Chapter 13: DNA, RNA, and Proteins Section 1: The Structure of DNA Gene:

DNA: _____________________________________________; the material that contains the information that determines inherited characteristics Nucleotide: a subunit in a nucleic acid chain, that consists of a sugar, phosphate and nitrogenous base Purine: Pyrimidine: I. DNA: The Genetic Material A. B. C. D. DNA is a primary material that causes recognizable, inheritable characteristics in related groups of organisms II. Searching for Genetic Material A. Three Major experiments led to the conclusion that DNA is the genetic material in cells: 1. Frederick Griffith’s Discovery of Transformation (1928) a.

b. worked with Streptococcus pneumoniae 2. 2 strains a. S strain: looks smooth; causes pneumonia b. R strain: looks rough; doesn’t cause pneumonia

1

3. Griffith’s Experiments a. S bacteria caused pneumonia and death when injected into mice. b. R bacteria had no visible effect when injected into mice. c. S bacteria were killed by heating. Heat-killed S bacteria did not harm mice. d. Griffith grew live R bacteria after mixing with heat-killed S bacteria. Mice injected with the mixture died of pneumonia. 4. Griffith’s Conclusions a. b. B. Oswald Avery’s Experiments with Nucleic Acid (1940s) 1. 2. Avery’s Experiment a. Used enzymes to destroy each of these molecules in heat killed S bacteria b. Found bacteria was missing protein and RNA was able to transform R cells into S cells c. Bacteria that were missing DNA did not transform R cells 3. Avery’s Conclusions a. C. Hershey-Chase Experiment (1952) 1. DNA or Protein? a. Experimented using viruses called bacteriophages (phage) b. Components of a phage 1) 2)

2

2. Hershey-Chase Experiment a. Phages with radioactive (green) DNA infected bacteria 1) 2) b. Phages with radioactive (green) Protein infected bacteria 1) 2) 3. Hershey-Chase Conclusion a. Only the DNA of viruses is injected into bacterial cells b. Injected DNA causes bacteria to produce viral DNA and proteins c. III. The Shape of DNA A. A Winding Staircase 1. DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits a. b. 2. Parts of the Nucleotide Subunits a. Nucleotide Components 1. 2. 3. b.

3

c. IV. The Information in DNA A. The information in DNA is contained in the order of the bases, while the base-pairing structure allows the information to be copied B. Nitrogenous Bases 1. Each nucleotide has the same sugar and phosphate backbone 2. Bases are what is different (1 of 4) a. 1) 2) b. 1) 2) C. Base-Pairing Rules 1. 2. 3. D. Complementary Sides 1. 2. Fit together like puzzle pieces 3. Information on one side is reverse of information on the other 4. A T C G A T T A C T A G G A 5.

4

V. Discovering DNA’s Structure A. Watson and Crick used information from experiments by Chargaff, Wilkins and Franklin to determine the 3D structure of DNA B. Observing Patterns: Chargaff’s Observations (1949) 1. For each organism he studied a. b. 2. Watson and Crick used this information to determine how bases paired C. Using Technology: Photographs of DNA (1952) 1. Rosalind Franklin and Maurice Wilkins developed high-quality Xray diffraction images of strands of DNA 2.

D. Watson and Crick’s Model of DNA 1. 2. Section 2: Replication of DNA DNA Replication: DNA Helicase: an enzyme that unwinds the DNA double helix during DNA replication DNA Polymerase: an enzyme that catalyses the formation of the DNA molecule I. DNA Replication A. B.

5

C. D. If strands are separated each can serve as pattern for new complementary strands E. F. G. Steps of Replication 1. a. Double helix unwinds b. Enzymes separate DNA strands and form Y-shapes c. Y-shapes are called replication forks 2. a. At replication fork new nucleotides are added to each side b. Original 2 strands serve as template for 2 new strands 3. a. Each double-stranded DNA molecule is made of one new strand and one original strand II. Replication A. During the replication of DNA, many proteins form a machinelike complex of moving parts B. DNA Helicase 1. C. DNA Polymerase 1. 2.

6

a. Section 3: RNA and Gene Expression RNA: __________________________________; a natural polymer that is present in all living cells and that plays a role in protein synthesis Gene Expression: the manifestation of the genetic material of an organism in the from of specific traits Transcription: Translation: the portion of protein synthesis that takes place at ribosomes and that uses the codons in mRNA molecules to specify the sequence of amino acids in polypeptide chains I. DNA provides the original information from which proteins are made A. B. RNA is essential in taking the genetic information from DNA and building proteins II. An Overview of Gene Expression A. B. Transcription: DNA to RNA 1. 2. 3. Transcription is similar to copying (transcription) notes from the overhead (DNA) to your note packet (RNA) C. Translation: RNA to Protein 1. 2.

7

3. Translation is similar to translating a sentence in one language (RNA, the amino acid language) to another language (protein, the amino acid language) III. RNA: A Major Player A. In cells, three types of RNA complement DNA and translate the genetic code into proteins B. RNA Versus DNA 1. Similar a. b. c. d. 2. Different a. b. c. 3. DNA base pairs a. b. 4. RNA base pairs a. b.

8

C. Types of RNA 1. 3 types of RNA play a role in gene expression a. 1) produced when DNA is transcribed into RNA 2) complementary to the DNA sequence of a gene 3) mRNA carries instructions for making a protein from a gene and delivers them to the site of translation b. 1) during translation tRNA “reads” the mRNA sequence 2) translates the mRNA sequence into a specific sequence of protein subunits or amino acids 3) have amino acids attached to them 4) act as decoders by matching mRNA sequence and placing amino acids on protein chains c. 1) RNA that is found in ribosomes to help make proteins IV. Transcription: Reading the Gene A. During transcription, the information in a specific region of DNA (a gene) is transcribed, or copied, into mRNA B. C. Steps of Transcription 1. Step 1 a. RNA polymerase binds to the specific DNA sequence in the gene called the promoter b. Promoter site is the start location 2. Step 2 a. RNA polymerase unwinds and separates 2 strands of double helix to expose DNA bases 3. Step 3 a. RNA polymerase reads the gene

9

b. RNA polymerase moves along the bases on the DNA like a train moves along the track c. Transcription follows same base pairing rules as DNA replication except uracil takes place of thymine d. Forms single strand of RNA e. DNA double helix closes up behind the moving RNA polymerase f. RNA polymerase eventually reaches a stop location D. Transcription vs. Replication 1. Similar a. 2. Different a. b.

V. The Genetic Code: Three-Letter “Words” A. B. Codons of mRNA 1. 2. Codons match 1 of 20 amino acids or acts as a stop or start signal 3. 4. 5. System of matching codons and amino acids is called genetic code 6. Genetic code is based on codons that each represent a specific amino acid

10

VI. Translation: RNA to Proteins A. B. 1. Step 1 a. Amino acid is added to one end of each tRNA b. Other end has anticodon c. Anticodon is 3-nucleotide sequence that is complementary to an mRNA codon d. After leaving the nucleus, mRNA joins with ribosome and tRNA e. mRNA start codon AUG signals the beginning of a protein chain f. tRNA molecule carrying methionine at one end and the anticodon UAC, at the other binds to the start codon 2. Step 2 a. tRNA molecule that has correct anticodon and amino acid to binds to the second codon on the mRNA b. Peptide bond forms between the two amino acids c. 1st tRNA is released from the ribosome d. tRNA leaves it’s amino acid behind 3. Step 3 a. Ribosome moves one codon down the mRNA b. Amino acid chain continues to grow as each new amino acid bonds to the chain 4. Step 4 a. Process is repeated until a stop codon is reached 5. Step 5 a. Newly made protein falls off the ribosome b. Ribosome is free to begin translation again with another mRNA C. Repeating Translation 1. 2. a.

11

VII. Complexities of Gene Expression A.

B. C. D. Final outcome of gene expression is affected by 1. 2. 3.

12