2. Objectives of this lecture;
• At the end of the lecture student should be able to
understand;
• The role of carbohydrates as main energy fueling
macromolecules
• the role of carbohydrates in exercises.
• The general outlines of the pentose phosphate pathway
Dr. Siham Gritly
3. Carbohydrates
• Introduction;-
• Carbohydrates are organic compound consist of
carbon, hydrogen, and oxygen atoms. ratio of
hydrogen to oxygen is 2:1. Carbohydrates range
from simple monosaccharides (glucose, fructose,
galactose) to complex polysaccharides (starch).
• The most important monosacchrides are; glucose,
fructose and galactose (hexoses sugar ) the main
dietary sources of metabolic energy or body fuels.
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4. Classification of carbohydrates
• a- Monosaccharides or simple sugar which
contain one sugar unit such as Trioses
(3carbon), tetro, ses (4 carbon molecules),
pentoses (5 carbon), hexoses (6carbon),
heptoses (7 carbon) .
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5. b-disaccharides, are formed by the condensation of two
mono-sacchrides with the elimination of one molecule
of water. the disaccharides of nutritional importance are
• 1-Sucrose; cane sugar, beat sugar, sucroses are
manufactured on large scale from cane sugar.
sucrose is present in certain fruits and
vegetables. Sucrose consists of –glucose
+fructose
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6. • 2-Maltose; present in malt, cereal grains. it is
formed when starch that present in the food is
digested by the salivary and pancreatic enzyme
Amylase. maltose consists of 2 glucose
molecules; maltose—glucose + glucose
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7. • 3-Lactose or called milk sugar is a
disaccharide occur in mammals milk, synthesis
in mammary gland by the glucose that
supplied through the food. in small intestine
lactose is hydrolyzed to glucose and galactose
by the action of lactase enzyme present in
intestinal juice. Lactose—glucose +
galactose.
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8. • C-polysaccharides; consist of many mono-
saccharides. Polysaccharides of nutritional
important are;
• a-starch; occur mainly in plant kingdom.
Important sources are cereals, millets, roots,
tubers formed in nature in large amounts.
• Starch hydrolyzed by amylase enzyme present
in saliva and in pancreatic juice to form
maltose (disaccharide).
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9. • during hydrolysis starch formed intermediate
product called dextrin. complete digestion of
starch formed glucose;
• starch--------dextrin----------maltose------------
glucose
• b-glycogen; polysaccharides, it is the storage
form of carbohydrates in the human body. the site
of storage is in the liver and muscles.
• It is the reserve of carbohydrates in body. the liver
contain enzyme which convert glycogen to
glucose through the process known as
glycogenlysis.
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10. • c- Dietary fiber is a carbohydrates (or a
polysaccharide) that is incompletely absorbed
in humans and in some animals.
• *Dietary fiber consists mainly of cellulose, a
large carbohydrate polymer that is indigestible
because humans do not have the required
enzymes to disassemble it. There are two
subcategories: soluble and insoluble fiber.
Whole grains, fruits (especially plums, and
figs) and vegetables are good sources of
dietary fiber.
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11. Digestion and absorption of carbohydrates
• Digestion is the process of breakdown large
particles into smaller one. the digestion of
carbohydrates start in the mouth and is
continue in the stomach and intestine.
Carbohydrates absorbed through the intestinal
mucosa as monosaccharides (glucose).
• Glucose enters the metabolic pathways to
release energy, which then is used for the
formation of the chemical compound ATP.
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13. Major function of carbohydrate in
human body
• *CHO is the main fuel for certain tissues during
rest such as brain, central nervous system (CNS)
and red blood cell (RBC)
• *Supply energy; glucose oxidized producing
water, energy, carbon dioxide and energy (ATP)
• *monosaccharide can form other carbohydrate
molecules such as trioses and pentoses, these
substances combined with other substances to
form essential compounds (glycolipids and
glycoprotein)
Dr. Siham Gritly
14. • Glycoprotein are very important components
of cell membrane
• Ribose sugar (pentose) are important in
formation of RNA (ribonucleic acid of the cell)
• excess of carbohydrates stored in the form of
glycogen in liver (glycogenesis).
Dr. Siham Gritly
15. Carbohydrate Needs
• The carbohydrate contribution is mainly from;-
*glycogen stores in skeletal muscle and that
stored in the liver,
• the diet for athletes and active people is that it
should include more carbohydrate-containing
foods that recommended by the health
professionals.
Dr. Siham Gritly
16. • Their diets should be about 60% of their daily
energy intake obtained from carbohydrates, 30 %
or less from fat and 10 to 15 % from proteins
• Adequate carbohydrate intake also helps prevent
protein from being used as energy
• It also fueling the central nervous system (CNS)
and brain
Dr. Siham Gritly
17. • During heavy training kcal must be increased
specially from carbohydrates (CHO), to meet
the energy demands. Failure to do so may
result in:
• Chronic muscular fatigue.
• - Weight and muscle mass loss
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18. Carbohydrates utilized by the body in
different ways;
• *for the immediate energy needs through
oxidation to carbon dioxide and water via the
processes of glycolysis and tri-carboxylic
acid cycle or Kerb cycle
• *stored as glycogen in the liver and muscles
tissue through the process glycogenesis.
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19. • *converted to fatty acids and stored as
triglyceride.
• *convert to other necessary CHO such as
ribose, fructose and deoxyribose which is
necessary for the formation of genetic material
DNA.
• *some become the carbon skeletons for
production of essential amino acids
Dr. Siham Gritly
20. Carbohydrates and exercises
• Carbohydrates come in two sources during
exercises ;
1-Simple sugar glucose
2-Storage form of glucose –glycogen; Glycogen
is stored in Muscles and Liver
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21. • During athletic endeavors (or activities)
blood glucose, liver glycogen and muscle
glycogen is the main source of energy
• - Carbohydrate are the main nutrient fueling
exercise of a moderate to high intensity, while
fat providing energy during exercise that
occurs at a lower intensity (supply about 40-
80%of the total calories in human diet).
Dr. Siham Gritly
22. • During moderate exercise muscle glycogen and
liver glycogen contribute equally to CHO
oxidation
• - As exercise intensity increases, carbohydrate
metabolism efficiency drops off and anaerobic
metabolism takes over.
• - This is because the body can not take in and
distribute oxygen quickly enough to use either fat
or carbohydrate metabolism easily.
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23. • - The liver is the only tissue that can release
stored glycogen in the form of glucose
• Muscle glycogen store is the first source of
glucose for the exercising muscle
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24. • when no glycogen;- the process of glycogenolysis
started and follow by gluconeogenesis in the liver
to make glucose available (main function of the
liver is to release glucose through glycogenolysis
and gluconeogenesis )
• if no enough glucose after 3 hours of heavy
exercise athletes enter to a condition known as
hoypglycemia (low glucose level in the blood)
Dr. Siham Gritly
25. Carbohydrates loading
• CHO Loading, or glycogen loading and
glycogen super-compensation;- is dietary
technique designed to promote a significant
increase in glycogen content in both the
liver and muscles to delay fatigue among
athletes.
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26. • It is generally used 3-7 days in preparation for
athletic competition
• It is used by endurance athletes with
continuous energy expenditure for prolonged
periods (long distance runners, swimmers) to
optimize physical performance during
prolonged endurance events.
Dr. Siham Gritly
27. Pentose Phosphate Pathway,
(hexose-mono-phosphate shunt)
• The Pentose Phosphate Pathway, generate
important intermediates not produced in other
pathways. it acts in the conversion of hexoses
sugar into pentose sugar (ribose) and in
regeneration of NADPH .
• when glucose increase in the blood it converted
to glycogen through the process of glycogenesis,
or when it needed as energy it enter into
glycolytic pathway for energy formation but;
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28. • some of glucose may enter alternative route in
the cytoplasm, this route is known as Pentose
phosphate pathway.
• in the presence of oxygen, hexoses sugar
(glucose ) converted to pentose mainly Ribose
and deoxy-ribose that enter in the formation of
DNA and RNA, the neuclic acid of the cells
(Genetic material of the cell).
Dr. Siham Gritly
29. • when excess pentose present can also
converted to hexoses (glucose) and thus enter
the glycolytic pathway for energy production.
• *in this process no carbon dioxide released, the
hydrogen molecules combined with NAD to
become NADPO and enter in the lipid
synthesis
Dr. Siham Gritly
30. • When carbohydrate intake is low, oxidation of
fatty acids accelerate to provide energy
through the production of acetyl CoA (TCA
substrate)
Dr. Siham Gritly
31. References
• Sareen Gropper, Jack Smith and James Groff, Advanced Nutrition
and Human Metabolism, fifth ed. WADSWORTH
• Melvin H Williams 2010; Nutrition for Health, Fitness and Sport. 9th
ed, McGraw Hill
•
• Heymsfield, SB.; Baumgartner N.; Richard and Sheau-Fang P. 1999.
Modern Nutrition in Health and Disease; Shils E Maurice,
Olson A. James, Shike Moshe and Ross A. Catharine eds. 9th
edition
• Guyton, C. Arthur. 1985. Textbook of Medical Physiology. 6th
edition, W.B. Company
Dr. Siham Gritly
