glucose

1. CARBOHYDRATES
Dr. Neelam H. Zaidi

2. Introduction
 Carbohydrates are one of the four major classes
of biological macromolecules.
 Carbohydrates are also the most abundant
organic molecules in nature.
 Carbohydrates derive their name from the
general formula (CH2O)n or CnH2nOn, n≥3
(hydrate of carbon)

3.  Carbohydrates contain the elements carbon,
hydrogen and oxygen.
 Carbohydrates are carbon compounds that contain
large quantities of hydroxyl groups.
 Saccharide means sugar; -ose indicates sugar
 They are oxidized in living cells to produce CO2,
H2O and energy.
Introduction

4.  Wide range of functions in living systems:
 Nutritional (fuels, energy storage, metabolic
intermediates)
 Structural (components of cell membrane and
nucleotides, plant and bacterial cell walls,
exoskeletons of insects, animal connective
tissue)
Functions

5.  Informational (cell surface of eukaryotes --
molecular recognition, cell-cell communication)
 Osmotic pressure regulation
 Precursor for synthesis of all other
carbohydrates in the body----glycogen,
ribose/deoxyribose, galactose
Functions

6. According to the number of subunits, all
carbohydrates can be classified as
Monosaccharides 1(simple sugars)
Disaccharides 2
Oligosaccharides 3-10
Polysaccharides >10
Classification

7.  Monosaccharides -- one unit, cannot be broken
down (glucose, fructose, galactose)
 Disaccharides--Two units of monosaccharides.
(sucrose, lactose)
 Oligosaccharides--three to ten units. Few (ABO
blood groups)
 Polysaccharides-- much larger, containing
hundreds of monosaccharide units. Many
(glycogen, starch, cellulose)
Classification

8. Other Forms of Carbohydrates
 Carbohydrates also can combine with lipids to
form glycolipids.
 Or combine with proteins to form glycoproteins.
 Components of cell membranes and receptors.

9. Monosaccharides
 Cannot be hydrolyzed to small molecules.
 Colorless, crystalline compounds.
 Freely soluble in water.
 Most have a sweet taste.
 Contain three to seven carbons with functional
aldehyde or keto group are present in nature.
 Carbon atoms at backbone are linked by single
bonds.

10. Monosaccharides
 Glucose is present in our blood and gives rise to
energy on oxidation, the most abundant.
 Fructose is the sweetest sugar, found in fruits and
honey. Also added to soft drinks, deserts.
 Galactose is constituent of lactose (milk sugar)

11.  According to the functional group that
monosaccharides contain:
 Aldoses: aldehyde group
 Ketoses: keto group
Classification of
Monosaccharides

13.  Based on the number of carbon atoms, the
monosaccharides are named
Trioses C3
Tetroses C4
Pentoses C5
Hexoses C6
Heptoses C7
Classification of
Monosaccharides

14. Examples

15. Physical
Properties of
Monosaccharides

16.  Compounds that have the same chemical formula,
but have different arrangement of the atoms in
space.(different structures).
 Examples of isomers (C6H12O6) :
1.Glucose
2.Fructose
3.Galactose
4.Mannose
Isomers

17. Example

18. Mannose
Example

19. Epimers
Epimers are sugars that differ in
configuration at ONLY one specific
carbon atom.
With the exception of the carbonyl
carbon
 Examples of epimers :
 glucose & galactose (epimeric at C4)
 glucose & mannose (epimeric at C2)

20. 4 4
Example

21. 2 2
Example

23. Enantiomers
Non-superimposable COMPLETE mirror
image
A special type of isomerism.
The two members of the pair are
designated as D and L forms.
Majority of the sugars in humans are D-
sugars.

26. Enantiomers
In the D form, the –OH group on the
asymmetric (chiral) carbon farthest from the
carbonyl carbon is on the right.
In the L form, -OH group is on the left.
Enzymes are specific for each form.
Racemases can interconvert D- and L-form.

27. Example

28.  Less than 1% of monosaccharides exist in the
open chain form in solution.
 Predominantly found in ring form or cyclic
structure.
 Involving reaction of C-5 OH group with the C-1
aldehyde group or C-2 of keto group.
Cyclization of
Monosaccharides

29. Example

30. Example

31. New Terms
 Six membered ring structures are called
Pyranoses .
 Five membered ring structures are called
Furanoses .

32.  The carbonyl carbon after cyclization becomes
the anomeric carbon.
 This creates α and β configuration, that are
anomers of each other.
 In α configuration the -OH is on the same side of
the ring in Fischer projection. In Haworths it is
on the trans side of CH2OH
Anomeric Carbon

33. Two projections

34. Example

36. Cont’d
 Such α and β configuration are called
diastereomers and they are not mirror images.
 Enzymes can distinguish between α and β these
two forms.
 α and β anomers spontaneously interconvert in
solution. This is called mutarotation.

37. Example
Glycogen Cellulose

38.  If –OH on the anomeric carbon of a cyclized sugar
is not linked to another compound, it can act as a
reducing agent and is termed a reducing sugar.
 All monosaccharides are reducing sugars.
 Such sugars can react with chromogenic agents
causing the reagent to be reduced and colored.
 A colorimetric test can detect a reducing sugar in
urine.
Reducing Sugars

39.  When a beam of plane-polarized light is passed
through a solution containing monosaccharides
the light will be rotated.
 This rotation is because of the presence of
asymmetric carbon atom.
 If it is rotated towards left- levorotatory (-)
 If it is rotated towards right- dextrorotatory(+)
 In solution, glucose is dextrorotatory, and glucose
solutions are sometimes known as dextrose.
Optical Activity

40.  Monosaccharides can be joined to form
di/oligo/poly-saccharides.
 The bonds that link sugars are called glycosidic
bonds.
 Glycosidic bonds are named according to the
numbers of carbons and the position of
–OH.(more details in video)
Joining of Monosaccharides

41. Example
H2O

42.  Carbohydrates can be attached by glycosidic
bonds to noncarbohydrate structures including:
 Purine and pyrimidine (found in nucleic acids)
 Aromatic rings (steroids and bilirubin)
 Proteins (glycoproteins and proteoglycans)
 Lipids (glycolipids)
 To form glycosides.
Complex Carbohydrates

43.  Disaccharides consist of two monosaccharide units.
 Glycosidic bond joints individual monosaccharides.
 Glucose is always present.
 Maltose, lactose and sucrose are examples.
 All disaccharides yields energy after their hydrolysis to
constituent monosaccharides.
Lactose
Maltose
Disaccharides

44. Example

45. Oligosaccharides
 They consist of short chains of monosaccharide
units or residues, joined by glycosidic bonds.
 They are trisaccharides, tetrasaccharides etc.
 Example: Maltotriose=Glucose+Glucose+Glucose

46. Polysaccharides
 Made up of more than ten monosaccharide units.
 They are polymers of monosaccharides, called
glycan.
 They serve structural and storage functions.
 Devided into
 HOMOpolysaccharides (all 1 type of monomer), e.g.,
glycogen, starch, cellulose, dextrins
 HETEROpolysaccharides (two or more different types of
monomer), e.g., glycoproteins, glycosaminoglycans

47.  Starch: glucose storage from plant sources. (tubers,
rice, wheat, pulses, grains etc)
 Starch -- 2 polymeric 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
Homopolysaccharides

49.  Glycogen: storage polysaccharides in animals.
 Present in liver and skeletal muscle.
 α(1 4) linkages in straight glucose chain,
residues with α(1 6) glycosidic bond linked
branches
 Like amylopectin but even more highly branched
and more compact
 Branches increase H2O-solubility
Homopolysaccharides

51.  Cellulose: structural polysaccharide in plants. (cell
wall)
 Fibrous, tough, water insoluble.
 Homopolymer, linear, unbranched, β(1 4) linked
glucose residues.
 Human cannot use cellulose because they lack of
enzyme(cellulase) to hydrolyze the β(1 4)
linkages.
 Dietary fiber.
Homopolysaccharides

52.  Dextrins: products of partial hydrolysis of starch.
 Highly branched homopolymers of glucose units.
 Do not easily go out of vascular compartment so
they are used for intravenous infusion as plasma
volume expander in the treatment of hypovolemic
shock.
Homopolysaccharides

53.  Glycosaminoglycans: GAGS
 Can bind large amounts of water so produce the
gel-like matrix.
 Stabilize and support cellular and fibrous
components of tissue.
 Anticoagulant (Heparin).
 Synovial fluid, serves as lubricant in joints, tendon
sheaths.
Heteropolysaccharides

54.  Glycoproteins
 Glycophorin, a glycoprotein found in human red cell
membranes.
 Human gastric glycoprotein (mucin)---Lubricant &
protective agent
 Collagen---Structural molecule
 Transferrin & Ceruloplasmin---Transport
 Immunoglobulin---Immunity
 Alkaline phosphatase---Enzymatic activity
 Many protein hormones, receptors
Heteropolysaccharides

55.  Carbohydrates present in food are polysaccharides,
disaccharides and very small amounts of
monosaccharides.
 Carbohydrate digestion: Is a process that
hydrolyzes food polysaccharides to their
constituent monosaccharides.
Digestion of Carbohydrates

56.  Main sites are the mouth and intestinal lumen.
 The digestion is rapid and is catalyzed by glycoside
hydrolases (glycosidases) that hydrolyze glycosidic
bonds.
 Glycosidases are specific for the structure and
configuration of the glycosyl residue and the type of
bond to be broken.
Digestion of Carbohydrates

58.  Digestion in Mouth
 Carbohydrates come in contact with saliva during
mastication.
 Saliva contains a carbohydrate splitting enzyme
called salivary α-amylase
 Hydrolyze α (1 4) glycosidic linkage
 Digest product is called dextrins
Digestion

60.  Digestion in Stomach: no enzymes are available in gastric
juice.
 Digestion in Duodenum
Pancreatic juice contains pancreatic amylase
Hydrolyze α (1 4) glycosidic linkage
 Digestion in Small Intestine
Pancreatic amylase
Lactase
Maltase
Sucrase
Digestion

61.  Small Intestine
 Mechanism of absorption
1. Passive facilitated diffusion
Fructose: GLUT-5
Concentration gradients
2.Active transport: glucose and galactose
Na+ symporter: SGLT-1
Requires energy
Absorption of Carbohydrates

62. Different sugars have different mechanisms of
absorption.
Absorption of Carbohydrates

63.  Lactose→ glucose + galactose
lactase
 For deficiency, lactose remains in the intestines and
gets fermented by the bacteria.
 The condition is called as lactose intolerance (Adult
hypolactasia)
 Watery diarrhea, abnormal intestinal flow, chloeic
pain, flatulence.
 No milk: yogurt or cheese
Lactose Intolerance

64. Lactose Intolerance

66.  Champ M, Langkilde A-M, Brouns F, et al: Advances in dietary fibre
characterisation. Nutrition Res Rev 2003;16:(1)71–82.
 Garg HC, Cowman KM, Hales CA: Carbohydrate Chemistry, Biology and
Medical Applications. Elsevier, 2008.
 Kiessling LL, Splain RA: Chemical approaches to glycobiology. Ann Rev
Biochem 2010;79:619–653.
 Lindhorst TK, Thisbe K: Essentials of Carbohydrate Chemistry and
Biochemistry, 3rd ed. Wiley-VCH, 2007.
 Sinnott M: Carbohydrate Chemistry and Biochemistry: Structure and
Mechanisms, Royal Society of Chemistry, 2007
 https://www.slideshare.net/abdulhaseeb11/carbohydrate-metabolism -
15554498
 https://www.slideshare.net/CantDecideMyUsername/introduction-to-
carbohydrates
References