Topic 6.3 Lecture Notes: Flow of Genetic Information and Transcription

Key Questions Addressed in the Lecture

• Explain the overall flow of genetic information within cells.
• What are the principal forms of RNA, and what is the function of each?
• Explain what happens during transcription.

The Central Dogma of Molecular Genetics

• Flow of Information: DNA → RNA → Protein.
• Information Flow:
  • DNA triplets → mRNA codons → Amino acids.

Definition of a Gene

• Gene: Basic unit of heredity, passed from parent to offspring.
• In molecular genetics: A sequence of DNA nucleotides coding for RNA, which in turn codes for protein.

Principal Forms of RNA and Their Functions

• mRNA (Messenger RNA):
  • Linear molecule.
  • Brings instructions from DNA to ribosomes.
• rRNA (Ribosomal RNA):
  • Forms catalytic part of ribosomes.
  • Binds amino acids during protein synthesis.
  • Ribosomes are enzymes composed of rRNA and protein.
• tRNA (Transfer RNA):
  • Transports specific amino acids to ribosomes for protein synthesis.
• Small RNAs:
  • Involve various shapes and sizes.
  • Play roles in eukaryotic gene regulation.

Transcription Process

• Overview: Creation of RNA from DNA.
• Key Steps:
  • Starts at a promoter region.
  • RNA polymerase binds to the promoter and transcribes the DNA template strand into RNA.
  • Reads DNA 3' to 5'; synthesizes RNA 5' to 3'.
  • Ends at a terminator region, where RNA polymerase dissociates from DNA.

Template Strand in RNA Transcription

• Template Strand (Non-coding/Antisense/Minus Strand):
  • Transcribed into RNA.
• Coding Strand (Sense/Plus Strand):
  • Has the same nucleotide sequence as mRNA (except T is replaced with U in RNA).

Unique Features of Prokaryotic Transcription

• Prokaryotes:
  • No nucleus; genetic material is not separated from the cytoplasm.
  • Transcribed RNA can be immediately translated by ribosomes.
  • Multiple ribosomes may read the same RNA strand (polysomes).

Learn More

• Visit learnbiology.com for interactive tutorials and exam reviews.
• Free trial and guarantee of success in AP Biology exams.