Chapter 18 Flashcards
what is an operon?
an operon is the entire stretch of DNA that includes the promoter, the operator, and the genes that they control
what can an operon be switched off by?
a protein repressor
what is a corepressor?
a corepressor is a molecule that cooperates with a repressor protein to switch an operon off
what is a trp operon?
by default a trp operon is on and the genes for tryptophan synthesis are transcribed, but it is repressible
tryptophan and trp operon relationship
- when tryptophan is present, it binds to the trp repressor protein to turn it off
- the trp operon is repressed/turned off if tryptophan levels are too high (feedback inhibition)
what does tryptophan act as?
tryptophan acts as the corepressor and can turn it off
what is an inducible operon?
an inducible operon is one that is usually off but an inducer inactivates repressor to turn on transcription
what is a repressible operon?
one that is usually on but binding of repressor shuts off the transcription
what is a lac operon?
the lac operon is an inducible operon (usually off), an inducer is needed to inactivate repressor and turn it on
what type of reaction are inducible enzymes?
inducible enzymes usually function in catabolic pathways (synthesis is induced by a chemical signal)
what type of reaction are repressible enzymes?
repressible enzymes usually found in anabolic pathways (synthesis is repressed by high levels of end product)
can you have positive control?
IT IS TRUE that you can have positive control through catabolite activator proteins (CAP)
what can cause a lac operon to not turn on and why?
if there is high glucose compared to lactose because ECOLI prefers glucose
what controls the lac operon?
the lac repressor and the CAP
what are the best conditions for lac operon to turn on?
need lactose and low glucose
is trp operon repressible or inducible?
trp operon is repressible; lac is inducible
what is differential gene expression?
the reason there are differences between cell types, the expression of different genes by cells with the same genome
define epigenetic inheritance?
the inheritance of traits transmitted by mechanisms not directly involving the nucleotide sequence
what are examples of epigenetic inheritance?
genomic imprinting, X chromosome inactivation, histone tails modified and methylated
define epigenetics
epigenetics is changing the base sequence and modifying histone tails because it affects how DNA acts together and how it is packed in the chromosome
do chromatin modifications alter DNA?
no, but they can be passed to future generations of cells
what is cell differentiation?
cell differentiation is the process by which cells become specialized in structure and function (ex: a stem cell becomes a liver cell)
what is morphogenesis?
the physical processes that give an organism its shape constitute morphogenesis
what are cytoplasmic determinants?
cytoplasmic determinants are maternal substances in the egg that influence early development
- as zygote divides by mitosis, cells contain cytoplasmic determinants
