1. Chapter 10

2.  Biologists knew that genes were located on chromosomes  2 components of chromosomes: ◦ Protein & DNA  Proteins were in the lead ◦ Appeared more structurally complex & functionally specific

3.  Griffith (1928) ◦ 2 Strains of Bacteria  R strain - harmless  S strain – disease-causing ◦ Procedure of Experiment  Heat-killed S strain  Mixed with R strain  Injected mice with mixture & some of the harmless strain transformed to pathogenic

5.  What materials were used & what was the set-up before the trials of the Hershey-Chase Experiment? ◦ Materials: chem. containing radioactive isotopes, radioactivity detector, blender, centrifuge ◦ Procedure: radioactive isotopes to label DNA & protein in T2  Grew T2 w/ E. coli in a solution containing radioactive sulfur (protein contains sulfur, but DNA does not) - yellow  New phages were made, radioactive sulfur atoms were incorporated only into their proteins  Grew separate batch in a solution containing radioactive phosphorus (phosphorus is only in DNA) - green

10.  “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”  Semiconservative model – each of the two daughter molecules will have one old strand and one new strand

14.  http://www.wiley.com/college/pratt/047139 3878/student/animations/dna_replication/in dex.html http://www.wiley.com/college/pratt/047139 3878/student/animations/dna_replication/in dex.html

16.  Discovery: Archibald Garrod (1909) ◦ Genes dictate phenotypes through enzymes ◦ Inherited disease reflects a person’s inability to make a particular enzyme ◦ Remember:  Each step in a metabolic pathway is catalyzed by a specific enzyme

17.  Tatum & Beadle (1940s) ◦ One gene-one enzyme hypothesis:  Function of a gene is to dictate the production of a specific enzyme ◦ Modifications:  All types of proteins (not just enzymes)  Ex: keratin & insulin  One gene-one protein  Many proteins are made from two or more polypeptide chains  Ex: hemoglobin – two kinds of polypeptides, encoded by 2 different genes  One gene-one polypeptide hypothesis

18.  Cells governed by a molecular chain of command ◦ DNA  RNA  Protein  Chemical language of DNA/RNA ◦ Polymers of nucleotide monomers  A, T(U), C, G  Written as a linear sequence of bases  Specific sequence of bases = a gene  Consists of hundreds/thousands of bases in a sequence

20.  DNA/RNA nucleic acid language is translated into Protein polypeptide language  Polypeptide language ◦ Polymers made up of monomers of amino acids ◦ Written in a linear sequence ◦ Sequence of RNA dictates sequence of amino acids ◦ RNA is the messenger carrying genetic info from DNA

21.  DNA & RNA consist of 4 bases ◦ In translation, these 4 must specify 20 amino acids ◦ Triplett code: Genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA & RNA as a series of 3-base words, called codons ◦ 3-base codons in DNA are transcribed into 3-base codons in RNA, and then the RNA codons are translated into amino acids that form the polypeptide

22.  Set of rules giving the correspondence between codons in RNA and amino acids in proteins ◦ 61 of 64 codons for amino acids ◦ AUG – Methionine or start of polypeptide sequence ◦ 3 other codons do not designate amino acids, but they stop the translation  Redundancy but no ambiguity  Nearly universal, shared by organisms from bacteria to plants and animals

25.  Transfer of genetic info from DNA to RNA  Occurs in nucleus (Eukaryotes)  RNA is transcribed from DNA template ◦ RNA nucleotides follow same base-pairing rules that govern DNA replication ◦ U pairs with A, instead of T with A ◦ RNA polymerase – link RNA nucleotides ◦ Promoter – nucleotide sequence that says “start transcribing”  Binding site for RNA polymerase

27.  Conveys genetic info from DNA to translation machinery  Transcribed from DNA – Translated into polypeptides  Modified before leaving nucleus ◦ Add nucleotides  Cap (G nucleotide) & tail (50-250 A’s) ◦ RNA splicing  Remove introns and join exons  Produce mRNA molecule that is continuous

29.  Translates codons into amino acids  Amino acids can not recognize mRNA codons  Up to the tRNA to match amino acids to the appropriate codons  2 Functions must be met: ◦ Picking up the appropriate amino acids ◦ Recognizing appropriate mRNA codons

30.  Structure ◦ Single strand of RNA – 80 nucleotides ◦ Twists & folds itself ◦ Anticodon: single-stranded loop at 1 end that contains a special triplet of bases  Complementary to codon triplet ◦ Opposite end of anticodon contains the amino acid ◦ tRNA molecules a slightly different for each amino acid it specifies  Specific enzyme that joins amino acids to tRNA

32.  Make up the large and small subunits of a ribosome  Ribosome is the site where translation occurs ◦ tRNA & mRNA bind here  Prokaryotic & Eukaryotic Differences ◦ Medically significant  Antibiotic drugs can inactivate prokaryotic ribosomes while leaving eukaryotic ribosomes unaffected

34.  Initiation, Elongation, & Termination  Initiation ◦ mRNA, tRNA w/ 1 st amino acid, 2 subunits of ribosome ◦ Role: establish exactly where translation begins – get correct sequence of amino acids ◦ 2 Steps: 1.mRNA molecule binds to small subunit, and tRNA (UAC) binds to start codon (AUG) – carries methionine 2.Large subunit binds to small; initiator tRNA fits into large subunit – P site – holds growing peptide; A site ready for next tRNA

35.  Elongation 1.Codon recognition: anticodon pairs w/ codon at site A 2.Peptide bond formation: polypeptide separates from tRNA on P site & attaches by a peptide bond to the amino acid carried by the tRNA on the A site 3.Translocation: P site tRNA leaves, the ribosome translocates the tRNA in the A site to the P site -Codon & anticodon remain bonded -Brings next codon & anticodon to the A site

36.  Termination ◦ When stop codon reaches the A site (UAA, UAG, UGA)  Don’t code for an amino acid  Stop translation ◦ Polypeptide is released from last tRNA & exits ribosome ◦ Ribosome subunits separate