- A change/mutation in the structure of a receptor protein or signaling molecule affects the activity of the signaling pathway and can alter the cellular response
- Chemicals that interfere with any component of the signaling pathway may activate or inhibit it: toxins, antibiotics
figure: on the left, the hedgehog would not create a signal transduction pathway because the inhibition prevents it from going any further.
Feedback Mechanisms
Negative Feedback and Homeostasis
- Organisms use feedback mechanisms to maintain their internal environments and respond to internal and external environmental changes.
- Negative feedback mechanisms maintain homeostasis
- Tend to push to stability after abnormality, counteracts change, processes that need to be maintained
- Processes operate at the molecular and cellular levels.
- Temperature regulation, blood glucose & calcium levels,
- Product accumulates, process that makes it slows down and less is made or output inhibits
- Tend to push to stability after abnormality, counteracts change, processes that need to be maintained
Positive Feedback and Homeostasis
- Positive feedback mechanisms amplify responses and processes in organisms.
- Move system away from starting state; tend to push organisms to extreme behaviors
- Still act to maintain homeostasis (less common); occur in abnormal situations and increase abnormality so situation becomes normal
- pregnancy contractions, fruit ripening, blood clotting
Example: Blood Vessel Injury
If there is an injury to a cell, molecules are released and trigger previously inactive clotting factors.
Clotting factors activated → activated more clotting factors → amplification continues until injury healed
Alterations in Loops
Disrupt homeostasis → Diabetes: cells don’t work so when glucose lvl increases, no insulin made to regulate