genes Flashcards
outline transcriptional control
how tightly or loosely histones are bound to DNA
euchromatin loosely wound DNA so that RNA polymerase can attach to the promoter site for translation to occur GENE IS SWITCH ON
heterochromatin tightly wound DNA so that RNA polymerase can’t attach to promoter site and GENE IS SWITCHED OFF
Addition of methyl groups (methylation) causes increased attraction between DNA and histone so DNA is not transcribed.
addition of acetyl groups (acetylation or phosphorylation) reduces the attraction between the negative nucleus and the positive histone which becomes less positive so the DNA is not transcribed.
what is epigenetic
this is the term used to describe the control of gene expression by the modification of DNA.
what is the lac operon
a group of genes that are under the same regulatory mechanism and expressed at the same time.
more common in prokaryotes then eukaryotes
it is a successful way in conserving products/materials that are not needed at the time.
if glucose is not in supply as a respiratory substrate then lactose can be used instead.
I POzY
I - regulatory gene
p - promoter site sequence of DNA that the RNA polymerase binds to for transcription
o - operator a sequence of DNA that a transcription factor can bind
z and y - structural genes that can only be transcribed when the lac operon is switched on.
what is the role of the regulatory gene
it codes for a repressor protein which will prevent transcription in the absence of lactose. in the absence of lactose the repressor protein will bind to the operator site which blocks the promoter so RNA polymerase cannot attach and the gene cannot be transcribed.
when lactose is present, lactose binds to the repressor protein so that the promoter site is available for RNA polymerase to bind with so the structural genes can be transcribed for.
what is the role of cyclic amp
a secondary messenger molecule
it increases the rate of transcription more then just binding of a RNA polymerase.
the levels of cAMP is reduced when glucose is present
