* Revisions made: not all proteins are enzymes
* Because proteins that are not enzymes are nevertheless gene products, molecular biologists began to think in terms of one gene-one protein. * Beadle and Tatum’s idea was restated as “one gene-one polypeptide hypothesis.” * BUT: many eukaryotic genes can each code for a set of closely related polypeptides via process call alternative splicing BUT: quite a few genes code for RNA molecules that have important functions in cells even though they are not translated into protein Basic Principles of Transcription and Translation
* Genes provide the instruction for making proteins. But a gene does not a build a protein directly. * Bridge between DNA and protein synthesis is the nucleic acid RNA. * Genes are typically hundreds or thousands of nucleotides long, each gene having a specific sequence of nucleotides. * Each polypeptide of a protein also has monomers arranged in a particular linear order (the protein’s primary structure), but its monomers are amino acids. * TRANSCRIPTION: the synthesis of RNA using information in the DNA (General term for the synthesis of any kind of RNA on a DNA template. * For a protein-coding gene, the resulting RNA molecule is a faithful transcript of the gene’s protein-building instructions. * (mRNA) messenger RNA carries a genetic message from the DNA to the protein-synthesizing machinery of the cell. * Translation: synthesis of polypeptide using the information in the mRNA; during this stage there is a change in language: cell must translate the nucleotide sequence of mRNA molecule into the amino acid sequence of a polypeptide; site is done at ribosomes: complex particle that facilitate the orderly linking of amino acids into polypeptide chains * Difference in Bacteria & Eukaryotes:
* Bacteria don’t have nuclear membranes and thus its DNA is not separated by other compartments such as ribosomes and other protein-synthesizing equipment: so for bacteria that allows translation of mRNA to begin while transcription is still in progress * In Eukaryotes, the nuclear envelope separates transcription and translation in space and time: transcription occurs in the nucleus and mRNA is transported to the cytoplasm, but before mRNA is sent out it is modified to produce function mRNA. Transcription of a protein-coding eukaryotic gene results in pre-mRNA, further processing yields the finished mRNA. Those that are not translated into proteins are called primary transcript. * DNA RNA Protein
The Genetic Code
* Flow of information from gene to protein is based on a triplet code: genetic instructions for a polypeptide chain are written in the DNA as series of non-overlapping, three-nucleotide words. * During transcription, the gene determine the sequence of nucleotide bases along the length of the RNA molecule that is being synthesized * For each gene, only one of the two DNA strands is transcribed, template strand, which provides the pattern for the sequence of nucleotides in an RNA transcript * The Triplet Code: A strand of DNA is blueprint for a particular gene, which is transcribed to mRNA, which is translated by an outside compartment to particular amino acids that make up polypeptide chain (protein): mRNA is read 5’ 3’ * mRNA is complementary rather than identical to DNA because it follows the base pairing rules, similar the strand...