Lecture on Transcription

Overview

• Transcription is the process of synthesizing messenger RNA (mRNA) from DNA.
• It is different from DNA replication, mitosis, or cell division.
• Essential for protein synthesis as it transfers genetic code from DNA in the nucleus to ribosomes where proteins are made.

Importance of Transcription

• Genetic instructions for protein synthesis are located in the DNA within the nucleus.
• Proteins are synthesized outside the nucleus, in the ribosomes found in the cytoplasm or rough endoplasmic reticulum.
• mRNA acts as a messenger, carrying genetic code from the nucleus to the ribosomes.

Process of Transcription

• Initiation
  • RNA polymerase enzyme attaches to a DNA segment called a gene.
  • A gene encodes a specific protein through a sequence of amino acids.
• Transcription Mechanism
  • RNA polymerase unwinds a section of the DNA helix.
  • DNA consists of two strands: template and non-template.
  • Transcription involves reading the template strand to assemble mRNA.
  • The non-template strand is not transcribed.
• Base Pairing in RNA
  • RNA polymerase uses base pair rules to match free nucleotides with the DNA template.
  • Adenine pairs with uracil (in RNA), not thymine.
  • Cytosine pairs with guanine, and vice versa.
• Completion of Transcription
  • The resulting mRNA is a complementary copy of the non-template DNA strand.
  • mRNA replaces thymine with uracil.
  • The mRNA exits the nucleus through nuclear pores to reach ribosomes.

Key Terms

• Gene: A DNA segment coding for a protein.
• Codon: A sequence of three DNA bases coding for a specific amino acid.
• Template Strand: The DNA strand read to create mRNA.
• RNA Polymerase: Enzyme that synthesizes RNA from the DNA template.

Next Steps

• Translation: The process of protein synthesis at the ribosome, covered in a subsequent session.