Biology 40S - Molecular Genetics: Mechanisms of Inheritance

Unit Objectives

• Outline significant scientific contributions to the understanding of DNA structure and function.
• Describe the structure of a DNA nucleotide and DNA molecule.
• Explain DNA replication, including enzyme roles and semi-conservative replication.
• Compare DNA and RNA structures, uses, and cellular locations.
• Outline protein synthesis steps: mRNA, codons, tRNA, ribosome, transcription, and translation.
• Relate gene mutation consequences to protein products, with examples like sickle-cell anemia.
• Discuss gene mutation implications for genetic variation.
• Investigate gene technology applications in bioresources and humans, including ethical, legal, and societal implications.

Understanding DNA: The Molecule of Life

What are Genes?

• Genes encode instructions for proteins or traits seen in phenotypes.
• Selective gene usage in cells; genome is the full genetic information set.

Nucleic Acids

• Discovered by Fredrich Meischer in 1869.
• Store protein structure information as nucleotide sequences.
• Three types: DNA, RNA, ATP (not covered in detail).

Structure of Nucleotides

• Components: five-carbon sugar, phosphate group, nitrogen base.
• Two nitrogen base groups:
  • Pyrimidines (cytosine, thymine)
  • Purines (adenine, guanine)

Structure of DNA

• DNA is a polymer of nucleotides (A, T, C, G).
• Chargaff's Rule: Equal amounts of adenine & thymine, cytosine & guanine.
• Rosalind Franklin's X-ray diffraction suggested a double helix structure.
• Watson and Crick concluded DNA is a double helix with anti-parallel strands.

DNA Replication

• Semi-conservative process: One old strand, one new strand.
• Steps:
  1. DNA Helicase unwinds the double helix.
  2. RNA Primase adds RNA primers.
  3. DNA Polymerase III adds nucleotides.
  4. DNA Polymerase I replaces RNA primers and fills gaps.
  5. DNA Ligase seals gaps between Okazaki fragments.

Mistakes and Mutation

• Replication errors and environmental factors can cause mutations.
• Proofreading enzymes reduce replication errors.

RNA Structure and Function

• Differences from DNA: single-stranded, ribose sugar, uracil replaces thymine.

Types of RNA

• mRNA: Carries genetic information.
• tRNA: Transfers amino acids.
• rRNA: Component of ribosomes.

Protein Synthesis

Process Overview

1. Transcription: DNA to mRNA in the nucleus.
2. Translation: mRNA to protein at the ribosome.

Translation Stages

• Initiation: mRNA attaches to ribosome, start codon signals beginning.
• Elongation: tRNA brings amino acids, forming polypeptide chains.
• Termination: Stop codon ends protein synthesis.

Gene Mutation

• Point Mutations: Affect one nucleotide/amino acid.
• Frameshift Mutations: Insertion or deletion affecting downstream sequence.

Genetic Engineering

Techniques

• Gene Transfer/Recombinant DNA, DNA Mapping, PCR, DNA Profiling, Cloning.
• GMO: Organisms with engineered genes for desired traits.

Applications

• Bacteria: Produce human proteins like insulin.
• Plants: Increase yield, resistance.
• Animals: Enhance growth, disease resistance.

Ethical Considerations

• Advancements vs. risks: Ecological impact, monopolies, food safety.
• Human Genome Project revealed DNA similarities among humans, aiding genetic disorder research.

Recombinant DNA

• Uses restriction enzymes and plasmid vectors for gene splicing.

DNA Fingerprinting

• Gel electrophoresis separates DNA fragments by size.
• Polymerase Chain Reaction (PCR) amplifies DNA samples.

Gene Therapy

• Methods: Gene surgery and modification.
• Used to treat genetic disorders, though with ethical debates.

Cloning

• Natural Cloning: Asexual reproduction.
• Reproductive Cloning: Producing identical organisms.
• Therapeutic Cloning: Repairing tissues/organs from stem cells.

These notes provide a comprehensive summary of key concepts in molecular genetics, mechanisms of inheritance, and related technologies, which are crucial for understanding advanced biological processes and the ethical considerations in genetic engineering.