Chapter 16 Flashcards
Operons
- groups of genes that are transcribed as a unit
-genes expressed in bacteria is often regulated through
Why is gene regulation necessary?
What are the differences between genes and regulatory
elements?
Regulatory genes code for proteins that affect transcription, while regulatory elements are the DNA sequences where those proteins bind to
How is gene expression controlled?
How can ecoli make what it needs when not given what it needs, and alter its own biochemistry?
Gene regulation
it decides and controls when to turn on what breaks down glucose
if enviorment changes…
new genes
expressed, new proteins synthesized!
gene expression is critical to all living things….
because it enables the synthesis of functional gene products that ultimately affect a phenotype
Structual genes
encoding proteins for metabolism or biosynthesis to break things down or play structural role in cell
Regulatory genes
regulating the expression (on and off button)
interacts with other
DNA sequences affect the transcription
translation of sequences.
Bacteria and eukaryotes use to control expression of many structural genes.
constitutive genes
expressed continually, not regulated
“Housekeeping genes”: integrity of cell, needs to keep turned on
Regulatory elements
DNA sequences not transcribed, regulating other nucleotide sequences
affecting expression of DNA sequences at which they are
physically linked
Regulation can occur through: Positive control and Negative control
P: stimulate
gene expression
N: inhibit
gene expression
not nessicarlly bad can turn off cells that are beneficial when off
many different places where gene expression is controlled
cant access genes if wrapped tightly around histones and bubble cant open
gene regulation at transcription
cant make the amount of transcript product pre-mRNA that it needs
any stages that we modify
what kind of mRNA we get and affects gene expression
stability changes gene expression by
decreasing stability decreases ability to get to transcription stage and changes the amount of protein made
Regulatory proteins have domains (section of protein)
- Typically consist of ~ 60-90 amino acids
- Responsible for binding to DNA
- Forming hydrogen bonds with DNA (bind dynamically: - transiently bind and unbind DNA and other
regulatory proteins)
Much of the gene regulation is accomplished by
proteins that
bind to DNA sequences and affect their expression
Motifs**
DNA-binding proteins , group binding proteins based on the similarities
What is the difference between a structural gene
and a regulator gene?
Structural genes encode proteins; regulator genes
control the transcription of structural genes.
Two types of transcriptional control: Negative control and Positive control
N: – regulatory protein is a repressor,
binding to DNA and inhibiting transcription
P: – regulatory protein is an activator,
stimulating transcription
Operons can also be either inducible or repressible:
I –transcription is normally off (not taking
place). has ability to be turned on and off but has to have something to do turn on
R – transcription is normally on (taking
place); has ability to be turned on and off but has to have something to do turn off
Regulator gene encodes an active repressor protein that binds to the operator.
This system is inducible because transcription is normally off
(inhibited) and must be turned on (induced).
In order to have transcription happen have an inducer bind to the opening to stop
– Binding of inducer changes shape & prevents DNA binding.
allosteric
proteins
– Proteins that change shape due to binding
Negative Inducible operons
control proteins that carry out degradative
processes – proteins that break down molecules
The proteins are not needed unless the substrate (the component that
needs to be broken down) is present!
Negative Repressible Operons
On and needs to be turned off
Repressor synthesized in inactive form that can’t immediately attach to operator
need to activate it (done by Product U or corepressor)
If U levels are
high…
it is available to bind to the repressor and activate it, preventing transcription
E coli binding
if glucose is available then used but, can use lactose as energy source but has to be brought into the cell by te permease
Economical Negative Repressible Operons:
The proteins they encode are synthesized only as needed!
Usually control proteins that carry out the biosynthesis of
molecules needed in the cell (such as amino acids).
Usually turned on and only turned off when there are
adequate amounts of product already present!
In positive transcriptional control…
– the regulatory protein
involved is an activator.
It binds to DNA (usually at a site other than the
operator) and stimulates transcription.
CAP
(catabolite activator protein) site in the lac operon!
Lactose
major carbohydrate found in milk; does not easily diffuse
across the membrane. Transported by a protein lactose permease.
To use lactose as an energy
source, E. coli must
break it into glucose and galactose –
a reaction catalyzed by
β-galactosidase.
Can also convert lactose to
allolactose
Enzymes β-galactosidase
permease and
transacetylase are encoded by adjacent structural
genes in the lac operon and have a common
promoter
coordinate induction
the simultaneous synthesis of several
protein stimulated by a specific molecule, the inducer!
Allolactose is responsible!
In the trp operon, what happens to the trp
repressor in the absence of tryptophan?
It cannot bind to the regulator gene and
transcription takes place
Ribozymes
mRNA molecules with catalytic activity
Riboswitches
molecules influence the
formation of secondary structures in mRNA
Antisense RNA
RNA molecules that are complementary to
particular sequences on mRNA
control gene
expression by binding to sequences on
mRNA and inhibiting translation
Enhancer
DNA element that affects
transcription but typically found some
distance from the gene whose transcription
it affects.
Enhancers contain binding sites for proteins
that increase the rate of transcription.
The repression of the lac operon never
completely shuts down
transcription
There is a very low level of transcription and molecule production
(basal level of transcription)
This is critical because a few molecules are necessary to
covert some of the lactose into allolactose – which then induces
transcription!
catabolite repression is when….
When glucose is available, genes that participate in the
metabolism of other sugars are turned off…
This is a positive control mechanism.
Catabolite repression:
using glucose when available and
repressing the metabolite of other sugars.
- activated by catabolite activator protein (CAP).
- cAMP binds to CAP; together CAP–cAMP complex binds to a site
slightly upstream from the lac gene promoter
cAMP:
adenosine-3′,
5′-cyclic
monophosphate
Derivative of ATP,
used in many
biological pathways
[cAMP] is inversely
proportional to the
level of available
glucose.
What is the difference between a structural gene
and a regulator gene?
structural encodes for protein
reg- encodes for tscript factors
In the presence of allolactose, the lac
repressor _____.
cannot bind to opressor
What is the effect of high levels of glucose
on the lac operon?
Little to none transcription takes place
- A negative repressible operon
(normally turned on and must be repressed when products of its
structural genes are not needed).
five enzymes
together convert chorismate to tryptophan
- Five structural genes
- trpE, trpD, trpC, trpB, and trpA—
attenuation
transcription begins at the start site
but terminates prematurely, before the RNA
polymerase even reaches the structural genes
what is the difference between a structural gene and a regulator gene?
Regulator genes control the transcription of structural genes, while structural genes encode specific proteins.
Permease
create opening for lactose to enter so beta gala can do its thing to create gluc
Allolactose
binds to regulatory protein acts as corepessor and lets RNA poly do its thing
CAP/cAMP how it influences gene expression
when gluc. is high this is low vice versa
“push” to RNA polymerase to go increases the system
