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Understanding Transcription and RNA Polymerases

Oct 22, 2024

Lecture Notes: Transcription and RNA Polymerase

Introduction

  • Medicosis Perfectionalis presents the biochemistry playlist.
  • Previous topics: DNA vs RNA, purines vs pyrimidines, nucleosides vs nucleotides, DNA replication.
  • Today's focus: Transcription and RNA polymerase.

Question from Previous Video

  • mRNA codon: 5'AUG3'.
  • Corresponding complementary anticodon: 3'GUA5'.
  • Base pairing: G pairs with C, A pairs with U in RNA.
  • Importance of understanding codons and anticodons.

Central Dogma of Molecular Biology

  • Replication: DNA to DNA.
  • Transcription: DNA to RNA.
  • Translation: RNA to proteins.
  • DNA is located in the nucleus; RNA can leave for the cytoplasm.

Key Differences Between DNA and RNA

  • DNA: Contains thymine (T).
  • RNA: Contains uracil (U) instead of thymine.
  • Purines: Adenine (A), Guanine (G).
  • Pyrimidines: Cytosine (C), Thymine (T), Uracil (U).
  • Thiamine is a nitrogenous base; thiamine (vitamin B1) is not the same.

Summary of DNA Replication

  • Enzymes involved:
    • Helicase: Unwinds double helix.
    • Primase: Synthesizes short RNA primer.
    • DNA Polymerase: Adds new DNA nucleotides.
    • Topoisomerase: Prevents supercoiling of DNA.
  • DNA replication requires a primer.
  • Leading strand vs. lagging strand differences.

Introduction to Transcription

  • Transcription: Process of making RNA from DNA.
  • RNA Polymerase: Enzyme that synthesizes RNA.
  • Coding Strand (Sense Strand) vs. Template Strand (Antisense Strand).
  • Transcription occurs in the nucleus.

Types of RNA

  1. Messenger RNA (mRNA)

    • Carries genetic info from nucleus to cytoplasm.
    • First codon: AUG (Methionine); stop codons: UAA, UGA, UAG.
    • Synthesized by RNA Polymerase II.

  2. Ribosomal RNA (rRNA)

    • Forms the ribosome with proteins.
    • Synthesized in the nucleolus by RNA Polymerase I.

  3. Transfer RNA (tRNA)

    • Carries amino acids and matches them to mRNA codons.
    • Anticodon pairs with mRNA codon.
    • Synthesized by RNA Polymerase III.

Activation of tRNA

  • tRNA must be charged with amino acids at the 3' end.
  • Aminoacyl-tRNA Synthetase: Enzyme that attaches amino acids to tRNA, requiring ATP to form high-energy bonds.

RNA Polymerases

  • RNA Polymerase I: rRNA synthesis.
  • RNA Polymerase II: mRNA synthesis.
  • RNA Polymerase III: tRNA synthesis.
  • RNA Polymerase does not require a primer, unlike DNA Polymerase.

Post-Transcriptional Modifications

  • mRNA undergoes modifications before translation.
  • mRNA exits nucleus via nuclear pores to reach ribosomes for translation.

Mutations and Their Effects

  • Point Mutations: Silent, missense, or nonsense mutations.
    • Example: Sickle Cell Disease (missense mutation).
  • Frameshift Mutations: Shift reading frame, leading to altered protein synthesis.
    • Example: Cystic Fibrosis (frameshift mutation).

Conclusion

  • Key differences between DNA and RNA polymerases.
  • Importance of understanding each type of RNA and their functions in protein synthesis.
  • Overview of the central dogma process and mutations.

Additional Resources

  • Medicosis Perfectionalis offers various premium courses on topics like pharmacology and renal physiology on the website.
  • Encouragement to subscribe and support the channel.

Full transcript