Question

Which feedback (Negative or Positive) gives you homeostasis?

Answer 1

Wasn't sure whether or not this was a trick question and the answer is actually BOTH. Or if it was just negative feedback that brought homeostasis.

Answer 2

It is both.

Negative feedback is certainly the most intuitive to understand in terms of homeostasis. The body doesn't want too much of Example Molecule 1 (EM1, for kicks) around. So presence of EM1 inhibits some synthetic step in its own production. When the cell already has enough EM1, it does not make more. When there is only a little, synthesis is not inhibited and it makes more. Real examples abound.

For positive feedback I'll use a real example because it is slightly less intuitive. Hypoxia Inducable Factor 1 (HIF1) is a signalling molecule produced/activated by cells in response to oxygen deficit. It is a transcription factor. So once produced and activated (i.e., in situations when the cell needs more oxygen) it activates transcription of genes involved in getting more aerobic respiration to happen: some of these genes are for metabolic proteins in aerobic metabolism (including several glycolytic enzymes), some favor formation of new blood vessels, etc.

The cell always needs these gene products, in low levels. So it turns out that HIF1 is under positive feedback control: presence of active HIF1 stimulates more HIF1 activation. This ensures that there is always some HIF1 in its active form and the cell is always making these constitutional enzymes and signalling molecules it needs.

As an overall and general rule, most "housekeeping" genes and their proteins are under positive feedback control whereas genes and proteins involved in specific cellular responses to very event specific stimuli are under negative feedback control. And both are equally important in maintaining homeostasis.

Answer 3

Thanks bunches :)

Answer 4

I understand now :D