Chapter 18 Carbohydrates
Chapter 18
Carbohydrates
Goals
• Distinguish and describe mono, di, oligo, and polysaccharides
• Classify and name monosaccharides• Know D aldose and ketose• Draw cyclic hemiacetals• Describe photosynthesis• Know mutarotation, oxidation, acetal
formation
Beginning of Biochemistry
• Biomolecules – 3 aspects to consider
Biomolecules
• Four main families– Carbohydrates
– Nucleic acids
Carbohydrates
• Called saccharides
• Functions
Where found
• Sugar
• Wood
Classifications
• Polyhydroxyketone (ketose)
• Monosaccharides
Naming
• IUPAC is not used… long and difficult names
• Most names are common names and end in
Structure
• Aldose
• Ketose
Classifying
• 5 carbon with aldehyde group
• 4 carbon with a ketone group
• See figures 18.1 and 18.2 p 528-9
D or L?
• Chiral recognition and the use of enzymes in organisms selectively produces the D form of the –ose
• L form is not produced in nature
Important monosaccharides
• D-Glucose
• D-Fructose
• D-Galactose
Monosaccharides
• D-Ribose
• D-Xylose
• D-glyderaldehyde and D-hydroxyacetone
Cyclic Hemiacetals
• Presence of both carbonyl carbon and hydroxyl group allows for cyclic structure
• The closed ring is called a
• Page 531
Cyclic hemiacetals
• Unlike straight chain hemiacetals, cyclics are
• Isomeric difference is important for function
Cyclics
• Ketohexoses form
– Addition of an –OH to C5– Two anomers are formed
• Haworth projections (figures 18.3 and18.4)
Mutarotation
• All aqueous solutions of D-glucose
• Isolate alpha and make a solution, after time the mixture
• Same process for each anomer
• Mutarotation is change in specific rotation of light to the equilibrium value
Oxidation of aldose
• Oxidation of open structure, not hemiacetal
• Governed by
Oxidation
• Alpha-hydroxy ketones
• Aldoses and ketoses are called “Reducing Sugars” – Reduce Cu2+ to Cu+
Glycosides• Formation of an acetal
– Page 537– Alpha and beta glycosides depending on
which anomer is converted– In organisms,
Glycosides• Acetals of carbos are
• Carbons are connected by a glycosidic linkage. Two types:–
• Nature is stereospecific –
• This bond forms di and polysaccharides
Monosaccharide derivatives
•
Disaccharides• Two monosaccharides connected with
glycosidic linkage
• Characterized by:
Four Important
• Maltose:
• Cellobiose:
• Lactose:
• Sucrose:
Digestion of Carbohydrates
• Large saccharides
• They must be broken down
Polysaccharides
• Large numbers of monosaccharide residues
Polysaccharides
• Differ from each other in many ways
Starch
• Amylose:
• Amylopectin: branched D-glucose
• Glycogen:
Digestion of Starch
• Digested to D-glucose in intestines by amylase
• Neither
• Dextrin is digested by
Starch Digestion
• Some
• Some polymerized
• Extra glucose (beyond needed)
• When needed,
Cellulose
• Structural polysaccharide
• Most abundant organic compound in biosphere
• Cotton is nearly pure cellulose
• Linear polyglucose: B(1-4) linkages
Starch and Cellulose
• A(1-4)• Add water?• Food for humans• Links not allow for
extended conformations
• Form helices fig 18.14
• B(1-4)• Add water?• Not good food• Links allow for
extended 3D conformations
• Fig 18.13 p 547
Cellulose - uses
• Build houses
• Fabrics –
• Paper
• Starting point
Cell recognition
• Process that ensures cells interact as they should within the organism
• Due to presence of
• Usually
Photosynthesis
• Source of energy for non-plant life and all organic molecules used
• Process of carbon fixation
Photosynthesis
• Plants convert glucose and other monosaccharides to: