Lecture 17.pptx

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Chapter 7



Section 7.1:

Monosaccharides



Section 7.2:

Disaccharides



Section 7.3:

Polysaccharides



Section 7.4:

Glycoconjugates



Section 7.5:

The Sugar Code

Carbohydrates

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Section 7.1:

Monosaccharides

Figure 7.1 General Formulas for the Aldose and Ketose Forms of

Monosaccharides

Figure 7.2

Glyceraldehyde (an Aldotriose) and

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Section 7.1:

Monosaccharides



Monosaccharide

Stereoisomers

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Section 7.1:

Monosaccharides



D-Ribose and L-Ribose are

enantiomers;

non-superimposible mirror images



Diastereomers

are

stereoisomers that are not

enantiomers (i.e.,not

mirror-image isomers) (i.e.,

D

-ribose

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Section 7.1:

Monosaccharides

 Diastereomers that differ at a single chiral carbon are epimers (e.g., glucose and D-galactose differ in position of –OH at C-4 and

D-glucose and D-mannose differ in position of

-OH group at C atom #2)

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Section 7.1:

Monosaccharides

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Section 7.1:

Monosaccharides

 _{The two possible}_{diastereomers}_{that form}

because of cyclization are called anomers (α or β)

Figure 7.6

Monosaccharide Structure-

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Section 7.1:Chemical reactions of

Monosaccharides



Oxidation

—

monosaccharides may readily

undergo several oxidation reactions in the

presence of metal ions or certain enzymes

Figure 7.12

Oxidation Products of Glucose

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Section 7.1: Chemical Reactions of

Monosaccharides

 _A_lactone_{can be produced if the carbonyl groups}

of aldonic or uronic acids react with an OH group in the same molecule

 _{Lactones are readily produced in nature, for}

example, L-ascorbic acid (vitamin C)

 _{Vitamin C is a powerful reducing agent that}

protects cells from reactive oxygen and nitrogen species

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

Reduction

—

Sugar alcohols (

alditols

) are

produced by the reduction of aldehyde and ketone

groups of monosaccharides

 _{Sugar alcohols are used in commercial food}

processing and in pharmaceuticals (e.g., sorbitol can be used to prevent moisture loss)

Figure 7.15 Structure of D

-Glucitol (Sorbitol)

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

Esterification

—

free OH groups of carbohydrates

can be converted to esters by reactions with

acids

 _{Esterification often dramatically changes a sugar’s}

chemical and physical properties

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Section 7.1: Examples of

Monosaccharides



Important Monosaccharides



Glucose (

_D

-Glucose)

—

originally called

dextrose, it is found in large quantities throughout

the natural world

 _{The primary fuel for living cells}

 _{Preferred energy source for brain cells and cells}

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

Fructose (

D

-Fructose)

is often referred to as

fruit sugar, because of its high content in fruit

 _{On a per}-gram basis, it is twice as sweet as sucrose;

therefore, it is often used as a sweetening agent in processed food

 _{Sperm use fructose as an energy source}

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

Galactose

is necessary to synthesize a variety of

important biomolecules

 _{Important biomolecules include lactose, glycolipids,}

phospholipids, proetoglycan, and glycoproteins

 _Galactosemia_{is a genetic disorder resulting from}

a missing enzyme in galactose metabolism

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

Monosaccharide Derivatives



Uronic Acids

:

_{D-Glucuronic acid is}

used in the liver to improve water solubility to remove waste molecules

 _{Amino Sugars}_{: D-Glucosamine (a) and}

D-galactosamine (b) are the most

common and often attached to proteins or lipids

 _{Deoxy Sugars}_{: Form of sugar found in}

DNA

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Section 7.2:

Disaccharides



Disaccharides



Two monosaccharides linked by a glycosidic

bond



Linkages are named by

a

- or

b

-conformation and

by which carbons are connected (e.g.,

a

(1,4) or

b

(1,4))

Figure 7.27

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Section 7.2:

Disaccharides



Disaccharides Continued



Lactose

(

milk sugar

) is the

disaccharide found in milk

 _{One molecule of galactose linked}

to one molecule of glucose (b(1,4) linkage)

 _{It is common to have a deficiency}

in the enzyme that breaks down lactose (lactase)

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Section 7.2:

Disaccharides



Maltose

(

malt sugar

) is an

intermediate product of

starch hydrolysis

 a(1,4) linkage between two molecules of glucose

 _{Does not exist freely in}

nature

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Section 7.2:

Disaccharides



Cellobiose

is a degradation

product of cellulose

 _{Cellobiose is composed of two}

molecules of glucose linked with a b(1,4) glycosidic bond

 _{Does not exist freely in nature}

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Section 7.2:

Disaccharides



Sucrose

is common table sugar

(cane or beet sugar) produced

in the leaves and stems of

plants

 _{One molecule of glucose linked}

to one molecule of fructose,

linked by an a,b(1,2) glycosidic bond

 _{Sucrose is a nonreducing sugar}

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Section 7.3:

Polysaccharides



Homoglycans

 _{Have one type of monosaccharide and are found in starch,}

glycogen, cellulose, and chitin (glucose monomer)

Figure 7.33 Amylose

 Starch—the energy reservoir of plant cells and a significant source of carbohydrate in the human diet

 Two polysaccharides occur together in starch: amylose and amylopectin

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Section 7.3:

Polysaccharides

Figure 7.34 (a)

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Section 7.3:

Polysaccharides



Cellulose

is a polymer of D-glucopyranosides

linked by

b

(1,4) glycosidic bonds



It is the most important structural

polysaccharide of plants (most abundant organic

substance on earth)

Figure 7.35 The Disaccharide

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Section 7.4:

Glycoconjugates

 _{Glycoconjugates}_{result from}

carbohydrates being linked to proteins and lipids

 _{Proteoglycans}

 _{Distinguished from other}

glycoproteins by their high carbohydrate content

 Have roles in organizing

extracellular matrix and are involved in signal transduction

 Metabolism of proteoglycans involved in many genetic

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Study Objectives

1. Classify monosaccahrides as isomers, and based on number of C atoms

2. Know structures and functions of monosaccharides, disaccharides, and polysaccharides

3. How does glycosidic bond formation happen? Identify compounds based on existing glycosidic bonds