Biological Molecules (1c)

Unit 2,Structure & Functions in Living Organisms: Part 1, c

Types of Biological Molecules

Categories:

• Carbohydrates

• Proteins

• Lipids (fats and oils)

All contain carbon, so are called organic molecules

Molecules and Chemical Elements

• Carbohydrates: Carbon, Hydrogen, Oxygen

• Proteins: Carbon, Hydrogen, Nitrogen, Oxygen

• Lipids: Carbon, Hydrogen, Oxygen

Structure of Carbohydrates

• Contain C, H, O

• can be small, simple sugars or larger, more complex molecules

• monosaccharide: simple sugar, eg, glucose (C₆H₁₂O₆)

• disaccharide: two monosaccharides joined together, eg, maltose = 2 glucose joined together

• large polysaccharides: many monosaccharides joined together, eg, starch, glycogen or cellulose = many simple glucose molecules joined together

• polysaccharides: insoluble = storage molecules

Structure of Lipids

• large molecules made of smaller basic units like glycerol and fatty acids

• solid at room temperature (fats) or liquid at room temperature (oils)

Storage of Glucose: Plants vs Animals

plants: starch

animals: glycogen

Structure of Proteins

• made of smaller molecules called amino acids

• when these are joined, proteins are formed

• can be arranged in any order

• specific amino acid gives protein its shape

• shape determines function

• ex: keratin, haemoglobin

Molecule vs Monomer

• Carbohydrate : glucose

• Lipids: glycerol and fatty acids

• Protein: amino acids

Food Samples can be investigated for:

• glucose

• starch

• fat

• protein

Preparing a Sample

• break up food with a mortar and pestle

• dilute with distilled water

• stir with a glass rod to mix

• filter through filter paper and collect solution

• proceed with food tests

OR

use powdered food

Preparing a Sample: Precautions

• eye protection

• wash splashes quickly

• don’t taste food substances

• avoid spilling hot water

Test for Glucose

Benedict’s Test

• add a few drops of bright blue reagent to the sample

• heat in very hot water for 5 mins

• observe if there’s a colour change

• positive result: blue>green>yellow>orange>brick red (depending on conc.)

Benedict’s Solution: Safety Precautions

• wear safety goggles

• switch of bunsen burner after water is almost boiling / use water bath

Test for Starch

Iodine Test