Transcription & Translation Notes

Transcription and Translation Practice

Messenger RNA Creation

  • DNA to mRNA conversion rules:
    • T in DNA becomes A in mRNA.
    • A in DNA becomes U in mRNA.
    • C in DNA becomes G in mRNA.
    • G in DNA becomes C in mRNA.
  • Example: DNA sequence T G C A C G
    • mRNA sequence: A C G U G C

mRNA Codon Grouping

  • Group the mRNA sequence into triplets (codons) to easily keep track of nucleotides.
    • Example: AUG CAU GUG GAA ACC UGU CGU UAA

Translation: mRNA to Amino Acids

  • Use a codon table (like the one on page 7) to translate mRNA codons into amino acids.
  • Each codon corresponds to a specific amino acid.
  • tRNA brings in the corresponding amino acid, and a peptide bond forms between adjacent amino acids.
  • The tRNA then leaves, and the next tRNA comes in.
Example Translation:
  • AUG - Methionine
  • CAU - Histidine
  • GUG - Valine
  • GAA - Glutamic Acid
  • ACC - Threonine
  • UGU - Cysteine
  • CGU - Arginine
  • UAA - Stop codon (signals the end of translation)

Key Terminology

  • Codon: A sequence of three nucleotides in mRNA that specifies a particular amino acid or a stop signal.
  • Anticodon: A sequence of three nucleotides in tRNA that is complementary to the codon in mRNA.
  • tRNA molecules have anticodons that pair with the mRNA codons through hydrogen bonds.

Table Completion Exercise

  • Complete a table to reinforce understanding of the relationships between DNA triplets, mRNA codons, tRNA anticodons, and amino acids.
Table Components:
  • DNA Triplet
  • mRNA Codon (complementary to DNA triplet, T becomes U)
  • tRNA Anticodon (complementary to mRNA codon)
  • Amino Acid (determined by the mRNA codon using a codon table)
Example 1
  • DNA: ATT
  • mRNA: UAA
  • tRNA: AUU
  • Amino Acid: Stop
Example 2
  • Anticodon: AUU
  • mRNA: UAA
  • DNA: ATT
  • Amino Acid: Isoleucine
Example 3
  • Amino Acid: Tryptophan (Trp), which has only one codon
  • mRNA: UGG
  • DNA: ACC
  • tRNA: ACC
Example 4
  • Codon: UUG
  • Amino Acid: Leucine
  • DNA: AAC
  • Anticodon: AAC
Quick Tip
  • The anticodon and the DNA triplet are the same unless there's a T in the triplet, which becomes a U in the anticodon.

Worksheet 9 Practice

  • Worksheet 9 involves identifying template and non-template strands of DNA, creating complementary mRNA strands, and translating mRNA into a peptide sequence.
Labeling
  • Strand 1: Complementary strand, no gene.
  • Strand 2: Template strand (contains the gene).
Complementary Base Pairing
  • Complete the complementary base pairs on the template strands (G to C, A to T, C to G, etc.).
mRNA Synthesis
  • Synthesize the mRNA strand from the template strand.
    • Example: DNA: G A C G A A C T T A T G
    • mRNA: C U G C U U G A A U A C
Ribosome and Translation Direction
  • The ribosome translates the mRNA sequence in a specific direction.
  • AUGAUG is the start codon, which codes for methionine.
Translation Example
  • mRNA Sequence in Ribosome: AUG CUU GAA GAC
  • Amino Acid Sequence:
    • AUG - Methionine
    • CUU - Leucine
    • GAA - Glutamic Acid
    • GAC - Aspartic Acid
Anticodon Pairing
  • Match tRNA anticodons to mRNA codons:
    • Methionine (AUG): UAC
    • Leucine (CUU): GAA
    • Glutamic Acid (GAA): CUU
    • Aspartic Acid (GAC): CUG