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Basic Concept of Transcription

  • Transcription: The process of synthesizing RNA from a DNA template.

The Genetic Code

  • Amino Acids: There are 20 different amino acids.
  • Nucleotide Bases: Only four bases in DNA: A, T, C, and G.
  • Triplet Code: The relationship between genes and proteins, where three nucleotides correspond to one amino acid.

Genetic Code Chart

  • RNA Codons and Amino Acids:
    • UCU → Ser
    • UAU → Tyr
    • UGU → Cys
    • UUC → Phe
    • UUA → Leu
    • UGC → Cys
    • UAA, UAG, UGA → Stop Codons
    • AUG → Start Codon (Met)

Transcription Process

  • RNA Polymerase: The enzyme that catalyzes the transcription process by unwinding the DNA strands.
  • Promoter: A sequence of DNA that initiates transcription. Includes the TATA box at the start point.

Stages of Transcription

  1. Initiation:

    • Promoter: Region of DNA where RNA polymerase binds.
    • Transcription Factors: Proteins that assist RNA polymerase in recognizing the promoter.

  2. Elongation:

    • Direction: RNA is synthesized in the 5' to 3' direction.
    • RNA polymerase adds RNA nucleotides complementary to the DNA template.
    • The transcription unit is the portion of DNA that gets transcribed.

  3. Termination:

    • The process concludes when RNA polymerase reaches a termination sequence, resulting in a completed RNA transcript.

Basic Concept of Translation

  • Translation: Synthesis of a polypeptide chain guided by mRNA.

Molecules Involved in Translation

  • mRNA: Messenger RNA that contains the genetic message.
  • tRNA: Transfer RNA that brings amino acids to the ribosome; each tRNA has a specific anticodon that pairs with mRNA codons.
  • Ribosome: The site of protein synthesis composed of rRNA and proteins.

Structure and Function of tRNA

  • tRNA Structure:
    • Single strand, ~80 nucleotides long.
    • Contains anticodon for pairing with mRNA and an amino acid attachment site.

Building a Polypeptide

  1. Initiation:

    • Start Codon: AUG, recognized by the initiator tRNA carrying Met.
    • Ribosome assembles around the mRNA, recruiting the initiator tRNA.

  2. Elongation:

    • Codon Recognition: tRNA anticodon pairs with mRNA codons.
    • Peptide Bond Formation: The amino acids are linked by peptide bonds.
    • Translocation: The ribosome moves along mRNA, continuing the elongation cycle.

  3. Termination:

    • Occurs at a stop codon (UAG, UAA, or UGA).
    • Release Factor: Protein that recognizes the stop codon, leading to release of the free polypeptide and disassembly of the translation complex.

The Wobble Hypothesis

  • Explains how a single tRNA can recognize multiple codons coding for the same amino acid, allowing for flexibility in codon-anticodon pairing.

Basic Concept of Transcription - Transcription: The process of synthesizing RNA from a DNA template.

The Genetic Code - Amino Acids: There are 20 different amino acids.

  • Nucleotide Bases: Only four bases in DNA: A, T, C, and G.
  • Triplet Code: The relationship between genes and proteins, where three nucleotides correspond to one amino acid.
Mnemonics for Genetic Code
  • Amino Acids: "A 20 Amino A