.Cathy is a young mum who is juggling a family of 2 young children, a part-time
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Question
.Cathy is a young mum who is juggling a family of 2 young children, a part-time job and studying at university part-time, so life is frequently stressful. However, recently she has been having some seizures. After several visits to specialists, her symptoms are diagnosed as being due to epilepsy, with an increased firing frequency in the neurons in some areas of her brain.
Genetic tests she has just got back show that Cathy has a mutation from alanine to glutamate at a key location in the voltage-gated sodium channels in her neurons. The mutation causes the channels to open at a lower membrane potential than normal. Part of the sequence in the mutated channel is glutamate-alanine-lysine, whereas it is normally alanine-alanine-lysine.
Note: The side chain structures of these amino acids are as follows: Alanine (Ala) –CH3
Glutamate (Glu) –CH2CH2COOH with a pKa of 4
Lysine (Lys) –CH2-CH2-CH2-CH2-NH3+ with a pKa of 10.
Answer the following questions based on this information.
a) Using the provided genetic code table on page 18, write out an mRNA sequence that encodes alanine-alanine-lysine. Mark the 5’ and 3’ ends clearly.
b) What is the minimum number of bases that would need to be mutated to change this sequence to one that encodes glutamate-alanine-lysine? On the sequence, clearly show the required base change/s
C) Briefly describe the roles of ion channels in generating an action potential in healthy individuals. You may use a diagram to answer the question if you wish.?
Explanation / Answer
a. Using the provided genetic code table, write out an mRNA sequence that encodes alanine-alanine-lysine. Mark the 5’ and 3’ ends clearly.
Alanine-alanine-lysine
Alanine is coded by triplet code: GCU, GCC, GCA, GCG.
Lysine is coded by triplet code: AAA, AAG.
mRNA sequence: 5’ GCG GCU AAA 3’ or 5’ GCA GCU AAA 3’
b. What is the minimum number of bases that would need to be mutated to change this sequence to one that encodes glutamate-alanine-lysine? On the sequence, clearly show the required base changes.
Glutamate-alanine-lysine
Glutamate is the anion of glutamic acid.
Glutamic acid is coded by triplet code: GAG, GAA
Answer: minimum number of base change to change the triplet code to code from alanine to glutamic acid is one.
GCG to GAG or GCA to GAA – where C is replaced with A.
c. Briefly describe the role of ion channels in generating action potential in healthy individuals.
Resting potential and action potential:
The resting potential depends on the concentration of four ions within the cell:
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