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: