
Glucose is the most important carbohydrate;
most dietary carbohydrate is absorbed into the
bloodstream as glucose, and other sugars are
converted into glucose in the liver.
Classes of carbohydrates
• It is taken up by the cells and either broken down to obtain
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energy (glycolysis) or converted into other metabolites.
Glucose is the major metabolic fuel of mammals and a universal
fuel of the fetus. It is the precursor for synthesis of all the other
carbohydrates in the body, including glycogen for storage;
ribose and deoxyribose in nucleic acids; and galactose in
lactose of milk, in glycolipids, and in combination with protein
in glycoproteins and proteoglycans.
Diseases associated with carbohydrate metabolism include
diabetes mellitus, galactosemia, glycogen storage diseases, and
lactose intolerance.
CARBOHYDRATES ARE ALDEHYDE OR KETONE DERIVATIVES
OF POLYHYDRIC ALCOHOLS
Classes of carbohydrates
• Monosaccharide:
Are those carbohydrates that cannot be
hydrolyzed into simpler carbohydrates: They
may be classified as trioses, tetroses,
pentoses, hexoses, or heptoses,
depending upon the number of carbon atoms;
and as aldoses or ketoses depending upon
whether they have an aldehyde or ketone
group. Examples are listed in Table 1.
– They are quickly absorbed from the intestine
into the blood stream and carried to the liver.
– Glucose, fructose, lactose.
Classes of carbohydrates
• Disaccharide: Are condensation products of two
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monosaccharide units.
- Sucrose, Lactose, Maltose.
Oligosaccharides: Are condensation products of
more than two to ten monosaccharides;
maltotriose is an example
Polysaccharide: Are condensation products of
more than ten monosaccharide units; examples
are the starches and dextrins, which may be
linear or branched polymers.
- Starch, Glycogen, Dietary fiber.
Monosaccharide
• Glucose:
- Is the form of sugar circulating in the blood and is
the primary fuel to the cells.
- The blood supply comes mainly from the digestion
of starch, & sometimes called dextrose.
- Is a moderately sweet sugar.
• Fructose: is found mainly in fruits, consider the
sweetest of the simple sugars.
• Galactose: comes mainly from the digestion of milk
sugar, or lactose.
Disaccharides
• Sucrose:
- Is common table sugar, its two sugar units are glucose &
fructose.
• Lactose:
- Is the milk sugar, formed in mammary glands
- Its two single sugar units are glucose & Galactose.
- Not found in plants.
- Aids in the absorption of calcium & phosphorus.
• Maltose:
- The two single sugar units that compose maltose are double
glucose molecule, occurs as a breakdown product of the
starches contained in malt (“malt sugar” and as an
intermediate in the digestion of starch.
Polysaccharides
• Polysaccharides are sometimes classified
as hexosans or pentosans, depending
upon the identity of the constituent
monosaccharides.
• Starch and glycogen are storage polymers
of glucose in plants and animals,
respectively.
• Starch is the major source of energy in the
diet.
Polysaccharides
• 1) Starch:
- They are found in grains, legumes, and other
vegetables, and some fruits.
- Breakdown more slowly and supply energy over a
longer period of time.
- Most important dietary carbohydrate
- The major food sources of starch include grains in
the form of pasta, crackers, bread, and other baked
goods, legumes in the form of beans, & peas,
potatoes, rice, corn, & bulgur.
Polysaccharides
- Whole grains: is used for food products such as
flours, breads, or cereals that are produced from
unrefined grain, which is grain that still retains its
outer bran layers and inner germ endosperm and
their nutrients (i.e. dietary fiber, minerals, &
vitamins)
- Enriched grains: are refined grain products to
which key nutrients, usually minerals (i.e. iron),
and vitamins (i.e. A, C, D, thiamin, riboflavin, &
niacin), have been added.
• 2) Glycogen: found in animal muscle tissue, and
liver
• 3) Dietary fiber
Polysaccharides: Dietary fiber
• Dietary fiber: in humans there is a lack in the necessary
enzymes to digest dietary fiber, used to treat
gastrointestinal problems.
- Cellulose: helps move the food mass along, stimulates
normal muscle action in the intestine, the main sources are
the stems and leaves of vegetables and the coverings of
seeds and grains.
- Noncellulose polysaccharides: they absorb water and swell to
a larger bulk, thus slowing the emptying of the food mass
from the stomach, and preventing spastic colon.
- Lignin: is a large compound that forms the woody part of
certain plants, it also combines with bile acids and
cholesterol in the human intestine, preventing their
absorption
Complex carbohydrates:
• Contain other sugar derivatives such as amino
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sugars, uronic acids, and sialic acids.
They include proteoglycans and
glycosaminoglycans, associated with structural
elements of the tissues; and glycoproteins,
proteins containing attached oligosaccharide
chains.
They are found in many situations including the
cell membrane.
Other sweeteners
• Used as sugar replacers
• 2 types:
1) Nutritive sweeteners:
- They are sweeteners such sugar alcohols that
contribute to total calorie intake.
- Sugar alcohols (sorbitol, mannitol, & xylitol)
- 2-3 kcalories/gram.
- Sorbitol: sucrose substitute.
- They are absorbed slowly in the small intestine.
- Use for diabetic patients
- Excessive amount= diarrhea.
- lowered risk than sugar to cause dental caries.
Other sweeteners
2) Nonnutritive sweeteners:
- Alternative sweeteners.
- Are sugar substitutes that do not have any
caloric value.
- Sweet taste without energy.
- Commonly used are aspartame & saccharin.
- Sweeter than table sugar.
Functions of carbohydrates
• 1) Primary energy function:
(a) Basic fuel supply:
- Primary fuel for the body.
- Fuel factor for carbohydrates is 4 kcal/gram.
(b) Reserve of fuel supply:
- Glycogen reserves fuel supply
- Individual must eat carbohydrate foods
regularly to meet energy demand (to maintain
blood glucose level & prevent a breakdown of
fat and protein in tissue).
Functions of carbohydrates
• 2) Special tissue functions:
- Liver: glycogen reserves in the liver &
muscles, protect cells from depressed
metabolic function.
- Protein & fat: (1) Carbohydrates protects
protein to be used in tissue growth &
maintenance (2) Prevent rapid breakdown
of fat & produce ketones (strong acid),
this action called antiketogenic effect.
Functions of carbohydrates
• 2) Special tissue functions:
- Heart: fatty acids are the regular fuel for
energy, in emergency situation glycogen.
- Central nervous system: the brain need
continues supply of glucose, otherwise low
sugar cause brain damage.
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