2 7 DNA Replication Transcription Translation DNA Replication

2. 7 DNA Replication, Transcription & Translation

DNA Replication Understandings: Ø Replication is semi-conservative & depends on complementary base pairing Ø Helicase unwinds double helix & separates strands by breaking H bonds Ø DNA polymerase links nucleotides to form new strand, using pre-existing strand as template Applications: Ø Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by PCR Nature of Science: Obtaining evidence Skills: for scientific theories: ØAnalysis of Meselson & Stahl’s Meselson & Stahl obtained evidence results to obtain support for the semi-conservative replication theory of semi-conservative of DNA. replication of DNA

Understanding: Replication is semi-conservative & depends on complementary base pairing • Semi-conservative = both DNA strands produced from replication composed of one original strand a newly synthesized strand • Complementary base pairing = one base always pairs with another (it is the principle that ensures 2 identical DNA molecules)

Nature of Science: Obtaining evidence for theory of semi-conservative replication • Matt Meselsohn & Frank Stahl’s 1958 experiment: How does DNA replicate? • Grew E. coli in medium with 15 N, then transferred bacteria to medium with 14 N. Samples of E. coli taken & separated by density gradient centrifugation (heavier molecules settle further down tube than lighter ones).

Evidence for the semi-conservative model:

Understanding: Helicase unwinds double helix & separates strands by breaking H bonds (requires ATP)

DNA Polymerase

DNA Replication animation http: //highered. mheducation. com/sites/0072943696/student_view 0/c hapter 3/animation__dna_replication__quiz_1_. html

Polymerase chain reaction

PCR

Transcription/Translation Understandings: Ø Transcription is the synthesis of m. RNA copied from the DNA base sequences by RNA polymerase. Ø Translation is synthesis of polypeptides on ribosomes. Ø The amino acid sequence of polypeptides is determined by m. RNA according to the genetic code. Ø Codons of 3 bases on m. RNA correspond to one amino acid in a polypeptide. Ø Translation depends on complementary base pairing between codons on m. RNA & anticodons on t. RNA. Applications: Ø Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species. Skills: ØUse genetic code to deduce which codon(s) corresponds to which amino acid. ØUse a table of m. RNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short m. RNA strand of known base sequence. ØDeducing the DNA base sequence for the m. RNA strand.

• http: //highered. mheducation. com/sites/0072507470/student_view 0 /chapter 3/animation__mrna_synthesis__transcription___quiz_1_. ht ml • http: //highered. mheducation. com/sites/0072507470/student_view 0 /chapter 3/animation__how_translation_works. html

Application: Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species. • Most diabetics use genetically-modified E. coli (bacteria), yeast (fungus), or safflower (plant) • Bacteria, fungus, plant – all are genetically altered so they produce HUMAN insulin • Possible because humans, bacteria, fungus, plants (and most other organisms) all use the SAME genetic code the code is UNIVERSAL! • Genetic engineers can transfer genes between different species!