Carbohydrates (unit 2)

What are the four major classes of carbohydrates and formula?

monosaccharides : single carbonyl group and 2/more hydroxyl groups

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disaccharides

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polysaccharides

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oligosaccharide: sugars linked by glycosidic bonds

.C_nH₂O_y

Role of carbohydrates

-Chemical energy( glucose, starch, glycogen)

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-supportive structures(Cellulose, crustacean shells)

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-Essential components of nucleic acids

What are monosaccharides and what is their general formula?

Simple sugars that cannot be broken down further; general formula (CH₂O)ₙ

How are monosaccharides named ?

-based on number of C present

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-the first part of the name represents the number of carbon atoms present and the suffix –ose then added

What three criteria are used to classify monosaccharides?

-Number of carbon atoms

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-position of carbonyl group

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-chirality of molecule

What are the names and molecular formulas of monosaccharides with 3–7 carbons?

Triose C₃H₆O₃; Tetrose C₄H₈O₄; Pentose C₅H₁₀O₅; Hexose C₆H₁₂O₆; Heptose C₇H₁₄O₇

How does the position of the carbonyl group classify monosaccharides?

Terminal carbonyl forms an aldose; molecule aldehyde

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internal carbonyl forms a ketose molecule ketone

Egs of aldoses and ketose

What does chirality mean in monosaccharides and what makes a carbon chiral?

Not superimposable on mirror image; carbon bonded to four different groups

How are D- and L- monosaccharides distinguished? bk

By spatial arrangement around the chiral carbon; D or L written before the sugar name

diagram bk

bk

What two structural forms can monosaccharides adopt and how are they represented?

Linear form as Fischer projection and ring form as Haworth projection

Which monosaccharides predominantly exist in ring form and why?

Hexoses because they form stable 5- or 6-membered rings

What is the difference between pyranose and furanose rings with examples?

-Pyranose is a 6-membered ring (glucose and galactose)

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-A five-membered ring is called a Furanose e.g. fructose

What forms when alcohol reacts with the carbonyl group of a monosaccharide?

A hemiacetal or hemiketal formed under acid or base catalysis

Why are Hemiacetals/hemiketals are usually unstable molecules and in an equilibrium mixture

Since the reaction is reversible they can easily break back down into a carbonyl compound and alcohol as the reaction is reversible

When the hydroxyl is apart of the same molecule with the carbonyl group what occurs

-A 5 or 6 membered ring can be formed

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-The tendency for this reaction to occur in a six-carbon aldose is greater because the hydroxyl and aldehyde functional groups are contained within the same molecule, and the intramolecular reaction can produce a relatively stable 6-membered ring

Why are cyclic hemiacetals more stable in monosaccharides?

They form stable intramolecular 5- or 6-membered rings

What are α and β anomers and how do they differ?

Isomers differing in OH orientation at the anomeric carbon (Carbon to the right of O₂)

What are the rules for converting a Fischer projection to a Haworth projection?bk

bk

What is mutarotation and in which sugars does it occur?

-The gradual change in specific rotation

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-Interconversion of α and β anomers in reducing sugars

What is the equilibrium ratio of glucose anomers in solution?

Approximately 36% α-glucose and 64% β-glucose(more stable as two OH groups allow electron repulsion allowing more space

How are glycosides formed and what bond is created?

Hemiacetal reacts with alcohol to form acetal or ketal ;

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- O-glycosidic bond (from anomeric carbon to the OR- group)

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-This bond links sugars together to form disaccharides and polysaccharides

Another name for glycosides and show acetal reaction bk

acetal (bk)

Why do glycosides not undergo mutarotation and how are they hydrolyzed?

Acetal form is locked

an acetal unlike the hemiacetal is no longer in equilibrium with the open-chain carbonyly containing compound

; hydrolyzed in aqueous acid to yield an alcohol and monosaccharide

How are glycosides named?

Alkyl group name followed by carbohydrate name ending changed from -e to -ide

How are monosaccharides reduced to alditols and what reagents are used?

Carbonyl reduced to hydroxyl using H₂ with catalyst or sodium borohydride

What happens when ketoses are reduced?

Two diastereomeric alditols are formed (e.g. fructose → sorbitol and mannitol)

How are alditols named and give an example?

Drop “-ose” and add “-itol”; glucose → glucitol (sorbitol)

Where is sorbitol found and what is its biological significance?

Fruits; sugar substitute; excess causes cataracts due to aldose reductase activity

What defines a reducing sugar and what product is formed on oxidation?

A sugar that oxidizes to form an aldonic acid

What is the difference between aldonic acids and aldaric acids?

Aldonic acids form by oxidation of aldehyde group; aldaric acids form when both ends are oxidized

How are uronic acids formed and give important examples?

Oxidation of C-6 primary alcohol; glucuronic acid (detoxification)

How do reducing sugars react with Benedict’s reagent?

Reduce Cu²⁺ to form a carboxylic acid

Compare glucose

fructose

What are disaccharides and how are they formed?

Two monosaccharides linked by an O-glycosidic bond via condensation

What glycosidic linkages commonly occur in disaccharides?

1→4 and 1→6 glycosidic bonds

What monosaccharides make up sucrose and is it a reducing sugar?

Glucose and fructose; non-reducing

What glycosidic bond forms sucrose?

α-1

What is invert sugar and why is it sweeter than sucrose?

Hydrolyzed sucrose producing glucose and fructose; fructose is sweeter

What are the biological effects of sucrose consumption?

Rapid energy release; excess causes tooth decay and chronic disease risk

What is lactose composed of and why is it a reducing sugar?

Glucose and galactose; free anomeric carbon present

Which enzyme digests lactose and what causes lactose intolerance?

Lactase; deficiency leads to intolerance

How is lactose used industrially?

Pharmaceutical diluent

What is maltose composed of and is it fermentable?

Two glucose units; fermentable by yeast

What glycosidic bond is present in maltose?

α-1

What are oligosaccharides and their general functions?

3–10 monosaccharides; receptors

What are raffinose and stachyose and where are they found?

Raffinose is trisaccharide; stachyose is tetrasaccharide; found in beans and vegetables

How are oligosaccharides related to blood groups?

Surface oligosaccharides determine blood groups A

What are polysaccharides and their two main categories?

High-molecular-weight carbohydrates; homopolysaccharides and heteropolysaccharides

What defines homopolysaccharides and give examples?

Yield one monosaccharide on hydrolysis; starch

What are the two components of starch and their structures?

Amylose (straight chain) and amylopectin (branched)

Which enzymes digest starch and what products are formed?

α-amylase and α-1

How does glycogen differ structurally from starch?

Glycogen is more highly branched

Why is glycogen biologically important?

Rapid energy storage; supports endurance and muscle activity

What glycosidic linkage is found in cellulose and why is it significant?

β-1

Why is cellulose important in human nutrition and ruminants?

Dietary fiber for humans; digested by microbes in ruminants

What defines heteropolysaccharides?

Yield more than one type of monosaccharide on hydrolysis

Describe the occurrence

structure

What is chondroitin sulfate and why is it important?

Cartilage component; resists compression; osteoarthritis treatment

Where is heparin found and what is its function?

Liver and lungs; anticoagulant preventing blood clots

What is chitin made of and where is it found?

β-1

What is chitosan and list its applications

Soluble fiber; antifungal

What are major industrial uses of cellulose?

Paper

What are key industrial uses of starch?

Papermaking

What are industrial uses of chitin?

Stabilizers