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DNA’s “JOBS”

DNA’s “JOBS”. DNA makes copies of itself (DNA replication) DNA encodes information (protein synthesis) 3. DNA controls cells and tells them what to do (gene expression) 4. DNA can change by mutation. Central Dogma of Molecular Biology. This is the genetic “ Flow of Information”

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DNA’s “JOBS”

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  1. DNA’s “JOBS” • DNA makes copies of itself (DNA replication) • DNA encodes information (protein synthesis) 3. DNA controls cells and tells them what to do (gene expression) 4. DNA can change by mutation

  2. Central Dogma of Molecular Biology This is the genetic “Flow of Information” DNAmRNAaa protein trait

  3. Protein SynthesisA 2-Step Process • Transcription • Writing the code • Translation • Reading the code

  4. DNA • DNAis often called “the blueprint of life” • DNA is the instructions for making proteins • Like a reference book; too big and important to leave nucleus

  5. RNA • Differences from DNA? • Sugar - ribose • Strand - 1 • N-bases • U not T

  6. RNA and Protein Synthesis Types of RNA • Messenger RNA (mRNA) – carries information from DNA to the ribosomes where the proteins are assembled. It is a partial copy of ONLY the information needed for that specific job. It is read 3 bases at a time – codon. 2. Ribosomal RNA (rRNA) – found in ribosomes and helps in the attachment of mRNA and in the assembly of proteins. 3. Transfer RNA (tRNA) – transfers the needed amino acids from the cytoplasm to the ribosome so the proteins dictated by the mRNA can be made. (The three exposed bases are complementary to the mRNA and are called the anticodon)

  7. Figure 5.28 DNA RNA  protein: a diagrammatic overview of information flow in a cell

  8. Figure 17.3 The triplet code

  9. TRANSCRIPTION(Making the Message) • DNA is in the nucleus • Proteins are made in the cytoplasm • Where?

  10. Transcription(Make the message) • Getting the genetic message from the _______ to the _________ in the _________in order to make __________ • DNA makes a messenger to do this = _______ ribosomes nucleus cytoplasm proteins mRNA

  11. transcription

  12. Transcription Section 12-3 Step 1 –Area of DNA need to copy opens up (helicase) Step 2 – RNA nucleotides floating in the nucleus pair up with the complementary base on the DNA strand to make a single-stranded mRNA (RNA polymerase) Step 3 –mRNA strand enters the cytoplasm RNApolymerase DNA RNA Go to Section:

  13. The dictionary of the genetic code = CODON CHART-mRNA codon64 Codons – only 20 amino acidsWobble positionLast letter can change without mutation…Ex: UUA & UUG both leucine

  14. The Genetic CodemRNA codon chart Section 12-3 Go to Section:

  15. Practice • What amino acid does the codon UUU code for? • What amino acid does the codon GAC code for?

  16. Start and Stop Codons – What’s a gene? NOTE: A “start” amino acid is found at the beginning of most proteins – methionine. The codon for this is AUG. A “stop” codon DOES NOT CODE FOR ANY AMINO ACID – it is the signal that the protein is complete and can be released…

  17. Transcription:You be the RNA polymerase! • DNA Strand = TACAAACATACT • What is the complementary mRNA? • AUGUUUGUAUGA • What amino acid sequence does this mRNA code for? • Met (Start)-Phe-Val-Stop (no aa)

  18. Transcription & Translation

  19. Write your own gene! • Must be at least 18 bases long; must include start and stop codon and code for real amino acids…. • Give your gene a name – what does the protein it makes do? • Give the • DNA sequence • mRNA transcript • amino acid sequence

  20. 2. Translation(cell’s way of decoding the mRNA message) • Happens on ribosomes • Transfer RNA (tRNA) reads mRNA and brings in the correct amino acid BOTTOM LINE: YOU Read the message sent from DNA (mRNA); Decode it and make the proper Amino Acid sequence = protein

  21. Translation: the basic concept • mRNA feeds into the ribosome • Codon • tRNA decodes the mRNA • How? Matching the Anti-codon to the codon • aa’s coded for by mRNA are attached to tRNA; • aa’s brought by tRNA link up to form a protein (peptide bond)

  22. The structure of transfer RNA (tRNA)

  23. Figure 17.15 The anatomy of a functioning ribosome

  24. Translation Section 12-3 Nucleus Messenger RNA Messenger RNA is transcribed in the nucleus. mRNA Lysine Phenylalanine tRNA Transfer RNA The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon. Methionine Ribosome Start codon mRNA Go to Section:

  25. Translation (continued) Section 12-3 Growing polypeptide chain Ribosome tRNA Lysine tRNA mRNA mRNA Translation direction Ribosome Go to Section:

  26. The triplet code

  27. What happens when need to use genes in the code? • Ex. Paper cut to repair – only need info for skin cell production • Copy only the portion of the master code that is needed (Transcription) into mRNA • Cut produces transcription factors that bind to DNA at certain sequences (TATA Box) to initiate RNA Polymerase to begin protein synthesis • Occurs in the nucleus • mRNA is translated into proteins to fix the cut at the ribosome

  28. Working with the Code – use the bullseye chart • Given TACGGGCCCCAAACT a. what is the mRNA made? b. what is the tRNA needed to bring the correct amino acids during translation? c. what is the protein made? (amino acid chain) 2. Given TACGCACATAATACT do a, b, and c as above…

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