Cellular control Flashcards
What are the two classes of DNA mutation?
- Point, a base is substituted for another
- Indel, a base is inserted or removed from the DNA sequence
What are three types of point mutation?
Silent, missense and nonsense
What is a silent mutation?
Where a base is replaced by another base but the same amino is still coded for by this triplet of bases, this means that the tertiary structure of the protein is unaffected. This is possible because the genetic code is degenerate
Why is the genetic code described as degenerate?
As the same amino acid is coded for by multiple triplets of bases
What is a missense mutation?
Where a base is swapped for another base and another amino acid is coded for instead, this results in a change to the amino acid sequence and therefore an altered tertiary structure of the protein being produced which will prevent it from carrying out its function properly
What is a nonsense mutation?
Where one base is swapped for another base and a stop codon is coded for in place of an amino acid meaning that a truncated protein is produced that will not function
What is an indel mutation?
Where a base is inserted or deleted from the DNA sequence, this results in a frameshift as all bases from the point of insertion/deletion move right if a base is added and left if a base is removed. This results in a completely different amino acid sequence after the point of insertion/deletion. This massively alters the tertiary structure of the protein and ultimately means that the protein will not function properly
Why do nucleotide repeats occur?
If an organism has the same codon repeated in base sequence then that codon could be replicated more than it’s supposed to in DNA replication as there it is is difficult for DNA polymerase to check if DNA replication occurred correctly
What does the Lac operon consist of?
A regulatory gene, a promoter region, an operator region, and the Z and Y genes that code for Beta-galactosidase and lactose permease respectively
How does the Lac operon know when to ‘switch off’?
The lac operon has a regulatory gene that codes for a repressor protein that binds to the promoter region and hence prevents RNA polymerase from binding to the promoter region meaning RNA polymerase can’t transcribe the Z and Y genes
How does the Lac operon know when to ‘switch on’?
When lactose is present, it binds to the repressor protein which alters the shape of the repressor protein meaning it can longer bind to the operator, this means that RNA polymerase can then bind to the promoter region and transcribe the Z and Y genes
How does the Lac operon know to switch off when Lactose is present but glucose is also present?
RNA polymerase can’t bind to the promoter region properly on its own, it requires the help of a CAP protein that is activated by cAMP. When glucose levels are high, cAMP levels drop meaning that the CAP protein isn’t activated and therefore RNA polymerase can’t bind to the operator so the Z and Y genes aren’t transcribed and therefore glucose isn’t allowed into the bacterial cell and isn’t broken down into glucose and galactose
What are the monomers for lactose?
Glucose and galactose
What are transcription factors?
Short non-coding pieces of DNA that act within the cells nucleus to control which genes are turned on or off
How do transcription factors work?
- Transcription factors slide along a length of DNA, seeking and binding to their specific promoter regions
- They may then aid or inhibit the attachment of RNA polymerase to the DNA and therefore activate or suppress the transcription of that gene
