3.1.1-2 - Monomers and polymers + Carbohydrates

Polymers

Large, complex molecules made of long chains of monomers

Monomers

Small, basic molecular units

Monomer examples

Monosaccharides, amino acids, nucleotides

Carbohydates contain ____

C, H, O

Monosaccharide examples

Glucose, fructose, galactose

Carbohydrates are (mono/polysaccharides)

Polysaccharides

Glucose

Hexose sugar - 6 C atoms per molecule

Has 2 isomers - alpha (α) and beta (β)

α-glucose structure

(alpha - H is on top)

β-glucose structure

(beta - H is on bottom)

Condensation reaction

Two molecules join with formation of new chemical bond

+ water molecule released

Monosaccharides are joined by ____

condensation reactions

Glycosidic bond

Bond between two monosaccharides

Sucrose

Disaccharide formed by glucose + fructose (via condensation reaction)

Lactose

Disaccharide formed by glucose + galactose (via condensation reaction)

Maltose

Disaccharide formed by glucose + glucose (via condensation reaction)

Hyrolysis reactions

Breaking of chemical bond between monomers using water molecule

What is starch made of?

Mixture of amylose + amylopectin - polysaccharides of α-glucose

Plants store excess glucose as ____

starch

Why is starch good for storage?

Insoluble in water → doesn’t affect water potential

• → doesn’t cause water to enter cells by osmosis

• → good for storage

Amylose

• Long, unbranched chain of α-glucose

• Angles of glycosidic bonds → coiled structure

  • → compact

  • → good for storage

Amylopectin

• Long, branched chain of α-glucose

• Side branches allow enzymes that break down molecule to reach glycosidic bonds easily

  • → glucose can be released quickly

Glycogen

• Polysaccharide of α-glucose

• Animals store excess glucose as glycogen

Glycogen structure

• Highly branched structure

  • → stored glucose can be released quickly

• Compact

  • → good for storage

Cellulose

• Made of long, unbranched chains of β-glucose

• When β-glucose molecules bond, they form straight cellulose chains

• Cellulose chains linked by H bonds to form microfibrils (strong fibres)

  • → strong fibres make cellulose a good structural support for cells

Which sugars are reducing sugars?

All monosaccharides + some disaccharides (e.g. maltose, lactose)

Test for reducing sugars

1. Add Benedict’s reagent (blue) to sample + heat in water bath at 100ᵒC

2. If positive test, coloured ppt forms

   • Higher conc. of reducing sugar = further colour change

Test for non-reducing sugars

If reducing sugar test negative, must do non-reducing sugar test

1. Get new sample of test solution, add dilute hydrochloric acid + heat in water bath at 100ᵒC

2. Add sodium hydrogencarbonate to neutralise

3. Carry out Benedict’s test (reducing sugar test)

4. If positive test, coloured ppt forms

5. If negative, solution stays blue → no sugar in solution

Test for starch

1. Add iodine dissolved in potassium iodide solution to sample

2. If positive test, sample changes from browny-orange → blue-black