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
What is an intron?
A non-coding region of DNA which are not expressed, they separate the coding regions of DNA (exons)
What is an exon?
A coding region of DNA that is expressed
What is primary mRNA?
The mRNA produced when both introns and exons are transcribed
What is mature mRNA?
Where the primary strand is edited so that the mRNA introns are removed and the remaining mRNA exons are joined together
How is cAMP involved in regulating transcription?
- A signalling molecule binds to the receptor on the plasma membrane of the target cell
- This activates a transmembrane protein that activates a a G protein
- G protein activates adenyl cyclase enzymes
- Activated adenyl cyclase enzymes catalyse the formation of many molecules of cAMP from ATP
- cAMP activates PKA (protein kinase A)
- Activated PKA catalyses the phosphorylation of many proteins, hydrolysing ATP in the process to provide the phosphate groups to phosphorylate the various proteins
- This phosphorylation activates many enzymes in the cytoplasm
- PKA may also phosphorylate a CREB protein that enters the nucleus as a transcription factor which aids or inhibits the attachment of RNA polymerase to the promotor region and therefore activates or suppresses transcription of a specific gene
What is a homeobox gene/sequence?
Sequence of 180 base pairs (excluding introns), found within genes that regulate patterns of anatomical development in animals, fungi and plants
What is a hox gene?
A subset of homeobox gene, found only in animals that are involved in formation of anatomical features in the correct locations of the body plan
What is a homeodomain sequence?
The sequence of 60 amino acids coded for by the homeobox gene
What axis are embryos developed on?
The anterior-posterior (head-tail) axis
What can a mutation of a hox gene lead to?
Abnormalities can occur such as antennae on the head of a fruit fly developing as legs
How many genes can each hox gene cluster contain?
Up to 10 hox genes
What is the function of a homeodomain protein?
Homeodomain proteins are coded for by hox genes, homeodomain proteins act in the nucleus as transcription factors and also cause cascades of activation of other genes that promote mitotic cell division, apoptosis, cell migration and also regulate the cell cycle
How are hox genes regulated?
Hox genes are regulated by gap and pair-rule genes
How does apoptosis occur?
- The cell’s cytoskeleton is broken down by enzymes
- The cytoplasm becomes dense with tightly packed organelles
- The plasma membrane begins to change and blebs form
- Chromatin condenses, the nuclear membrane breaks down and DNA breaks down into fragments
- The cell breaks into vesicles that are easily ingested by phagocytic cells, this prevents cell debris from damaging any other cells
How is apoptosis controlled?
Apoptosis has many signalling molecules such as nitric oxide, nitric oxide can induce apoptosis by making the inner membrane of the mitochondria more permeable to hydrogen ions and therefore dissipating the proton gradient. This signals for proteins to be released into the cytoplasm where they can bind to apoptosis inhibitor proteins, allowing apoptosis to occur
How is apoptosis involved in limb development?
Apoptosis causes digits to separate from each other
What can a lack of apoptosis lead to?
Tumours
What can too much apoptosis lead to?
Cell loss and degeneration
