Molecular Biology

Tissues, Cells & Molecular Biology

Nucleic Acids

  • Definition of Nucleic Acids:

    • Molecules of life
    • Store information (the genetic code) that controls cellular activity and organism development
    • Control protein synthesis, which forms much of the body's structure and regulates cell chemical processes

  • Types of Nucleic Acids:

    1. DNA (Deoxyribonucleic Acid)
    2. RNA (Ribonucleic Acid)

DNA – Deoxyribonucleic Acid

Organization of DNA in the Nucleus
  • DNA is organized into structures called chromosomes. Mitochondrial DNA exists separately.
Origin of Mitochondrial DNA
  • Theory: Mitochondria originated as bacteria that invaded ancestral eukaryotes and established a symbiotic relationship.
  • Over evolution, bacteria transferred some genetic material to host chromosomes but retained essential genes on mitochondrial DNA.
  • Mitochondrial DNA:
    • Inherited maternally, almost unchanged, aiding in lineage identification.
    • Study by Allan Wilson on mitochondrial DNA revealed that African lineages represented the earliest branches, leading to the concept of "Mitochondrial Eve" indicating a common female ancestor for all humans approximately 200,000 years ago.

Structure of DNA

  • Physical Structure:
    • DNA resembles a twisted ladder structure; each side (the outer strands) consists of sugar (deoxyribose) and phosphate groups, forming the sugar-phosphate backbone.
    • The rungs consist of nitrogenous bases (A, T, G, C) connected by weak hydrogen bonds.
  • Base Pairing Rules:
    • Adenine (A) pairs with Thymine (T) via 2 hydrogen bonds.
    • Guanine (G) pairs with Cytosine (C) via 3 hydrogen bonds.
  • Nucleotides:
    • Composed of a sugar, phosphate group, and nitrogenous base.
Importance of DNA
  1. Carries genetic coded information in each cell.
  2. Capable of replication (self-copying).
  3. Supervises protein synthesis indirectly.
  4. Controls cellular activities.

RNA – Ribonucleic Acid

  • Involved in protein synthesis.
  • Structure of RNA:
    • Composed of nucleotides, single-stranded, shorter than DNA.
    • Sugar is ribose; nitrogenous bases: A, C, G, and Uracil (U replaces T).
  • Types of RNA:
    • mRNA (messenger RNA)
    • tRNA (transfer RNA)
    • rRNA (ribosomal RNA)
Function of RNA
  • Carries code from DNA in the nucleus to the ribosomes in the cytoplasm, directing protein synthesis by arranging amino acids in the required sequence.
  • Protein Synthesis Process:
    1. Transcription:
    • Occurs in the nucleus; when needed, DNA unwinds at the target gene, breaking hydrogen bonds between bases, exposing coding strands.
    • RNA nucleotides align with complementary bases on the DNA strand, facilitated by RNA polymerase, forming mRNA.
    • Uracil in RNA binds to adenine in DNA.
    • mRNA departs nucleus into cytoplasm.
    1. Translation:
    • Occurs in the cytoplasm at ribosomes where mRNA binds at start codon.
    • A tRNA carrying an amino acid attaches via its anticodon to the corresponding mRNA codon.
    • Further reading of mRNA codons continues to link amino acids through peptide bonds, forming polypeptides (proteins).
Amino Acids
  • Proteins consist of sequences of amino acids; the sequence determines the specific protein produced.
  • Shortest proteins have at least 50 amino acids, while 20 different amino acids exist in nature.

Aberrations in Protein Synthesis

  • Mutations:
    • Random changes to the DNA sequence known as point mutations can lead to errors during replication, transcription, or crossing over in meiosis.
    • Mutagens (e.g., UV light, X-rays, chemicals) increase mutation rates.
Types of Mutations
  • Point Mutations:
    • Involves a single base change, which can be a substitution, addition, or deletion of nucleotides.
  • Frameshift Mutations:
    • Changes in reading frame might occur due to insertion or deletion.

DNA Technology and Applications

DNA Extraction Methods
  1. Detergent and Enzymes:
    • Lysis of cells using detergent to disrupt membranes.
    • Proteases and RNAse treatment to clear proteins and RNA.
    • Centrifugation and precipitation of DNA with ethanol.
  2. Magnetic Beads:
    • Lysis of cells using buffer, followed by binding to magnetic beads for extraction.
DNA Profiling (Fingerprinting)
  • Unique DNA patterns using gel electrophoresis create genetic fingerprints useful in forensics, paternity testing, and identifying casualties from disasters.
Ethical Concerns of DNA Technology
  • Privacy issues, decision-making power over genes, treatment productivity, and accuracy concerns.

Chromosomes and Meiosis

Chromosomal Structure
  • Chromosomes contain DNA wrapped around histones, forming chromatin. Each chromosome consists of many genes specifying traits.
Chromosome Types
  • Somatic Cells: 2 sets of chromosomes (diploid).
  • Gametes: 1 set (haploid) produced through meiosis for sexual reproduction.
Meiosis Overview
  • Importance: Reductive division in reproductive organs to produce gametes with half the chromosome number for sexual reproduction.
  • Stages of Meiosis: 1 (Reduction Division) and 2 (Mitotic Division), resulting in viability of zygotes with proper genetic material.
Key Events in Meiosis I
  • Crossing over produces genetic diversity, independent assortment further increases variability.
Defined Terms Related to Genetic Inheritance
  • Gene: Basic unit controlling traits located at specific loci on chromosomes.
  • Alleles: Variants of a gene at the same locus.
  • Phenotype: Observable traits based on genotype.
  • Genotype: Genetic makeup.

Genetic Engineering

Definitions
  • Genetic engineering: Manipulation of an organism's genetic material.
  • Recombinant DNA: DNA formed by combining sequences from different sources.
  • Transgenic Organism: Contains one or more genes from another species.
Applications of Genetic Engineering
  • Improved crop varieties, production of insulin, and genetic therapies for hereditary diseases.
    • Techniques involve plasmid vectors, viral vectors, and direct methods like microinjection or gene guns.

CRISPR Technology

  • A powerful tool for editing genomes, allowing modification of genes to treat diseases and modify traits.
  • Uses Cas9 enzyme to target and edit DNA sequences, expanding potential applications in medicine, agriculture, and conservation.
Ethical Considerations in Genetic Engineering
  • Risks related to designer babies, environmental impacts, and the balance of biotechnology benefits and societal implications.