transcription Flashcards
define transcription
process that makes RNA from DNA
why is the process of transcription called it?
the information in a specific region of DNA is being transcribed into the slightly different language of RNA (uracil has replaced thymine)
where does transcription take place?
nucelus
genes are transcribed to what?
mRNA
how is the process of pre-mRNA initiated?
unwinding a specific portion of the DNA double-helix and the binding of RNA polymerase to a sequence at the start of the gene called the promoter region
what is elongation?
RNA polymerase adds the appropriate nucleotides (adenine, uracil, guanine, and cytosine) to elongate the pre-mRNA
true or false: RNA nucleotides are only added in the 5’-3’ direction
true
what is the result of RNA nucleotides added in the 5’-3’ direction?
the pre-mRNA that is produced has the same nucleotide sequence as the complementary strand of DNA, except that each thymine will be replaced by uracil.
what is termination?
RNA polymerase reaches the terminator sequence and the pre-mRNA is released from the DNA
true or false: in bacterial cells, the pre-mRNA is ready to leave the nucleus
true
what 3 things must occur before non-bacterial cells’ pre-mrna can leave the nucleus?
1) a special cap has to be added to the 5’ end 2) a tail has to be added to the 3’ end
3) RNA sequences that aren’t going to be included in the final version of the protein made in the cytoplasm have to be removed.
what is the 5’ cap?
a modified guanine nucleotide that is involved in getting the mRNA out of the nucleus
what does the 3’ tail consist of?
a series of adenine nucleotides and is called a poly-A tail
what does the cap and tail protect the ends of the mRNA from?
exonucleases
what are the “non-sense” sequences?
introns
what are the sequences that are important for making the protein?
exons
what is splicing?
processes responsible for removing the introns from pre-mRNA to yield mRNA
what does a spliceosome consist of?
short nuclear RNAs and some associated proteins
describe the process of how a spliceosome is formed
The short nuclear RNAs attach to the ends of the exons on either side of an intron and then move together
what happens to the introns when the formation of a spliceosome forms?
intervening intron forced into a loop
what happens as the spliceosome tightens?
the ends of the exons are linked together and the intron is released
why can the introns be rapidly degraded by the nuclear exonucleases?
because it lacks a cap or polyA tail
what are the nucleotides in the introns released and used for?
subsequent reactions
describe the process of alternative splicing
- the short nuclear RNAs attach to the ends of exons separated by more than one intron.
- As the spliceosome forms, this simultaneously results in the excision of both introns and exons.
- the sequence of nucleotides in the mRNA that leaves the nucleus results in the production of a different protein than if just introns had been removed.
what is the advantage to genes if alternative splicing is used?
allows the genes to be more flexible and adaptable when it comes to the proteins the cell produces
why are exons called exons?
exit the nucleus where they can be expressed.
summary:
, the first arrow, transcription, consists of three phases: initiation, elongation and termination. The end result is a pre-mRNA transcript whose nucleotide sequence was determined by the nucleotide sequence in the specific region of DNA from which it was transcribed. So, if part of the DNA sequence was AGACGA, the corresponding part of the mRNA will have the following sequence UCUGCU; a U for every A, and a C for every G. The pre-mRNA then is processed, either by the ‘normal’ splicing approach or the alternative splicing approach, depending on the needs of the organism (i.e., you!).
true or false: transcription is DNA -> mRNA
true
where do RNA polymerase attach to?
promoter sequence
what happens after RNA polymerase attaches?
it separates the strands and then codes for RNA
what is the only end that RNA polymerase can add nucleotides too?
3’
true or false: RNA polymerase only adds information or codes complementary information to one side
true
which side is the RNA polymerase interacting with?
template strand
when the mRNA migrates out of the nucleus, where does it go to be translated?
ribosome
