Question

1. Rachel is studying cholesterol synthesis in mice. Some mice had a mutation in their sterol regulatory element binding protein (SREBP) that is normally active when cholesterol levels are low in the cell. This mutation can no longer bind to the gene promoter for cholesterol synthesis pathway enzyme HMG-CoA reductase. What would happen to HMG-CoA reductase levels?   Again, identify this type of effect and briefly define it.

Answer 1

HMG-CoA reductase levels decrease as there is no binding of SREBP. Normally, increased cholesterol level has a negative feedback effect on HMG-CoA reductase to reduce its levels. Here, low levels of cholesterol can trigger the enzyme level to increase. But the stimulatory action or the binding if SREBP can not happen, HMG-CoA reductase production in the body is kept low. After it lifespan period, it is degraded.