CHAPTER 4 Biological molecules 1

Page 1: Biological Molecules

Overview

• Biological molecules are essential for life and play a crucial role in cellular functions.

Page 2: Chemical Elements

Categories of Biological Molecules

• Most biological molecules fall into three primary categories:

  • Carbohydrates

    • Composed of carbon, oxygen, and hydrogen.

  • Proteins

    • Contain carbon, oxygen, hydrogen, and nitrogen; may also include sulfur in small amounts.

  • Lipids

    • Composed of carbon, oxygen, and hydrogen.

Page 3: Large Molecules from Smaller Molecules

Carbohydrates

Carbohydrates consist of long chains of simple sugars.

• Types of Carbohydrates:

  • Monosaccharides:

    • e.g., Glucose (simple sugar).

  • Disaccharides:

    • e.g., Maltose (formed by joining 2 glucose molecules).

  • Polysaccharides:

    • e.g., Starch, glycogen, and cellulose (formed by many glucose molecules).

Page 4: Fats (Lipids)

Structure of Fats

• Most dietary fats are triglycerides, which consist of:

  → 1 Glycerol molecule + 3 Fatty Acid chains.

• (Fatty acids vary in size and structure)

• Lipids are divided into two categories:

  • Fats → Solid at room temperature.

  • Oils → Liquid at room temperature.

Page 5: Proteins

Structure of Proteins

• Composed of long chains of amino acids (around 20 different types).

• Each amino acid consists of a similar basic structure but has a unique 'R' group.

• Small differences in amino acid sequence yield different proteins.

Page 6: Food Tests - Testing for Glucose

Glucose Test Procedure

• Materials: Benedict's solution, food sample, water bath.

• Method:

  1. Add Benedict's solution to the food sample in a test tube.

  2. Heat at 60-70°C in a water bath for 5 minutes.

  3. Observe the color change.

     → Benedicts solution + Glucose = to orange or brick red

• Result:

  • Positive test shows a color change from blue to orange or brick red.

• Negative test: remains blue, indicating the absence of reducing sugars.

• Safety Precautions: Handle test tube with tongs, wear safety goggles, use heatproof gloves.

Page 7: Test for Starch Using Iodine

Iodine Test Procedure

• Materials: Iodine food sample.

• Method:

  1. Add Iodine solution to the food sample.

  2. Observe the color change.

     → Starch + Iodine = Blue-black color change.

• Result:

  • Positive test shows a color change from previous colour to blue-black.

• Negative Test: Iodine does not change color with maltose molecules.

• Example: Potato contains starch, turning iodine blue-black.

Page 9: Test for Protein

Procedure for Protein Testing

• Materials: Biuret solution, food sample, test tube.

• Method:

  1. Add Biuret solution to food sample, in the test tube.

  2. Mix gently

  3. Observe the color change.

     → biuret solution + protein = colour change to violet/ purple

• Result: Positive test shows a color change from blue to violet/purple.

• Negative test: remains blue, indicating the absence of proteins in the food sample.

Page 10: Test for Lipids

Lipid Testing Steps

• Materials: 2cm³ ethanol, food sample, testing tube.

• Method:

  1. Mix food sample with 2cm³ ethanol and shake.

  2. Add an equal volume of cold water.

  3. Observe the color change.

     → ethanol + fats = cloudy white emulsion

• Result:

  • Positive test shows a color change from previous colour to blue-black.

• Negative Test: No color change occurs, indicating the absence of fats in the sample.

Page 11: Test for Vitamin C

Vitamin C Testing Method

• Materials: 1cm³ DCPIP, food sample solution, testing tube.

• Method:

  1. Add 1cm³ of DCPIP to a test tube.

  2. Add a small amount of food sample (as a solution).

  3. Observe the color change.

     → DCPIP + Vitamin C = loss of colour

• Result:

  • Positive test shows blue dye color disappears turning colorless.

• Negative Test: Colour remains blue.

Page 12: Exam Tip for Food Tests

Important Examination Advice

• When describing food tests, mention the starting color and the end color resulting from a positive test.

Page 13: Structure of DNA Molecule

DNA Overview

• DNA (contains instructions for the growth and development of organisms).

• Consists of two strands of DNA in a double helix formation.

• Individual units of DNA are called nucleotides.

Page 14: Nucleotide Structure

Components of a Nucleotide

• Each nucleotide contains:

  • Backbone of DNA strand: Phosphate group.

  • Backbone of DNA strand: Deoxyribose sugar.

  • Base: A nitrogenous base (A, T, C, or G).

Page 15: Base Pairing

Base Pair Specifications

• Base pairing rules:

  • Adenine pairs with Thymine (A-T).

  • Cytosine pairs with Guanine (C-G).

Page 16: Structure of DNA-Strands

DNA-Backbone and Base Pair Interaction

• The sugar-phosphate backbone looks like the sides of a ladder.

• Base pairs connect to form the rungs of the ladder.

• Gene Definition: Gene is a sequence of bases, not base pairs.

Page 17: Gene Composition

Key Points on Genes

• Each DNA strand is separate and holds genetic information as sequences of bases.

• DNA helix structure is stabilized by hydrogen bonds.

• Exam Tip: Remember base pairings (A-T, C-G)