DNA/RNA

Overview of DNA and RNA

  • Single-Stranded DNA Sequence

    • Codons: Groups of three nucleotide bases that code for amino acids in proteins.

DNA Replication

  • Complementary Strand Creation

    • Example: For the DNA codon TAC, the complementary sequence is ATG.

Transcription Process

  • Transcription Definition: The process of creating messenger RNA (mRNA) from a DNA template.

  • Example:

    • DNA Sequence: TAC

    • Resulting mRNA: AUG

  • Key Point: In RNA, uracil (U) replaces A

Types of RNA Involved in Translation

  • Messenger RNA (mRNA): Carries the genetic information from DNA.

  • Ribosomal RNA (rRNA): Constitutes the structure of ribosomes, the protein synthesis machinery.

  • Transfer RNA (tRNA): Delivers the correct amino acids to the ribosome based on the codon sequence in the mRNA.

Translation Process

  • The role of tRNA includes the following:

    • Each tRNA has an anticodon complementary to the mRNA codon.

    • It carries a specific amino acid corresponding to its anticodon.

  • Amino Acid Sequence Formation: Determined using a codon chart; example of start codon is AUG coding for Methionine (MET).

Stopping Translation

  • Point of Termination: When the ribosome reaches a stop codon, translation ceases, releasing the newly formed protein.

Introduction to Mutations

  • Definitions:

    • Genotype: Genetic makeup, represented by letters (e.g., A, T, C, G).

    • Phenotype: Physical characteristics resulting from the genotype.

Types of Mutations

Point Mutations

  • Definition: A mutation involving a single base substitution, altering one nucleotide in the DNA sequence.

  • Types of Point Mutations

    • Missense Mutation:

    • Changes one amino acid in the protein sequence, potentially altering its function.

    • Example: A change from CCG to TCG results in the amino acid change from Glycine (GGC) to Serine (AGC).

    • Nonsense Mutation:

    • Substitution results in a premature stop codon, truncating the protein.

    • Example: Change from AAG to UAG stops the translation process early.

    • Silent Mutation:

    • Does not affect the amino acid sequence due to redundancy in the genetic code.

    • Example: TTC changes to TTT still encodes for the same amino acid (Lysine).

Frameshift Mutations

  • Definition: Resulting from insertions or deletions that alter the reading frame of the code.

  • Effects include complete changes in the subsequent amino acid sequence, usually leading to non-functional proteins.

Mutation Origins

  • Spontaneous Mutations: Errors during DNA replication not caught by DNA polymerase.

  • Induced Mutations: Caused by external agents known as mutagens (chemical or radiation).

  • Examples of Mutagens: X-rays or chemicals that may incorporate into DNA or cause structural damage.

Radiation Effects on DNA

  • Thymine Dimers: Formed when UV light causes neighboring thymine bases to bond together instead of across strands, creating kinks in the DNA helix.

  • Repair Mechanisms:

    • Nucleotide Excision Repair: Enzymatic removal of damaged DNA followed by synthesis of new DNA segments.

    • Photoreactivation: Light-dependent repair that cleaves thymines bonded together.

Gene Transfer Mechanisms

Vertical Gene Transfer

  • Transfer from parent to offspring in asexual reproduction, causing identical genetic copies.

Horizontal Gene Transfer

  • Genetic material transfer between organisms of the same generation, enhancing genetic diversity.

  • Methods of Horizontal Gene Transfer:

    • Conjugation: Direct transfer between bacteria via a conjugation pilus.

    • Transformation: Uptake of free DNA from the environment by bacteria.

    • Transduction: DNA transfer mediated by bacteriophages (viruses that infect bacteria).

Genetic Engineering

  • Definition: Manipulation of an organism's DNA for beneficial purposes, often using microbes like bacteria and yeast.

  • Tools Used: Plasmids can serve as vectors to transfer genetic material.

Polymerase Chain Reaction (PCR)

  • Purpose: Amplifies DNA to produce multiple copies from a small sample.

  • Applications: Used in diagnostics, forensic science, and genetic research.

  • Basic Steps:

    • Denaturation: Heat separates DNA strands.

    • Annealing: Primers attach to the single strands.

    • Extension: DNA polymerase synthesizes new strands, doubling the amount of DNA with each cycle.

CRISPR Technology

  • Function: A gene-editing tool enhancing the ability to target and modify specific sequences in an organism's DNA.

  • Applications: Potentially treating genetic disorders and various diseases.

mRNA Vaccines

  • Mechanism: Inject RNA coding for viral proteins, prompting an immune response without using live pathogens.

  • Benefits: Simpler and faster production, offering an efficient approach to vaccination against emerging infections and diseases.

Conclusion

  • Understanding DNA function, mutation types, and genetic manipulation techniques is crucial for advancements in genetics, medicine, and biotechnology.