Lecture on Transcription and Translation

Introduction

• Purpose: How DNA becomes proteins.
• DNA is a recipe for assembling proteins.
• DNA remains in the nucleus, only mRNA exits to the cytoplasm.

Processes Overview

• Transcription: DNA to mRNA in the nucleus.
• Translation: mRNA to protein on ribosomes in the cytoplasm.

Importance of mRNA

• DNA is protected in the nucleus.
• Allows multiple mRNAs to be made at once for efficient protein synthesis.

Transcription

• Location: Nucleus.
• Differences from DNA replication:
  • Copying only one gene (region of DNA), not entire DNA.
  • Continuous process, unlike DNA replication which occurs once per cell cycle.
• RNA Structure:
  • String of nucleotides with ribose sugar.
  • Bases: Adenine (A), Guanine (G), Cytosine (C), Uracil (U).
  • Complementary base pairing: DNA A = mRNA U; DNA T = mRNA A; G = C; C = G.
• Transcription Process:
  • Only one DNA strand is read.
  • RNA polymerase creates complementary mRNA.
  • mRNA exits nucleus to ribosomes.
  • Promoter sequence indicates the start of a gene.

Types of RNA

• mRNA (Messenger RNA): Carries genetic information.
• rRNA (Ribosomal RNA): Part of the ribosome.
• tRNA (Transfer RNA): Carries amino acids for protein synthesis.

Translation

• Codons: Triplets of bases on mRNA.
  • Each codon specifies one amino acid.
  • Universal genetic code for all organisms.
  • Redundancy in the code (e.g., multiple codons for glycine).
• Process:
  • Ribosome reads mRNA codons.
  • tRNA delivers amino acids based on anticodon matching with mRNA codon.
• Ribosome Functionality:
  • Start (AUG) and stop codons regulate translation.

Example of Protein Synthesis

• Transcribe DNA to mRNA.
• Translate mRNA to amino acid sequence.
  • Example DNA: ATGCCTAT
  • mRNA: AUGCCUAU
  • Protein: Methionine, Alanine, Tyrosine.

Mutations and Impact

• Single base change can lead to incorrect amino acid.
• Misfolded proteins can lead to disease or dysfunction.

Conclusion

• Transcription and translation are vital for protein synthesis.
• Occurs continuously in cells, essential for cellular function.

Visual Aid

• A video clip depicting the dynamic process of transcription and translation was suggested for a better understanding of the continuous nature of these processes.