Lec 7-3 Flashcards
Gene expression
Process by which a gene creates a gene product that has some kind of cellular/organismal function
Gene regulation
Types of mechanisms that control the flow of information
Gene regulation responds to
The environment
Bacteria gene regulation
Gene regulation maintains internal flexibility, turning genes on and off in response to environmental changes
Multicellular eukaryotic organisms
Gene regulation also brings about cell differentiation
Structural genes
Encode proteins used in metabolism, biosynthesis, or structural roles in the cell
Not involved in gene regulation
Regulatory genes
Encode products that interact with DNA sequences and regulate transcription
RNA or proteins
Often regulatory genes are DNA binding proteins
Can regulate in a positive or negative way
Housekeeping genes
Constitutive genes are not regulated and continually transcribed
Constitutive expression
Always on
Regulatory expression
Gene will only transcribe depending on the environment
Regulatory elements
Affect the expression of DNA sequences (genes) they are physically linked to the gene
They are not transcribed
Positive control
Regulatory genes acts as an activator and increases transcription
Negative control
Regulatory genes acts as a repressor and blocks transcription
Transcription is regulated by
Operons
Francois Jacob and Jacques Monod
Used classical genetics to uncover the “Operon Model” of how bacteria regulate genes
Operon
Multiple genes clustered together under control of a single promoter
Single mRNA but translated into multiple proteins
Operon advantage
Allows the cell to coordinate expression of multiple gene products with on promoter
Operons are controlled by
Regulatory genes
They can be distant and not physically linked to the operon to control it
Negative control on operons
Repressors bind to operators (partially overlap the promoter or beginning of first gene)
Physically blocks RNA polymerase from proceeding with transcription
Allosteric proteins
Proteins that change shape and function when binding to another protein or molecule
Small molecule that binds to allosteric proteins is called a
Ligand
Inducible operon
Ligand increasing operon transcription
Repressible operon
Ligand decreasing operon transcription
Negative inducible operon
Operon is negative because
Regulator protein inhibits transcription when bound
Ligand causes increased transcription and is called the inducer
Inducer inhibits the function of the repressor
Negative repressible operons
Operon is negative because regulator protein inhibits transcription when bound
Ligand causes decreased transcription and is called a co-repressor.
Co-repressor is required for repressor protein function
Operons can also be regulated by their
Own products
Inducer is precursor for enzymes produced by the operon, thus transcription itself leads to more enzymes and thus effects levels of inducer
This feedback system allows bacteria to adapt to their environment and function more economically
Lactose overview
Glucose preferred energy source for E.coli
Lactose can also be used as energy if broken down by B-Galactosidase, through catabolism, where on of the products is glucose
Lac Operon
Used to respond to changing glucose/lactose levels in the environment by efficiently switching on and off lactose metabolism
lac Operon structural genes
lacZ- B-Galactosidase
lacY-Permease
lacA- (dont need to know
lac regulatory gene
lacl-repressor
It is a repressor putting Lac operon under negative control
B-Galactosidase breaks down
Lactose into galactose and glucose
Low glucose leads to
High cAMP
Cell responds to low glucose by increasing energy metabolism of lactose
Jacob and Monod
Used mutational analysis of a partial-diploid strain of bacteria that contains a F plasmid
F plasmid
Contains lac operon that they could mutate
