Genetic differences leading to disease

Question 1

What is the PKU mutation ?

Answer 1

An A has been mutated to go to a T which changes the amino acid formed, would be Arg, R, but codes for Trp, W, due to the mutation. R408W in PAH, results in incorrect folding which forms an aggregate that the cell degrades hence no active PAH protein is made

Question 2

Difference between normal and mutated PKU protein

Answer 2

Normal PAH folds correctly which functions to break down phenylalanine hence when this mutation occurs phenylalanine is not broken down forming an excess of phenylalanine resulting in PKU

Question 3

Types of mutations

Answer 3

Substitution mutation : change of one letter in the codon, point mutation, may not affect function of protein
Deletion mutation : loss of one letter, frameshift mutation, causes protein to function differently or can cause loss of function if stop codon is formed
Insertion mutation : gain of one letter, frameshift mutation, causes protein to function differently or can cause loss of function if stop codon is formed

Question 4

Glucokinase gene mutation

Answer 4

Pancreatic beta cells sense how much glucose is in the blood and release insulin when glucose is high
Glucokinase is a key enzyme in glucose sensing as it determines how much glucose is broken down - therefore how much insulin is produced
Amount of glucokinase in cell determines how much pyruvate is produced hence how much insulin is produces

Question 5

MODY 2 mutation

Answer 5

MODY 2 is a mutation in one glucokinase gene (heterozygous) resulting in persistent mild hyperglycaemia, a type of diabetes
Homozygous individuals for this mutation have severe diabetes and very high blood glucose levels as hardly any insulin is produced

Question 6

PCR process

Answer 6

1. Denature DNA to 95º to separate DNA strands
   
   2. Cool down to 60º to let primers bind - will only stay there if 20 nucleotides long
   3. Heat DNA to 72º to allow Taq DNA polymerase to copy the DNA
   4. New DNA double stranded molecule produced, then repeat cycle ~20 cycles of PCR you’ll create about 1 million molecules

Question 7

How does PCR allow us to see mutations in DNA?

Answer 7

Once we have many molecules we can look at a sequence to see what changes there are. A way we can detect sequence differences is using restrictions enzymes that specifically target sequences of DNA which can cut DNA to give two DNA fragments allowing us to distinguish mutations present in individuals (PCR will show two strands rather than one)