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Lecture notes about carbohydrates, Lecture notes of Biochemistry

University of Eastern Philippines (UEP)Biochemistry

lecture notes in biochemistry about carbohydrates

Typology: Lecture notes

2019/2020

Uploaded on 10/30/2021

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OCCURRENCE AND FUNCTIONS OF CARBOHYDRATES
Carbohydrate oxidation provides energy.
oGlycogen - storage form of
carbohydrate. Serves as a reserved
energy if no food intake.
It stored in liver and muscle
cells, provides a short-term
energy reserve.
Carbohydrates supply carbon atoms for the
synthesis of other biochemical substances
oproteins,
olipids, and
onucleic acids
Carbohydrates form part of the structural
framework of DNA and RNA molecules.
oRNA is mainly involved in protein
synthesis
oDNA genetic material that contains
material for building the whole body.
Carbohydrates are one of the plasma
membrane:
oGlycolipid
oGlycoprotein
Carbohydrates linked to lipids are structural
components of cell membranes.
Carbohydrates linked to proteins function in a
variety of cell–cell and cell– molecule
recognition processes.
oWhen two molecules restricted to the
plasma membrane they will bind to
each other. Which results to:
Response to communication
Cooperation
Transport
Defense
And Growth
FUNCTIONAL GROUP PRESENT IN CARBOHYDRATES
A carbohydrate is a polyhydroxy aldehyde, or a
polyhydroxy ketone, or a compound that yields
polyhydroxy aldehydes or polyhydroxy ketones
upon hydrolysis.
oHydrolysis - it is any chemical reaction
in which in molecule of water breaks
one or more chemical bond
Common Carbohydrates that we have:
oGlucose - polyhydroxy aldehyde
oFructose - polyhydroxy ketone.
The carbohydrate glucose is a polyhydroxy
aldehyde, and the carbohydrate fructose is a
polyhydroxy ketone.
Classification of Carbohydrates
Monosaccharides are classified as aldose or
ketose on the basis of the type of carbonyl
present.
oMono -one
Disaccharides are glycosides formed from the
linkage of two monosaccharides.
oDi - two
oGlycosidic Linkage - they form two
monosaccharides to form disaccharide
Oligosaccharides are carbohydrates that contain
three to ten monosaccharide units.
oOligo - three to ten
Polysaccharides are polymers in which
monosaccharides are the monomers.
oPolymerization
oConsidered as monomers.
Pinakamarami.
CHIRALITY: HANDEDNESS IN MOLECULES
Most monosaccharides exist in two forms: a
“left-handed” and “right-handed” form.
Superimposable Mirror Images
o- are images that coincide at all points
when the images are laid upon each
other.
Non-Superimposable Mirror Images
o- are images where not all points
coincide when the images are laid upon
each other.
Chirality
Chirality - handedness in molecules
Chiral - center
A chiral center is an atom in a molecule that has
four different groups bonded to it in a
tetrahedral orientation.
A molecule that contains a chiral center is said
to be chiral.
A chiral molecule is a molecule whose mirror
images are not superimposable.
STEREOISOMERISM: ENANTIOMERS AND
DIASTEREOMERS
Stereoisomerism- the atoms of stereoisomers
are connected in the same way but are
arranged differently in space.
oGlyceraldehyde
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OCCURRENCE AND FUNCTIONS OF CARBOHYDRATES

 Carbohydrate oxidation provides energy. o Glycogen - storage form of carbohydrate. Serves as a reserved energy if no food intake.  It stored in liver and muscle cells, provides a short-term energy reserve.  Carbohydrates supply carbon atoms for the synthesis of other biochemical substances o proteins, o lipids, and o nucleic acids  Carbohydrates form part of the structural framework of DNA and RNA molecules. o RNA is mainly involved in protein synthesis o DNA genetic material that contains material for building the whole body.  Carbohydrates are one of the plasma membrane: o Glycolipid o Glycoprotein  Carbohydrates linked to lipids are structural components of cell membranes.  Carbohydrates linked to proteins function in a variety of cell–cell and cell– molecule recognition processes. o When two molecules restricted to the plasma membrane they will bind to each other. Which results to:  Response to communication  Cooperation  Transport  Defense  And Growth FUNCTIONAL GROUP PRESENT IN CARBOHYDRATES  A carbohydrate is a polyhydroxy aldehyde, or a polyhydroxy ketone, or a compound that yields polyhydroxy aldehydes or polyhydroxy ketones upon hydrolysis. o Hydrolysis - it is any chemical reaction in which in molecule of water breaks one or more chemical bond  Common Carbohydrates that we have: o Glucose - polyhydroxy aldehyde o Fructose - polyhydroxy ketone.  The carbohydrate glucose is a polyhydroxy aldehyde, and the carbohydrate fructose is a polyhydroxy ketone. Classification of Carbohydrates  Monosaccharides are classified as aldose or ketose on the basis of the type of carbonyl present. o Mono -one  Disaccharides are glycosides formed from the linkage of two monosaccharides. o Di - two o Glycosidic Linkage - they form two monosaccharides to form disaccharide  Oligosaccharides are carbohydrates that contain three to ten monosaccharide units. o Oligo - three to ten  Polysaccharides are polymers in which monosaccharides are the monomers. o Polymerization o Considered as monomers. Pinakamarami. CHIRALITY: HANDEDNESS IN MOLECULES  Most monosaccharides exist in two forms: a “left-handed” and “right-handed” form.  Superimposable Mirror Images o - are images that coincide at all points when the images are laid upon each other.  Non-Superimposable Mirror Images o - are images where not all points coincide when the images are laid upon each other. Chirality  Chirality - handedness in molecules  Chiral - center  A chiral center is an atom in a molecule that has four different groups bonded to it in a tetrahedral orientation.  A molecule that contains a chiral center is said to be chiral.  A chiral molecule is a molecule whose mirror images are not superimposable. STEREOISOMERISM: ENANTIOMERS AND DIASTEREOMERS  Stereoisomerism - the atoms of stereoisomers are connected in the same way but are arranged differently in space. o Glyceraldehyde

 Two Types: Enantiomers and Diastereomers: o Enantiomers have structures that are nonsuperimposable mirror images of each other. o Diastereomers have structures that are not mirror images of each other. Fischer Projection Formulas  A Fischer projection formula is a two- dimensional structural notation for showing the spatial arrangement of groups about chiral centers in molecules.  This would be the simplest carbohydrate that we have.  In a Fischer projection formula, a chiral center (Carbon) is represented as the intersection of vertical and horizontal lines o Vertical Line - from the chiral center it represents bond to groups directly onto the printed page. o Horizontal Line - from chiral center it represents bond to group out into the printed page.  D and L stands for DEXTRO ROTATORY AND LEVOROTATORY o Dextro Rotatory - mainly involved of plane polarized light  D and L system used to designate the handedness of glyceraldehyde enantiomers.  The D,L system used to designate the handedness of glyceraldehyde enantiomers can be extended to other monosaccharides with more than one chiral center.  The carbon chain is numbered starting at the carbonyl group end of the molecule, and the highest-numbered chiral center is used to determine D or L configuration. Properties of Enantiomers  Nearly all the properties of a pair of enantiomers are the same; o they have identical boiling points and melting points  Enantiomers exhibit different properties in only two areas: (1) their interaction with plane- polarized light and (2) their interaction with other chiral substances. Interaction of Enantiomers with Plane-Polarized Light  Ordinary light waves—that is, unpolarized light waves—vibrate in all planes at right angles to their direction of travel.  Plane-polarized light waves, by contrast, vibrate in only one plane at right angles to their direction of travel. o Polarimeter - instrument to identify which way the light will rotate. Dextrorotatory and Levorotatory Compounds  A dextrorotatory compound is a chiral compound that rotates the plane of polarized light in a clockwise direction.  A levorotatory compound is a chiral compound that rotates the plane of polarized light in a counterclockwise direction. *The handedness of enantiomers (D or L) and the direction of rotation of plane- polarized light by enantiomers [(+) or (-)] are not connected entities. *There is no way of knowing which way an enantiomer will rotate light until it is examined with a polarimeter. CLASSIFICATION OF MONOSACCHARIDES  Monosaccharides are often classified by both their number of carbon atoms and their functional group.  A six-carbon monosaccharide with an aldehyde functional group is an aldohexose;  a five-carbon monosaccharide with a ketone functional group is a ketopentose. o Aldoses o Ketoses

—OH groups in the Haworth projection formula.  In situations where α or β configuration does not matter, the —OH group on carbon 1 is placed in a horizontal position, and a wavy line is used as the bond that connects it to the ring REACTIONS OF MONOSACCHARIDES Five important reactions of monosaccharides:  Oxidation to acidic sugars  Reduction to sugar alcohols  Glycoside formation  Phosphate ester formation  Amino sugar formation Oxidation  Oxidation to Acidic sugars: The redox chemistry of monosaccharides is closely linked to the alcohol and aldehyde functional groups present in them.  Oxidation can yield three different types of acidic sugars depending on the type of oxidizing agent used o Adonic Acid - oxidation of aldehyde o Aldaric Acid - oxidation of of both ends of aldehyde and alcohol o Alderonic Acid - oxidation of alcohol. Sugar Alcohols  Reduction to sugar alcohols: Hydrogen  The carbonyl group in a monosaccharide (either an aldose or a ketose) is reduced to a hydroxyl group using hydrogen as the reducing agent. Glycoside  The general name for monosaccharide acetals is glycoside.  A glycoside is an acetal formed from a cyclic monosaccharide by replacement of the hemiacetal carbon -OH group with an -OR group. Phosphate Ester Formation  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. Amino Sugar Formation  Amino Sugar Formation: An amino sugar - one of the hydroxyl groups of a monosaccharide is replaced with an amino group  Amino sugars and their N-acetyl derivatives are important building blocks of polysaccharides. o D glucosamine o D gakactosamine o D manosamine Blood Types and Monosaccharides  Blood Types and Monosaccharides: Human blood is classified into four types: A, B, AB, and O:  The biochemical basis for the various blood types involves monosaccharides present on plasma membranes of red blood cells.  The monosaccharides responsible for blood groups are D-galactose and its derivatives. DISACCHARIDES  Two monosaccharides can react to form disaccharide  The bond that links the two monosaccharides of a disaccharide (glycoside) together is called a glycosidic linkage. Cellobiose  Cellobiose is produced as an intermediate in the hydrolysis of the polysaccharide cellulose.  Cellobiose contains two b - Dglucose monosaccharide units linked through a b (1—4) glycosidic linkage.  Cellobiose cannot be digested by humans.

Maltose  Maltose, often called malt sugar, is produced whenever the polysaccharide starch breaks down, as happens in plants when seeds germinate and in human beings during starch digestion.  Structurally, maltose is made up of two D- glucose units, one of which must be a-D- glucose. Lactose  Lactose is made up of b-D-galactose unit and a b-D-glucose unit joined by a b (1-4) glycosidic linkage.  Lactose is the major sugar found in milk.  Lactose intolerance : a condition in which people lack the enzyme lactase needed to hydrolyze lactose to galactose and glucose.  Lactase hydrolyzes b (1-4) glycosidic linkages.  Deficiency of lactase can be caused by a genetic defect, physiological decline with age, or by injuries to intestinal mucosa Sucrose  Sucrose (table sugar): The most abundant of all disaccharides and found in plants.  It is produced commercially from the juice of sugar cane and sugar bee.  Sucrose is a nonreducing sugar.

GENERAL CHARACTERISTICS OF POLYSACCHARIDES

The Polymer Chain  A polysaccharide is a polymer that contains many monosaccharide units bonded to each other by glycosidic linkages.  A homopolysaccharide is a polysaccharide in which only one type of monosaccharide monomer is present.  A heteropolysaccharide is a polysaccharide in which more than one (usually two) type of monosaccharide monomer is present. Starch  A storage polysaccharide is a polysaccharide that is a storage form for monosaccharides and is used as an energy source in cells.  Starch: o Starch is a homopolysaccharide containing only glucose monosaccharide units. o It is the energy-storage polysaccharide in plants o Amylopectin, the other polysaccharide in starch, has a high degree of branching in its polyglucose structure. o All of the glycosidic linkages in starch (both amylose and amylopectin) are of the type. Glycogen  Glycogen, like starch, is a polysaccharide containing only glucose units.  Liver cells and muscle cells are the storage sites for glycogen in humans.  Glycogen is an ideal storage form for glucose. Cellulose

CARBOHYDRATES: TESTS BASED ON THE

FORMATION OF FURFURAL AND ITS

DERIVATIVES

A carbohydrate is a:  polyhydroxy aldehyde,  a polyhydroxy ketone,  or a compound that yields polyhydroxy aldehydes or polyhydroxy ketones upon hydrolysis.

CLASSIFICATION OF CARBOHYDRATES

  • Monosaccharides – “simple sugars”, are highly soluble in water, less soluble in ethanol, and insoluble in ether. GLYCANS
  • They are either aldoses or ketoses
  • They may also be classified into tetroses, pentoses, or hexoses
  • Free monosaccharides are all reducing sugars.
  • They also exhibit mutarotation
  • Disaccharides – are formed by two molecules of monosaccharides. Examples are maltose, which are abundant in germinating barley; sucrose, also known as cane sugar or beet sugar; and lactose or milk sugar, which does not taste very sweet and is not fermented by yeast.
  • Polysaccharides – found in nature function either as structural units (e.g. cellulose), or for storage such as starch, dextrin, glycogen, and inulin

Tests for Carbohydrates:

1.General Tests for Carbohydrates

  • Tests based on the formation of furfural and its derivatives 2.Reducing tests for Carbohydrates

GENERAL TESTS FOR CARBOHYDRATES

MOLISCH TEST

  • is the general test for carbohydrates.
  • The sugars are mixed with a-naphthol.
  • The test tube is inclined, and concentrated H2SO4 is added along the side of the tube, causing the formation of a lower layer of acid.
    • The concentrated H2SO4 will dehydrate the sugar allowing it to react with the alcohol forming furfural or Hydroxymethyl-furfural.

PROCEDURE

  • Mix 4 ml of distilled water and two drops of the Molisch’s reagent in a test tube. This tube will serve as the control.
  • Place 4 ml of 3% solution of glucose in a second test tube. Add two drops of the Molisch’s reagent and mix the contents by gently shaking the test tube.
  • Incline the test tube and cautiously add about 5 ml of concentrated sulfuric acid, allowing the acid to run down the side of the tube. Sulfuric acid is denser than water and will form a lower layer. Note the color of the ring formed at the junction if the two liquids.
  • In the same manner of adding acid, add sulfuric acid to the control tube. What do you observe?
  • Repeat the above test with 3% sample solutions of fructose, lactose, and sucrose
  • Record all results.

BIAL’S ORCINOL TEST

 Concentrated HCl  Ferric Chloride  5-hydroxymethyl furfural

  • used to determine the presence of pentoses and nucleotides and nucleotides that contain pentose sugars.
  • When pentoses are treated with orcinol, furfurals are formed and they will yield a blue green compound in the presence of ferric ions.
  • The reaction is not specific for pentoses because other compounds like trioses, uronic acids, and certain heptoses will also give blue or green products.
  • Hydroxymethyl furfural is formed from hexoses to give yellow-brown condensation products.

PROCEDURE

  1. Place 1 ml of each 3% solution of xylose, and glucose in separately labeled test tubes
  2. Add 3 ml of Bial’s reagent to each test tube
  3. Carefully heat each tube over a Bunsen flames until the solution begins to boil.
  4. Note the color of the product formed
  1. Record your results in the table

SELIWANOFF’S TEST

  • This test is used to differentiate ketohexoses from aldohexose. Ketohexoses react faster with the solution containing hydrochloric acid and resorcinol than aldohexose.
  • The dehydrated ketohexoses form a bright cherry red condensation product, while the aldohexose yields only a pale pink coloration, a negative result.
  • In this test, prolonged heating of samples should be avoided.

PROCEDURE

  1. Place 1 ml each of 3% glucose, fructose, lactose and sucrose in separately labeled test tubes.
  2. Add 4 ml of Seliwanoff’s reagent to each test tube
  3. Place the test tubes in a water bath filled with boiling water and allow them to stay there for exactly 1 minute
  4. Note the changes and record which test tube gives a positive result in the shortest time.
  5. Continue heating and observe the color changes at 1 minute intervals
  6. Record the time required for a positive test for each sample