C ELL COMMUNICATION LEARNING CHECK

D OES CELL SIGNALING OCCUR IN BACTERIA AND PROTISTS ? No, only in multicellular organisms

L IST A VARIETY OF SIGNALING MOLECULES THE CELL USES Steroids, hormones, peptides, amino acids, large proteins, nucleotides

I N ANY GIVEN MULTICELLULAR CELL, HUNDREDS OF DIFFERENT CHEMICAL SIGNALS IN THE ENVIRONMENT. H OW DOES A CELL RESPOND TO CERTAIN SIGNALS AND IGNORE THE REST ? Receptor proteins are specific

W HAT HAPPENS WHEN A SIGNAL MOLECULE APPROACHES THE SPECIFIC RECEPTOR ? Induced fit, conformational change of the protein, ultimately producing a response in the cell

T ECHNIQUES THAT HAVE ALLOWED SCIENTISTS TO DISCOVER RECEPTOR PROTEINS Monoclonal antibodies : Each individual’s immune system can make only 1 particular type of antibody which can target only 1 specific molecule. Using clones (monoclonal antibodies) that bind to specific receptors, scientists have isolated them. Gene analysis : studying mutants and isolating their gene sequences has led to the finding that receptor proteins can be grouped in families of related receptors

W HAT ARE THE DIFFERENT TYPES OF CELL SIGNALING ? Direct: 2 cells in direct contact such as gap junctions Paracrine signaling: signal molecules released by cells that ravel short distance through extracellular fluid to neighboring cells; short-lived, destroyed by enzymes Endocrine signaling: using hormones that are released through the circulatory system; longer lived signal molecules Synaptic signaling: rapid communication with distant cells using the nervous system and neurotransmitters; shorter-lived molecules

N AME ALL THE PHYSICAL CONTACTS THAT EXIST Surface markers: glycolipids in cell membrane involved in identifying cell such as blood groups, antibodies Tight junctions: leak-proof fibrous protein that hold cells together so that material passes through but not between the cells (epithelial cells in the gut) Desmosomes: intermediate filaments that that link cells found in epithelial cells Adherens junctions: transmembrane fibrous proteins Gap junctions: protein connections that “pipe” connect cells in animals (ex in heart muscle) Plasmodesmata: cytoplasmic connections between gaps in adjoining plant cells

D ES INTRACELLULAR SIGNALING REQUIRE BINDING TO A CELL - SURFACE RECEPTOR ? No, these molecules are lipid- soluble, nonpolar, small Examples include NO, steroid hormones, vitamin D, thyroid hormone

W HERE DO INTRACELLULAR RECEPTORS BIND ? They bind inside the cell to a receptor located in the cytoplasm or directly go across the nuclear membrane to bind with a receptor there. In the nucleus, they can directly bind to DNA

N AME THE 3 CELL SURFACE RECEPTORS AND DESCRIBE HOW THEY WORK G-protein-linked receptor: a signal binds, G protein changes shape and binds to GTP and can cause a number of events/pathways. (such as activating adenyl cyclase) This is short lived. If there are numerous signals then G protein can stay activated. More than 100 different G-protein-linked receptors. They arose from a single ancestral sequence.

Ion channels: These transmembrane proteins open when a neurotransmitter binds to it. They allow passage of ions such as Ca,Na, K, and Cl.

Enzymatic Receptors such as tyrosine kinase. They are transmembrane proteins that add phosphate groups to proteins.

W HAT ARE 2 ND MESSENGERS. P ROVIDE EXAMPLES Cyclic amp: bind and activate kinase which in turn adds phosphatases to specific proteins in the cell. The effect is to phosphorylate. (activation of enzymes that breakdown glycogen)

2 ND MESSSENGERS Calcium : initiate skeletal muscle contraction,. They open by a G-protein-linked receptor IP3: are an intermediate that diffuse through the ER and bind to calcium ions. This opens the channels that allow them to flow into the cytolplasm

A MPLIFICATION IN VISION A light-activated rhodopsin (G-protein-linked receptor) activates 100’s of molecules An enzyme modifies 1000’s of cGMP In 1 sec, a single rhodopsin signal splits into more than 10 5 cGMP molecules

C ELL DIVISION Cell division(protein kinase activated): responds to growth promoting signals by phosphorylating an intracellular signal called ras. Ras activates phosphorylation cascades. Mutation in the ras protein causes uncontrolled cell proliferation-- cancer