Protein size in most eukaryotes eukaryotic cells have

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Unformatted text preview: for bacterial and viral genes - there is a general correlation It is also generally true for single-celled eukaryotes Multicellular eukaryotes have genes containing far more DNA than would be predicted using bacterial and viral genes as a model Eukaryotic Genes Colinearity predicts that the number of nucleotides in a gene should be proportional to the number of amino acids in a protein There is no correlation between gene size and protein size in most eukaryotes Eukaryotic cells have very large nuclear RNA species that are never observed in the cytoplasm Is there a difference between mRNA sequence and gene sequence? Introns To compare mRNA and genomic sequence: 1. Mix DNA and RNA and allow complimentary sequences to “hybridize” (base pair) 2. Electron micrograph reveals many loops 3. Loops are regions where the two molecules can’t pair Introns Genes in eukaryotes are interrupted Introns are common in multicellular eukaryotes and rare in unicellular eukaryotes Exons are fairly uniform in length (averaging 150 nt) Introns Introns vary in size, averaging 3 kb The range of sizes is quite large; 30% of human introns are more than 10 kb in length. This accounts for the “no correlation between gene size and protein size”. Introns All types of eukaryotic genes are interrupted (protein-coding and otherwise) Four major types of introns Group I - rRNA genes; self-splicing Group II - Organelle genes; self-splicing Nuclear pre-mRNA - Nuclear protein-encoding genes; spliceosomal tRNA - tRNA genes; enzymatic splicing Introns All types of eukaryotic genes are interrupted (protein-coding and otherwise) Four major types of introns Group I - rRNA genes; self-splicing Group II - Organelle genes; self-splicing endosymbiont theory Nuclear pre-mRNA - Nuclear protein-encoding genes; spliceosomal tRNA - tRNA genes; enzymatic splicing To summarize: Gene sequences...
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This document was uploaded on 02/25/2014.

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