Lecture Notes on DNA Chapter

Introduction

• Chapter Location: Paper 2
• Marks: Approx. 27 marks
• Study Tip: Always refer to exam guidelines to focus study efforts.

General Cell Structure

• Focus Areas: Ribosomes, cytoplasm, nucleus parts.
• Nucleic Acids: DNA and RNA, both made up of nucleotides.

Ribosomes

• Function: Responsible for protein synthesis (production).
• Structure: Composed of a large and a small subunit.

Cytoplasm

• Description: Jelly-like fluid, mostly salt and water.
• Function: Gives cell shape, keeps organelles in place.

Nucleus

• Function: Stores hereditary material (DNA), coordinates activities like protein synthesis and cell division.
• Structure: Includes endoplasmic reticulum, nucleolus, nuclear membrane, nucleoplasm, chromatin.
  • Nuclear Membrane: Porous, allows material transport.
  • Nucleoplasm: Jelly-like fluid inside nucleus.
  • Nucleolus: Produces RNA and ribosomes.
  • Chromatin Network: Composed of DNA and proteins, forms chromosomes when condensed.

Nucleic Acids

• Types: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid).
• Function: Control protein synthesis.
• Structure: Made up of nucleotides (nitrogenous base, penta sugar, phosphate group).

DNA Structure and Function

• Locations: Found as nuclear DNA and mitochondrial DNA.
• Shape: Double helix, can be illustrated with a stick diagram.
• Function: Carries hereditary information, codes for protein synthesis.

Historical Discovery

• Key Figures: James Watson, Francis Crick, Rosalind Franklin, Maurice Wilkins.
• Important Event: X-ray photo of chromosome by Franklin (Photo 51), led to double helix model.
• Controversy: Franklin's contribution was pivotal, but she was not awarded a Nobel Prize.

DNA Structure Details

• Components: Nucleotides made of nitrogenous base, phosphate, and sugar.
• Nitrogenous Bases: Adenine (A), Thymine (T), Guanine (G), Cytosine (C).
  • Base Pairing Rule: A with T, G with C.
• Bonding: Weak hydrogen bonds between bases, enabling unzipping for replication.

DNA Replication

• Process: Occurs in nucleus during interphase.
• Steps:
  • DNA unwinds and unzips.
  • Free nucleotides form complementary strands.
  • Results in two genetically identical DNA molecules.
• Importance: Ensures identical DNA is passed to daughter cells, maintains chromosome number.

DNA Profiling (Fingerprinting)

• Definition: Mapping DNA or determining its sequence.
• Applications: Crime investigation, paternity testing, identifying organisms and missing persons, genetic disorder testing, organ transplant matching.

Interpreting DNA Profiles

• Use in Crime: Match DNA on evidence (e.g., murder weapon) with suspects.
• Paternity Testing: Match child's DNA with potential fathers.

Conclusion

• This lecture covered the foundational concepts of DNA necessary for understanding its role in cell functions, replication, and applications in DNA profiling. Additional resources include videos on the discovery of DNA for further exploration.