Cell Communication and Signaling Mr Freidhoff AP Biology

Cell Communication and Signaling Mr. Freidhoff AP Biology

Cell Communication • All multicellular organisms must “communicate and cooperate” to maintain homeostasis • Cells communicate by sending/receiving signals and then convert the signals into a response.

Cell to Cell Communication • Membranes that are touching have membrane proteins that help with communication. • Gap Junctions for Animals, Plasmodesmata for plants. • Helps with immune response. • AKA: Juxtracrine • Analogy: Paper note. You can pass the note to the person sitting next to you.

Short Distance Communication • No connection. • Communication of molecules, creates response in other cells. • Paracrine: Cell secretes signaling molecules to near by cells. • Synaptic: Stimulation of nerve cells by neurotransmitters. • Analogy: Like a snapchat, goes to the receiver and then goes away.

Long Distance Communication • Longer distance or larger number of cells. • Many of the cells in the body are affected. • AKA: Endocrine • Hormones: Organs create hormones that travel throughout the body via the circulatory system. • Analogy: Facebook post. Message goes to everyone, however how people react is up to them.

Signal Transduction • Messenger molecule bonds with receptor on cell membrane. • Ligand: Chemical molecules that bond with proteins. Can’t pass through membrane. • Receptor: Membrane protein that bonds with ligands.

Stage One: Reception • The signaling molecule (a ligand) binds to the specific receptor protein which will change its shape.

Stage Two: Transduction • Reception sets off a relay team of communication proteins in the cell; second messengers carry the original exterior signal to the inside of the cell.

Stage Three: Response • The cell will respond to the signal as directed (e. g. make a protein, produce more energy, enter mitosis, etc. )

Specificity of the Signal • The same signal can trigger different responses depending on the receiving cell. • Example: adrenaline increases the activity of heart cells but slows digestive cells

Phosphorylation Cascade • Kinases: Transfers phosphate groups from ATP to other molecules. • Phosphatases: Remove phosphate groups from proteins. • Phosphorylation activates proteins. • Sometimes can deactivate proteins. • Series of kinases add a phosphate to the next one in line, activating it, and sending the signal to the target. • Like a bucket brigade.

Amplification of Signal • One enzyme within the pathway can activate several other enzymes or secondary messengers. • A small amount of ligand can produce a large cellular response.

G protein-coupled receptor • Plasma membrane receptor that works with the help of a G protein. • The G protein acts as an on/off switch. • If GDP is bound to the G protein, the G protein is inactive • If GTP is bound to the G protein, the G protein is ACTIVE

Receptor tyrosine kinases • Membrane receptors that attach phosphates (from ATP) to tyrosine's (tyrosine is an amino acid) on a substrate protein. • A receptor tyrosine kinase can trigger multiple signal transduction pathways at once

Ligand-gated ion channel • Receptor that acts as a gate. • When the ligand binds with the receptor, it changes shape and allows certain molecules to cross membrane. • Receptor is closed until a ligand binds the receptor

Diagrams • Arrows: Shows molecule that is being activated or moved. • Bar Headed Lines: Shows molecule that is being inhibited.

Hormone Signals • Hormones are released by organs from the endocrine system. • Receptor on cell membrane can create signal transduction of hormone message. • Intracellular Receptor: Ligand bonds with protein within the cell.

Feedback loops • Positive Feedback: Maintains homeostasis by a stimulus back to the original signal. The original stimulus is further amplified by the control system.

Feedback loops • Negative Feedback: Maintains homeostasis by returning a changing condition back to its stable target point.