Post on 11-May-2015
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Principle of Biochemistry 3-Simple and Complex Carbohydrates
Course code: HFB324
Credit hours: 3 hours
Dr. Siham Gritly
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Terms should be learned vocabulary
• Carbohydrate; generic name for simple and complex sugars; chemically carbohydrates are polyhydroxyl aldehydes or polyhydroxyl ketones
• Aldose; sugar containing an aldehyde functional group
• Ketose; sugar containing a ketone functional group• anomeric carbon; the carbon atom in a cyclic
monosaccharide which, in the linear monosaccharide, holds the aldehyde or ketone functional group
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vocabulary • Asymmetric carbon; carbon atoms attached to four different atoms or groups or
chiral carbon
• Chiral carbon; atoms have four different atoms or groups covalently attached to them
-linked sugars; refers to;
(a) the geometry of the glycosidic bond (α = opposite side of the sugar ring from the free CH2OH; β = same side),
(b) which carbon on ring A is linked to which carbon on ring B.
• Stereoismers; are compounds having two or more chiral carbons that have the same four groups attached to carbon atoms but are not mirror images to each other
• D-sugar; the stereoisomeric form of monosaccharide. One of a set of isomers whose molecules have the same atoms bonded to each other but differ in the way these atoms are arranged in space.
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vocabulary
• Furanose; cyclic form of glucose monosaccharide whose structure is a five-membered ring
• Pyranose; cyclic form of glucose; monosaccharide in a six-membered ring form
• glycosidic bond; ether bond joining two monosaccharides
• hemiacetal or hemiketal; cyclic conformation of simple carbohydrates; formed by reaction of the aldehyde (or ketone) and one of the hydroxyls on the carbohydrate
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vocabulary
• Monosaccharides. "Simple sugars" with the formula (C H2O)n. The word carbohydrate refers to the fact that this class of molecules consists of hydrates of carbon.
• Disaccharides; "Simple sugars" contain two monosaccharides units attached to one another through acetal bonds or as known glycosidic bonds
• Oligosaccharides. complex sugar Polymeric molecule of sugar comprising 2-10 covalently linked monosaccharide units. Often found conjugated to other classes of biomolecules including lipids and proteins.
• Polysaccharides. complex sugar Larger polymers of simple sugars. On the order of hundreds to thousands of monosaccharide units as linear or branched polymers
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vocabulary• Aldehyde ; Any of a class of highly reactive organic chemical
compounds obtained by oxidation of primary alcohols, characterized by the common group CHO, and used in the manufacture of dyes, and organic acids.
• Aldehydes are oxidized to carboxylic acids and take part in many addition reactions
• ketone Any of a class of organic compounds, such as acetone, having a carbonyl group linked to a carbon atom in each of two hydrocarbon radicals and having the general formula R(CO)R ,
• Ketones don't have that hydrogen atom and are resistant to oxidation. They are only oxidised by powerful oxidising agents which have the ability to break carbon-carbon bonds.
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Carbohydrates are polyhydroxy aldehydes or ketones (Constructed from the atoms of
carbon, oxygen and hydrogen)
• In aldehydes (aldose) the carbonyl is bonded to one carbon and one hydrogen and are located at the ends of carbon chains. Formula H-(CHOH)x(C=O)-
• In ketones (Ketoses) carbonyl group (C= O) is bonded to two carbons within a carbon skeleton
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In aldehydes (aldose) the carbonyl is bonded to one carbon and one hydrogen and are located at the ends of carbon chains. H-(CHOH)x(C=O)- easily oxidized In ketones (ketose) carbonyl group (C= O) is bonded to two carbons within a carbon skeleton no hydrogen atom
Glycerildyhide
H H | |H—C—C—C—H | " | H O H
H H H | | |H—C—C—C=O | | H H
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• The major carbohydrates found in the body are structurally related to the;-
• 1-aldotriose glyceraldehyde • 2-ketotriose dihydroxyacetone. • All carbohydrates contain at least one
asymmetrical (chiral) carbon and are, therefore, optically active.
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Aldotriose and ketotriose glyceraldehyde is especially
important because the more complex monosaccharides may be considered to be derived from them
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Carbohydrate Nomenclature
• Monosaccharide• Disaccharides, • Oligosaccharides• Polysaccharides
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Monosaccharides
• The common monosaccharides (hexoses) of living organisms are:
• (glucose, galactose, fructose) C₆H₁₂O₆• (ribose, deoxyribose, ribulose, xylose) 5-
carbon pentoses (C5H10O4).
• Contain 3-7 carbon atoms.(trioses, tetroses, pentoses, hexoses and heptoses)
• Contain hydroxyl groups -OH• Carbonyl group C=O
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• The 5-carbon monosaccharide ribose is an important component of;-
• - coenzymes (e.g., ATP, FAD, NAD)• - the backbone of the genetic molecule RNA• Deoxyribose which is a component of DNA •
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Aldoses contain an aldehyde (-CHO ) functional groupat one end e.g. glucose
Ketoses contain a ketone (C=O) functional group usually at C #2. e.g. fructose
glucose is the most important monosaccharide
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the nomenclature and functional group for monosaccharides
Number of Carbons
(Generic monosaccharide
name)
Aldose Functional
Group
Ketone Functional Group Relevant examples
3
(Triose)Aldotriose
Ketotriose
TriuloseGlyceraldehyde, Dihydroxyacetone
4
(Tetrose)Aldotetrose
Ketotetrose
TetruloseErythrose
5
(Pentose)Aldopentose
Ketopentose
PentuloseRibose, Ribulose, Xylulose
6
(Hexose)Aldohexose
Ketohexose
HexuloseGlucose, Galactose, Mannose, Fructose
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Conformation of monosaccharides trioses, tetroses, pentoses, hexoses
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StereochemistryIsomerism
• Stereochemistry deals with arrangements of atoms in molecules and the effects of these arrangements on the chemical and physical properties of substances
• Isomerism are compound have the same structural formula but differ in configuration
• The presence of asymmetric carbon or chiral (carbon atoms attached to four different atoms or group) allows the formation of isomer
• Different groups are attached it is easy to move any two or groups of atoms to other position and rotate the new structure
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D and L isomerism
• Organic substances usually are optically active• The presence of asymmetric carbon atoms give optical
activity on the compound • If Plane-polarized light is passed through a solution of
the substances, ;-the plane of light is rotated to• - the right (dextrorotary substances) • -or to the left (for levorotatory )• expressed as• *dextrorotary (D)• *levorotary (L)
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• The direction and extend of the rotation of a particular compound depend on;
• -concentration of the substances• -temperature • -wave of the light• Enzyme function specify the particular
configuration such as L-glutamate dehydrogenase
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The majority of saccharides in nature have the "D" isomer
The orientation of the –H and –OH groups around the carbon atom adjacent to terminal alcohol carbon (CH2OH) carbon 5 determine whether the sugar is D or L isomer
Fischer projection Haworth Projection of β-D-Glucose
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Haworth Projection of α- and β D-GlucoseIn α-D-glucose the anomeric carbon’s –OH group is on the right. In the Haworth projection of α-D-glucose illustrated below the –OH group points down and β D glucose OH pointed up.
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Cyclic Fischer Projection of α-D-GlucoseIn cyclic structure or Fisher projection the anomeric hydroxyl are positioned to right resulting in alpha
configuration
Cyclic Fischer Projection of α-D-Glucose
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Ring and chair configuration of glucose
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aldose-ketose isomerism
• The carbonyl group of the keto or aldose functional group is considered to be closest to the "start" of the carbon chain.
• The carbon thus identified as the "first" carbon in the chain is carbon #1. The remaining carbons are numbered sequentially.
• In Fischer Projections, the "D" isomer will have the hydroxyl (-OH) functional group located on the right-hand side of the chiral C.
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Fischer projection of glyceraldehyde Aldotriose D,L designation refers to the configuration the
highest-numbered asymmetric center
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Fischer projections for some aldotetroses
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• aldotetroses: – Carbon 1 is at the end closest to the aldehyde carbonyl – Carbon 3 is the highest numbered carbon that is chiral
(carbon 4 is not chiral because it contains two hydrogens)
– The "D" or "L" nomenclature therefore refers to the chirality of carabon 3. The "D" form has the OH group on the right-hand side of carbon 3; the "L" form has the OH group on the left-hand side.
– Carbon 2 is chiral, and the different isomers of this aldotetrose are indicated by different common names
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Fischer projections for some ketopentoses
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ketopentoses
• Carbon 1 is the end closest to the keto group • Carbon 4 is the highest chiral carbon and
determines the "L" or "D" isomer nomenclature for the saccharide
• Carbon 3 is also chiral, and its chirality determines the common name
• Carbon 2 is not chiral, neither is carbon 1, or carbon 5.
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Cyclic monsaccharide structures and anomeric formsα and β anomers
• Ring structure of CHO• In solution the molecules cyclize by a reaction between
carbonyl group and hydroxyl group • If the sugar contain an aldehyde it is called hemiacetal• If the sugar contain a keto group it is called hemiketal• In cyclic structure or Fisher projection the anomeric
hydroxyl are positioned to right resulting in alpha configuration
• If the anomeric hydroxyl are positioned to left the structure would be in beta configuration
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• The resulting chirality of the aldehyde carbon (or keto carbon in ketoses) in the cyclic structure can be either the α- or β- form. This carbon is termed the anomeric carbon, and the α - and β - forms are anomers.
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pyranose and furanose ring structures
• "Pyranose" is used to refer to the pyran ring structure (6-membered ring with 5 carbons and 1 oxygen) Cyclic sugars that contain a six membered ring are called "pyranoses
• For five membered rings (four carbons and 1 oxygen) the structure is a furanose ring. Cyclization is reversible
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Cyclic form of glucose is a pyranose Cyclic form of fructose is a furanose
• The pyranose ring is formed by the reaction of the hydroxyl group on carbon 5 (C-5) of a sugar with the aldehyde at carbon 1.
• This forms an intramolecular hemiacetal.
• If reaction is between the C-4 hydroxyl and the aldehyde, a furanose is formed hemiketal.
• The pyranose form is more stable than the furanose form,
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• glucose forms an intra-molecular hemiacetal by reaction of the aldehyde on C1 with the hydroxyl on C5, forming a six-member pyranose ring, named after the compound pyran
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The furanose and pyranose forms of D-glucose
The furanose forms of D-glucose four carbons and 1 oxygen
The pyranose forms of D-glucose 6-membered ring with 5 carbons and 1 oxygen
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glucopyranose The ring structure representations of "Haworth
Projections“
The pyranose ring is formed by the reaction of the hydroxyl group on carbon 5 (C-5) of a sugar with the aldehyde at carbon 1. This forms an intramolecular hemiacetal
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chair configuration of the glucopyranose ring
chair configurationThe α and β anomers of glucose chair form. the position of the hydroxyl group (red or green) on the anomeric carbon relative to the CH2OH group bound to carbon 5: they are either on the opposite sides (α), or the same side (β).
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mutarotation of glucose rings Two ring forms of glucose differ in whether the hydroxyl group attached to carbon number 1 is fixed below (alpha glucose ) or above (beta glucose )
A change in the specific optical rotation of light that takes place in the solutions of freshly prepared sugars; Carbohydrates can change
spontaneously between the α and β configurations: a process known as
mutarotation.
α and β configurations Found in equilibrium and spontaneously are
interconverted (mutarotation
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Pentose sugar ribose
• Ribose is an organic compound with the formula C5H10O5
• Ribose constitutes the backbone of RNA, a biopolymer that is the basis of genetic transcription
• Once phosphorylated, ribose can become a subunit of ATP, NADH, important in metabolism
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Ribose is an aldopentose (a five-carbon aldehyde)
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Deoxyribose
• deoxyribose, also called d-2-deoxyribose, five-carbon sugar component of DNA (deoxyribonucleic acid), where it alternates with phosphate groups to form the “backbone” of the DNA polymer and binds to nitrogenous bases.
• The presence of deoxyribose instead of ribose is one difference between DNA and RNA (ribonucleic acid).
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Deoxyribosereplacement of the hydroyl group at the C2
position with hydrogen, leading to the net loss of an oxygen deoxy.
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Disaccharides • Disaccharides; contain two monosaccharides units
attached to one another through acetal bonds or as known glycosidic bonds
• Covalent bonds between the anomeric hydroxyl of a cyclic sugar and the hydroxyl of a second sugar (or another alcohol containing compound) are termed glycosidic bonds, and the resultant molecules are glycosides.
• The linkage of two monosaccharides to form disaccharides involves a glycosidic bond. Several physiogically important disaccharides are sucrose, lactose and maltose
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Glycosidic bond
• Glycosidic bond are formed between hydroxyl group of one monosaccharide and hydroxyl group of the next with the removal of water
• Glycosidic bonds involve the hydroxyl group of the anomeric carbon (keto or aldehyde) of one member of the pair of monosaccharide and hydroxyl group on carbon 4 or 6 of the second member
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• Glycosidic bond can be α or β• Glycosidic bonds may be designated • - α 1-4, β 1-4, α 1-6 and so on• Important disaccharides are• 1-maltose• 2-lactose• 3-sucrose
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Lactose. This disaccharide is comprise of a galactose linked to glucose via a β-1-4 glycosidic bond. "Milk sugar" - it is the principle carbohydrate of milk. Must be broken down into galactose and glucose by the enzyme lactase.
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Sucrose. This disaccharide is glucose-α-1,2-fructose. "Table sugar". No free anomeric carbon, therefore, not a reducing sugar.
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Maltose. This disaccharide is glucose-α-1,4 glucose. "Grain sugar". Formed from the partial hydrolysis of starch. Has a free anomeric carbon and is therefore a reducing sugar.
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Complex carbohydrates • When polysaccharides are composed of a single
monosaccharide building block, they are termed homopolysaccharides example starch and glycogen.
• Polysaccharides composed of more than one type of monosaccharide are termed heteropolysaccharides, give sugar and
non-sugar like SO4 or NH4 gp e.g.
glycosaminoglycans ( found in connective tissue)
heparin present in mast cells as anticoagulant
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polysaccharides; consist of many mono-saccharides. the main
monosaccharide found in polysaccharides is D-glucose. Polysaccharides of nutritional important are
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Polysaccharides
Glycogen 1- Glycogen
• Made and found in human bodies• Glycogen is the major form of stored carbohydrate in
animals. Stored in liver and muscle• This vital molecule is a homopolymer of glucose in α–(1,4)
linkage• Glycogen is a very compact structure that results from the
coiling of the polymer chains• Not found in plants• Saved for later use; the liver contain enzyme which
convert glycogen to glucose through the process known as glycogenlysis.
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Glycogen
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2-Starch
is a storage polysaccharide composed of glucose monomers
• Its structure is identical to glycogen,
Starch -- 2 forms: • amylose: linear polymer of α(1-> 4) linked glucose
residues
• amylopectin: branched polymer of α(1-> 4) linked glucose residues with α(1-> 6) linked branches
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• 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).
• during hydrolysis starch formed intermediate product called dextrin. complete digestion of starch formed glucose;
• starch--------dextrin----------maltose------------glucose
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Starch formsamylose
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amylopectin
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• 3-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 digest 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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CelluloseCellulose in fibers is also a polymer of glucose
monomers ,but using beta rings (1-4 bond)
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Polysaccharide Functions
• Polysaccharides functions related to• storage, • structure • protection.• Energy
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Carbohydrates metabolism
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Diseases associated with Carbohydrates
• Diabetes mellitus• Galactosemia• Glycogen storage diseases • Lactose intolerance
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References
• Murry K. Robert, Granner K. daryl, Mayes A. peter, Rodwell W. Victor (1999). Harpers Biochemistry. Appleton and Lange , twent fifth edition
• Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology: Exploring Life. Boston, Massachusetts: Pearson Prentice Hall
• A. Burtis, Edward R. Ashwood, Norbert W. Tietz (2000), Tietz fundamentals of clinical chemistry
• Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health. Englewood Cliffs, New Jersey, USA: Prentice Hall. pp. 52–59
• Maitland, Jr Jones (1998). Organic Chemistry. W W Norton & Co Inc (Np). p. 139. ISBN 0-393-97378-6.
• Nelson DL, Cox MM (2005). Lehninger's Principles of Biochemistry (4th ed.). New York, New York: W. H. Freeman and Company.
• Matthews, C. E.; K. E. Van Holde; K. G. Ahern (1999) Biochemistry. 3rd edition. Benjamin Cummings.• http://wiki.answers.com/Q/What_is_dehydration_synthesis#ixzz2BuiK645
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• 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
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• Lehninger. Principles of bochemistry. by Nelson and Cox, 5th Edition; W.H. Freeman and Company
• Emsley, John (2011). Nature's Building Blocks: An A-Z Guide to the Elements (New ed.). New York, NY: Oxford University Press. ISBN 978-0-19-960563-7.
• Koppenol, W. H. (2002). "Naming of New Elements (IUPAC Recommendations 2002)" (PDF). Pure and Applied Chemistry 74 (5): 787–791. doi:10.1351/pac200274050787. http://media.iupac.org/publications/pac/2002/pdf/7405x0787.pdf.