扬州大学：《生物化学 Biochemistry》课程教学课件（PPT讲稿）chapter21 transcription and RNA

Transcription and RNA

Transcription and RNA

Replication,Transcription,TranslationRepetitive processes Build polymers of nucleotides or amino acidsEach has 3 major steps口InitiationBind polymerizing machine, first monomer to templateDNA polymerase, RNA polymerase, RibosomeElongation Read template, add next monomerDNA, RNA, ProteinTermination Release machine and completed product

Replication, Transcription, Translation ◼ Repetitive processes  Build polymers of nucleotides or amino acids ◼ Each has 3 major steps  Initiation • Bind polymerizing machine, first monomer to template • DNA polymerase, RNA polymerase, Ribosome ◼ Elongation  Read template, add next monomer • DNA, RNA, Protein ◼ Termination  Release machine and completed product

Replication,Transcription,TranslationReplicateTo duplicate Making an exact copy of the DNATranscribe To make a copy in a different form Making a copy" of the coding strand of DNA in the form of RNA Different form (RNA vs. DNA), but same language (nucleic acid)Translate Torender inanotherlanguage Converting the language of nucleic acid into the language of amino acids(proteins)

◼ Replicate  To duplicate  Making an exact copy of the DNA ◼ Transcribe  To make a copy in a different form  Making a “copy” of the coding strand of DNA in the form of RNA  Different form (RNA vs. DNA), but same language (nucleic acid) ◼ Translate  To render in another language  Converting the language of nucleic acid into the language of amino acids (proteins) Replication, Transcription, Translation

OHHPhoateBaseuracilphosphateo'HO1NaO=P-O-CH2o'SugarriboseHH2'OHOHOH

guanineadenineHHH1NH-NOpurinesHeCHHNNNpyrimidines1HuracilHthyminecytosineHRNAonlyDNA only

Whatisagene?mRNA transcripts → sequence of amino acids But rRNA and tRNA (& others) are not translated into proteinIn most cases, 1 mRNA = 1 polypeptide Many mRNAs in prokaryotes are polycistronic (multiple genes) Some mRNAs contain code for two proteins in overlappingsequences

What is a gene? ◼ mRNA transcripts → sequence of amino acids  But rRNA and tRNA (& others) are not translated into protein ◼ In most cases, 1 mRNA = 1 polypeptide  Many mRNAs in prokaryotes are polycistronic (multiple genes)  Some mRNAs contain code for two proteins in overlapping sequences

Whatisagene?DNA control elements ≠RNA Promoters and other regulatory regionsRNA transcripts undergo processing before reaching functional form Splicing of introns inmRNA A typical gene consists of 8 exons (protein-coding segments) Other RNAs are processed as well (rRNA, tRNA)

What is a gene? ◼ DNA control elements ≠ RNA  Promoters and other regulatory regions ◼ RNA transcripts undergo processing before reaching functional form  Splicing of introns in mRNA  A typical gene consists of 8 exons (protein-coding segments)  Other RNAs are processed as well (rRNA, tRNA)

Noncoding RNAs2 types of genes Protein-coding(DNA-RNA→protein) Noncoding RNAs (DNA→RNA)About 8o% of the human genome may undergo transcription to producenoncoding RNAs[TABLE21-1]Some Noncoding RNAsTypeSize (nudeotides)FunctionRibosomal RNA (rRNA)120-4718Translation(ribosomestructureandcatalyticactivity)TransferRNA (tRNA)54-100DeliveryofaminoacidstoribosomeduringtranslationSmall interfering RNA (siRNA)2025Sequence-specificinactivationofmRNA20-25MicrORNA(miRNA)Sequence-specificinactivationofmRNAUpto17,200LargeinterveningnoncodingTranscriptional controlRNA (linCRNA)Small nuclearRNA (snRNA)60-300RNAsplicingSmallnucleolarRNA(snoRNA)70-100Sequence-specificmethylationofrRNACJohaWley&SonsInc.Allriphtsreserved

Noncoding RNAs ◼ 2 types of genes  Protein-coding (DNA→RNA →protein)  Noncoding RNAs (DNA→RNA ) ◼ About 80% of the human genome may undergo transcription to produce noncoding RNAs

TranscriptionWhich of the 2 DNA strands get transcribed? RNAsynthesisproceedsbycomplementarybasepairingwithoneoftheDNA strandsThis strandacts as templateto determinewhichribonucleotide gets addedandinwhatorderThemRNAsynthesizedcontainsthegeneticcodeAGCCodingstrandDNA(nontemplate)GGTAGCGCTTACGACCATCGAATGCTDNANoncodingstrand(template)

Transcription ◼ Which of the 2 DNA strands get transcribed?  RNA synthesis proceeds by complementary base pairing with one of the DNA strands  This strand acts as template to determine which ribonucleotide gets added and in what order  The mRNA synthesized contains the genetic code

TranscriptionWhich of the 2 DNA strands get transcribed? The DNA strand that guides its synthesis is therefore thenoncoding"ortemplate strandThe complementary strand of DNA is therefore the coding strand口 The mRNA product is therefore an RNA copy of the coding strand of theDNA (U in placeofT)Coding strandDNA(nontemplate)GGTAGCGCTTACGA5CCATSGCGAATGCTDNANoncodingstrand(template)

Transcription ◼ Which of the 2 DNA strands get transcribed?  The DNA strand that guides its synthesis is therefore the “noncoding” or template strand  The complementary strand of DNA is therefore the coding strand  The mRNA product is therefore an RNA copy of the coding strand of the DNA (U in place of T)