RNA: Structure, Function, and Synthesis

RNA: Structure and Function

• RNA is a macromolecule closely related to DNA, playing important roles in protein synthesis, communicating cellular signals, and catalyzing chemical reactions.
• Major RNA classes include:
  • Messenger RNA (mRNA): carries information about a protein sequence to the ribosomes; synthesized inside the nucleus; a group of 3 nucleotides in mRNA makes up a codon.
  • Ribosomal RNA (rRNA): comprises the majority of RNA found in typical eukaryotic cells; catalytic component of the ribosome; combines with proteins to form the ribosome.
  • Transfer RNA (tRNA): small RNA with approximately 80 nucleotides; transfers amino acids to growing polypeptide chains at the ribosomal site of protein synthesis; important regions include the anticodon (complementary to the codon in mRNA) and the site for amino acid attachment.

Central Dogma of Molecular Biology

Replication

• Process that synthesizes DNA by copying existing DNA; occurs in the nucleus during the Synthesis Phase of the cell cycle prior to cell division.
• Models of DNA replication include:
  • Conservative Model: the two parental DNA strands separate and act as templates for the synthesis of new DNA strands; the two parental strands re-pair or reassociate after acting as templates.
  • Semiconservative Model: the two parental DNA strands separate and act as templates for the synthesis of new DNA strands; the two parental strands do not re-associate; supported by the experiment of Matthew Meselson and Franklin Stahl.
  • Dispersive Model: each strand of both daughter molecules contains a mixture of old and newly synthesized DNA.
• Proteins required for replication include:
  • Helicase: unwinds DNA strands apart ahead of the DNA polymerase.
  • Topoisomerase: relieves torsional stress ahead of the replication fork.
  • Primase: copies a DNA template strand by making an RNA strand complementary to it.
  • DNA polymerase III: major polymerizing enzyme that catalyzes the formation of phosphodiester bonds (in the presence of an RNA primer).
  • Single-strand DNA-binding protein: binds single-stranded DNA, keeping them from re-associating.
  • DNA polymerase I: enzyme with exonuclease function (removes RNA primers) and polymerase function (replaces primers with deoxynucleotides).
  • DNA ligase: catalyzes covalent joining of the lagging strand pieces.

Transcription

• Synthesis of RNA molecules, particularly mRNA, using dsDNA as the template.
• Occurs inside the nucleus.
• Involves three stages: initiation, elongation, and termination.

This quiz covers the molecular structure and functions of RNA, including its role in protein synthesis, cell signaling, and chemical reactions. It also explores the different classes of RNA, such as mRNA.