cellular control Flashcards
What is a gene mutation?
A change in the base sequence of DNA which randomly occur during DNA replication
What makes random mutations more likely to occur?
If you are exposed to mutagenic agents e.g. high energy radiation, ionising radiation (gamma rays & X rays), and chemicals e.g. cigarette smoke, which all interfere with DNA replication
What is the subsitution mutation?
One base is substituted for another
what is a silent mutation?
a base has been substituted, but the codon still codes for the same amino acid
what is the deletion mutation?
a base has been deleted, causing a frameshift
why does a silent mutation sometimes allow the codon to still code for the same amino acid?
the genetic code is degenerate (multiple codons can code for the same amino acid)
what is the insertion mutation?
an extra base is added, causing a frameshift
how do gene mutations affect the primary structure?
mutations alter the gene which can result in a different amino acid sequence in the encoded polypeptide
how do gene mutations affect the secondary structure?
if the amino acid sequence changes, the folding & coiling will be different
how do gene mutations affect the tertiary structure?
it will form hydrogen and ionic bonds in different places, causing it to fold differently
how do gene mutations affect the quarternary structure?
the change in tertiary structure will result in a different 3D shape, meaning that a non-functioning protein could be made
how can protein synthesis be controlled?
through transcription factors
what are transcription factors?
protein molecules which bind to different base sequences on DNA, initiating transcription of genes
how do transcription factors bind to the gene?
they have a complimentary 3D shape to a particular gene
what happens when the transcription factor binds to the gene?
it enables RNA polymerase to bind, initiating transcription, creating the mRNA molecule for that gene which can then be translated into the cytoplasm to create the protein
What is an operon?
A group of simultaneously controlled genes that are either all expressed or not
What is the lac operon?
An operon found in E. coli, and is a sequence of 3 genes that collectively aid lactose digestion
Where are operons more commonly found?
Prokaryotes
What is the function of the lac operon in low lactose concentrations?
The repressor protein is constantly produced and binds to the operator which prevents RNA polymerase from binding to the DNA at the promoter region, and transcription is inhibited
What is the function of the lac operon in high lactose concentrations?
Lactose binds to the operon, causing it to change shape which prevents the repressor protein from binding to the operator, this allows RNA polymerase to bind to the promoter and transcription of the lac operon occurs
What 3 genes does the lac operon contain?
Lac Z, lac Y, lac A
What is lac l?
A regulatory gene found near the operon, which codes for a repressor protein that inhibits transcription when there is no lactose present
What is the role of cyclic AMP (cAMP)?
- It increases the rate of transcription of the lac operon - in order for sufficient enzymes to be produced by lac Z, lac Y, lac A, cAMP receptor proteins (CRP) must bind
- CRP can only bind and increase the rate of transcription once it has bound to cAMP
