Transcription Flashcards
(28 cards)
coding strand vs non coding strand
coding is identical to RNA. non coding is the template.
what are the stop and start codons?
start- AUG; stop: UAA, UAG, GUA
operon
a group of genes that code for proteins with related functions and are regulated by the same promoter
polycistronic
found in prokaryotes only, when 1 transcription unit codes for multiple proteins
intron
non-coding piece of the transcription unit that will eventually be spliced out of mRNA
exon
coding sequence transcribed in mRNA
what are 3 types of cis-acting sequences?
core promoter elements, promoter proximal elements, and enchancers`
describe core promoter elements
very close to the start of transcription which start and direct RNA polymerase assembly/transciption factors necessary for initiation (TATA box in eukaryotes/prinbow box in prokaryotes)
give an example of a core promoter element
TATA box. Prinbow box. -35 sequence
describe promoter proximal sequences
further upstream of core elements, ~200 bp, positive regulators for assembling transcription complex
enhancers
can be introns or extremely far upsteam- serve as binding sites for transcription factors that can either activate or repress transcription
how genetic material is coding in eukaryotes?
1.2%
what is a gene family
genes with closely related functions. not necessarily on the same chromosome.
Describe transcription initiation in prokaryotes
bacterial RNA polymerase consists of a core enzyme with 4 units (2 alpha and 2 similar but not identical beta units). The sigma unit binds creating the holoenzyme. the sigma unit recognizes the -35 and -10 promoter elements, forming H-bonds. The core enzyme then binds the promoter, the sigma element disassociates, and transcription begins
how many types of RNA polymerase exist in eukaryotes? which one is important?
4 types. RNA 2 is important.
what elements are preserved across DNA in eukaryotes?
TATA box/ initiator/ downstream promoter elements
describe transcription initiation in eukaryotes
5 complexes and RNA Pol2 form together to make the preinitiation complex at the promoter. The TATA binding protein (TFB) from TFIID recognizes and binds the TATA box. Helicases from TFIIH unwind the DNA. RNA Pol2 disassociates and begins transcribing. The remainder of the initiation complex remains so multiple copies can be made
What are the 3 stabilizing factors of mRNA processing?
5’ cap/intron splicing/poly A tail
describe the 5’ cap
a 5’-5’ bond is made between the first base and 7-methylguanasine. this occurs while transcription is occuring and stabilizes the growing mRNA
describe intron splicing
requires a splice donor (GU) and splice acceptor (AG) site which mark where cuts will be made. The branchpoint is also important. it is a key A nucleotide that forms the H-bond for the eventual Lariat shape of the intron
describe the poly-A tail
the pre-mRNA is cleaved at a specific squence (AAUAAA) and a poly A tail is added (30-50) by poly(A) polymerase
what 3 genes are coded for by the lac operon
beta-galactosidase- cleaves lactose into glucose and galactase (Z)
permease- increases amount of lactose into cell (Y)
transactylase- unknown mechanism (A)
Describe the functionality of the lac operon
codes for X,Y,A. within the promoter there is a operator. usually, this operator is bound by an inhibitor (I) which prevents RNA Pol2 from transcribing. The inhibitor is a trans acting factor coded for upstream. Lactose can bind the inhibitor, changing it so it cannot bind the promoter, allowing transcription. Additionally, glucose regulates the system. A lack of glucose produces an increase in cAMP. cAMP forms a complex with CAP which binds at the promoter and encourages RNA Pol to bind, increasing transcription efficacy
describe how enhancers work
they are sequences that help regulate transcription. they serve as binding sites for transcription factors. Transcription factors usually have a binding subunit and a loosely connected binding site for repressors or coactivators
