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Ribonucleic Acid (RNA) & Protein Synthesis

Ribonucleic Acid (RNA) & Protein Synthesis. Ms. Napolitano & Mrs. Haas CP biology. Recall: DNA Structure. A  T C  G Double helix. Genes. Genes – coded DNA instructions that control the production of proteins within the cell. Part I: RNA Structure. RNA Structure.

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Ribonucleic Acid (RNA) & Protein Synthesis

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  1. Ribonucleic Acid (RNA) & Protein Synthesis Ms. Napolitano & Mrs. Haas CP biology

  2. Recall: DNA Structure • A  T • C  G • Double helix

  3. Genes • Genes – coded DNA instructions that control the production of proteins within the cell

  4. Part I: RNA Structure

  5. RNA Structure • Long chain of nucleotides • Sugar • Phosphate • Nitrogenous base • Differences between DNA & RNA: In RNA: • Sugar is ribose (instead of deoxyribose) • Single stranded (instead of double stranded) • Contains uracil (instead of thymine)

  6. Types of RNA • Messenger RNA (mRNA) • Carries copies of DNA instructions out of the nucleus • Ribosomal RNA (rRNA) • Make up ribosomes • Transfer RNA (tRNA) • Transfers amino acids to the ribosome that are coded in the mRNA

  7. Part II: Protein Synthesis

  8. Protein Synthesis • How proteins are made • Need instructions from DNA • Made of 2 parts: • Transcription • Translation

  9. Transcription • Copying of the DNA sequence • Occurs in the nucleus • Makes a complimentary strand of mRNA • Uses protein RNA Polymerase • Separates DNA strand • Uses 1 strand of DNA as a template to make mRNA • Starts at a promoter – specific sequence of DNA

  10. RNA Editing • DNA contains segments of introns • Not involved in protein coding • Exons code for proteins • Introns are cut out of the mRNA sequence after transcription • Exons are spliced together

  11. The Genetic Code • The genetic code is read just 3 letters at a time • Codon – 3 consecutive nucleotides that specify for a single amino acid • Ex: Consider the RNA sequence UCGCACGGU • This would be read UCG-CAC-GGU • 3 different codons: UCG, CAC, & GGU • Codons represent different amino acids • UCG= serine • CAC = histidine • GGU = glycine

  12. The Genetic Code • Since 4 different bases, 44 = 64 possible codons • Some amino acids have more than one codon choice • AUG is always a “start” codon • Where protein synthesis begins • 3 stop codons (end of protein synthesis): • UGA • UAA • UAG

  13. Codon Wheel

  14. Codon Chart

  15. Translation • Recall: During transcription, mRNA code was made from DNA, mRNA proofread (introns cut out) • Translation – decoding of mRNA to produce proteins • mRNA moves from the nucleus to the ribosomes

  16. Steps of Translation • mRNA attaches to the ribosome. • As each codon moves through the ribosome, the proper amino acid is brought in by tRNA. • Each tRNA carries only 1 type of amino acid • tRNA has 3 unpaired bases (anticodon) that is complementary to mRNA codons • Peptide bonds form between amino acids & tRNA is released. • Polypeptide chain grows until a stop codon is reached.

  17. Translation

  18. Example of Protein Synthesis DNA strand: TAACGAGGTACT Transcription (nucleus): mRNA formed by base pairing mRNA strand: AUUGCUCCAUGA Translation: mRNA moves to ribosome, read as codons AUU-GCU-CCA-UGA Using codon chart, find amino acids that match Isoleucine-Alanine-Proline-Stop this is our new protein!

  19. Part III: Mutations

  20. Mutations • Mutations – changes in genetic material • Point mutations – occur at a single DNA point • Substitutions • Frameshift mutations – shift the reading frame of the genetic message • Dangerous! Could change every following amino acid • Insertions • Deletions

  21. Substitution • Point mutation • One base is changed to a different base • May/may not affect the protein code

  22. Insertions • Frameshift mutation • An extra base pair is (or extra base pairs are) added

  23. Deletions • Frameshift mutation • A base pair is (or base pairs are) removed

  24. Chromosomal Mutations • Chromosomal mutations – changes in the number or structure of chromosomes • Types: • Deletion – loss of part of a chromosome • Duplication – extra copies of part of a chromosome • Inversion – reverses the direction of part of the chromosome • Translocation – part of the chromosome breaks off & attaches to another

  25. Chromosomal Mutations

  26. Significance of Mutations • Most mutations do not have an effect on gene expression • Can be very harmful or fatal • Cystic fibrosis • Sickle cell anemia • Cancer • Source of genetic variability • Resistance to HIV • Polyploidy – extra sets of chromosomes • Beneficial in plants – larger and stronger than diploid plants

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