DNA Replication & Protein Synthesis

DNA Replication & Protein Synthesis

1. DNA Replication

   • 1. The hydrogen bonds between the two polynucleotide DNA strands are broken by the enzyme DNA helicase
   • 2. The original single strand acts a template for a new strand.
     • Free-floating DNA nucleotides are joined together by the enzyme DNA polymerase; hydrogen bonds form between the exposed bases following the base pairing rule.
   • Semi-conservative replication

2. DNA contains genes which are instructions for protein

   • A gene is a sequence of DNA nucleotides that codes for a protein
     • Protein are made from amino acids
     • Different proteins have a different number and order of amino acids
       • It's the order of nucleotide bases in a gene that determines the order of amino acids in a particular protein
     • Each amino acid is coded for by a sequence of three bases in a gene
       • Different sequences of bases code for different amino acids

3. Protein Synthesis

   • DNA carries the instructions to make proteins
   • Transcription
     • 1.The hydrogens bonds between the two polynucleotide DNA strands are broken temporally by the enzyme DNA helicase
     • 2. RNA polymerase reads the unzipped strand and produces mRNA
     • 3. mRNA leaves the nucleus via the nuclear pores
   • DNA molecules are too large to move out of the nucleus
   • Translation
     • The process of converting mRNA codon into a sequence of amino acids
     • 1. Initiation- A ribosome attaches to the mRNA
       • usually AUG, sometimes GUG or UUG
     • 2. Elongation- tRNA brings the corresponding amino acid to each codon as the ribosome moves down the mRNA strand
     • 3. Termination- Reading of the final mRNA codon (aka the STOP codon), which ends the synthesis of the peptide chain and releases it.