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Chapter 8

Chapter 8. RNA Protein Synthesis Mutations. RNA Structure & Function. Structure of RNA. RNA differs from DNA in three ways: an RNA molecule consists of a single-strand of nucleotides RNA has ribose (5-C sugar) rather than deoxyribose RNA has the pyrimidine uracil instead of thymine.

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Chapter 8

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  1. Chapter 8 RNA Protein Synthesis Mutations

  2. RNA Structure & Function

  3. Structure of RNA • RNA differs from DNA in three ways: • an RNA molecule consists of a single-strand of nucleotides • RNA has ribose (5-C sugar) rather than deoxyribose • RNA has the pyrimidine uracil instead of thymine

  4. Types of RNA

  5. 3 Types of RNA

  6. Protein Synthesis Has 2 stages: Transcription and Translation

  7. Protein Synthesis Part 1: Transcription Transcription is the first part of protein synthesis. * What does it mean to transcribe? Step 1: An enzyme called RNA polymerase attaches to DNA and “unzips” it. Step 2: RNA polymerase then uses one strand of DNA as a template from which nucleotides are assembled into a strand of mRNA.

  8. Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNApolymerase DNA RNA

  9. Protein Synthesis Part I: Transcription The nucleotide sequence of DNA is converted into an RNA nucleotide sequence. Let’s say one strand of a DNA molecule had this sequence AGCCTACGTAAG What would the mRNA sequence produced be?

  10. Protein Synthesis Part 1: Transcription mRNA: UCGGAUGCAUUC DNA: AGCCTACGTAAG

  11. Review of Proteins Proteins are made by joining amino acids together into a long chain. This chain is a protein. The functions and properties of a protein are determined by the order in which 20 different types of amino acids are joined. The “language” of mRNA is called the genetic code.

  12. The Genetic Code RNA has 4 bases: adenine, uracil, cytosine, and guanine. The “language” of RNA is written in only 4 letters – AUGC The code is read three letters at a time Each “word” is 3 letters long Each “word” of 3 nucleotides is called a codon

  13. The Genetic Code • The 4 different bases can be arranged into 64 possible codons (4X4X4=64), but make only 20 different amino acids. • This is because some amino acids correspond to several different codons. • Example:

  14. Genetic Code Practice: • For what amino acid does the codonCGG code? • For what amino acid does the codonAUG code? • For what amino acid does the codonUGA code?

  15. AUG UAA UAG UGA Codons With Special Roles Start Codon: Stop Codons:

  16. Protein Synthesis Part 2: Translation The 2nd stage of protein synthesis is translation. *What does it mean to translate? The sequence of nucleotides in mRNA serves as instructions for the order in which amino acids should be joined together in a protein. Think of mRNA as the “recipe” for a protein.

  17. Protein Synthesis Part 2: Translation Transcription occurs in the nucleus. In translation, the mRNA travels out of the nucleus, and moves through the cytoplasm and attaches to a ribosome. So, translation occurs at the ribosomes.

  18. Protein Synthesis Part 2: Translation Steps of translation: 1. mRNA attaches to a ribosome 2. As each codon of the mRNA molecule moves through the ribosome, the proper amino acid is brought to the ribosome by tRNAmolecules. 3. Each tRNA molecule has 3 unpaired bases on it. These bases are called anticodons.

  19. Protein SynthesisPart 2: Translation 4. The amino acids are strung together like a chain (remember, a protein is a polymer) by the ribosome, forming a long protein molecule. 5. The tRNA’s are released from the amino acids. 6. The protein chain grows longer and longer until the ribosome reaches a stopcodon on the mRNA molecule. Then the protein is released from the ribosome.

  20. Practice DNA: mRNA: tRNA: Poly- peptide:

  21. Mutations Gene Mutation – produce changes in a single gene Chromosomal Mutations – produce changes in an entire chromosome

  22. Gene Mutations A gene mutation is a change in a DNA sequence. Gene mutations that involve changes in only one or just a few nucleotides are called point mutations b/c they occur at a single point in the DNA sequence. There are 3 types of point mutations: substitutions, deletions, and insertions.

  23. Gene Mutations Substitution Mutations One base is changed to another Usually affect no more than a single amino acid, but could still have an effect on a protein.

  24. Gene Mutations Insertion Mutations One extra base is inserted into the DNA sequence. Deletion Mutations One base is left out of the DNA sequence.

  25. Genetic Mutations Since the genetic code is read 3 letters at a time, the message is shifted for every codon that follows. Hence, insertions result in frameshift mutations. They have a dramatic effect on the amino acid sequence, and thus, the protein. * Question…during what event do these mutations usually occur?

  26. Deletion Insertion Substitution Gene Mutations

  27. Chromosomal Mutations Chromosomal mutations involve changes in the number or structure of chromosomes. We discussed many of these last chapter. Examples are Down syndrome, Turner syndrome, Fragile-X syndrome, Prader-Willi syndrome, and Klinefelter’s syndrome.

  28. Deletion Duplication Inversion Translocation Chromosomal Mutations

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