Chapter 9 DNA: THE Genetic Material

1. Chapter 9DNA: THE Genetic Material Section1 Identifying the Genetic Material

2. Transformation • Frederick Griffith, a bacteriologist, prepared a vaccine against pneumonia • Vaccine – a substance that is prepared from killed or weakened disease-causing agents, including certain bacteria • To protect the body against future infections by the disease-causing agent

3. Griffith’s Experiments • Griffith worked with 2 strains of S. pneumoniae • 1st strain had a smooth capsule that protected the bacterium from body’s defense systems (S) • Virulent – (full of poison) able to cause disease • 2nd strain lacked capsule and didn’t cause disease (R) • Mice injected with (S) strain died; mice injected with (R) strain lived

4. Griffith injected mice with dead S bacteria – mice lived • Griffith injected mice with heat-killed S bacteria-mice still lived • Meaning the capsule was not involved with killing the mice • He mixed harmless live R bacteria with the harmless heat-killed S bacteria-mice died • Transformation- a change in genotype caused when cells take up foreign genetic material

5. Avery’s Experiments • Oswald Avery & co-workers demonstrated that DNA is the material responsible for transformation • Almost 100 years after Mendel’s experiments

6. Viral Genes and DNA • Many scientists remained skeptical • Knew little about DNA, so they could not imagine how DNA could carry genetic information

7. DNA’s Role Revealed • Alfred Hershey and Martha Chase performed an experiment that settled the controversy • Viruses are composed of DNA or RNA surrounded by a protective protein coat • Bacteriophage (phage)– a virus that infects bacteria

8. Step 1 – grew E. coli contained radioactive sulfur (35S) protein coat incorporated the sulfur • Grew second batch E.coli with radioactive phosphorus (32P) would become part of the phages’ DNA • Step 2 Labeled phages used to infect two separate batches of E. coli

9. Step 3 Used centrifuge tubes to separate the bacteria (heavy) from the viral parts (lighter) • Concluded that the DNA of viruses is injected into the bacterial cells, while most of the viral proteins remain outside • Experiments have shown that DNA is the molecule that stores genetic information in living cells

10. The Structure of DNA Section 2

11. Watson & Crick determined that a DNA molecule is a double helix – two strands twisted around each other • Nucleotides – the subunits that make up DNA • 3 parts: a phosphate group, a 5-carbon sugar, and a nitrogen-containing base

12. Deoxyribose – sugar molecule from which DNA gets its full name, deoxyribonucleic acid • Nitrogen base may be : adenine, guanine, thymine, and cytosine • Adenine (A) and guanine (G) are classified as purines –two rings of carbon & nitrogen atoms • Thymine (T) and cytosine (C) are classified as pyrimidines –single ring C & N atoms

13. Discovering DNA’s Structure • Chargaff’s 1949 observations – the amount of adenine always equaled the amount of thymine; amount of guanine always equaled the amount of cytosine; but amount varied between different organisms

14. Wilkins & Franklin’s Photographs • X-ray diffraction to study the structures of molecules • 1952 Wilkins & Franklin developed high-quality X-ray diffraction photographs of strands of DNA which suggested that the DNA resembled a tightly coiled helix and was composed of two or three chains of nucleotides

15. Rosalind Franklin • was an English scientist who contributed to the discovery of the molecular structure of deoxyribonucleic acid (DNA), 1951

16. Watson & Crick’s DNA Model • 1953 Watson & Crick used the information from Chargaff, Wilkins, & Franklin along with their knowledge of chemical bonding, to make the “spiral staircase” configuration of DNA

17. Pairing Between Bases • Watson & Crick determined that a purine on one strand of DNA is always paired with a pyrimidine on the opposite strand • Base-pairing rule – cytosine pairs with guanine and adenine with thymine • Complementary base pairs – sequence of bases on strand determines the sequence of N bases on the other strand of DNA

18. HOMEWORK • Section 1 Review p. 193 3-6 • Section 2 Review p. 197 1-6

19. The Replication of DNA section 3

20. Watson & Crick proposed that one DNA strand serves as a template, or pattern, on which the other strand is built • DNA replication – the process of making a copy of DNA, which occurs during the (S) phase of the cell cycle

21. Step 1 – The double helix needs to unwind before replication can begin • Accomplished by enzymes called DNAhelicases which open the double helix by breaking the hydrogen bonds between the two strands

22. Additional proteins prevent the strands from assuming their double-helical shape • Replication forks – areas where the double helix separates • Enzymes known as DNA polymerases add nucleotides to the exposed nitrogen bases, according to the base-pairing rules – forming two double helixes

23. Step 3 The process continues until all of the DNA has been copied & the polymerases are signaled to detach • Nucleotide sequences are identical in the two DNA molecules • Checking for errors – DNA polymerases are important in “proofreading” the nucleotides – can backtrack • Errors in DNA replication about one error per 1 billion nucleotides

24. Rate of Replication • Replication does not begin at one end & end at the other • Prokaryotes usually have two replication forks • Eukaryotic cells – length a problem – 33 days if done with a single point • Each human chromosome is replicated in about 100 sections – replicated in about 8 hours

25. HOMEWORK • Section 3 Review p. 200 1-5 • Performance Zone p. 202 1-4, 6-12 • STP p. 203 1-3

26. How Proteins Are Made Chap. 10 Section 1

27. Decoding the Information in DNA • Traits are determined by proteins that are built according to instruction coded in DNA • Ribonucleic acid is also involved • RNA differs from DNA 3 ways a single strand five-C sugar, ribose Uracil (U) instead of thymine (T)

28. A gene’s instructions for making a protein are coded in the sequence of nucleotides in the gene • Transcription – a process were the instructions for making a protein are transferred from a gene to an RNA molecule

29. Translation – the protein synthesis that takes place at ribosomes & that uses the codons in mRNA molecules to specify the sequence of amino acids to make protein • Gene expression (protein synthesis) – the process by which proteins are made based on the information encoded in DNA

30. Transfer of information from DNA to RNA • RNA polymerase, an enzyme that adds and links complementary RNA nucleotides during transcription, is required • Step 1 RNA polymerase binds to the gene’s promoter-a specific sequence of DNA that acts as a “start” signal for transcription

31. Step 2 - RNA polymerase unwinds and separates the 2 strands of the double helix, exposing the DNA nucleotides • Step 3 – RNA polymerase adds & then links complementary RNA nucleotides as it “reads” the gene –transcription follows the base-pairing rules for DNA except that uracil pairs with adenine

32. The RNA polymerase eventually reaches a “stop” signal in the DNA • RNA nucleotides are linked together with covalent bonds during transcription • Behind the RNA polymerase, the DNA closes up reforming the double helix • In transcription, new molecule is RNA and only part of one of DNA strands serves as a template

33. Transcription in prokaryotic cells occurs in the cytoplasm; in eukaryotic cells, in the nucleus • Many identical RNA are made simultaneously from a single gene • Look at Figure 3 page 210

34. The Genetic Code: Three-Nucleotide “Words” • Different types of RNA are made during transcription • Messenger RNA (mRNA) carries the instructions for making a protein from a gene and delivers it to the site of translation • Translated from the language of RNA (nucleotide) to language of proteins (amino acid)

35. Codons - a series of three-nucleotide sequences on the mRNA Marshall Nirenberg, American, deciphered the first codon by making artificial mRNA that contained only the base uracil (U) • mRNA was translated into a protein phenylalanine amino-acid subuntis

36. Genetic code – the amino acids and “start” and “stop” signals that coded for by each of the possible 64 mRNA codons

37. RNA’S Roles in Translation • Translation takes place in the cytoplasm • Transfer RNA molecules and ribosomes help in the synthesis of proteins. • Transfer RNA (tRNA) are single strands of RNA that temporarily carry a specific amino acid on one end & an anticodon at the other • Anticodon – a three-nucleotide sequence on a tRNA that is complementary to an mRNA codon

38. Ribosomes are composed of both proteins & ribosomal RNA (rRNA) • Ribosomal RNA molecules are part of the structure of ribosomes • Each ribosome temporarily holds one mRNA and 2 tRNA molecules

39. Step 1 The mRNA and the tRNA carrying methionine bind together “start” codon AUG, signals the beginning of a protein chain • Step 2 – The tRNA carrying the amino acid specified by the codon in the A site arrives • Step 3 – A peptide bond forms between adjacent amino acids • S 4 – The tRNA in the P site detaches and leaves its amino acid behind

40. S 5 – The tRNA in the A site moves to the P site. The tRNA carrying the amino acid specified by the codon in the A site arrives. • S 6 – A peptide bond is formed. The tRNA in the P site detaches and leaves its amino acid behind. • S 7 – The process is repeated until a stop codon is reached. The ribosome complex falls apart. The newly made protein is released.

41. Another ribosome can find the AUG codon on the same mRNA and begin making a second copy of the same protein • The genetic code is the same in all organisms, but for a few exceptions

42. mutations

43. duplicating DNA at rates as high as 1000 nucleotides per seconBecause each of the two daughters of a dividing cell inherits a new DNA double helix containing one old and one new strand (Figure 5-5), the DNA double helix is said to be replicated “semiconservatively” by DNA polymerase.d.

44. Homework Section 1 review p. 214 1-6 Chapter review p. 222 1,2,6,7,8,12 P. 223 STP 1-3