2Protein Synthesis / Gene Expression Gene expression: The translation of information encoded in a gene into protein or RNA. Expressed genes include genes that are transcribed into messenger RNA (mRNA) and then translated into protein, as well as genes that are transcribed into types of RNA such as transfer RNA (tRNA) and ribosomal RNA (rRNA) that are not translated into protein.
3Gerrodgenes dictate phenotype through enzymes that catalyze specific chemical reactions in the cellsymptoms of an inherited disease reflect a person’s inability to synthesize a particular enzyme
5Development of the Theory one gene - one proteinnot all proteins are enzymesone gene - one polypeptidemany proteins are composed of several polypeptides, each of which has its own gene
6RNA contains ribose as its sugar substitutes the base uracil for thymineconsists of a single strand
7transcription and translation Transcription DNA strand provides a template for the synthesis of a complementary RNA strandTranslation the information contained in the order of nucleotides in mRNA is used to determine the amino acid sequence of a polypeptide
8Transcriptiontemplate strand of DNA provides a template for the sequence of nucleotides in RNAThe complementary RNA molecule is synthesized according to base-pairing rulesexcept that uracil is the complementary base to adenine
9RNA polymerase separates the DNA strands at the appropriate point bonds the RNA nucleotides as they base-pair along the DNA template
13At the 5’ end of the pre-mRNA molecule, a modified form of guanine is added, the 5’ cap At the 3’ end, an enzyme adds 50 to 250 adenine nucleotides, the poly(A) tail
14RNA splicingMost eukaryotic genes and their RNA transcripts have long noncoding stretches of nucleotidesSpliceosome removes introns and joins exons to create an mRNA molecule with a continuous coding sequence
15What’s the point of splicing? at least some introns contain sequences that control gene activity in some waysplicing itself may regulate the passage of mRNA from the nucleus to the cytoplasmone clear benefit of split genes is to enable a one gene to encode for more than one polypeptide.
16Translationblocks of three nucleotides, codons, are decoded into a sequence of amino acidscodons are read in the 5’->3’ direction along the mRNAribosome adds each amino acid carried by tRNA to the growing end of the polypeptide chain
17tRNAcarries a specific amino acid at one end and has a specific nucleotide triplet, an anticodon, at the otherThe anticodon base-pairs with a complementary codon on mRNA