Unit 4 Chapter 10 - 11

Ligands: chemical signals in which the cells use to receive, send, and respond to chemical signals
Autocrine signaling - the cell secretes the ligand, binds to a receptor on the cell that secreted the ligand, inflicts the action/response to itself.
Juxtacrine Signaling - direct contact between the cell that is sending the ligan and the cell that is receiving and responding to it
- Ex. plasmodesmata in plants
Paracrine Signaling - cell secretes the ligand and it travels a short distance, eliciting an effect on cells in the nearby area
- Referred to as local regulators since they only affect cells in the immediate vicinity of the cells
Endocrine signaling - travel a long distance, these ligands are called hormones

Signal transduction determines how a cell responds internally to a signal in its environment
- Gene expression, cell growth and division, release of hormones
Ligands interact with specific target cells that respond to the presence of the ligand
The binding of the ligand to the cell membrane receptor then triggers a series of chemical reactions (A → B, C → D, E→ F)
Three major steps
1. Reception: ligand binds to a specific receptor
  - If a cell does not have the receptor for a specific ligand, the cell will not respond to that ligand
2. Transduction: series of chemical reactions that helps the cell choose the appropriate response
  - Signal cascades, a series of chemical reactions activates multiple molecules, amplifying the cell’s response to a signal
  - Kinases: transfer phosphate groups to other molecules
  - Phosphates: remove phosphate groups from other molecules
  - Enzymes: produce secondary messengers (cAMP)
3. Response: ultimate result generated by the ligand

Mutations in a gene that codes for a receptor protein could result in a change of shape
- Androgen insensitivity syndrome (AIS)
- Nephrogenic diabetes insipidus (NDI)
- Antidiuertic hormone (ADH)
Disrupted by molecules in the environment interfere with the ligand’s ability to bind