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BIOA01H3 (202)
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Chapter 12

Chapter 12

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Biological Sciences

My Notes Chapter 12Lecture 8 9 121 What is the evidence that genes code for proteins y The molecular basis of phenotypes was actually discovered before it was known that DNA was the genetic materialThe major phenotypic differences were the result of differences in specific proteins y Model organism one that is easy to grow in the laboratory or observe in the field and which shows the phenomenon to be studiedmutations have simple effects and that each mutation y Onegene oneenzyme hypothesiscauses a defect in only one enzyme in a metabolic pathwayy Onegene onepolypeptide relationship the principle that each gene codes for a single polypeptide In other words the function of a gene is to control the production of a single specific polypeptide122 How does information flow from genes to proteins y The expression of a gene to form a polypeptide occurs in to major stepsTranscription copies the information of a DNA sequence a gene into corresponding information in an RNA sequenceTranslation converts this RNA sequence into the amino acid sequence of a polypeptide y RNA ribonucleic acid an often single stranded nucleic acid whose nucleotides use ribose rather than deoxyribose and in which the base uracil replaces thymine found in DNAServes as a genome from some viruses y Central dogma the statement that information flows from DNA to RNA to polypeptide in retroviruses there is also information flow from RNA to cDNA y The messenger hypothesis and transcriptionTo answer the question of how information gets from the nucleus into the cytoplasm Crick and his colleagues proposed the messenger hypothesisThey proposed that an RNA molecule forms as a complementary copy of one DNA strand of a particular genemRNA a transcript of one of the strands of DNA carries information as a sequence of codons for the synthesis of one or more proteinsthe synthesis of RNA using one strand of DNA as the templateTranscriptiony The adapter hypothesis and translationTo answer the question of how a DNA sequence gets transformed into the specific amino acid sequence of a polypeptide Crick proposed the adapter hypothesis there must be an adapter molecule that can both bind a specific amino acid and recognize a sequence of nucleotidestRNA a family of doublestranded RNA moleculesEach tRNA carries a specific amino acid and anitcodon that will pair with the complementary codon in mRNA during translationTranslation the synthesis of a protein polypeptideTakes place on ribosomes using the information encoded in messenger RNAy Viruses are acellular infectious particles that reproduce inside cellsMany viruses have RNA rather than DNA in their genetic material
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