Cell Communication

The “Cellular Internet” All multicellular organisms must “communicate and cooperate” to maintain homeostasis Science has identified universal mechanisms of cell-to-cell communication. Communication in cells is similar to communication in general. Cells communicate by sending/receiving signals and then converting the signals into a response

Overview of cell signaling EXTRACELLULAR FLUID Receptor Signal molecule Relay molecules in a signal transduction pathway Plasma membrane CYTOPLASM Activation of cellular response Figure 11.5 Reception 1 Transduction 2 Response 3

Cell Signaling Animal cells communicate by: Locally by direct contact (gap junctions) Locally by secreting local regulators (growth factors, neurotransmitters) Long distance (hormones)

LOCAL SIGNALING EXAMPLES Direct transport between cells protein tunnels directly connecting adjacent cells allow material to pass through (e.g. chem signals or water) and be shared gap junctions in animal cells plasmodesmata in plants); Plasma membranes Plasmodesmata between plant cells Gap junctions between animal cells Figure 11.3 (a) Cell junctions. Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes.

LOCAL SIGNALING EXAMPLES local regulators- messenger molecules that travel only short distances Local regulator diffuses through extracellular fluid Target cell Secretory vesicle Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse is stimulated Local signaling (Left: Paracrine, Right: Synaptic)

LONG DISTANCE SIGNALING EXAMPLES Used by all multicellular organisms to coordinate effort between cells that are not close together Hormones travel through the circulatory system abd can go anywhere in the body or even to another organism Target cells contain surface receptors that recognize and respond to the specific hormone Slow method of communication, but it can cause changes in a lot of cells simultaneously Hormone travels in bloodstream to target cells (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all body cells. Long-distance signaling Blood vessel Target cell Endocrine cell

Stage One: Reception EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!) Receptor Signaling molecule The shape determines function! Only cells that contain the right receptor can receive the signal

Stage Two: Transduction EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 1 Reception 2 Transduction Receptor 2nd Messenger! Relay molecules in a signal transduction pathway Signaling molecule Reception sets off a “relay team” of INTERIOR communication molecules; proteins and/or second messengers (non-proteins) carry the original exterior signal to the inside of the cell

Stage Three: Response EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 Reception 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signaling molecule The cell will respond to the signal as directed (e.g. make a protein, produce more energy, enter mitosis, etc.)

Termination of Communication Inactivation mechanisms are an essential aspect of cell signaling When signal molecules leave the receptor, the receptor reverts to its inactive state