AP Bio Unit 4 Cell Communication and Signaling

Ligands

Chemical signals that living organisms survive on - communication by sending/receiving/responding chemical signals

Autocrine Siganaling

Cell signaling itself to generate a response. Releases a ligand that binds to a receptor = creates a response.

Ex: Cancer cells - release its own growth hormones (ligands) that stimulate cancer cells to grow and divide

Juxtacrine Signaling

Depends on direct contact between the cell that is sending the ligand and the cell that is receiving it via a surface receptor.

Ex: Plasmodesmata in plants - ligand travel in between channels that connect cells

Paracrine Signaling

Near by signal sending. Only affects cells that are hear the cell that is sending a signal. Also know as local regulators. 

Ex: Neurotransmitters - Travel short distances across synapse to comm. with other cells

Endocrine Signaling

Long distance between sending and receiving signals. Ligands that travel long distances are hormones.

Ex: Insulin - hormone produced and released by pancreas, travels through circulatory system to trigger all across the body

Hormones

Ligands that travel long distances

Signal Transduction

Determines the response of a cell to its surroundings

Target Cells

Specific cells that respond to ligands

Cell membrane receptors

Hydrophilic ligands that bind to receptors in the cell membrane.

Reception

A ligand binds to a receptor on the cell membrane.

A second messenger usually cyclic AMP (cAMP) carries the message further

What if the receptor is on the inside of the membrane?

Only hydrophobic chems. can pass through the membrane. These will be the ligands that bind to those receptors.

Transduction

The transmission of molecular signals from a cell’s exterior to its interior.

A signal transduction pathway is often used to amplify the initial message. Cascade effect - molecule results in multiple sending that message.

Ex: A kinase (which transfers phosphate groups to other molecules) activates those molecules.

Response

Results generated by the ligand, end process where the signal is carried out.

Often genes are turned on and off to regulate the protein synthesis.

Ex: Apoptosis - opening channels

Apoptosis

Programmed cell death

Why does apoptosis happen?

• Removing damage cells

• Preventing cancer

• Maintaining homeostasis

Negative feedback 

Returns the system to its original state = stabilizes it.

To reverse in order to maintain homeostasis.

Ex: Temperature, blood glucose level, blood pH

Positive feedback

Amplifies an already existing cell response. Moves away from stable point.

Ex: Lactation in mammals, On set of labor in childbirth.

Plants: ripening of fruit