Chapter 12 - Chapter 12 From DNA to Protein What Is the...

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Chapter 12 From DNA to Protein What Is the Evidence that Genes Code for Proteins? The molecular basis of phenotypes was known before DNA was found to be the genetic material Studies of many different organisms showed that major phenotypic differences were due to specific proteins A gene is defined as a DNA sequence Many steps between genotype and phenotype Genes cannot by themselves produce a phenotype In 1940s, Beadle and Tatum,deveoped the one-gene, one-enzyme hypothesis Gene-enzyme relationship has been revised to the one-gene, one-polypeptide relationship Example: In hemoglobin, each polypeptide chain is specified by a separate gene (on separate chromosomes) ribosomal RNAs, other types of RNA) Some “regulatory” genes are involved in controlling other genes (though no protein is produced) DNA, RNA, and the Flow of Information Gene expression takes place in two steps: Transcription – makes single-stranded RNA copy of a DNA segment Translation – uses information encoded in RNA to make a polypeptide RNA ( ribonucleic acid ) differs from DNA: RNA is usually only one polynucleotide strand the sugar is ribose, not deoxyribose RNA has uracil (U) instead of thymine How Does Information Flow from Genes to Proteins? RNA can form complementary base pairings with a single strand of DNA… except that adenine pairs with uracil instead of thymine Single-strand RNA can fold into complex shapes by internal base pairing Francis Crick’s central dogma stated that information flow is: DNA codes for RNA, and RNA codes for protein The central dogma raises two fundamental questions… How does information get from the nucleus to the cytoplasm? What is the relationship between a specific nucleotide sequence in DNA and a specific amino acid sequence in protein? Messenger RNA (mRNA) Produced by transcription as a complemetary copy of DNA
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moves from nucleus of eukaryotic cells into cytoplasm serves as template for protein synthesis Transfer RNA (tRNA ) “Adapters” binds specific amino acids and recoginize nucleotide sequence of mRNA Translation – tRNA with attached amino acids line up on mRNA in proper sequence for polypeptide synthesis An exception to the central dogma Viruses are acellular particles that reproduce inside cells Many are “retroviruses” that have RNA instead of DNA ± Synthesis of DNA from RNA is reverse transcription How Is the Information Content in DNA Transcribed to Produce RNA? In normal prokaryotic and eukaryotic cells, transcription requires: DNA template for complementary base pairing appropriate ribonucleoside triphosphates (ATP, GTP, CTP, and UTP) to act as substrates RNA polymerase enzyme Transcription: DNA-Directed RNA Synthesis Within a gene, just one DNA strand is transcribed to RNA – the template strand DNA double helix partly unwinds to allow access to the template region
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This note was uploaded on 12/03/2010 for the course BSC 2010 taught by Professor Bowes during the Spring '08 term at University of Florida.

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Chapter 12 - Chapter 12 From DNA to Protein What Is the...

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