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STUDY GUIDE-CHAPTER 12 BIO II - Study GuideChapter 12...

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Study Guide—Chapter 12 Biology II From DNA to Protein: Genotype to Phenotype WHAT IS A GENE? -George Beadle and Edward Tatum (1941) In experiments with the red Bread mold Neurospora crassa Produce mutants (auxotrophs) that could grow only on complete growth medium (containing all 20 amino acids) ~Transferred mutants to vials with minimum growth medium plus one amino acid or a precursor of that amino acid. ~Identified mutants that had their synthesis pathway for amino acid arginine blocked at different steps. They reasoned that: ~Each step in the pathway was mediated by an enzyme and that each enzyme was coded for by a specific gene. FORMULATED THE ONE-GENE-ONE ENZYME HYPOTHESIS; LATER MODIFIED TO: ONE-GENE-ONE POLYPEPTIDE [Fig 12.1] HOW DOES DNA ENCODE PROTEIN STRUCTURE? -By encoding information about the specific sequences of amino acids found in proteins. Sanger (1953) demonstrated that specific sequences of amino acids Ingram (1956) showed that a particular genetic disorder (sickle cell disease) is result of a mutation that changes a particular amino acid. IF GENES CODE FOR PROTEINS (MOST DO) THEN WHERE IN THE CELL ARE PROTEINS PRODUCED? -In the cytoplasm of both prokaryotes and eukaryotes in association with RNA-protein complexes called ribosomes . -Both prokaryotic and eukaryotic ribosomes consist of two subunits (one small/one large) Both subunits consist of RNA (rRNA) and many proteins. The proteins and rRNA molecules of prokaryotic and eukaryotic ribosomes are different (prokaryotes=smaller ribosomes)
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A) [Fig 12.10] TYPES OF RNA USED IN PROTEIN SYNTHESIS -rRNA—catalytic (ribozymal) in function within ribosomes -Transfer RNA (tRNA)—molecules that transfer amino acids to the site of protein synthesis and positions them in the correct order. -Messenger RNA (mRNA)—carries a transcription of a gene to the site of protein synthesis RNA DIFFERS FROM DNA -It is usually single stranded -The sugar is ribose, not deoxyribose -It has the nitrogenous base, uracil, not thymine. -Some people think RNA was the first genetic material. THE CENTRAL DOGMA -Coded information in DNA is transcribed into an RNA copy of the code and the code is used to assemble amino acids into a protein (polypeptide) via translation. DNA RNA PROTEIN -Protein is regulating expression of genes, protein synthesis, RNA synthesis, etc. BUT HOW DOES DNA SPECIFY PARTICULAR AMINO ACIDS? -The Genetic Code The sequence of nucleotides in DNA must, via RNA, specify the 20 amino acids that occur in proteins. The smallest number of nucleotides in combination that will provide code sequence for all 20 nucleotides is 3 . ~4
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STUDY GUIDE-CHAPTER 12 BIO II - Study GuideChapter 12...

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