mbb 201 topic 7

transcription \ the process of synthesizing RNA from a DNA template;

translation \ the process of synthesizing protein from an RNA template;

DNA vs RNA \ dna-deoxyribose sugar (h), bases gcat double stranded

rna-ribose sugare (oh) 2’ gcau, single stranded;

key steps in transcription\ -performed by RNA polymerases, DNA needs to be unwound, one dna strand acts as a template, NTPs (instead of dNTPs) are added one at a time 5’-3’;

ntps vs dntps \ ntp-RNA transcription, dntps dna synthesis replication;

transcription vs DNA replication \ RNA molecules much shorter, RNA polymerases catalyze instea of DNA polymerases, uses ntps instead of dntps, can start an RNA chain w/o a primer, newly synthesized RNA is displaced and the DNA reforms a double helix;

types and functions or RNA \ 1.messenger RNA-code for proteins, 2.ribosomal RNAs -form the core of the ribosomes structure and catalyze protein synthesis (platform) 3.micrornas regulate gene expression 4.transfer RNAs serve as adaptors between mRNA and amino acids during protein synthesis, 5. other noncoding RNAs used in RNA splicing gene regulation, telomere maintenance and many other processes;

steps of transcription in bacteria \ 1. RNA polymerase binds tightly to a promoter: a specific sequence that is immediately upstream of the transcription start site 2.double helix is opened, transcription begins using one strand as a template 3. transcription stops when the RNA polymerase encounters a specific sequence know as the terminate (stop site);

what happens during promoter initiantion \ both promotor and terminator have conserved sequences, numbers represent the nucleotide position relative to the first nucleotide transcribed, the promoter has conserved sequences at the -10 and -35 regions, these regions are bound by a subunit of the RNA polymerase known as the sigma factor;

what is a sigma factor \ helps RNA polymerase recognise where to begin transcription, it binds to the -10 and -35 regions in only one direction ensuring that the polymerase binds in on orientation, sigma factor binds the -35 region and promotes unwinding of downstream DNA;

differences in eukaryotic transcription compared to bacteria \ eukaryotic transcription… 1.has greater # of RNA polymerases 2. requires general transcription factors 3. has more elaborate control mechanisms 4. must take DNA packing into account 5. processes mRNA;

what does RNA polymerase 2 do \ synthesizes mRNAs, most small nuclear RNAs (snRAs and sno RNAs), most microRNAs and telomerase RNAs;

what are general transcription factors \ accessory proteins eukaryotes need that allow transcription to occur , help position the RNA polymerase, separate the DNA and initiate transcription (TFIID, TFIIB, TFIIA, TFIIF, TFIIE, TFIIH)(6);

steps in eukaryote transcription \ 1. TFIID binds to the TATA box (a conserved sequence often used to locate the promoter)foudn within the promoter, binding causes change in DNA structure that helps other general transcription factors to assemble

2.other transcirption factors assemble to form trasncription preinitiation complex (when all general Tfs are present and RNApII)

3. TFIIH contains a kinase domain which phosphorlyates the C-terminal domain (CTD), of the RNA polymerase, allowing the RNA polymerase to clear the promoter (transcription starts)

4.other transcription factors dissociate;

what are regulatory DNA sequences \ several segments of DNA that controls eukaryote gene expression, can by thousands of bps away, requries interaction of several proteins and complexes, allows eukaryote to respond to a greater variety of signals;

why does chromatin have to be condensed \ to allow access by the transcription factors bc eukaryotic DNA is packed on nucleosomes;

whats RNA capping \ its an atypical methylated guanin nuceotide linked to the RNA using an unusual linkage (5’-5’) -5’ cap increases the stability of the mRNA and helps with its export to the cytoplasm;

whats polyadenylation (3’ poly A tail addition ) \ adds a series of repeating adenine nucleotides to the 2’ end of the molecule, a few hundred nucleotides long, labels the RNA as mRNA, also increases the stability of the mRNA and helps with its export;

whats splicing \ introns (non coding sequences) interrupt exons (coding sequences) of gene, introns must be removed before being translated which is achieved through splicing;

what performs splicing \ spliceosome complex - several sn RNPs work togthr (small nuclear ribonucleoproteins ) - containt both RNA and protein, RNA component performs majority of the catalysis;

what does alternative splicing do \ allows many different products such as proteins to be produced from a single gene→transcript of many eukaryotic genes can be spliced in different ways;

how and when are mRNAs exported \ -mature eukaryotic mRNA are eported from the nucleus, export mediated by the nuclear pore complex, mRNA must be bound to specific proteins including polyA binding proteins, a cap binding protein and the exon juction coplex that binds to mRNAs that have been appropriately spliced, entire set of proteins decides and guids mRNA out;

what affects mRNA degredation \ 3’ untranslated region of the mRNA which lies between coding region and poly A tail, (poly a and 5’ cap protect fromdegredation );