Mod 4 - From DNA to RNA Flashcards
what is a gene?
a genetic unit containing information to make a functional product
what are the 4 levels of information that a gene contains?
- structural
- temporal
- positional
- inducible
what is the function of the promoter region?
defines transcriptional start site and it’s direction
what is the leader / spacer region in prokaryotic genes?
section of DNA which is nontranslated
what is a cistron in prokaryotic genes?
a segment of DNA that corresponds to one polypeptide (protein)
what is the function of enhancer region in eukaryotic class II (mRNA-encoding) genes?
contain transcription factor binding sites
what are introns?
nucleotide sequences that are present in the primary transcript but are removed in the mature transcript
what are exons?
nucleotide sequences that are present in both primary and mature transcript
what is the coding (sense) strand?
- 5’ -> 3’
- has same sequence as RNA product
what is the template (antisense) strand?
- 3’ -> 5’
- sequence is complementary to RNA product
what are the different subunits in prokaryotic RNA polymerase used for?
sigma - promotor recognition
alpha - assembly + activation
beta - catalysis + termination
omega - assembly, folding
what subunits does prokaryotic RNA polymerase consist of?
- 1 sigma
- 2 alpha
- 2 beta (B + B’)
- 1 omega
what subunits does the core enzyme in prokaryotic RNA polymerase consist of?
- 2 alpha
- 2 beta (B + B’)
how many RNA polymerases do prokaryotic cells have?
one
how many RNA polymerases do eukaryotic cells have?
three
Pol I
- ribosomal RNA (rRNA)
Pol II
- protein coding genes (mRNA)
- small nuclear RNA (snRNA)
Pol III
- transfer RNA (tRNA)
- rRNA
-snRNA
What is TFIID?
a complex formed from the TATA binding protien (TBP) and the TBP-associated factors (TAF’s)
what are the functions of subunits TFIIE, F, H, J, K in RNA polymerase II ?
- interaction with D-A-B complex and recruitment of Pol II
- blocks non-specific binding of polymerase II to DNA
- promotor clearance
how is transcription initiated with RNA Polymerase I ?
- upstream binding factor (UBF) binds to UCE and core elements in DNA
- this acts as a binding site for SL1 (TBP + pol I - specific TAF’s)
- this complex then allows RNA polymerase I to bind, initiating transcription
end complex contains UCE, core, and SL1
what is the mode of action of RNA polymerase III ?
- Firstly, TFIIC is recruited to the B box (promotor)
- then, TFIIB is recruited upstream of TFIIC
- TFIIB consists of TBP + 2 pol III - specific TAF’s
- once TFIIB is recruited, TFIIC is dispensable
- RNA polymerase recruited by TFIIB - transcription can begin
what is the difference in the mode of action of RNA Pol III between 5S rRNA genes and tRNA genes?
- 5S rRNA requires an additional TFIIIA to be recruited before TFIIC can be recruited, which is a precursor to the rest of the process.
what is an operon?
a cluster of genes transcribed by the same promotor that gives rise to a polycistronic mRNA
describe the function of the Lac Operon
- no lactose = repression of lac operon, due to repressor protein binding to operator region. prevents RNA polymerase from binding to promotor.
- allolactose binds to repressor - dissociates repressor from operator
- RNA polymerase can now move down the molecule and transcribe
kind of like a lock
how is the lac operon under negative feedback control?
LacZ transcribes galactosidase, an enzyme that hydrolyses lactose to galactose + glucose
- gets rid of lactose
what is the difference between a cis-acting and a trans-acting factor?
cis - will only regulate DNA to which it is directly joined (dominant)
trans - will regulate genes anywhere - mostly protein transcription factors - recessive (mostly)
what is catabolite repression?
the process by which several operons are repressed by glucose and only become active when all the glucose is used up
- preferential use of glucose
how does catabolite repression work in the lac operon?
- RNA polymerase requires CRP (catabolite repressor protein)
- this is because cAMP binds to CRP, which allows DNA binding
- high glucose = low cAMP, so lac operon is always off, even if lactose is available
- low glucose = high cAMP, so lac operon is on if lactose is available
what is the Trp operon responsible for?
contains genes for synthesis of amino acid tryptophan
how does the Trp operon function?
- Trp operon codes for trp repression (inactive)
- genes downstream of leader code for tryptophan
- active trp repressor formed by recruitment of tryptophan into trp repressor
- binds to operator region - stops transcription.
What do the different mutations of the lac operon do?
- LacOc - mutated operator doesn’t allow repressor to bind
- cis-dominant (mutation cannot be corrected)
- LacI- - mutated repressor cannot bind to the operator
- trans-recessive - mutation can be corrected by introducing I+, which forms healthy repressor
