BIO1107 Test 3 Spring 2012 Chapter 17 From Gene to Protein Genes Specify Proteins using Transcription Translation DNA RNA Protein Gene Expression the process where DNA directs the synthesis of proteins in some cases just RNAs Gene Protein requires 2 stages transcription synthesis of RNA under the direction of DNA DNA read 3 to 5 DNA serves as a template for the newly synthesized strand of mRNA DNA and RNA use the same language mRNA carries a genetic message from the DNA to the protein synthesizing machinery of the cell acts like a transcript for a protein coding gene sending out multiple copies which is why RNA is preferred over DNA RNA can make multiple copies of the original or DNA BIO1107 Test 3 Spring 2012 translation synthesis of a polypeptide which occurs under the direction of mRNA Change of language Base sequence of of mRNA molecule is translated to an amino acid sequence of a polypeptide Ribosomes are the site of translation orderly linkage of amino acids polypeptide chains Transcription Translation Eukaryotes vs Bacteria Eukaryotes contains nuclear envelope to separate the two stages Transcription occurs in the nucleus rst resulting in pre mRNA eventually making mRNA which exits via nuclear pores Translation is a separate process in the cytoplasm assisted by ribosomes equipment Bacteria no nucleus or membrane bound organelles DNA not segregated from ribosomes or other protein synthesizing Allows for translation to occur while transcription is still in progress The Genetic Code Redundancy but no ambiguity Only 4 nucleotides to specify 20 amino acids Triplets are the smallest units of uniform length that can code for amino acids doublets or single nucleotides would not be enough to code for ALL 20 amino still somewhat redundant more than one codon speci ed per each amino acid Triplet Code example base triplet AGT along a particular position of DNA strand codes for amino acid Serine Template strand the one strand of a DNA double stranded molecule that is being acids transcribed BIO1107 Test 3 Spring 2012 Acts as a template or sets pattern for developing strand mRNA strand is complementary to its DNA template rather than identical because Uracil instead of Thymine base triplets of mRNA called codons because codons are base triplets it takes 3 times the amount of nucleotides than amino acids in protein synthesis Start codon AUG codes for Methionine Stop codons UGA UAA UAG therefore all protein polypeptide chains start with Met Transcription is the DNA directed synthesis of RNA RNA polymerase pries open double stranded DNA molecule also joins together RNA nucleotides as they base pair along the DNA template strand can only assemble in 5 to 3 direction DON T NEED A PRIMER like DNA polymerase Instead contains regions on DNA strand acting as Promoter sequence initiating transcription Eukaryotic promoter commonly includes TATA box pg 333 Terminator sequence signaling for the end of transcription Transcription unit the stretch of DNA that is transcribed into RNA molecule BIO1107 Test 3 Spring 2012 RNA polymerase in Prokaryotes vs Eukaryotes Prokaryotes contain one type Eukaryotes contain 3 types RNA polymerase II is the type used in mRNA synthesis 3 Stages of Transcription Initiation transcription starts Elongation after RNA polymerase binds to promoter the DNA strands unwind Polymerase initiates RNA synthesis at the start point of the template strand In addition to serving as binding site for RNA pol and determining where the promoter determines which of 2 DNA strands will serve as template The polymerase moves downstream unwinding the DNA and elongating the RNA transcript 5 to 3 In the end of transcription the DNA strands reform a double helix Exposes about 10 20 nucleotides at a time Termination of RNA chain RNA transcript is released and the polymerase detaches from the DNA Differs in BACTERIA and EUKARYOTES Bacteria terminal signal transcribed terminator an RNA sequence causes polymerase to detach from DNA and release the transcript available for immediate use as mRNA Eukaryotes polyadenylation signal sequence that codes for a polyadenylation signal AAUAAA in the pre mRNA pre mRNA then gets processed to form product mRNA Eukaryotic cells modify RNA after transcription RNA processing modi cation of pre mRNA in speci c ways before the genetic messages are sent to the cytoplasm most of the time sections of RNA molecule are cut out while the remaining pieces are spliced together during process BOTH ends of the primary transcript are altered http www stolaf edu people giannini flashanimat molgenetics transcription swf BIO1107 Test 3 Spring 2012 Split Genes and RNA splicing in nucleus of eukaryotes RNA splicing the removal of large portions of the RNA molecule that is initially synthesized pre mRNA Most eukaryotic genes DNA and their RNA transcripts have long noncoding stretches of nucleotides regions that are not translated Introns or intervening sequences are the noncoding segments located in between coding regions Functional importance of introns the presence of introns in genes is that a single gene can encode more than one kind of polypeptide Alternative RNA splicing is when many genes are known to give rise to multiple kinds of polypeptides depending on which segments are treated as exons during RNA processing one reason humans can get by with such a small number of genes but with so much variation Allows for higher number of different protein products an organism produces than its number of genes Exon shuf ing introns increase the probability of bene cially crossing over between the exons of alleles g 17 12 Exons are the other regions and are eventually expressed by being translated to amino acid sequences exit the cell Both terms intron and exon are used for both DNA and RNA BIO1107 Test 3 Spring 2012 RNA pol II transcribes both the introns and exons of the DNA but the mRNA that exits to the cytoplasm is the abridged version or introns have been taken out Spliceosome how pre mRNA splicing is carried out made of up many snRNPs almost as big as a ribosome recognize signal for RNA splicing snRNPs small nuclear ribonucleoproteins pronounced snurps RNA in these particles called snRNA releases introns joins together exons g 17 11 Domains different regions of a polypeptide protein that have speci c structures functions Different exons code for different domains of a protein Pyruvate Kinase Red regulation Purple substrate binding Green ADP binding Ribozymes RNA molecules that