Question

1. We talked about the production of ferritin as an example of translational regulation. Explain what would happen if a cell had a nonfunctional IRP gene. Be specific in your answer, with an explanation of what IRP normally does and how the loss of IRP would affect the production of ferritin.

2. The pathway of glycogen breakdown provides several examples of mechanisms to regulate protein function. Describe each of these, with specific reference to the components of the pathway and the mechanisms of regulation demonstrated.

Answer 1

Answer:

1):

Role of IRP in ferritin mRNA synthesis:

• IRE is also known as iron responsive element.
• It will bind to the IRE ( iron responsive site) which is present in ferritin mRNA. This binding prevents the translation of ferritin mRNA.
• When iron concentration becomes high in the cytoplasm, then iron molecule binds to this IRE element and leads to removal of IRE from ferritin mRNA and leads to synthesis of ferritin. Ferritin acts as storage of iron molecule.

loss of IRP:

• when IRP protein is not found in the cytoplasm, then ferritin mRNA IRE site remains free.
• This leads to continuous synthesis of ferritin protein whether iron is present or absent.

(Additional information about IRP on transferrin receptor:

• IRP is also binds on transferrin receptor mRNA, it will stabilise transferring receptor mRNA synthesis by activating its translation.
• But when iron is bind to the IRP element, it will remove IRP and transferrin receptor synthesis stops.)

2):

Breakdown of glycogen to glucose is called glycogenolysis.

It is directly connected to regulation of protein functioning as follows

• when glycogeneolysis is taking place in liver it increases the blood glucose levels which in turn stimulate insulin (a protein acting as hormone) production by beta cells of pancreas.
• Insulin then increase the permeability of cells for the uptake of glucose and hence reduces blood sugar.
• when the sugar levels fall below the normal range then it stimulate production of glucagon by alpha cells of pancreas which increases blood sugar by promoting glycogenolysis.
• insulin and glucagon are antagonistic to each other.

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