lectrue 13 Flashcards
Genetic information directs
the synthesis of protein (and RNA) products
Transcription
the process of synthesizing RNA from a DNA template
Translation
the process of synthesizing protein from an RNA template
DNA
-bases include A, T, G and C
-linear polymer
-usually double stranded (ds)
RNA
-contains a 2’ hydroxyl group
-RNA contains a ribose sugar instead of a deoxyribose sugar
-RNA uses uracil instead of thymine. Uracil forms a base pair with adenine
Transcription produces an RNA transcript that is
complementary to the template stand except it uses uracil in place of thymine
Sense strand
coding strand
template strand
noncoding strand
Gene expression includes
the process of transcription and/or translation (because translation will not always occur)
Several RNA polymerases can be
working on the same gene at the same time
RNA can form — that allow for the ability to adopt a variety of shapes/do diff functions
nonconventional base-pair interactions
Transcription and DNA replication similarities
- DNA needs to be unwound
- one DNA strand acts as a template
- NTPs (instead of dNTPs for DNA replication) are added one at a time in a 5’ to 3’ manner
Transcription in bacteria (4 steps)
- RNA polymerase binds to promoter (upstream of the transcription start site)
- double helix is opened, transcription begins using template strand
- transcription stops when the terminator (stop site) is reached
- RNA and RNA polymerase dissociate from the DNA
The promoter has conserved sequences at the — regions
-10 and -35
What are the -10 and -35 regions bound by?
the sigma factor (a subunit of the RNA polymerase)
the sigma factor
is important for recognizing where to begin transcription
binds to the -10 and -35 regions in only one direction
(so polymerase can only bind in one orientation)
Eukaryotic transcription differences when compared to bacterial transcription (5)
- has more RNA polymerases
- needs general transcription factors
- has a more elaborate control mechanism
- takes DNA packing into account
- has mRNA
general transcription factors help to
position the RNA polymerase, separate the DNA and initiate transcription
Transcription in euk (sequence of events/general transcription factors)
TFIID, TFIIH, CTD
-TFIID binds to the TATA box found in the promoter
-TFIIH (general transcription factor) contains a kinase domain that phosphorylates the C terminal domain (CTD), allows the RNA polymerase to clear the promoter
-then transcription is complete, the CTD is dephosphorylated
TATA box
binding of the TATA binding protein (subunit of TFIID) to the TATA box causes a change in DNA structure that helps other general transcription factors assemble
chromatin must be — to allow access by —
modified
the transcription factors
(eukaryotic DNA is packed in nucleosomes)
eukaryotic mRNA undergoes processing before being exported
- addition of a 5’ cap (capping)
- polyadenylation
- splicing of introns
processed RNA is exported from the — to the —
nucleus to the cytoplasm
what does the addition of the 5’ cap do? (RNA capping)
increases the stability of the mRNA and helps w its export to the cytoplasm
polyadenylation
adds a series of repeating adenine nucleotides to the 3’ end of the molecule
increases stability of the mRNA and helps w export
splicing
in euk immature mRNA, introns (noncoding) sequences interrupt exons (coding) sequences of genes
–> splicing= removing introns before translation occurs
what carries out splicing?
small nuclear ribonucleoproteins (snRNPs) which contain both RNA and protein
snRNPs work together to form the spliceosome
export of mRNA– what proteins does it need to bind to?
poly-A-binding proteins, a cap-binding complex and proteins that bind to mRNAs that have been appropriately spliced
3 steps of splicing
- branch point adenine attacks the 5’ splicing site and cuts the sugar phosphate backbone of the RNA
- the 5’ end of the intron becomes covalently linked to the 2’ OH group of the ribose of the A to form a branched structure.
3’ OH end of the exon sequence reactions w the start of the next exon sequence - two exons join together to form a continuous coding sequence.
Introns are released in the form of a “lariat structure” which is further degredated
export of mRNA
- mediated by?
- bound to?
mediated by the nuclear pore complex
bound to specific proteins (the poly-A-binding proteins, a cap-binding complex and proteins that bind to mRNAs that have been appropriately spliced)
how is mRNA degraded?
degraded in the cytosol by nucleases (ribonucleases)
it is affected by the 3’ untranslated region of the mRNA which is between the end of the coding region and the poly-A-tail
