Cell Communication AP Biology The Cellular Internet All

Cell Communication AP Biology

The “Cellular Internet” • All multicellular organisms must “communicate and cooperate” to maintain homeostasis • universal mechanisms of cellular regulation involve cell-to-cell communication. • Basically, a signal is received and then converted into a response within the cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Methods used by Cells to Communicate • Cell Signaling using chemical messengers (proteins, steroids, etc) 1. 2. Local signaling over short distances • Cell-Cell Recognition Proteins attached to cell exterior; glycolipids and glycoproteins (e. g. blood type proteins) • Local regulators (chem signals from the neighboring cells) – Paracrine- secreted signal (e. g. growth factors) – Synaptic- directed signal (e. g. neurotransmitter) Long distance signaling • Hormones - ENDOCRINE Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Cell-Cell Communication • Transport between cells – cell junctions are protein tunnels directly connecting adjacent cells (called gap junctions in animal cells & plasmodesmata in plants); allow material to pass through (e. g. chem signals or water) Plasma membranes Gap junctions between animal cells Plasmodesmata between plant 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Local Signaling Example: Cell-Cell Recognition • Used to guard against unfamiliar cells and invaders; part of immune response • Membrane bound cell surface molecules • Glycoproteins • Glyolipids Figure 11. 3(b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Local Signaling Example: Local Regulators - Communicate with neighbors using local regulators, only work over a short distance - Paracrine signaling communicates with all cells surrounding (e. g. growth factor to stimulate mitosis near a wound) - Synaptic signaling is directed to one neighbor cell (e. g. neurotransmitters from one neuron to the next) Local signaling Target cell Secretory vesicle Local regulator diffuses through extracellular fluid (a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell.

Long-distance Signaling Example: Hormones • long-distance signaling used by both plants and animals; hormones (natural steroids) are released into bloodstream by glands and can go anywhere in the body causes changes in a lot of cells simultaneously (e. g. adrenaline) Long-distance signaling Blood vessel Endocrine cell Hormone travels in bloodstream to target cells Target cell Figure 11. 4 (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all C body cells. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Long-Distance Signaling Systems § Nervous System (Animals only) u Quick long distance communication through Electrical signals sent through neurons § Endocrine System (Animals only) u Glands that secrete hormones into cell spaces or into blood stream (lymph nodes, adrenal gland, pituitary gland, etc) § Note: Plants also use hormones u AP Biology Transported through vascular system, plasmodesmata, or released into air (e. g. ripening fruit)

The Three Stages of Cell Signaling • All cell signaling (long or short distance) occurs in three stages 1. Reception – receive the signal 2. Transduction – signal causes a cascade of communication inside the cell 3. Response – cell responds to the signal • Called Signal transduction pathways – Note: Pathways are similar in all life, supporting evolution Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Overview of cell signaling EXTRACELLULAR FLUID 1 Reception CYTOPLASM Plasma membrane 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Figure 11. 5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Stage One: Reception EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 Reception Receptor The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!) Signaling molecule § The signaling molecule (a ligand) binds AP Biology to the specific receptor protein; shape determines function!

Stage Two: Transduction CYTOPLASM EXTRACELLULAR FLUID Plasma membrane 1 Reception 2 Transduction Receptor 2 nd Messenger! Relay molecules in a signal transduction pathway Signaling molecule § Reception sets off a relay team of communication proteins in the cell; second messengers carry the original exterior signal to the inside of the cell AP Biology

Stage Three: Response CYTOPLASM EXTRACELLULAR FLUID Plasma membrane 1 Reception 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signaling molecule Can be catalysis, activation of a gene, triggering apoptosis, almost anything! § The cell will respond to the signal as directed (e. g. make a protein, produce AP Biology more energy, enter mitosis, etc. )

Signal Transduction Animation § http: //media. pearsoncmg. com/bc/bc_ campbell_biology_7/media/interactiv emedia/activities/load. html? 11&A § http: //www. wiley. com/legacy/college/bo yer/0470003790/animations/signal_tran sduction/signal_transduction. htm AP Biology

Common Receptor Proteins (stage one) § G-protein coupled receptors § Receptor tyrosine-kinases § Ion channel receptors AP Biology

G-Protein Coupled Receptors are often involved in diseases such as bacterial infections. G-Protein Receptors Plasma membrane G protein-coupled receptor Activated receptor Signaling molecule Enzyme GDP 1 CYTOPLASM 2 G protein (inactive) GDP GTP Activated enzyme i GTP GDP P 4 3 Cellular response AP Biology Inactive enzyme

Receptor tyrosine kinases Signal-binding site Signal molecule Helix in the Membrane Tyrosines Tyr Tyr Tyr Tyr Tyr Receptor tyrosine kinase proteins (inactive monomers) CYTOPLASM Dimer Activated relay proteins Figure 11. 7 Tyr Tyr P Tyr Tyr P P Tyr P 6 ATP Activated tyrosinekinase regions (unphosphorylated dimer) 6 ADP Fully activated receptor tyrosine-kinase (phosphorylated dimer) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Inactive relay proteins Cellular response 1 Cellular response 2

Ion Channel Receptors § Very important in the § § 1 Opening the channel allows ions to rush down a concentration gradient, creating an electrical signal from the moving charges AP Biology Ions Signaling molecule (ligand) nervous system Ligand-gated ion channel receptor Creates an action 2 potential Gate open Signal triggers the opening of an ion channel u Gate closed Plasma membrane Cellular response 3 Gate closed

Notes about Transduction • Reminder, Transduction is the second stage. It occurs when cascades of molecular interactions relay signals from the receptor to the target molecules inside the cell • It is a multistep pathway – can amplify a signal and create a large response from a single ligand – Requires communication and coordination within the cell itself – Transduction Example: Protein Phosphorylation Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Protein Phosphorylation and Dephosphorylation • Protein Phosyphorylation cascade - An example of transduction in which a series of protein kinases add a phosphate to the next one in line, activating it, and sending the signal to the target (like a bucket brigade!) – enzymes then remove the phosphates to reset the cascade after “Response” stage Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

• A phosphorylation cascade Signal molecule Receptor Activated relay molecule Inactive protein kinase 1 1 A relay molecule activates protein kinase 1. ory ph ATP 5 Enzymes called protein phosphatases (PP) catalyze the removal of the phosphate groups from the proteins, making them inactive and available for reuse. Figure 11. 8 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings ATP Pi ADP Active protein kinase 3 PP Inactive protein P 4 Finally, active protein kinase 3 phosphorylates a protein (pink) that brings about the cell’s response to the signal. ATP ADP Pi PP de Inactive protein kinase 3 a sc ca PP on Pi 3 Active protein kinase 2 then catalyzes the phosphorylation (and activation) of protein kinase 3. P Active protein kinase 2 ADP i lat Inactive protein kinase 2 os Ph 2 Active protein kinase 1 transfers a phosphate from ATP to an inactive molecule of protein kinase 2, thus activating this second kinase. Active protein kinase 1 P Active protein Cellular response

Small Molecules and Ions as Second Messengers • Transduction Example: – Secondary messengers: small, nonprotein, water-soluble molecules or ions that act as secondary messengers to carry the signal to the target (example- cyclic AMP) – (Note: Membrane Proteins would be the primary messengers since they get the signal first) Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Cyclic AMP • c. AMP is often found with the G-protein receptors; made from ATP that has only one phosphate; secondary messenger First messenger (signal molecule such as epinephrine) G protein G-protein-linked receptor Adenylyl cyclase GTP ATP c. AMP Protein kinase A Figure 11. 10 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular responses

Cyclic AMP • Cyclic AMP (c. AMP) – Is made from ATP NH 2 N N O O O N N – O P O P O Ch 2 O O O N N O Pyrophosphate P Pi N N Adenylyl cyclase O OH OH ATP NH 2 O CH 2 O OH Cyclic AMP Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Phoshodiesterase O P O N N O HO P O CH 2 O O H 2 O OH OH AMP

Fig. 11 -11 First messenger Adenylyl cyclase G protein-coupled receptor GTP ATP c. AMP Second messenger Ex Diagram: Protein kinase A Transduction in a G -protein pathway Cellular responses using c. AMP AP Biology

Second Messenger Example: Calcium Ions • Calcium ions act as a secondary messenger in many different pathways because cells can regulate its concentration and location EXTRACELLULAR FLUID ATP Plasma membrane Ca 2+ pump Mitochondrion Nucleus CYTOSOL Ca 2+ pump ATP Key Ca 2+ pump Endoplasmic reticulum (ER) High [Ca 2+] Low [Ca 2+] Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other secondary messengers trigger the release of concentration gradients of Ca 2+ in various areas of the cell, creating moving charges and electrical signals. Pumps then reset the Ca 2+ concentration gradient to be used again.

Calcium Ion Diagram example 1 A signal molecule binds 2 Phospholipase C cleaves a to a receptor, leading to plasma membrane phospholipid activation of phospholipase C. called PIP 2 into DAG and IP 3. EXTRACELLULAR FLUID 3 DAG functions as a second messenger in other pathways. Signal molecule (first messenger) G protein DAG GTP G-protein-linked receptor Phospholipase C PIP 2 IP 3 (second messenger) IP 3 -gated calcium channel Endoplasmic reticulum (ER) Ca 2+ (second messenger) Figure 11. 12 4 IP 3 quickly diffuses through the cytosol and binds to an IP 3– gated calcium channel in the ER membrane, causing it to open. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Various proteins activated 5 Calcium ions flow out of the ER (down their concentration gradient), raising the Ca 2+ level in the cytosol. Cellular response 6 The calcium ions activate the next protein in one or more signaling pathways.

Signaling molecule § Cellular Response (Stage 3) u Receptor Specificity of the signal § The same signal Relay molecule can molecules trigger different responses depending on other signals and Response 1 Response 2 Response 3 various receptor proteins or SMs Cell A. Pathway leads Cell B. Pathway branches, u Many responses can come from one signal! AP Biology to a single response. leading to two responses.

§ The signal can also activate, inhibit , or create multiple responses from one signal Activation or inhibition Response 4 Response 5 Cell C. Cross-talk occurs Cell D. Different receptor between two pathways. leads to a different response. AP Biology

Response example- cell signaling leads to regulation of transcription (turn genes on or off) AP Biology

Long-distance Signaling Response Example Some hormones induce transcription. Once inside the cell, the hormone attaches to a protein that takes it into the nucleus where transcription can be stimulated. (ex: testosterone, which is a transcription factor) AP Biology

Termination of Communication • Response is terminated quickly by the reversal of ligand binding Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Any Questions? ? Can You Hear Me Now? AP Biology

Two body systems control MOST communication 1. Nervous System – uses ion concentration gradients and action potentials to communicate quickly through electrical impulses and neurons 2. Endocrine System - uses hormones secreted into the bloodstream (faster, further reach) or surrounding cell space; slower than nervous system, but longer lasting effect AP Biology

Cell Communication/Signaling § This is an extremely important part of § § understanding how an organism actually maintains homeostasis and survives. View Page 55 in your Test Prep book (Look @ YOU MUST KNOW) section. Make sure you have these written down and have notes to address each of them. DNA LEARNING CENTER ANIMATION link Bozeman videos, #37, #38, #39 and #32 all explain and give examples of Cell Signaling and WHAT Happens if it goes WRONG! KHAN ACADEMY simplifies CELL COMMUNICATION using basic terminology AP Biology

Human Endocrine System AP Biology

Major Vertebrate Endocrine Glands Their Hormones (Hypothalamus–Parathyroid glands) AP Biology

AP Biology

Neurosecretory cells in endocrine organs and tissues secrete hormones. These hormones are excreted into the circulatory system (ex. Adrenaline) or the surrounding cell space (ex. Lymph). AP Biology

Are the following hormone pathways Positive or Negative Feedback systems? Stress and the Adrenal Gland AP Biology http: //highered. mcgrawhill. com/olcweb/cgi/pluginpop. cgi? it=swf: : 535: : /site s/dl/free/0072437316/120109/bio 48. swf: : Action%20 of% 20 Epinephrine%20 on%20 a%20 Liver%20 Cell

http: //bcs. whfreeman. co m/thelifewire/content/ch p 42/4202003. html AP Biology

http: //vcell. ndsu. nodak. edu/animations/regulatedsecre AP Biology tion/movie. htm

Answers § Stress and Adrenaline – Positive § Feedback (induces a response/change) Calcium and Blood Sugar regulation – Negative Feedback (prevents a change, maintains a normal level) AP Biology