Carbohydrates

What are monosaccharides?

Monomers – single sugars named according to the number of carbon atoms in the molecule.

What elements are found in all carbohydrates?

Carbon, Hydrogen, and Oxygen.

What is the general formula for monosaccharides?

(CH₂O) or C (H₂O) or C H₂ O , where n = number of carbon atoms.

Give an example of a monosaccharide with 6 carbons (hexose sugar).

(CH₂O)₆ = C₆(H₂O)₆ = C₆H₁₂O₆.

What are structural isomers?

Molecules with the same molecular formula but different arrangements of atoms.

Give examples of structural isomers in monosaccharides.

Glucose, Galactose, and Fructose – all C₆H₁₂O₆.

Why are ribose and deoxyribose not structural isomers?

They have different molecular formulae: Ribose → C₅H₁₀O₅ Deoxyribose → C₅H₁₀O₄

Can monosaccharides exist in different structural forms?

Yes – straight chain forms or ring forms.

What is the difference between alpha (α) and beta (β) ring isomers?

The position of the OH group on carbon atom 1: Alpha (α): OH below Beta (β): OH above

What acronym helps remember α and β glucose?

ABBA → Alpha OH Below, Beta OH Above.

What is the ring structure of fructose?

A central ring of four carbon atoms and one oxygen atom, with a CH₂OH group at carbons 1 and 6.

What is the ring structure of glucose and galactose?

A central ring of five carbon atoms and one oxygen atom, with a CH₂OH group at carbon 6.

Do glucose and galactose exist in α and β forms?

Yes – they can form both alpha and beta isomers.

What is the position of the OH group on carbon 1 in α and β glucose/galactose?

α Glucose: below, β Glucose: above, α Galactose: below, β Galactose: above

What is the position of the OH group on carbon 2 in α and β glucose/galactose?

α Glucose: below, β Glucose: below, α Galactose: above, β Galactose: above

What is the position of the OH group on carbon 3 in α and β glucose/galactose?

α Glucose: above, β Glucose: above, α Galactose: below, β Galactose: below

What is the position of the OH group on carbon 4 in α and β glucose/galactose?

Below for all four (α Glucose, β Glucose, α Galactose, β Galactose).

What are disaccharides?

Sugars made from two monosaccharide units.

How are disaccharides formed?

By a condensation reaction between OH groups on two monosaccharides, with the loss of water.

What bond holds monosaccharides together in disaccharides?

A glycosidic bond.

How can a glycosidic bond be broken?

By hydrolysis – the chemical addition of water, which reforms the OH groups.

What determines the name of a glycosidic bond?

Whether the bond lies above or below the carbon atom: α (alpha) = above, β (beta) = below. The numbers of the carbon atoms that the OH groups are attached to.

What type of bond is found in maltose?

An α-1-4 glycosidic bond, where water is lost from C1 on one glucose and C4 on the second glucose.

What does hydrolysis of maltose do?

Breaks the α-1-4 glycosidic bond and reforms the OH groups.

Which two other disaccharides must you be able to recognise?

Lactose and Sucrose.

Why does fructose sometimes use carbon 2 instead of carbon 5 in bond naming?

Because fructose has the same group (CH₂OH) at both ends of the carbon chain. In this case, the smallest number is used.

What are polysaccharides?

Complex carbohydrates made of chains of monosaccharides linked by glycosidic bonds.

What types of functions do polysaccharides have?

Some are metabolic (storage and energy release), others are structural (support in cells/organisms).

Which two polysaccharides act as storage molecules?

Starch (plants) and Glycogen (animals).

What type of monomer are starch and glycogen made from?

Chains of α-glucose.

What is starch made of?

A mixture of two polysaccharides: Amylose → coiled molecules, Amylopectin → branched molecules

What type of glycosidic bonds are in amylopectin?

α-1,4 bonds within branches, α-1,6 bonds at branching points

Why does amylose coil into a helix?

Because hydrogen bonds form between Oδ⁻ on C2 of one glucose and Cδ⁺ on C3 of the next.

Why is starch suited for glucose storage?

Coiled → compact, Less soluble in water → ideal for storage, Insoluble → does not affect water potential → osmotically stable

How is glycogen similar to amylopectin?

Both are branched polymers of α-glucose.

How is glycogen different from amylopectin?

Glycogen is more highly branched, with glycosidic bonds forming between C1–C4 and C1–C6 OH groups.

What form does glycogen take in cells?

Granules that act as a carbohydrate/energy store.

Why do branches make glycogen and amylopectin efficient for glucose release?

More branch ‘ends’ means more glycosidic bonds can be hydrolysed simultaneously → faster glucose release for respiration and ATP production

What is cellulose made of?

A polymer of β-glucose molecules linked by β-1,4 glycosidic bonds.

How are the –CH₂OH groups arranged in cellulose?

On opposite sides of adjacent glucose molecules due to the β-1,4 linkage.

Why are adjacent glucose molecules in cellulose rotated 180°?

To align the OH groups so a water molecule can be removed and a glycosidic bond formed.

Do hydrogen bonds form within a cellulose chain?

No – they form between glucose molecules in different chains.

What structure results from hydrogen bonding in cellulose?

Cross-linkages hold chains together, forming long threads called microfibrils.

Why is cellulose insoluble?

Because of its tightly packed, hydrogen-bonded microfibril structure.

How are cellulose microfibrils arranged in plant cell walls?

In overlapping layers.

Why is cellulose called a structural polysaccharide?

It provides strength and rigidity in plant cell walls.

Why is cellulose difficult to digest?

The large number of hydrogen bonds between chains makes it highly resistant to breakdown.

What gives cellulose its high tensile strength?

Extensive hydrogen bonding between chains.

How does cellulose help cells resist osmotic lysis?

The strong cell wall prevents excessive water entry and bursting.

Where is chitin found?

In fungal cell walls and insect exoskeletons.

Why is chitin not considered a true polysaccharide?

It contains the element nitrogen, making it a heteropolysaccharide.

How is chitin similar to cellulose?

It has a similar structure and function, forming microfibrils.

How does chitin differ from cellulose?

Chitin has side groups containing nitrogen, which allow more hydrogen bonds to form.

How does the tensile strength of chitin compare to cellulose?

Greater tensile strength due to additional hydrogen bonding.

What is the monosaccharide unit of chitin?

N-acetyl glucosamine, joined by β-glycosidic bonds.