Cell Communication  2007-2008

Regulation & Communication Animals rely on 2 systems for regulation endocrine system system of ductless glands secrete chemical signals directly into blood chemical travels to target tissue target cells have receptor proteins slow, long-lasting response nervous system system of neurons transmits “electrical” signal & release neurotransmitters to target tissue fast, short-lasting response Hormones coordinate slower but longer–acting responses to stimuli such as stress, dehydration, and low blood glucose levels. Hormones also regulate long–term developmental processes by informing different parts of the body how fast to grow or when to develop the characteristics that distinguish male from female or juvenile from adult. Hormone–secreting organs, called endocrine glands, are referred to as ductless glands because they secrete their chemical messengers directly into extracellular fluid. From there, the chemicals diffuse into the circulation.

Local and Long-Distance Signaling Cells in a multicellular organisms communicate by chemical messengers Animal and plant cells have cell junctions that directly contact the cytoplasm of adjacent cells Paracrine: In local signaling, animal cells may communicate by direct contact In many other cases, animal cells communicate using local regulators, messenger molecules that travel only short distances (Synaptic) Endocrine: In long-distance signaling, plants and animals use chemicals called hormones

Local Direct contact Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells Local Cell junctions Direct contact Cell-cell recognition

Long Distance Local Paracrine Synaptic Endocrine Local signaling Long-distance signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Endocrine cell Blood vessel Neurotransmitter diffuses across synapse Secreting cell Secretory vesicle Hormone travels in bloodstream to target cells Local regulator diffuses through extracellular fluid Target cell is stimulated Target cell Paracrine Paracrine signaling Synaptic Synaptic signaling Hormonal signaling Endocrine

Regulation by chemical messengers Neurotransmitters released by neurons Hormones release by endocrine glands endocrine gland neurotransmitter axon hormone carried by blood receptor proteins receptor proteins Lock & Key system target cell

Ligand A signaling molecule Binds to a Receptor Protein Can be a… Individual Amino acid Nucleotide Steroid or another lipid Dissolved Gasses Binds to a Receptor Protein DO NOT make this harder than it needs to be!

How do hormones act on target cells Lipid-based hormones hydrophobic & lipid-soluble diffuse across cell membrane & enter cells bind to receptor proteins in cytoplasm & nucleus bind to DNA as transcription factors turn on genes Protein-based hormones hydrophilic & not lipid soluble can’t diffuse across cell membrane bind to receptor proteins in cell membrane trigger secondary messenger pathway activate internal cellular response enzyme action, uptake or secretion of molecules…

Action of lipid (steroid) hormones target cell blood S 1 S cross cell membrane protein carrier S 2 cytoplasm binds to receptor protein becomes transcription factor 5 mRNA read by ribosome 3 S plasma membrane 4 DNA mRNA 6 7 nucleus protein protein secreted ex: secreted protein = growth factor (hair, bone, muscle, gametes)

Action of protein hormones signal-transduction pathway Action of protein hormones 1 signal protein hormone P plasma membrane binds to receptor protein activates G-protein activates enzyme cAMP receptor protein acts as 2°messenger ATP transduction GTP transduction: the action or process of converting something and especially energy or a message into another form activates cytoplasmic signal ATP activates enzyme 2 secondary messenger system cytoplasm activates enzyme 3 response target cell produces an action

Relay molecules in a signal transduction Protein-based Hormones EXTRACELLULAR FLUID CYTOPLASM Plasma membrane Reception Transduction Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule

Benefits of a 2°messenger system 1 signal Activated adenylyl cyclase receptor protein 2 Not yet activated amplification 4 amplification 3 cAMP amplification 5 GTP G protein protein kinase 6 amplification Amplification! enzyme Cascade multiplier! 7 amplification FAST response! product

Regulation Why are hormones needed? chemical messages from one body part to another communication needed to coordinate whole body daily homeostasis & regulation of large scale changes solute levels in blood glucose, Ca++, salts, etc. metabolism growth development maturation reproduction growth hormones

Nervous & Endocrine systems linked Hypothalamus = “master nerve control center” nervous system receives information from nerves around body about internal conditions releasing hormones: regulates release of hormones from pituitary Pituitary gland = “master gland” endocrine system secretes broad range of “tropic” hormones regulating other glands in body hypothalamus posterior pituitary anterior

Any Questions?? Robert Wadlow 1918-1940 8' 11"