Ch 12 Control of Gene Expression Flashcards
gene regulation
encompasses the mechanisms and systems that control the expression of genes, is critical for the control of numerous life processes in all organisms
structural genes
encode proteins that are used in metabolism or biosynthesis or that play a structural role in the cell
regulatory genes
the products of these, either RNA or proteins, interact with other DNA sequences and affect the transcription or translation of those sequences
constitutive
a few structural genes, particularly those that encode essential cellular functions are expressed continually
these are not regulated
regulatory elements
DNA sequences that are not transcribed at all
affect the expression of DNA sequences to which they are physically linked
common in both bacterial and eukaryotic cells and much of gene regulation in both types of organisms takes place through the action of proteins produced by regulatory genes that recognize and bind to regulatory elements
two processes play a role in gene regulation
DNA methylation and changes in chromatin
operon
a group of bacterial structural genes that are transcribed together, along with their promoter and additional sequences that control their transcription
regulator gene
helps to control the expression of the structural genes of the operon by increasing or decreasing their transcription
regulator protein
the regulator gene has its own promoter and is transcribed into a short mRNA which binds to a region of the operon called the operator and affect whether transcription can take place
negative control
a regulatory protein is a repressor, binding to DNA and inhibiting transcription
positive control
a regulatory protein is an activator, stimulating transcription
inducible operons
those in which transcription is normally off (not taking place)
repressible operons
those in which transcription is normally on (taking place)
inducer
transcription is turned on when a small molecule binds to the repressor
allosteric proteins
proteins which change shape upon binding to another molecule
corepressor
a small molecule that binds to the repressor and makes it capable of binding to the operator
coordinate induction
stimulation of the simultaneous synthesis of several proteins by a specific molecule, the inducer
lacZ gene
encodes B-galactosidase
lacY gene
encodes permease
lacA gene
encodes thiogalactoside transacetylase
partial diploid
the cells of these strains possessed two different DNA molecules: the full bacterial chromosome and an extra piece of DNA
constitutive mutations
causing the lac proteins to be produced all the time, whether lactose was present or not
superrepressors
mutations that produced defective repressors that could not be inactivated by an inducer
catabolite repression
when glucose is available, genes that participate in the metabolism of other sugars are repressed through a process known as this
results from positive control in response to glucose
catabolite activator protein (CAP)
positive control is accomplished through the binding of this protein to a site about 22 nucleotides long that is located within or slightly upstream of the promoter of the lac genes
adenosine-3’,5’-cyclic monophosphate (cyclic AMP, or cAMP)
before CAP can bind to DNA, it must form a complex with this modified nucleotide which is important in cellular signaling processes in both bacterial and eukaryotic cells
