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Protein Synthesis

Protein Synthesis. An Overview. Archibald Garrod. British physician from the 20 th century Studied patients with alkaptonuria A genetic disorder which causes black urine, containing alkapton Garrod’s Hypothesis: one gene directs the production of one enzyme

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Protein Synthesis

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  1. Protein Synthesis An Overview

  2. Archibald Garrod • British physician from the 20th century • Studied patients withalkaptonuria • A genetic disorder whichcauses black urine,containing alkapton • Garrod’s Hypothesis: • one gene directs theproduction of one enzyme • A defective enzymecauses an “inborn error ofmetabolism” which resultsin the inability to breakdown alkapton • Enzymes are controlled by heretic material • An error in heretic material meant an error in an enzyme

  3. George Beadle and Edward Tatum • Represented the relationship explain by Garrod through experiments on red bread mould, Neurosporacrassa • One strand of the mould was able to synthesize all theamino acids and vitamins it needed foroptimum growth, given minimum nutrients • Mutant strains were created using X-raysand UV lighting and were not able toreplicate with minimum nutrients • 4 mutant strains were discovered, eachhad a different defective gene • Beadle and Tatum concluded that onegene acts by directing the production of only one enzyme • Their hypothesis is known as the one gene-one polypeptide hypothesis

  4. Vernan Ingram • Studied the amino acid sequence of hemoglobin from individuals with sickle cell anemia • Discovered a base switch in one of the polypeptides • The switch caused achange in the structureof the red blood cell • Ingram’s research showedthat a gene specifies thekind and location of aminoacids in polypeptide chains • Ingram linked heretidy abnormality to a single alteration in the amino acid sequence of a protein

  5. Central Dogma • Genes are expressed in the phenotype of an individual • Two parts: Transcription & Translation • Moves in one direction: gene  protein • More than one protein is made per gene, therefore multiple copies must be made • The desired template sequence of DNA is copied (transcription) then made into a polypeptide chain (translation) • DNA  RNA  Protein

  6. Ribonucleic Acid (RNA) • Contains a ribose sugar (remember: DNA has a deoxyribose sugar) • Contains Uracile, whichpairs with Adenine, instead of Thyamine • RNA is only ever insingle-stranded form • There are 3 kinds of RNA • mRNA: messenger RNA • tRNA: transfer RNA • rRNA: ribosomal RNA

  7. Ribonucleic Acid (RNA) • mRNA • Sequence of base pairs transcribed from DNA • tRNA • Transfers the appropriate amino acids to the ribosome to build proteins • rRNA • A structural component that forms a ribosome

  8. Transcription VS Translation • Initiation • Ribosome recognises mRNA • Elongation • Amino acids are strung together • Termination • Stop codon is reached, polypeptidechain isreleased • Initiation • RNA polymerase binds to promoter region • Elongation • Building of mRNA by adding RNA nucleotides • Termination • The mRNA is finished when stop signal is reached

  9. The Genetic Code • Nucleotides are grouped in threes • Each triplet is called a codon • Four bases, in triplets give us 43 = 64 possible combinations • Each codon codes for 1/20 amino acids • Since there are 20 amino acids and 64 possible codons, multiple codons code for the same amino acids • AUG is the start codon, whereas UAA, UAG, and UGA are stop codons

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