National 5 Biology: DNA and the Production of Proteins

Introduction

• Focus: DNA and protein production
• Review of cell biology:
  • Cell contains a nucleus
  • Nucleus contains genetic information

Structure of Genetic Information

• Hierarchy of genetic components:
  1. Nucleus (largest)
  2. Chromosomes
  3. Genes
  4. DNA (smallest)
• Chromosomes:
  • Made up of chromatids
  • Chromatids held together by a centromere
• DNA:
  • Twisted ladder shape called double-stranded helix
  • Composed of a backbone and base pairs
  • Backbone: sugar and phosphate
  • Base pairs: adenine (A) pairs with thymine (T), cytosine (C) pairs with guanine (G)

Function of DNA

• Purpose: Genetic information in DNA is used to make proteins
• Bases in DNA:
  • A, C, G, T (adenine, cytosine, guanine, thymine)
  • Base Pairing Rule: C pairs with G, A pairs with T

Nucleotide Structure

• Components:
  • Phosphate
  • Sugar
  • Base
• Nucleotide: Basic unit of DNA comprising phosphate, sugar, and base

mRNA (Messenger RNA)

• Difference from DNA:
  • Single-stranded
  • Transports genetic information from nucleus to ribosomes
• Role:
  • mRNA carries the genetic code from DNA to the site of protein synthesis (ribosome)

Protein Synthesis Process

1. Unwinding of DNA:

• DNA double helix unwinds and unzips into two strands

2. Formation of mRNA:

• Complementary mRNA strand made
• Matches DNA base pairs (e.g., if DNA strand is ATGC, mRNA complementary strand is UACG)

3. mRNA leaves nucleus:

• mRNA exits the nucleus and travels to ribosome

4. Protein synthesis at ribosome:

• Ribosome reads mRNA strand
• Amino acids are assembled in correct order to form proteins

Exam Tips and Common Questions

• Base pairing rules: Remember A-T and C-G
• Process of protein synthesis: Understand the sequence from DNA to protein

Examples of common exam questions:

• Identifying mRNA molecule in DNA transcription
• Matching complementary DNA base pairs
• Describing basic units that make up proteins at the ribosome
• Differentiating code for different proteins (e.g., amylase vs insulin)

Summary

• Thorough understanding of DNA structure and function
• Know base pairing rules by heart
• Familiarize with the steps of protein synthesis
• Practice common exam questions related to this key area

Next Steps

• Follow up with quizzes to solidify knowledge
• Prepare for next key area in cell biology