Binding of proteins to DNA.
The binding of proteins to DNA determines whether a gene is expressed or not. Small molecules determined if the protein interacts with the DNA.
lac
Nota:
The lactose transported into the the cell by the lactose transporter, it then break down by p-galactosidase into glucose and galactose.
Negative control
Nota:
The genes are coordinately controlled.
If there's presence of lactose, it is broken down to a galactoside which interact with a the protein so to unbind it.
CAP
Nota:
Catabolite Activator Protein.
This complexes with cAMP to bind with RNA polymerase to initiate transcription.
cAMP and CAP complex is a positive effector.
Mutations
Nota:
Two types are:
High level expression:
1. i- inactive repressor, hence the gene transcription/translation is unhindered due to the inability of the repressor to bind to the operator.
2. o- mutation to operator to disable the repressor to bind.
No induction at all:
1. is: Inducer cannot bind to the repressor hence the repressor permanently binds to the operator
2. p- mutation to the promoter to prevent RNA polymerase to bind.
Repressible: Trp
Mechanism
Nota:
Repressor is generated by the i DNA sequence.
RNA polymerase will bind if the repressor isn't bound to the protein.
If there are levels of tryptophan detected, the tryptophan then bound to the repressor to bind to the
Attenuation
Nota:
Depending on binding, the site may change to bind with either the 2nd or 4th.
If bound with tryptophan, shorter mRNA is generated, i.e 2 will bind with 3 where if there are no tryptophan mRNA generated will be long.
Eukaryotic Gene Expression
Nota:
Difference in the proaryotic and eukaryotic gene expression differs as so.
More positive regulatory genes
Larger more complex multimeric regulatory proteins
Restricted by chromatin structure
Transcription separated by time in space from translation in the cytoplasm.
Level of Control
Nota:
level of control can occur at different stages
7 possible stages:
Transcription
Posttranscriptional processing
Translation
Postranslational processing
Protein degradation
mRNA degradation
Protein targeting and transport.
Typical Sequence of Genes
Nota:
TATA Box
GC box
CAAT box
TO increase the level of transcription, there's a enhancer normally consisting of Hormone Response Element (hormone receptor protein plus hormone)
They loop back to the the start zone to bind with a RNA Polymerase complex.
Transcription Factors
Nota:
Many transcription factors are needed and if all the necessary factors are present, the transcription can take place.
Most important one is TFIIH or (Transcription Factor, Interacting with RNA polymerase II, H)
Action
Nota:
2 actions: Helicase action and Signalling initiation of transcription
TFIIH helicase activity, then COO domain of RNA polymerase II is phosphorylated by TFIIH, after termination, the RNA polymerase II is released and dephosphorylated and recycled.
Chromatin
Nota:
Chromatin acts negatively on gene expression, condensed chromatin and nucleosome prevent transcription by steric hindrance. Hence nucleosome needs to be removed or altered.
Mostly by acetylation of histones where chromatin is activated for transcription by removing one nucleosome to allow gene expression