Protein Synthesis_ An Overview.ppt by hcj


									Protein Synthesis: An Overview

          SBI 4UI – 5.2
         Where is the DNA?
• Cytoplasm?
• Nucleus?
• Outside the cell?
            Central Dogma
• DNA is too important to leave the nucleus
• Plus, there are only 2 copies of DNA in a
  somatic cell
• Plus, ribosomes often need to make large
  amounts of protein
• Plus, DNA would then have to reenter the
• What to do?
            Central Dogma
• Messenger RNA (mRNA)
• DNA is transcribed into mRNA
• mRNA can travel to ribosomes to translate
  into polypeptide chains
• This process in known as the central dogma
  of molecular genetics
• DNA à mRNA
• Transcription is like making a carbon copy
• Ribosomes
• mRNA à amino acid sequences
• Translation is like translating
       Ribonucleic Acid
      DNA                  RNA
 Carries genetic      Carries genetic
 information          information
Deoxyribose sugar      Ribose sugar
Adenine pairs with   Adenine pairs with
thymine              uracil
 Double stranded      Single stranded
                     Resides in nucleus
Resides in nucleus
                     and cytoplasm
            Messenger RNA
• Varies in length
• Intermediary between DNA and ribosomes
  – Like a blueprint for protein production
• Contains codons
            Transfer RNA
• Delivery system of amino acids to
  ribosomes as they make proteins
• Very short (70-90 base pairs)
• Contains anticodons
           Ribosomal RNA
• Central component of the ribosome
  – Protein manufacturing machinery
• Varies in length
• Initiation
  – RNA polymerase binds to the promoter
• Elongation
  – Begins adding ribonucleotides à mRNA
• Termination
  – “Stop” signal ends transcription and mRNA is
• Initiation
   – Ribosome recognizes a sequence on mRNA and binds
     to it
   – Ribosome moves along mRNA 3 nucleotides at a time
     (3 nucleotides = 1 amino acid)
• Elongation
   – tRNA delivers appropriate amino acid
• Termination
   – 3 base nucleotide codes as “stop” signal and
     polypeptide is released
              Genetic Code
• 20 amino acids, but only 4 bases
• Triplet(3) of nucleotides = codon
  – 43 = 64 possible combinations
• Start codon signals initiation
• Stop codon signals termination
                  To Do:
• Section 5.2
  – Understanding Concepts #1-11

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