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Chapter 8

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Chapter 8

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  1. Chapter 8 From DNA to Proteins Introduction to Protein Synthesis

  2. 8.1 Identifying DNA as the Genetic Material

  3. Griffith finds a ‘transforming principle.’ • Griffith experimented with the bacteria that cause pneumonia. • He used two forms: the S form (deadly) and the R form (not deadly). • A transforming material passed from dead S bacteria to live R bacteria, making them deadly. Experiment Video

  4. Avery identified DNA as the transforming principle. • Avery isolated and purified Griffith’s transforming principle. • Avery performed three tests on the transforming principle. • Qualitative tests showed DNA was present. • Chemical tests showedthe chemical makeupmatched that of DNA. • Enzyme tests showedonly DNA-degradingenzymes stoppedtransformation.

  5. Hershey and Chase confirm that DNA is the genetic material. • Hershey and Chase studied viruses that infect bacteria, or bacteriophages. • They tagged viral DNA with radioactive phosphorus. • They tagged viral proteins with radioactive sulfur. • Tagged DNA was found inside the bacteria; tagged proteins were not.

  6. 8.2 Structure of DNA

  7. The Genetic code • The program of the cell is the genetic code. • Genetic code- the way in which cells store the program that they seem to pass from one generation of an organism to the next generation

  8. Genetic Code

  9. DNA is the nucleic acid that stores and transmits information from one generation to the next. • DNA (Deoxyribonucleic Acid)

  10. The structure of DNA • DNA is formed from units called Nucleotides • Each Nucleotide is made of: • A 5-carbon sugar called deoxyribose • A phosphate group • A nitrogenous base/nitrogen containing base

  11. Nucleotide

  12. Nitrogenous bases • DNA had 4 nitrogenous bases divided into two groups: • 1. Purines: • Adenine • Guanine • 2. Pyrimidines • Cytosine • Thymine • Bases come together to form a chain

  13. Nitrogenous bases

  14. X-Ray Evidence • Rosalind Franklin used x-ray diffraction to visualize the DNA molecule • She discovered that they are twisted, and that it is spaced out in intervals

  15. Chargaff discovered that there is the same amounts of adenine as Thymine and cytosine as Guanine in DNA

  16. The Double Helix • Watson and Crick saw Franklin’s work and came up with the Double Helix model • The nitrogenous bases of each of the strands of DNA are positioned opposite each other • Causes Hydrogen bonds to form

  17. Adenine bonds with Thymine • Cytosine bonds with Guanine • They only bond With each other • Known as base pairing Holds two strands together

  18. 8.3 DNA Replication

  19. The Replication of DNA • The strands of DNA are complimentary, meaning they are not exact copies but you know what the other side looks like • One strand can direct the sequence of the other by complimentary base pairing

  20. Complimentary Base Pairing

  21. Each strand is a template for another

  22. A cell must duplicate its DNA before it divides • The copying process is known as Replication (synthesis) • This is carried out by enzymes (proteins)

  23. The enzymes unzip the two strands of DNA and insert the appropriate bases • They then insert the appropriate bases for the new strand • Some enzymes even proofread the strands to make sure the DNA is replicated

  24. DNA Replication

  25. Replication starts when the molecule unzips (hydrogen bonds are broken) • Each strand is a template for complimentary bases • T-A-C-G-T-T What is the complimentary Strand? • DNA Replication Video!!!

  26. 8.4 Transcription

  27. RNA • Knowing the structure of DNA doesn’t explain how it holds information • The first step into decoding the DNA is by copying part of it in RNA (ribonucleic acid) • RNA-the nucleic acid that acts as a messenger between DNA and the ribosomes and carries out the process by which proteins are made from amino acids

  28. RNA

  29. The Structure of RNA • RNA is a long chain of nucleotides like DNA • Made up of a sugar, phosphate, and a nitrogenous base • This makes up the backbone just like DNA

  30. The Structure of RNA

  31. Three main differences


  33. RNA follows base pairing: • Adenine – Uracil Cytosine – Guanine • RNA is used as a copy • There are three types we will talk about

  34. Transcription: RNA Synthesis • Transcription-a molecule of DNA is copied into a complementary strand of RNA • Process of transferring info from DNA to RNA • Why do you think this is necessary?


  36. Transcription: RNA Synthesis • DNA is in nucleus and ribosomes are in cytoplasm • Messenger RNA (mRNA)- a molecule that brings a copy of DNA from the nucleus to the cytoplasm • One of the three types of RNA


  38. Transcription: RNA Synthesis • RNA polymerase (enzyme) separates the strands of the DNA double helix • It then creates a mRNA strand • mRNA is complementary to one of the strands • Base pairing makes it complimentary


  40. Transcription: RNA synthesis • Special sequence of DNA serves as start signals • Special sequences of DNA serves as termination sites • RNA polymerase recognizes those spots

  41. Transcription Video Video

  42. 8.5 Translation

  43. The info that DNA transfers to mRNA is in code depending on the arrangement of the bases • Two questions come up: • What kind of info is contained in DNA? • How is the info decoded?

  44. The bases in DNA direct protein synthesis (creation) • Why proteins? • Responsible for: control biochemical pathways; direct the creation of lipids, carbohydrates and nucleotides; cell structure; and cell movement


  46. DNA issues orders to the organelles of the cell to make proteins • DNA and RNA are the nucleic-acid executives who run the cell factory


  48. The Nature of the Genetic Code • Proteins are made of long chains of amino acids which form chains called polypeptides • Each polypeptide is made of the 20 different amino acids • How can a particular order of nitrogenous bases in DNA and RNA be translated into a particular order of amino acids in a polypeptide?

  49. Amino acid<polypeptide<protein

  50. Genetic code • There is a four letter alphabet arranged by bases • The code words are copied from DNA to RNA in transcription • Each combination of three bases on a mRNA makes a codon or three letter code word