Chapter 11~ Cell Communication 2xnwU Pohttp://youtu.be/U6uHotlXv Po Real action in the body oMhttp://youtu.be/QGd5kg9Jq oM - Part 1 EWMhttp://youtu.be/12QHDoSi EWM Part 2 Boseman Intro:

Cell Junctions b When cells come in close contact with each other they create intercellular junctions: b Desmosomes: hold adjacent animal cells tightly to each other (attach) b Gap junctions are protein complexes that form channels in mem. And allow communication between the cytoplasm of adjacent cells (attach and communicate) b Tight junctions: between membranes of adjacent animal cells (attach) ex seal off body cavities. to prevent leaks

Stages of cell signaling 3 steps: Reception: chemical message binds to a protein on the cell surface. Transduction: The binding of the signal molecule alters the receptor protein in some way. b The signal usually starts a cascade of reactions known as a signal transduction pathway. Response: The transduction pathway finally triggers a response. b The responses can vary from turning on a gene, activating an enzyme, rearranging the cytoskeleton. b There is usually an amplification of the signal (one hormone can elicit the response of over 108 molecules.

Reception b The binding between a signal molecule(ligand) and a receptor is highly specific. A conformational change in a receptor is often the initial transduction of the signal. b Two locations of receptors: Intracellular receptors found inside the plasma membrane and therefore must be hydrophobic ex. Steroid, testosterone, Plasma membrane receptors bind to water soluble ligands. Ex. G-protein coupled receptor Once the enzyme is activated it can trigger the next step in the pathway leading to a cellular response.

Another example of membrane protein: b Receptor tyrosine kinase Key difference between the two: receptor tyrosine kinase can use a single ligand to activate multiple cellular responses.

Signal-transduction pathway b Definition: Cascades of molecular interactions relay signals form receptors to target molecules in cell. b Local signaling (short distance): √ Paracrine (growth factors) √ Synaptic (neurotransmitters) b Long distance: hormones

Ex: Protein phosphorylation b Protein activity regulation b Adding phosphate from ATP to a protein (activates proteins) b Protein kinase is enzyme involved in phosphorylating and thereby activating many proteins at the next level. b Example: cell reproduction b Reversal enzyme: protein phosphatases –removes phosphate groups and inactivates protein kinases.

Ex: Second messengers b Non-protein signaling pathway (calcium ions) b Example: cyclic AMP (cAMP) b Ex: Glycogen breakdown with epinephrine b Enzyme: adenylyl cyclase b G-protein-linked receptor in membrane (guanosine di- or tri- phosphate)

Cellular responses to signals b Cytoplasmic activity regulation – regulates the activity rather than synthesis b The final activated molecule in a signaling pathway functions as a transcription factor b Cell metabolism regulation b Nuclear transcription regulation

Apoptosis b cell suicide, where cell is dismantled and digested b triggered by signals that activate the cascade of “suicide” proteins in a cell b normal part of development of hands and feet in humans and is essential for a normal nervous system, and for operation of immune system

Nervous System Nervous System b all-or-nothing response, immediate action involves nerve impulses caused by changes in membrane potential (electrical charge difference across a membrane) A stimulus changes membrane permeability and a reversal of charges (depolarization) happens along axon. The sodium-potassium pump (active transport) is involved here!

Nervous System b To be passed to another neuron, muscle, or gland, neurotransmitters must cross a synapse by exocytosis. b Common neurotransmitters are acetylcholine, epinephrine, and serotonin.

hormone: chemical signal that causes a response in a target cell; very slow hormones secreted into body fluids (ex. blood) regulated by positive and negative feedback + ex. childbirth (more gets you more) - ex. glucose regulation using insulin and glucagon Endocrine System

involves cell surface markers (glycoproteins, glycolipids) MHC: major role in self vs. nonself highly specific: Each B or T cell responds to only 1 kind of antigen! Antibodies tag foreign invaders so that they can be destroyed by phagocytosis or killer cells. Immune System