Describe the role of signal molecules in activating gene expression at the appropriate time

Some genes only need to be expressed or produced when needed. For example, fibrinogen is a protein that needs to be produced when a person needs to clot. A signal protein 'signals' or tells the DNA to start producing that particular protein. Imagine if the protein was produced all of the time at the same quantities...a person would be prone to strokes and other sicknesses that are caused by blocking the flow of blood to tissue.

1. when the tempature rises,your sweat glands and then springs into action making perspiration. some sweat evaporates with your skin taling heat with it.2.some of the blood pumped by the heart travels by your lungs to get rid of carbon dioxide and pick up oxygen.3.saliva produces by, you drinking water which saliva is 98% of. when mucus builds up in your body it also creates saliva as well as, antibacterial compunds.4.when the core body tempature drops, the shivering reflex is triggered to maintain homeostasis. for example: when you get out the pool you start to shiver because it is cold.