2. Cellular Internet Cell to cell communication is essential in order for organisms to coordinate activities that develop, survive and reproduce Cell communication between cells is also important and more complicated in unicellular organisms Biologists have discovered some universal mechanisms of cell regulation and these same small set of cell signals appear repeatedly - evidence of evolutionary relatedness of all life

3. Signal Conversion What kind of cell conversation do you think would be most prevalent? Sex – is the answer – reproduction - Chemical signaling of yeast in the attraction of a cells and alpha cells Signal transduction pathway – process of converting a signal on a cell’s surface into a specific response in a series of steps -striking similarities between way yeast cells and animal cells communicate - suggests same signals used today evolved before multi- cellular organisms existed

4. Yeast Cell Communication

5. Local Signaling Cell have different ways of communicating messages a. Direct contact – cell junctions connect cytoplasms of adjacent cells -signaling substances dissolved in the cytosol pass freely in adjacent cells -possible in plant and animal cells b. Cell-Cell recognition – communication between membrane bound surface molecules (remember glycoproteins & glycolipids) -important for embryonic development & immune response

6. Local and Long Distance Local regulators – influence cells by secreting messenger molecules to target cells - known as Paracrine signaling - Ex: growth factors targeting numerous cells to grow and multiply - Synaptic signaling – electrical signal between nerve cells is converted to chemical signal or neurotransmitter, that travels across the synapse to next nerve cell or target nerve cell pathway

7. Long Distance Signaling Hormones – chemical messengers that are released by specialized cells into vessels or glands to target cells in other parts of the body. - vary in size and type Ex: ethylene in plants causes ripening – only 6 atoms (C 2 H 4 ) Insulin – regulates sugar levels in blood- protein of thousands of atoms

8. Stages of Cell Signaling 1. Reception – target cell’s detection of a signal molecule from outside the cell - usually involves binding of a receptor protein on the surface or within cell 2. Transduction – signal molecule changes receptor protein to initiate phase. -converts signal to form that will evoke a cellular response - may occur as a single step, but most often is a series of relay molecules 3. Response – signal triggers a cellular response

9. Chapter 11.2 Reception Most signal receptors are plasma membrane proteins Receptor proteins in or on the target cell all it to hear the signal and respond to it Ligand – refers to a molecule specifically binding to another molecule -ligand binding usually causes a receptor protein to change in shape -signal molecule fits like a key in a lock and allows activation and interaction with other molecules leading to signal transduction

10. Membrane Receptors G protein linked receptors – extremely widespread and diverse in function such as embryonic development and sensory reception Examples are yeast mating factors, neurotransmitters, hormones, and epinephrine Diseases such as cholera, pertussis, and botulism make victims sick by producing toxins that block G protein function - G protein acts as a molecular switch on or off to trigger certain cellular responses - Enzyme attachment to G protein is temporary allowing rapid shutdown to pathway

11. G Protein Receptor

12. Membrane Receptors Receptor tyrosine kinases – help cell regulate and coordinate many aspects of cell growth & reproduction Can trigger more than one signal transduction pathway ( up to 10) from single ligand event Kinase is an enzyme that catalyzes the transfer of phosphate groups (ATP to tyrosine) - two receptor tyrosine kinases exist close to one another - signal molecule binding cause association of receptors (forming a dimer) - each tyrosine kinase adds a phosphate from ATP to activate receptor protein - activated proteins attract relay proteins that trigger transduction pathways that lead to cellular response

13. Tyrosine Kinase

14. Membrane Receptors Ion channel receptors – signal molecule (ligand) has specific shape that allows binding with receptor channel -binding on extracellular side allows the opening of the channel to certain ions - ions flow in or out cause rapid change in concentration to exert cellular response - ligand dissociates from receptor cause gate or channel to close *Ex: neurotransmitter signals between neurons

15. Intracellular Receptors Typically found in the cytoplasm or the nucleus of a cell Hydrophobic nature or small size allows the movement of these receptors into the cell Ex: steroids – travel through the blood entering cells all over the body. - target cells only contain receptor molecule for that steroid in the cytoplasm, - binding occurs, then activation, in which receptor molecule enters nucleus to turn on specific genes (transcription factors)

16. Intercellular receptors