Monomers & Polymers

Spec Reference: 3.1.1, 3.1.2, 3.1.3, 3.1.4

Explain how plants & animals containing the same amino acids to make proteins suggests evidence for the theory of evolution

Amino acids being present within plants & animals suggests that they have all descended from the same ancestor, meaning plants & animals have evolved overtime, which is why they are mainly different but share some similarities overall

Monomer

A small, single molecular unit which can join together to form polymers

Polymer

A long, complex molecule composed of monomers

Give 3 examples of Monomers

Monosaccharides, amino acids & nucleotides

Give 3 examples of Polymers

Carbohydrates, proteins & nucleic acid

Condensation Reaction

The formation of a chemical bond between monomers involving the release of a water molecule

Hydrolysis Reaction

Breaking down a polymer into multiple monomers by breaking the chemical bond between them using a water molecule

What elements do all carbohydrates contain?

Carbon, Oxygen & Hydrogen

Monosaccharide

A monomer of carbohydrates

Give 3 examples of Monosaccharides

Glucose, Fructose & Galactose

Isomer

Molecules with the same molecular formular, but with the atoms connected in a different way

Draw alpha-glucose

Draw beta-glucose

Disaccharide

Two monosaccharides joined together by a glycosidic bond via a condensation reaction

Give 3 examples of Disaccharides

Sucrose, Lactose & Maltose

How is maltose formed?

By a condensation reaction between two alpha-glucose molecules

How is sucrose formed?

By a condensation reaction between a glucose molecule & a fructose molecule

How is lactose formed?

By a condensation reaction between a glucose molecule & a galactose molecule

What are the two types of sugars?

Reducing sugars & non-reducing sugars

Examples of Reducing Sugars

Monosaccharides, maltose & lactose

How to test for reducing sugars

Add blue benedict’s reagent to a sample & heat it in a water bath until it has been brought to a boil:

If positive - the sample will form a precipitate which will go green —> yellow —> orange —> brick red. The higher the conc. of reducing sugars, the further the colour change goes

If negative - the sample stays blue & no reducing sugars are present

How to compare the amount of reducing sugars in different solutions

Complete the benedict’s test on both solutions. Filter the solutions & weigh the amount of precipitate.

Or

Complete the benedict’s test on both solutions. Filter the solutions & use a colorimeter to measure absorbance of both amounts of precipitate.

How to test for non-reducing sugars

Add blue benedict’s reagent to a sample & heat it in a water bath until it has been brought to a boil:

If positive - the sample will form a precipitate which will go green —> yellow —> orange —> brick red. The higher the conc. of reducing sugars, the further the colour change goes. This shows that reducing sugars are present

If negative - the sample stays blue & no reducing sugars are present

Then, heat a new sample of dilute hydrochloric acid then neutralize it with sodium hydrocarbonate. Reheat sample with benedict’s reagent

If positive - the sample will form a precipitate which will go green —> yellow —> orange —> brick red. The higher the conc. of reducing sugars, the further the colour change goes. This shows that non-reducing sugars are present

If negative - the sample stays blue & no non-reducing sugars are present

Polysaccharide

A polymer formed when more than two monosaccharides join together in a condensation reaction

Give 3 examples of Polysaccharides

Starch, Glycogen & Cellulose

Starch

The store of excess glucose in plants

What two polysaccharides make up Starch?

Amylose & Amylopectin

Amylose

• Long, unbranched helix chain of alpha-glucose monomers

• Bonded via 1-4 glycosidic bonds

• The angle of these bonds give it a coiled shape, making it compact & therefore very good for storage

• 20% of Starch

Amylopectin

• Long, branched chain of alpha-glucose

• Mostly bonded by 1-4 glycosidic bonds, but when it branches, its forms a 1-6 glycosidic bond instead

• Branching allows enzymes to break down the glycosidic bonds easily, resulting in quicker release of glucose

• 80% of Starch

Glycogen

The storage of excess glucose in animals

Properties of Glycogen

• Long, branched chain of alpha-glucose

• Contains much more side branching than amylopectin, which helps it to release glucose quicker

• Compact so good for storage of glucose

Cellulose

Provides structural support for the cell wall in plant cells

Properties of Cellulose

• Long, straight, unbranched chains of beta-glucose

• Singular straight chains of cellulose are bonded together by 1-4 glycosidic bonds

• When beta-glucose bonds, they invert

• Multiples straight chains of cellulose are bonded together by weak hydrogen bonds