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From Gene to Protein How Genes Work
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What do genes code for? How does DNA code for cells & bodies? DNA
how are cells and bodies made from the instructions in DNA DNA proteins cells bodies
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The “Central Dogma” (main idea)
Flow of genetic information in a cell How do we move information from DNA to proteins? transcription translation DNA RNA protein trait To get from the chemical language of DNA to the chemical language of proteins requires 2 major stages: transcription and translation DNA gets all the glory, but proteins do all the work! replication
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How did we learn about genes?
Inheritance of diseases suggested that genes coded for enzymes each disease (phenotype) was caused by a missing enzyme For example: Tay sachs PKU (phenylketonuria) albinism Am I just the sum of my proteins? Tay Sachs - Hexosaminidase A is a vital hydrolytic enzyme, found in the lysosomes, that breaks down lipids. When Hexosaminidase A is no longer functioning properly, the lipids accumulate in the brain and interfere with normal biological processes. PKU = phenylalanine hydroxylase missing can’t break down phenylalanine into tyrosine Albinism – In tyrosinase-negative cases, either the tyrosinase enzyme is not produced or a nonfunctional version is produced. metabolic pathway disease disease disease disease A B C D E enzyme 1 enzyme 2 enzyme 3 enzyme 4
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DNA mRNA protein trait From gene to protein nucleus cytoplasm
aa From gene to protein nucleus cytoplasm transcription translation DNA mRNA protein ribosome trait
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from DNA language to RNA language
Transcription from DNA language to RNA language
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DNA RNA Review: RNA ribose sugar N-bases single stranded lots of RNAs
uracil instead of thymine U : A C : G single stranded lots of RNAs mRNA, tRNA, rRNA… transcription DNA RNA
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Matching bases of DNA & RNA
Match RNA bases to DNA bases on one of the DNA strands Same method as DNA replication DNA strands stick together again after the RNA is made A C U G A G U G U C U G C A A C U A A G C RNA polymerase U 5' A 3' G A C C T G G T A C A G C T A G T C A T C G T A C C G T
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Transcription Making mRNA (messenger RNA) RNA polymerase
Use DNA to make a complementary RNA strand transcription bubble Copies the template strand of DNA Enzyme RNA polymerase coding strand 3 A G C A T C G T 5 A G A A A G T C T T C T C A T A C G DNA T 3 C G T A A T 5 G G C A U C G U T 3 C unwinding G T A G C A rewinding mRNA RNA polymerase template strand build RNA 53 5
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Eukaryotic genes have extra DNA!
Eukaryotic genes are in small pieces exons = the real gene expressed / coding DNA introns = the “garbage” inbetween sequence introns come out! intron = noncoding (inbetween) sequence eukaryotic DNA exon = coding (expressed) sequence
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mRNA processing mRNA splicing make mature mRNA transcript
edit out introns make mature mRNA transcript only exons (gene parts) left eukaryotic RNA is about 10% of eukaryotic gene. intron = noncoding (inbetween) sequence ~10,000 bases eukaryotic DNA exon = coding (expressed) sequence pre-mRNA primary mRNA transcript ~1,000 bases mature mRNA transcript spliced mRNA
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Many combinations possible
Different mRNAs can be produced from same gene different segments treated as exons Starting to get hard to define a gene!
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DNA mRNA protein trait From gene to protein nucleus cytoplasm
aa From gene to protein nucleus cytoplasm transcription translation DNA mRNA protein ribosome trait
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