Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
GENE EXPRESSION: THE USE OF INFORMATION Protein Synthesis Genes (DNA information) are used to synthesize enzymes Mutation number: Neurospora crassa (fungus) The colinearity of DNA and proteins • • • • DNA information determines enzyme/protein structure. DNA information is stored in the base sequence. Protein structure depends on the amino acid sequence. Thus DNA base sequence must determine protein amino acid sequence (through a “genetic code”). amino acid 1 amino acid 2 amino acid 3 amino acid 4 How many DNA bases are needed to “code” for one amino acid? •There are four kinds of bases (base pairs). •There are 20 kinds of amino acids (plus “stop” signs). •Thus, the cells must use permutations of multiple bases to code for one amino acid. amino acid 1 amino acid 2 amino acid 3 amino acid 4 Three bases make a “codon.” (Degenerate, but not ambiguous) Transcription: RNA synthesis ! DNA is not directly involved in protein synthesis ! Instead, DNA base sequence is “transcribed” to an RNA base sequence. ! RNA is directly involved in protein synthesis (“translated”). transcription translatio n (This is Crick’s “Central Dogma”. Not as dogmatic now, it has been modified in two important ways.) PROTEIN SYNTHESIS ! Use of DNA information to synthesize proteins ! First step: transcription of DNA information Transcription: RNA synthesis Several types of RNA are needed for protein synthesis; each is made using information carried by DNA Structure of RNA ! Polynucleotide chain like DNA ! Sugar is ribose (-OH on C2’) ! U replaces T (no methyl) ! Molecule is generally single-stranded (though there may be some helix in hairpins). OH I O OH I O OH I O OH I O Synthesis of RNA Players ! Nucleoside triphosphate substrates (ATP, CTP, GTP, UTP) ! Enzyme (RNA polymerase) ! DNA “template” to direct the sequence of bases polymerized. Initiation RNA pppG Template DNA….…CpApApTp… Elongation p p RNA pppG pU Template DNA….…CpApApTp… RNA pppGpU Template DNA….…CpApApTp… (Add an NTP) p p p p RNA pppGpU pU Template DNA….…CpApApTp… (Form the phosphodester bond) (Add an NTP) p p RNA pppGpUpU Template DNA….…CpApApTp… (Form the phosphodester bond) Result ! One RNA polynucleotide chain ! Base sequence determined by (complementary to—not identical to) the base sequence of the template strand Summary ! DNA base sequence ("codons") provides information for protein amino acid sequence ! DNA information transcribed onto RNAs: ribosomal, messenger, transfer RNAs ! Next: use of RNAs to synthesize proteins