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DNA Replication and Protein Synthesis. Watson and Crick…again. After describing the structure of DNA, they released a second paper Basically stated that the base pairing model indicated a method for replication

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watson and crick again
Watson and Crick…again
  • After describing the structure of DNA, they released a second paper
    • Basically stated that the base pairing model indicated a method for replication
  • Each strand would serve as a template for a new companion chain, called the complement

As a result, each daughter strand has a strand from the original molecule

  • This is referred to as semi-conservative replication
  • So, from the parent strand, new bases are added to added according to the base pairing model
  • A strand of ATTCGACT would match up with TAAGCTGA
  • A wide variety of enzymes are used during the replication process (recall anything ending in –ase is an enzyme)
  • The enzyme that opens the parent molecule by breaking the hydrogen bonds is helicase
  • It “unzips” the molecule
  • The other principle enzyme is DNA polymerase (actually three variations on it!)
  • It moves along the unwound strand, adding the appropriate bases
protein synthesis
Protein Synthesis
  • Now that we know the structure of DNA, we can analyze how proteins are made
  • Broken down into two processes: transcription and translation
  • This is where RNA is used in our body
  • Structurally, RNA contains a ribose sugar
    • The 2’ carbon contains a hydroxyl group as opposed to a hydrogen
different types of rna
Different Types of RNA
  • In protein synthesis, three unique types of RNA are used:

Messenger RNA (mRNA)

  • RNA copy of the DNA strand to be “read” during translation

Transfer RNA (tRNA)

  • Carries individual amino acids to site of replication

Ribosomal RNA (rRNA)

  • Attached to ribsome complex, site of protein synthesis



  • A complementary strand of mRNA is made, first by unzipping the DNA molecule
    • This time, by RNA polymerase
  • This only happens on specific regions of DNA known as promoter regions
  • That way, it isn’t just a random region
  • Similar regions cause the transcription process to stop
rna splicing
RNA Splicing
  • Certain regions of DNA do not code for any proteins that we use, called introns
    • We mentioned these before as the “junk” regions
  • The introns must be spliced out, joining all the coding regions known as exons
  • Finally, a 5’ cap and poly A tail must be tacked on to the ends to finish the editing process
  • The processed mRNA is now reading to be decoded
  • The “language” is spoken in three base “words”

Translation begins when the mRNA binds to the rRNA on a ribosome

  • This moves along the sequence until an AUG codon is found
    • This is the start codon, and the methionine code, hence all protains begin with Met
  • tRNA then attaches and drops off the appropriate amino acid
    • It does this by have a matching anticodon
  • Sequential amino acids are linked by peptide bonds
    • So, it is called a polypeptide

This process continues until a stop codon is found

  • Polypeptide and mRNA are release
  • Polypeptide goes through up to four stages of folding to become a mature protein