Hormones and Cell Signaling

Hormones and Cell Signaling

• The term "hormone" comes from the Greek word "hermon", meaning "to excite or set into motion".
• Hormones are chemicals produced in one area of the body that have an effect on another area.
• Hormones are named based on their effect on the body, not their location of production.

Types of Hormone Signaling

• Autocrine signaling: ligands function internally and on other target cells.
• Paracrine signaling: ligands target cells only in the vicinity of the original emitting cell.
• Endocrine signaling: hormones that target distant cells and often travel through the circulatory system.
• Intracrine signaling: ligands are produced by the target cell and bind to a receptor within the cell.
• Juxtacrine signaling: ligands target adjacent cells.

Cell Signaling Mechanisms

• Each cell type displays a set of receptors that enable it to respond to a set of signal molecules.
• An individual cell often requires multiple signals to survive, grow, and differentiate.
• If deprived of appropriate survival signals, a cell will undergo apoptosis (cell suicide).

Receptor Signaling

• A receptor and some intracellular signaling proteins are preassembled into a signaling complex on the inactive receptor.
• The activated receptor phosphorylates itself at multiple sites, which then act as docking sites for intracellular signaling proteins.
• Activation of a receptor leads to the increased phosphorylation of specific phospholipids in the adjacent plasma membrane.

Intracellular Signaling Proteins

• Types of interaction domains in signaling proteins:
  • Src homology 2 (SH2) domains
  • Phosphotyrosine-binding (PTB) domains
  • Src homology 3 (SH3) domains
  • Pleckstrin homology (PH) domains

Signaling Systems

• Response timing varies in different signaling systems, according to the speed required for the response.
• Sensitivity to extracellular signals varies greatly, with hormones acting at very low concentrations on distant target cells.
• Signal amplification is a mechanism for increasing the sensitivity of a signaling system.
• Dynamic range of a signaling system is related to its sensitivity, with some systems responding over a narrow range of extracellular signal concentrations and others over a broader range.

Signal Processing

• Signal processing can convert a simple signal into a complex response, such as an abrupt, switch-like response or an oscillatory response.
• Feedback lies at the heart of biochemical switches and oscillators.
• Integration allows a response to be governed by multiple inputs.

Coordination of Multiple Responses

• Coordination of multiple responses in one cell can be achieved by a single extracellular signal.
• Coordination depends on mechanisms for distributing a signal to multiple effectors, including branches in the signaling pathway.

Hormone Synthesis and Processing

• Many protein and peptide hormones are synthesized within a larger precursor protein.
• The process is catalyzed by specific proteases that cleave the protein at specific sites.
• Alternative splicing of mRNA for hormones can also occur.

Receptor Structure

• A receptor typically consists of a ligand-binding domain that noncovalently binds the correct hormone and an effector domain that responds to the presence of the hormone bound to the ligand domain.

Zinc Finger Proteins

• The coordination of a Zn2+ atom by four cysteines causes the formation of a loop in zinc finger proteins.
• The P-box in the first zinc finger is involved in binding to specific DNA binding sites and discriminating between closely related sites for different hormones.

G Proteins and Ion Channels

• Smell and vision depend on GPCRs that regulate ion channels.
• Olfactory receptor neurons possess modified cilia that contain the olfactory receptors and the signal transduction machinery.
• The axon of the receptor neuron conveys electrical signals to the brain when an odorant activates the cell to produce an action potential.

This quiz covers the basics of hormones, their production, and effects on the body, as well as cell signaling and its mechanisms.