6.1.1 Cellular control Flashcards
Define gene mutation
Change in the base sequence of DNA which occurs randomly during DNA replication
What makes random mutations in DNA more likely?
Exposure to mutagenic agents e.g. high energy radiation, gamma radiation and chemicals.
What are the types of gene mutation?
Deletion, insertion and substitution
Why might a base substitution be silent?
The new codon may still code for the same amino acid because the genetic code is degenerate.
What do base deletions/insertions result in?
Frameshift. Removal/addition of one base changes all of the subsequent codons. (Multiple incorrect amino acids coded for)
What are base deletions and insertions collectively known as?
Indel mutations
What are transcription factors?
Proteins which can bind to different base sequences on DNA and control transcription of genes. Can be activators or repressors.
How do activator TF’s work?
Bind to the beginning of a gene (promoter region) helping RNA polymerase to bind and transcribe the gene.
How do repressors work?
.Bind to the gene and block RNA polymerase from binding.
What is an operon?
A group of genes controlled by the same promoter (regulatory region).
What happens when lactose is absent (Lac operons)?
A regulatory gene (lacl) produces a protein called the lac repressor. This TF binds to the operator region blocking RNA polymerase from binding at the promoter region.
What happens when lactose is present?
Lactose binds to the repressor and changes its shape so the repressor can no longer bind to the operator region. This means RNA polymerase can bind to the promoter region and transcribe the structural genes lacZ, lacY and lacA.
What is splicing?
Post transcriptional control (before translation) in which introns are removed from primary mRNA. (introns are sections of DNA which don’t code for amino acids).
Describe the role of cAMP in post translational control.
Activates proteins which are synthesised in the inactive form by phosphorylation.
What are homeobox genes?
Genes involved in regulating expression of other genes involved in embryo development. They are highly conserved and similar in plants, animals and fungi.
