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Protein Synthesis

Protein Synthesis. Chapter 15. Objectives. Understand the relationship between genes and proteins Understand the overall process by which genetic information is converted to polypeptide chains Recognize where, how, and why transcription occurs Recognize where, how, and why translation occurs.

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Protein Synthesis

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  1. Protein Synthesis Chapter 15

  2. Objectives • Understand the relationship between genes and proteins • Understand the overall process by which genetic information is converted to polypeptide chains • Recognize where, how, and why transcription occurs • Recognize where, how, and why translation occurs

  3. Linking Genetic Information to the Synthesis of Proteins • If Genes (bits of information on DNA) contain knowledge of how to assemble a polypeptide, then there must be a process by which information on the DNA is conveyed to the protein making machinery of the cell • Transcription: the synthesis of RNA under the direction of DNA • Translation: Synthesis of a polypeptide under the direction of mRNA

  4. Overview • Transcription • players include: • DNA • messenger RNA • RNA Polymerase • Occurs in the nucleus • Translation • players include: • mRNA • ribosomal RNA • transfer RNA • Occurs in the cytosol

  5. Review • Nucleotides each consist of a sugar, Phosphate and Base • Polymers of nucleotides form either DNA or RNA • DNA nucleotides have: • Deoxyribose as sugar • Bases ATGC • Double stranded nucleic acid with complimentary bases pairedas A-T & G-C • Found only in the nucleus • RNA nucleotides have: • Ribose as sugar • Bases AUGC • Single stranded nucleic acid • Found in the nucleus and cytoplasm

  6. 3 sequential nucleotides code for 1 AA • Remember that proteins are built from 20 different Amino Acids • 4 nucleotide bases cannot independently code for 20 different AA • Pairs of bases would only account for 16 AA • Triplet bases would give us 64 possible AA that could be coded, exceeding the required amount necessary

  7. Info Sharing • Only one strand of the double stranded DNA molecule is involved in transcription • Complimentary nucleotide triplets of mRNA are called a Codon (remember that U is substituted for T as a complimentary pair for A)

  8. Codons Deciphered • All 64 possible codon “words” have been determined • Redundancy occurs • Start (AUG) and Stop codons (UAA, UAG, UGA) occur • Reading frame: sequence and groupings of the words

  9. Transcription involves the making of messenger RNA from a DNA template • The region of a molecule of DNA called a gene is defined by a promoter (beginning) and terminator (ending) area • An enzyme (protein) called RNA polymerase attaches to the DNA

  10. mRNA synthesis • RNA Polymerase makes a molecule of mRNA complimentary to one of the two strands of DNA (Template Strand) • This continues until the terminator region of the gene is copied

  11. mRNA • The messenger RNA is then modified. Some areas of the molecule are removed (introns) while other regions remain (exons) • The coded regions are linked and the mRNA is finished • Transcription ends as the mRNA leaves the nucleus through the nuclear pores

  12. Translation • Flow of genetic information from mRNA to protein • Change in cellular language from nucleotide to protein • tRNA acts as the interpreter

  13. Transfer RNA • Transfer RNA is the molecule that interacts with both the mRNA and an Amino Acid • Each type of tRNA is bound to only a single form of amino acid • The region of the tRNA that “reads” the mRNA is called the anticodon There is a different tRNA for “each kind of codon” except the stop codons

  14. Ribosome Anatomy • Ribosomes: structures composed of rRNA (2 subunits) and protein • Responsible for aligning tRNA with mRNA codons • Stage for synthesis of peptides

  15. How does translation proceed? • mRNA binds to the ribosome • tRNA binds to the ribosome over the start codon region of mRNA • The ribosome aligns the codon of the mRNA with the complimentary anticodon of the tRNA

  16. Translation continued • A second tRNA molecule binds to the ribosome • The amino acid from the first tRNA is connected to the amino acid of the second tRNA with the assistance of the ribosome • This process continues until the stop codon on the mRNA is reached • At the stop codon, a chemical reaction frees the polypeptide chain

  17. Mutations in the DNA result in changes in the intended polypeptide • Point mutations:chemical changes in just a single or a few base pairs in a gene • Base-pair substitutions: replacement of one nucleotide with another • Silent • Missense • Nonsense • Insertion/Deletion: change in the number of nucleotide pairs • Frame shift

  18. Sickle Cell Disease

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