chemical changes in just one base(nucleotide) pair of a gene

change of a single nucleotide in DNA can lead to the production of an abnormal protein

base-pair substitutions - replaces One nucleotide and its partner with another pair of nucleotides

base-pair insertions or deletions 

- additions or losses of nucleotide pairs in a gene

have disastrous effect on the resulting protein more often than substitutions do 

may alter the reading frame producing a frameshift mutation

have no effect on the amino acid produced by a codon because of redundancy in the genetic code

Most amino acids are encoded by several different codons. For example, if the third base in theTCT codon for serine is changed to any one of the other three bases, serine will still be encoded. Such mutations are said to be silent because they cause no change in their product and cannot be detected without sequencing the gene (or its mRNA).

still code for an amino acid, but not necessarily the right one...

With a missense mutation, the new nucleotide alters the codon so as to produce an altered amino acid in the protein product.

change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein

With a nonsense mutation, the new nucleotide changes a codon that specified an amino acid to one of the STOP codons (TAA, TAG, or TGA). Therefore, translation of the messenger RNA transcribed from this mutant gene will stop prematurely. The earlier in the gene that this occurs, the more truncated the protein product and the more likely that it will be unable to function.

some cases of male infertility

2/3 of cases of Duchenne muscular dystrophy

physical or chemical agents that can cause mutations

(ionizing radiation, cigarette smoke UV light)

feedback inhibition - a form of metabolic control in which the end product of a chain of enzymatic reactions reduces the activity of an enzyme early in the pathway

gene regulation

a cluster of functionally related genes under coordinated control by a single on-off switch

the switch is a segment of DNA called an operator (usually found within the promoter (nucleotide sequence in DNA to which RNA polymerase binds to begin transcription))

a protein repressor

which prevents gene transcription

binds to operator and blocks RNA polymerase

molecule that cooperates with a repressor protein to switch an operon off. 

activates an inactive repressor

if tryptophan is present, it binds to the trp repressor protein turning the operon off. (repressor is only active in the presence of its corepressor tryptophan)

trp operon is turned off if tryptophan levels are high

a repressible operon is usually on, a binding repressor shuts off the transcription

an inducible operon is one that is usually off, a molecule called an inducer inactivates the repressor and turns on transcription

stimulatory protein

catabolite activator protein (CAP)

or an activator of transcription

inducible --> catabolic pathways

repressible --> anabolic pathways