Bulges RNA STRUCTURE Hairpin is a pattern of intermolecular base pairing that occurs when two regions of the or number of mismatched base pairs affects this Only a small amount are okay Biology Final Exam Comprehensive Study Guide Chapter 17 Transcription and RNA processing Background info DNA Replication double helix splits the two helices and separate from each other to become templates for each other by pairing bases with their complementary pairs through attraction DNA transcription double helix splits but instead of having deoxyribonucleic acid nucleotides pair up the mRNA nucleotides will pair up is the step where you go from DNA to mRNA and the mRNA leaves the nucleus of the cells and goes to the ribosomes DNA Translation is the process of making a linear chain of amino acids polypeptide chain in which the amino acids are joined by peptide bonds The sequence of amino acids in the polypep tide chain is determined by the sequence of nucleotides in the mRNA Every three nucleotides in the mRNA is a codon that codes for one amino acid same strain usually complementary nucleotide sequence when read in opposite directions base pair to form a double helix that ends in a unpaired loop The formation of this structure de pends on its stability Pseudoknot contains at least two stem looped structures in which half of one in intercalated between the two halves of another Internal loops interruptions in the helical structures of RNA Messenger RNA is transcribed from the template strand of a gene it is the cell s protein syn thesizing machinery Transcription RNA polymerase an enzyme pries the two strands of DNA apart and joins the RNA nucleotides as they base pair along the DNA template just like DNA polymerase RNA polymerase can only assemble a polynucleotide in its 5 3 direction RNA however is able to start a chain from scratch without a primer Specific sequences of nucleotides along the DNA mark where transcription of a gene begins and ends Promoters are the DNA sequences where RNA polymerase attaches and initiate transcription and also determines which of the two strands of the DNA helix is used as a template The direction of transcription is considered downstream and the other direction is consid ered upstream The terms describe the positions of the nucleotide sequences within the DNA or RNA RNA Polymerase II is used for mRNA synthesis The other RNA polymerases I and III are used to transcribe molecules not used for synthesis Synthesis of an RNA Transcript is in order as follows Initiation after RNA polymerase binds to the promoter the DNA strands unwind and the poly merase initiates RNA synthesis at the start point on the template strand Promoter sequence is thus upstream from the terminator the synthesis of RNA using a DNA template signals the end of transcription in bacteria Terminator The RNA polymerase adds nucleotides to the 3 end of the growing RNA molecule in bacteria RNA polymerase binds directly to the promoter but in eukaryotes transcription factors a collection of proteins mediate this binding of RNA polymerase and the initiation of transcription Transcription Initiation Complex is the whole complex of transcription factors and a crucial promoter DNA sequence know as a TATA box Elongation Polymerase moves downstream unwinding the DNA and elongating the RNA tran script 5 3 IN the wake of transcription the DNA strands reform a double helix In the wake the RNA peels away from the DNA template allowing the helix to reform Transcription is about 40 nucleotides per second The gathering of multiple polymerases si multaneously transcribing a single gene increases the amount of mRNA transcribed helping the cell make the protein thats being encoded in large amounts Termination Eventually the RNA transcript is released and the polymerase detaches from the DNA In bacteria transcription proceeds through a terminator sequence in the DNA the transcribed terminator sequence is the termination signal causing polymerase to detach and release the transcript immediately being used for mRNA In eukaryotes RNA polymerase II transcribes a polyadenylation sequence AAUAAA in the pre MRNA 10 35 nucleotides down from that proteins cut the transcript free from the polymerase releasing Pre MRNA But the polymerase continues transcribing DNA for awhile past the site where the pre MRNA was released Post transcription mRNA leaves nucleus of the cell to ribosomes and proteins are then formed Translation RNA processing when the enzymes in the eukaryote modifies pre mRNA before the mes sages are dispatched to the cytoplasm During this process both ends of the primary transcript are altered certain interior sections of the RNA are cut out and remaining parts are spliced together The 5 end is synthesized first receiving a 5 cap a modified form of a guanine G nucleotide added to the end after transcription of the first 20 40 nucleotides The 3 end is also altered before the mRNA exits the nucleus It receives a Poly A tail an enzyme added 50 250 more adenine A nucleotides to the 3 end after the AAUAAA Polyadenylation signal UTR untranslated regions they lie at both ends of the sequence before the 5 cap and poly A tail They will not be translated into protein but function with ribosome binding Both the 5 cap and Poly A tail serve many functions protection of the mRNA from degradation by hydrolytic enzymes helping ribosomes attach to the 5 end of the mRNA once the mRNA reaches the cytoplasm RNA splicing the removal of large portions of the RNA molecule that is initially synthesized Since the average length of a human DNA molecule is 27 000 base pairs long the RNA tran script is that long too It takes only 1200 nucleotides in RNA to code for the average size protein of 400 AA triplets These extra nucleotides are noncoding stretches that aren t translated Each end of a pre mRNA molecule is modified in a different way facilitation of the export of the mature mRNA from the nucleus Introns the noncoding segments of nucelic acid that are between coding regions The noncoding regions are interspersed between coding segments of the pre mRNA The se quence of DNA is thus split up into segments Exons the other regions on the DNA sequence that are eventually expressed through amino acid sequences Except the UTR s of the exons at the ends of the RNA think exon exit the nucleus RNA polymerase II transcribes both introns and exons from DNA but the mRNA molecule that enters the cytoplasm is an abridged version The introns are cut
View Full Document
Unlocking...