Study sets, textbooks, questions
Upgrade to remove ads
Terms in this set (50)
How does a single gene produce a trait which we can see or measure ?
If all cells contain the same set of genes, how do the genes in different cells of an organism produce so many different cell types?
Is the expression of genes controlled?
Why do we need model systems?
They help to explain the mechanism by which gene expression is controlled.
In order to grow on lactose, the E.coli cell must produce
a protein enzyme known as beta-galactosidase
When would it make no sense for a bacterium to produce the beta-galactosidase enzyme
In an environment where lactose is a common food source
What does it mean to describe lactose as "inducible?"
Signifigant amountsnn of b-gala enzyme are only made when lactose is added to the growth medium
three genes that operate together
what are the 3 protein coding genes?
Z = beta-galactosidase
Y = lac permease
A = transacetylase
what are the 2 control regions
lac operon description
RNA polymerase binds to promoter DNA sequence
Moves past operator region to transcribe the 3 genes into a single mRNA molecule
the lac mRNA molecole has 3 sets of start and stop signals for translation producing 3 different protein products
Lac Z gene product
beta-galactosidase breaks down lactose inside the cell
Lac Y gene product
galactoside permease transports lactose into the cell
helps lactose to enter cell
Lac A gene product
puts acetyl groups on sugars
binding of this repressor protein prevents RNA polymerase from moving past the operator to reach the structural genes
how does lactose act as an inducer
it binds to the repressor and causes a confrontational change that makes the repressor unable to bind to DNA
no transcription, so save the cost of making proteins that aren't needed
operon is transcribed, so enable the cell to use lactose as an energy source
amino acid produced in a pathway that involves 5 enzymes
these 5 enzymes are coded for by five genes found in teh tryp operon
the tryp repressor is coded for by the trpR gene
tryp repressor must first bind to tryptophan itself (serving as a corepressor) before it can bind to operator DNA to block transcription of the operon
Lac is an inducible operon
repressor itself binds to DNA
Tryp is a repressible operson
repressor itself does not bind to DNA
Tryp and lac are both examples of negative control because
all a repressor can do is to BLOCK transcription
(DNA binding protein blocks transcription)
What would a positive control mechanism do
It would ENHANCE transcription
(DNA binding protein triggers transcription)
Why does it make sense for a cell to "prefer" glucose to lactose?
CAP protein (catabolite-activated protein)
region near the promoter that a protein can bind to
it bends the DNA in the promoter region and dramatically increases its affinity for RNA polymerase
strengthens lac promoter to increase expression
essential to efficient transcription
Hhow the CAP protein activated?
It is activated by a small molecule called cyclic AMP (cAMP) whose levels rise when glucose is scarce
when glucose levels are high,
cAMP levels are
cAMP levels are low
as a result of this, the operon is not transcribed
5-carbon sugar that can easily be converted to ribose
an example of a positive control
no arabinose = no transcription
arabinose present = active transcription
When is AraC protein an activator?
It is an activator when it is bound to arabinose
When is AraC protein a repressor?
It is a repressor when arabinose is absent
Similarities between prokaryotes and eukaryotes in context to gene expression
How are eukaryotes more complicating than prokaryotes in terms of expression?
- lots more DNA
- DNA extensively bound to proteins (histones, and non-histones)
- multiple levels regulating gene expression the rule rather the exception
- 3 forms of RNA polymerase
how is a transcription complex formed?
the start of transcription involves the binding of multiple factors to form this complex
Blocking gene expression by means of an miRNA silencing complex.
A system of proteins and RNAs that, when activated, destroys specific mRNAs blocking gene expression
the extra pigmentation RNA actually blocks expression of the native genes
Beta Galactosidase (Z gene product)
splits lactose into galactose and glucose
Lac permease (Y gene product)
allows lactose to rapidly enter the cell
The AraC protein binds arabinose, and then binds to the Initiator site where it enhances
RNA Polymerase binding.
deleting lactose binding site from the lac repressor protein will result in
low transcription levels of lac operon regardless of amount of lactose or glucose
deleting the cAMP binding site of the CAP protein will
result in low transcription levels of lac operson regardless of amount of lactose or glucose
delete DNA binding site of lac repressor protein
lac operon is
under both positive and negative control
tryp operon is
under only negative control
the gene for the repressor is indicated by
the letter i
- has a binding site for the operator sequence
- has a second binding site for lactose
- when repressor is bound to operator, transcription cannot occur
When lactose is fermented by this enzyme a pink color develops as result of lactic acid production.
catalyzes the hydrolysis of β-galactosides into monosaccharides through the breaking of a glycosidic bond
involved in the transport of lactose into cell
tryp operon codes for 5 enzymes that catalyze synthesis of trptophan from tyrosine
repressor protein for tyrp operon
- has binding site for tryptophan
- participates in feedback inhibition
Sets found in the same folder
Mitosis and Meiosis
02.Biology and Energy
Sets with similar terms
Chapter 18: Regulation of Gene Expression
Biology Chapter 18: Control of Gene Expression Pro…
Mastering Biology Chapter 18
Genetics Chapter 16
Other sets by this creator
05. /06. Adrenergic and Cholinergic Phar…
04. Local Anesthetics