Transcription and RNA
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
◼ 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
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
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 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
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
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)