Flashcards in Chapter 7 Deck (20):
How is the info encoded in DNA used to make protein?
1. DNA to RNA
2. mRNA processing
3. mRNA export from nucleus to cytosol
4. RNA to protein
What makes RNA different from DNA?
-fold up in a variety of shapes and can form intramolecular base pairs (stem loop structure)
- a c u g
What are the 3 roles of RNA in cells?
Characteristics of Transcription
- RNA is identical to sense strand and complementary to template strand
-RNA polymerase is used to add nts and form new phosphodiester bonds
-transcription is conservative
-Molecules are much shorter than DNA and there might be several rna polymerases on a single stretch of DNA
What are the differences between RNA and DNA polymerase?
Rna poly adds ribonots, doesn't need a primer, and there is no elaborate proofreading mechanism (thus transcription not as acuurate)
What the 4 different types of RNA
1- mrna= code for protein
2- rRNA make up ribsomes
3- tRNA= form the adapters that select a.a and holds them in place
4- small RNA used in splicing and gene regulation
Differences between Euk and Prok transciption
- euk has 3 RNA polymerases and each RNA carries info from a single gene and thus different transcripts
- prok= 1 RNA poly and set of genes can be made into 1 transcript
What are the three types of RNA polymerases and what do they do?
1- most of rRNA
2- mRNAs and some small RNAS
3- tRNAs and some rRNA and some small RNA
What are the 3 general steps in transcription?
What is transcription in prokaryotes likes?
-transcription will begin once sigma factor binds to rna poly and this will make the poly bind to the DNA
- poly slides along DNA until it reaches a promoter (site with -35 to -10 pribnow box)
-helix is opened by helicase
-template strand is exposed and rna synstheiszes short strand of 10 nts and sigma factor falls off
-Rna poly synthesizes RNA until it reachesa terminator sequence
-RNA poy falls off of DNA and reassociates with SF to start process again
What do general transcription factors do?
-help position RNA poly 11 correctly at promoter like SF
- helps rna poly 2 pull apare 2 DNA strands like helicase would
-helps rna poly 2 to leave promoter as transcription begins
What is the TATA box?
-Dna sequence composed of As and Ts
-found in promoters of most eukaryotic genes that are transcribed by RNA poly 2
-specifies where transcription begins
-25 bp upstream of transcription start site
What is the transcription mechanism in eukaryotes? (step 1)
1- binding of TF2D (general TF) to the TATA box by the TF2D's TBP (tata box binding protein) which causes the DNA to bend which results in the attraction of other transcription factors
2- Binding of TF2B
3-Binding of TF2E TF2H and RNA poly 2 (making the transcription initiation complex)
4- TF2H used ATP to pry apart DNA helix, allowing transcription to begin
5- TF2H phosphorylates RNA poly 2; TF2H has protein kinase which adds Phosphate group to RNA poly 2 at CTC (c terminal domain or the long tail) which causes a change in the shape and transcription to begin.
6- general transcription factors are released from DNA and are recycled
What does mRNA processing entail (step 2 in process)
-mRNA is chemically modified, as the primary transcript becomes the mature transcript
- the phosphoraltaion of the CTD allows for RNA processing like capping as they bind to the phosphorylated CTD of RNA poly 2
1. mRNA capping
What is RNA capping?`
-The chemical modification of the 5' end of the transcript
- 5' end is capped by the addition of a special nt (7-methylguanosine)
- cell adds this cap before transcription is complete
What is polyadehylation?
-the 3' end of the transcript is trimmed (at a particular sequence)
-addition of a series of A (adenine) ribonucleotides at 3' end of the transcript
-series of As at 3' end is called a polyatail (only in euk)
What is splicing?
-splicing out introns which is a region of non coding RNA that is part of the primary transcript; keeps exons which are segments of euk genes that a part of the mature and primary transcript
-produce a strand of exons
What are the functions of mRNA modification?
1- stabilizes mRNA
2- aid in export from the nucleus
3- used by translation machinery to indicate that a transcript is complete and in tact
What are some splicing requirements? Benefits?
- need enzymes called snRNA or snurps (Small nuclear ribonucleotide particles) which form spliceosome
-benefits: allows different types of proteins to be made from the same RNA transcript by splicing it in different ways