1362-SU09-Lecture-4-_40689

1362-SU09-Lecture-4-_40689 - From Gene to Protein Thus far,...

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From Gene to Protein us far, we know: Thus far, we know: –An organism’s phenotype is largely determined by the collection of genes it has inherited; genes are located on chromosomes. – Chromosomes Æ DNA; specific nucleotide sequences of DNA are organized into genes. –Wh a t , specifically, does a gene do and how does it do it? Gene Expression: the process of DNA directed synthesis of proteins (and sometimes RNA). he action of the gene product a protein produces a trait The action of the gene product, a protein, produces a trait –P ro t e in s are the link between genotype & phenotype •H ow do we know genes specify the amino acid sequence of proteins? – Garrod (1908) & others: found link between inheritance of an altered gene & its’ affect on metabolism. –B e ad l e & Tatum (1940’s): first to provide evidence linking a specific gene (DNA) to a specific protein; “one gene one enzyme hypothesis”
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The Central Dogma of Biology: DNA RNA Protein • Universal process common to all life forms • Genes themselves do not produce p proteins, rather various RNA molecules mediate the process of rotein synthesis. p y Transcription: –RNA copy of DNA (a gene) is first synthesized Æ mRNA transcript Translation: – Transfer RNA’s & RNA containing ribosomes decode & convert the mRNA to a protein. enetic code NA “language” Genetic code : DNA language (nucleotides) converted to a protein “language” (amino acids)
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NA Differences Between DNA & RNA dCTP CTP DNA RNA OH ytosine iphosphate 2 deoxy Cytosine triphosphate (deoxyribonucleotide) Cytosine triphosphate (ribonucleotide) • Ribose sugar racil ot thymine(A U C G): • Uracil, not thymine(A,U,C,G): where DNA=A, RNA=U where DNA=T, RNA=A ngle stranded but forms • Deoxyribose sugar •A, T, C, G • Double stranded helix • Single stranded, but forms secondary structures RNA’s are relatively unstable •Very stable
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Transcription • Transcription is executed by RNA polymerase , which synthesizes (5’ 3’) a single stranded RNA copy of a DNA template, i.e., a gene . No RNA primer is required RNA synthesis –A l l genes have these basic components: Promoter : binding site for anscriptional unit termination site 1 DNA strand: 3’ 5’ RNA polymerase; orients it in front of gene. transcriptional unit (the gene) •B o t h D N A strands possess genes, thus mRNA’s can be transcribed p g, from both templates; promoters on the 3’ side. 5’ NA RNA promoter Gene Z 5’ 5’ 3’ 3’ 3’ 3’ DNA mRNA **Key: 5’ to 3’ transcript made from 3’ to 5’ DNA template 5’ mRNA promoter Gene A
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• Transcription follows a 3 step process: Initiation : unwind DNA; RNA polymerase binds to promoter Elongation: RNA polymerase copies 3’ to 5’ DNA template synthesizing a 5’ 3’ transcript.
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1362-SU09-Lecture-4-_40689 - From Gene to Protein Thus far,...

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