Lecture 10_250 review

Exam 2 Review: Central Dogma

Key Concepts

• Overview of the Central Dogma process: Transcription and Translation in both prokaryotes (Bacteria) and eukaryotes.

Bacteria

Transcription

• Template vs. Coding Strand

  • Template Strand: The DNA strand that is used as a template for RNA synthesis.

  • Coding Strand: The DNA strand with the same sequence as the RNA (except for uracil replacing thymine).

• Initiation

  • Promoter Role: Specific DNA sequence where RNA polymerase binds to initiate transcription.

  • Sigma Factor Role: A protein that helps RNA polymerase recognize the promoter site in prokaryotic transcription.

• Elongation

  • Uracil Role: RNA polymerase incorporates uracil instead of thymine in RNA synthesis.

  • Primer Requirement: RNA synthesis does not require a primer to begin.

• Termination

  • Rho-dependent Termination: Termination occurs with the aid of a rho protein that unwinds the RNA-DNA hybrid.

  • Rho-independent Termination: Involves the formation of a hairpin loop in the RNA that causes transcription to cease.

Translation

• Roles of Key Components

  • Codon: A sequence of three nucleotides on mRNA that specifies an amino acid.

  • Stop Codon: Codons (UAA, UAG, UGA) that signal the termination of protein synthesis.

  • Start Codon: The codon (AUG) that signifies the start of translation.

  • Reading Frame: The way nucleotides are divided into codons during translation.

• Roles of Molecular Machinery

  • Ribosome Role: Cell machinery that facilitates the translation of mRNA into a polypeptide chain.

  • tRNA Role: Transfer RNA molecules that bring amino acids to the ribosome; each tRNA has an anticodon that matches the mRNA codon.

  • Release Factor Role: Proteins that recognize stop codons and help disassemble the translation complex once a protein is synthesized.

Eukaryotes

Transcription

• Initiation

  • Differences in RNA Polymerases: Eukaryotes have three types of RNA polymerases (I, II, III) compared to one in prokaryotes.

  • Number of Polymerases: Eukaryotes have three distinct RNA polymerases, each responsible for different types of RNAs (mRNA, rRNA, tRNA).

  • Transcription Factors: Proteins that assist the binding of RNA polymerase to the promoter.

• Elongation

  • Reason for RNA Processing: Pre-mRNA undergoes modifications before it can be translated, including splicing and capping.

  • Role of 5' Cap: Provides stability and aids in ribosome binding during translation.

  • Role of 3' Poly-A Tail: Increases mRNA stability and facilitates export from the nucleus.

• Termination

  • RNA Splicing: Involves the removal of introns (non-coding regions) and the joining of exons (coding regions) to produce mature mRNA.

Translation

• 5' Cap Role: Important for the initiation of translation, helps protect mRNA from degradation, and facilitates ribosome binding.