AP Biology Unit 4: Cell Communication and Signaling

Autocrine Signaling

In this signaling, the cell secretes a ligand. This ligand then binds to a receptor on the cell that secreted the ligand, triggering a response within that same cell.

Juxtacrine Signaling

This is signaling that depends on direct contact between the cell that is sending the ligand and the cell that is receiving and responding to it via a surface receptor.

Paracrine Signaling

In this signaling, the cell secretes a ligand(/local regulator) that travels a short distance, eliciting an effect on the cells nearby.

Endocrine Signaling

Some ligands travel a long distance between the sending and receiving cells. Ligands that travel a long distance are called hormones.

Taxis

The movement of an organism in response to stimulus and can be positive or negative.

Chemotaxis

Movement in response of chemicals

Ligands

Signaling molecules that bind to receptors.

Receptors

Receptors that located on the cell membrane that trigger a series of chemical reactions within the cell.

Signaling Transduction

The process by which an external signal is transmitted to inside of a cell.

Steps of Signal Transduction

1. A signaling molecule binding to a specific receptor.

2. Activation of a signal transduction pathway

3. Production of a cellular response.

Target Cells

Respond to the presence of the ligand.

Reception

1. The ligand binds to a specific receptor on or in the target cell. The receptor may be located on the cell membrane (as is the case for hydrophilic ligands) or in the cytosol of the target cell (as is the case for hydrophobic ligands) Heceptors contain ligand-specific binding domains If a cell does not have the receptor for a specifie ligand, the cel will mot respond to that ligand. Upon the binding of the ligand to the receptor, the receptor under. goes a conformational (shape) change, which triggers the neat step in the process on the inside of the cell.

Transduction

This is the series of chemical reactions (triggered by the binding of the ligand to its receptor) that helps the cell choose the appropriate response. This is often the most complicated part of signal transduction. Possible components of transduction include signaling amplification, kinases, phosphatase, and enzymes.

Signal Amplification

Signaling cascades, a series of chemical reactions in which one molecule activates multiple molecules, amplifying the cell's response to a signal.

Kinases

It can transfer phosphate groups to other molecules (which activates those molecules)

Phosphatases

Removes phosphate groups from other molecules.

Secondary Messangers

Produced by enzymes through signal transduction.

Response

Final step of signal transduction where the final result is generated by the ligand.

Signal Transduction Pathways

The series of chemical reactions that mediate the sensing and processing of stimuli.

Homeostasis

The set of conditions under which living things can successfully survive.

Three kinds of membrane receptors

1. Ligand gated Ion Channels

2. Catalytic Receptors

3. G Protein Linked Receptor

Ligand Gated Ion Channels

This is when the plasma membrane opens or closes an ion channel upon binding a particular ligand.

Catalytic Receptors

They have an enzymatic active site on cytoplasmic side of the membrane. Enzyme activity is initiated by ligand binging at the extracellular surface.

G Protein Linked Receptor

This is when it bings to a different version of a G protein on the intracellular side when a ligand is bound extracellularly. This causes the activation of secondary messengers.

Negative Feedback

used to maintain homeostasis, it turns off the end product of the pathway

ex: Sweating when too hot, shivering when too cold

Positive Feedback

This further stimulates the product.

Ex: When a baby pushes against the mother, the walls release a hormone that causes contractions to be bigger/ entering labor.