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Protein Synthesis

Protein Synthesis . RNA vs. DNA . Both nucleic acids Chains of nucleotides Different: Sugar Types of bases Numbers of bases Number of chains Site of action Function. Constructing DNA with the Model. 1. Make a strand of DNA (bases pointing away from you): GGACTCCTCTTC

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Protein Synthesis

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  1. Protein Synthesis

  2. RNA vs. DNA • Both nucleic acids • Chains of nucleotides • Different: • Sugar • Types of bases • Numbers of bases • Number of chains • Site of action • Function

  3. Constructing DNA with the Model 1. Make a strand of DNA (bases pointing away from you): GGACTCCTCTTC This is your coding strand of DNA. What color paper is this made of? How do you know? 2. Make a molecule of DNA by complementary base pairing the coding sequence

  4. Types of RNA Messenger RNA- mRNA- Dictates the order of amino acids in a protein using a series of three bases codons. Ribosomal RNA- rRNA- Major component of the ribosome Transfer RNA- tRNA- Transports the correct amino acid to the ribosome based on the codon in the mRNA

  5. Protein Synthesis • Gene → Protein • Transcription: DNA → RNA • Translation: RNA → Protein

  6. Transcription Nucleotide → nucleotide • DNA → RNA • Template strand or coding strand of DNA • RNA polymerase

  7. Transcription • RNA polymerase • Finds “promoter” region • Adds complementary nucleotides to template strand making the mRNA • Stops at “terminator” sequence • Produces pre-mRNA • Where must this occur?

  8. Transcription with the Model • This is a portion of the sickle cell gene. We are reading the sequence from the middle of the gene. The promoter would be found upstream and the terminator sequence would be found downstream, neither are part of this model activity. • Using your CODING STRAND transcribe your DNA into mRNA • What color paper is this new strand made of? How do you know? • You can put away the DNA now Notice!! There is a uracil rather than a thymine. G-C A-U

  9. Why thymine vs. uracil? Not on test Why thymine rather than uracil in DNA? • Cytosine is easily changed to uracil by removing a amine group: • Occurs about 100 times per cell, per day. • If DNA used uracil the cell would not know if that uracil was supposed to be there or if it was supposed to be cytosine. • DNA has thymine so the cell can easily recognize that when cytosine is changed to uracil there is a problem because uracil should not be in the DNA. Cytosine Uracil This would cause major mutations!

  10. Modification • Introns – internal sequences that will be cut out • Exons – sequences that will not be cut out • RNA splicing – cuts out introns and rejoins exons • This is not part of the model we are using

  11. The mRNA Strand is Read as a Series of Codons to Make a Protein • Each unique sequence of three bases is called a codon • There are 64 codons that make up the information in the genetic code

  12. Genetic Code • Codon – sequence of three (3) nucleotides • Genetic Code – translates codons into amino acids

  13. Translation Nucleotide → amino acid • Ribosomes are within cytosol • Requires mRNA, tRNA and rRNA • Final product is a polypeptide

  14. Translation • mRNA • template for translation • tRNA • attaches to amino acids • Anticodon: complementary binds to the codon of mRNA and

  15. Initiation • Ribosome, made of rRNA and proteins, binds to mRNA • The ribosome travels down the mRNA until it finds the start codon • Methionine tRNAbinds to start codon

  16. Elongation • The next codon signals its respective tRNA to enter the ribosome and alines with the previous tRNA • The two amino acids are brought close together so that they can be bound together.

  17. Elongation • Once the two amino acids are bond together the mRNA and tRNAs are moved • The next tRNA is brought in • This allows the correct amino acids to be brought close contact so they can be bound together in the correct sequence.

  18. Elongation • This process continues down the length of the mRNA resulting in a complete polypeptide with amino acids in the correct order. • The process ends when a stop codon enters the ribosome

  19. Translation with the Model • Get out your green tRNA and pink amino acids • “Bind” the correct amino acids to their respective tRNA • Connect your first anti-codon to the first codon of the mRNA • Do this for the rest of the tRNA:aa molecules • How is this part of the model different that what occurs in the ribosome?

  20. Please paperclip all like pieces together and place back into the bagsMake sure you get all the pieces and only the pieces from your kit.

  21. Practice: Translate & Transcribe DNA Sequence: TAC CCG GAT ACC

  22. Types of Mutations • Substitution – replacement of one base for another Framshift: • Insertion – addition of base(s) • Deletion – removal of base(s)

  23. Types of Mutations: FrameshiftMutation • Insertion or deletion of nucleotides not in multiples of three • Sequence is “non-sense” • Alters amino acids “downstream” from site

  24. Example: Tay-Sachs Disease • Insertion/deletion of four (4) base pairs results in frameshift mutation • Lack enzyme that would breakdown lipids in brain • Results in death of brain cells, poor muscles, etc

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