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Chapter 14 Notes

Chapter 14 Notes - The Central Dogma of Molecular Biology...

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From DNA to Protein: Gene Expression 14.1 What is the Evidence that Genes Code for Proteins? The molecular basis of phenotypes was actually discovered before it was known that DNA was the genetic material. Observations in humans led to the proposal that genes determine enzymes Identification of a gene product as a protein began with a mutation o Archibald Garrod (English physician) saw that a number of children had a disease called alkaptonuria- urine turned dark brown in air o He noticed that the disease was common in children whose parents were first cousins o Proposed that the disease was a phenotype caused by a recessive, mutant allele o Homogentisic acid, which accumulated in bloods, joints and urine, was not broken down properly Lab studies on model organisms Common bread mold- Nerospora crassa Mutant strains (created by X-rays) were isolated Mutant strains required additional nutrients in order to grow Confirmed that one-gene, one-enzyme hypothesis 14.2 How Does Information Glow from Genes to Proteins?
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Unformatted text preview: The Central Dogma of Molecular Biology • DNA RNA Polypeptide • Transcription- the information in a DNA sequence is copied into a complementary RNA sequence • Translation- RNA sequence is used to created the amino acid sequence of a polypeptide RNA • Usually single- stranded • Sugar is ribose • Uracil instead of thymine • Three types of RNA in protein synthesis o mRNA- messenger o tRNA- transfer o rRNA- ribosomal 14.3- How is the Information Content in DNA Transcribed to Produce RNA? Trascription occurs in three steps • Initiation- required a promoter which is a special sequence of DNA to which the RNA polymerase binds very tightly • Promoters are important control sequences that “tell” the RNA polymerase 2 things: o Where to start transcription o Which strand of DNA to transcribe • The Genetic Code o Redundant but not ambiguous o Only 1 start codon: AUG aka Methionine o 3 stop codons: UAA, UAG, UGA...
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