Topic 3: Genetic Regulation Flashcards
What is a gene
Sequence of DNA that encodes a specific trait or product
Turning genes on/off in bacteria vs eukaryotes
Bact = turn genes on/off in response to environment
Euk = turn genes on and off in response to environment, for cell differentiation, tissue coordination, based on developmental stage
Where can gene expression be controlled
Before transcription (important, first step before DNA->RNA->protein)
Post transcription
Translation
Post translation
Which part of gene expression control do prokaryotes not have
mRNA processing
What are structural genes? what are they controlled by?
Genes that encode proteins (e.g. enzymes), controlled by DNA binding proteins
What do DNA binding proteins control, what are they produced by
Control structural genes
Produced by regulatory genes
What are regulatory genes?
Encoding products that interact with other sequences and affect the transcription and translation of these sequences
Make DNA binding proteins
What are regulatory elements
DNA sequences that are not transcribed but play a role in regulating other nucleotide sequences
What kind of proteins are transcription factors
DNA binding
What can DNA binding proteins recognize? What do they form bonds with? What type?
Information in the major and minor grooves of DNA
Form H-bonds with groups on the bases
What is a protein domain
~60-90 amino acids, responsible for doing a specific job or forming a specific structure
What is a motif
Within the binding domain, a simple structure that provides specificity (recognizes DNA seq)
Domains and motifs are found in…
DNA binding proteins
Examples of protein domains
Helix-turn-helix
Zinc fingers
Leucine zipper
What are operons
In bacteria, a set of related genes are regulated together
Transcribed as a single mRNA with multiple coding regions
Controlled by the same promoter and regulatory proteins
Multiple proteins transcribed off single mRNA with diff start and stop codons
Operons are regulated at the…
Operator
Slide 10
Operon
What is constitutive expression
Continuously expressed under normal cellular conditions
What is positive control? Negative control?
+ = control at the operator is positive ie TF that binds operator stimulates transcription
- = control at the operator is negative ie TF that binds operator inhibits transcription (repressor)
What is an inducible operon? Repressible?
Inducible = transcription is usually off, needs to be turned on
Repressible = transcription is normally on, needs to be turned off
What is the regulatory gene doing in negative inducible control? Negative repressible control?
Neg inducible = regulatory gene that controls operon produces a repressor, normally active
Neg repressible = regulatory gene makes a repressor, normally it is inactive
Slides 14, 15, 16, 17***
Neg repressible and inducible
What is positive control
Regulatory protein involved is an activator
Operator can be inducible or repressible
What is controlled by positive and negative control
Transcription
Structural genes of the lac operon and their functions
lacZ: encodes B-galactosidases (metabolism of lactose)
lacY: encodes permease (transport lactose into cell)
lacA: encodes transacetylase
What kind of system is the lac operon
negative inducible
What are the regulatory genes/elements of the lac operon
lacI: repressor encoding gene (produces repressor protein LacI)
lacP: operon promotor (RNA polymerase assembles)
lacO: operon operator (LacI binds)
Under normal conditions, the lac operon is…
off
What is the inducer of the lac operon? What does it do?
allolactose (binds LacI and changes its conformation to deactivate it/close active site)
Does repression completely shut down transcription
No, tiny amount ongoing
What is permease
membrane protein that transports lactose into the cell
What does B-galactosidase do to lactose
Converts it to allolactose or galactose+glucose
In the presence of lactose, does transcription continue?
Yes, allolactose binds the repressor protein and prevents it from binding the operator
What is the partial diploid lac mutation
Full bacterial chromosome + an extra piece of DNA on F plasmid (genomic copy+plasmid copy)
What is the plasmid in partial diploids
Extra piece of DNA that can carry a fully functional complement of the lac operon
What does the partial diploid mutation allow us to do
Mutate different components on the genomic or plasmid copies
What is the structural gene mutation of the lac operon
Affects the structure of the enzyme but not the regulations of their synthesis
What is wrong with lacY-? lacZ-?
y- = no functional permease
z- = no functional B-gal
No metabolism of lactose
How do pseudodiploids help with structural gene mutations of the lac operon
The genomic copy may have a non-functioning gene, but if the plasmid has the wildtype gene then there is functioning lactose metabolism (or vice versa)
What are regulator gene mutations in the lac operon
Affect the actions of the regulator protein (producing LacI)
What are operator mutations in the lac operon
Affects the function of the operator
lacO^c = no operator
Dominant over lacO+ because the operators are cis acting
Which is dominant, lacI- or lacI+
lacI+, genes are trans acting, normal regulation of operon
What are cis vs trans genes
cis = acting on the same piece of DNA its located on
trans = act on different pieces of DNA
Slides 24 -> 32**
Lac operon mutations
What is the promotor mutation
lacP-
cis acting
non-functional P = RNA polymerase cannot assemble
What is positive control through catabolite repression
Using glucose when available and repressing the metabolism of other sugars
High levels of glucose repress the lac operon, low levels of glucose STIMULATE the lac operon
Positive control can occur through..
catabolite repression
How does the cell know when glucose is present
cAMP, its concentration is inversely proportional to the level of available glucose
What complex is the positive regulator of the lac operon
cAMP/CAP complex (binds and stimulates transcription of operon; activator)
Slides 36/37
Positive control of lac operon
What happens to the structure of DNA when cAMP-CAP binds
Produces a sharp bend in DNA that activates transcription
