CBG.04 Flashcards
what is the maximum length of most RNA strands?
no more than a few thousand nucelotides long
Transcription
Copying of a section of DNA into a complementary strand of RNA via RNA Polymerase
What are the four nucelsoide triphosphates?
ATP, CTP, UTP, GTP
How many transcripts can be made form a single gene in an hour in eukaryotes?
over a thousand
What are the important difference between DNA polymerase and RNA polymerase?
RNA polymerase catalyzes the linkage of ribonucleotides, not deoxyribonucleotides
unlike the DNA polymerases involved in DNA replication, RNA polymerases can start an RNA chain without a primer
RNA polymerases make about one mistake for every 104 nucleotides copied into RNA (compared with an error rate for direct copying by DNA polymerase of about one in 107 nucleotides)
small nuclear RNA
direct the splicing of pre-mRNA to form mRNA
small nucelolar RNA
used to process and chemically modify rRNAs
Promotor
Nucleotide sequence in DNA to which RNA polymerase binds to begin transcription/ a special sequence of nucleotides indicating the starting point for RNA synthesis
what is the speed of chain elongation in bacteria
approximately 50 nucleotides/sec for bacterial RNA polymerases
How do the signals in the DNA (termination signals) stop the elongating polymerase
Termination signal consists of a string of A-T nucleotide pairs preceded by a two-fold symmetric DNA sequence, which, when transcribed into RNA, folds into a “hairpin” structure through base-pairing, the hairpin may help to wedge open the movable flap on the RNA polymerase and release the RNA transcript from the exit tunnel. At the same time, the DNA-RNA hybrid in the active site, which is held together predominantly by U-A base pairs (which are less stable than G-C base pairs because they form two rather than three hydrogen bonds per base pair), is not sufficiently strong enough to hold the RNA in place, and it dissociates causing the release of the polymerase from the DNA
consensus sequence
Average or most typical form of a sequence that is reproduced with minor variations in a group of related DNA, RNA, or protein sequences. The consensus sequence shows the nucleotide or amino acid most often found at each position. The preservation of a consensus implies that the sequence is functionally important.
Will promotors be stronger for proteins which are anundant or rarer proteins?
Promoters for genes that code for abundant proteins are much stronger than those associated with genes that encode rare proteins, and their nucleotide sequences are responsible for these differences.
Terminator
Signal in bacterial DNA that halts transcription.
How many RNA polymerases do eukaryotes have?
3 -
RNAP I - rRNA
RNAP II - mRNA
RNAP III - tRNA
What are the differences between becaterial and eukaryotic RNAP?
- they are structurally fairly similar, The eucaryotic polymerase is larger than the bacterial enzyme
- bacterial RNA polymerase (with σ factor as one of its subunits) is able to initiate transcription on a DNA template in vitro without the help of additional proteins, eucaryotic RNA polymerases cannot. They require the help of a large set of proteins called general transcription factors, which must assemble at the promoter with the polymerase before the polymerase can begin transcription.
- Eucaryotic transcription initiation must deal with the packing of DNA into nucleosomes and higher order forms of chromatin structure, features absent from bacterial chromosomes.
