DNA Synthesis (Replication) Helicase – Separates parental DNA strands (unwind double helix) ssB (single-stranded Binding) proteins – Prevents single strands from re-associating RNA Primase – Synthesizes RNA primers, required to initiate DNA nucleotide insertion DNA Polymerase III – Responsible for synthesis of lagging strand & leading strand DNA Pol I – Removes RNA primers & Fills lagging strand gaps (Exonuclease Activity) DNA Ligase – Forms Phosphodiester bond joining 2 adjacent DNA strands
rRNA (Ribosomal RNA) – in nucleolus gives rise to ribosomal precursors; makes Ribosome, and is the central component of the Ribosome’s protein-manufacturing machinery.
mRNA (Messenger RNA) - encodes chemical "blueprint" for protein (The Genetic Code); carries coding information from Nucleus to Ribosomes (sites of protein synthesis). Details of mRNA: Encoded in sequence of nucleotides (AUCG), which are arranged into codons consisting of three bases each Each codon encodes a specific amino acid, except the stop codons • Stop codons terminate protein synthesis
tRNA (Transfer RNA) - adaptor molecule composed of RNA used to bridge the genetic code (AUCG) in mRNA with the twenty amino-acids code in proteins. Details of tRNA: The role of tRNA is to specify which sequence from the genetic code corresponds to which amino acid One end of the tRNA complements the genetic code in a three-nucleotide sequence called the anticodon On the other end of the tRNA is a covalent attachment to the amino acid that corresponds to the anticodon sequence Each type of tRNA molecule can be attached to only one type of amino acid • The genetic code contains multiple codons that specify the same amino acid; therefore, there are many tRNA molecules, each bearing a different anticodon, which also carry the same amino acid.
Translation *AUG (Methionine) – Start Codon *UAG, UGA, UAA – Stop Codons
Initiation: Binding of mRNA to small ribosomal subunit containing tRNAimet mRNA is scanned for AUG start codon First amino acid is Methionine
Elongation: Met-tRNAi already bound to (P) site mRNA codon in (A) site determines which aminoacyl-tRNA binds to (A) site Methionine binds (peptide bond) to aminoacyl1 at (A) site Methionine & aminoacyl1 translocate to (A) site, which now is (P) site – freeing (A) site for a new aminoacyl-tRNA Steps 1-3 repeat until termination
Termination: A termination (stop) codon is placed into the (A) site on the ribosome UAG, UGA, UAA There are NO tRNA anticodons that bind Stop Codons Release Factors (RF) bind to ribosome Newly peptide chain is released from ribosome