Cell Communication AP Biology Chapter 11

Jot down ideas for communication: You would like to tell your friend across the room about a party that is happening tonight, but you don’t want to disrupt your teacher or let anyone else in class know about it. How could you get this message to them before class is over? Teacher wants to remind everyone in the class that they have a test on Friday. What would be the most efficient way to contact every student?

You are a college counselor [Mr. Mead] at ARHS and you need to give an application to all the seniors who are applying for early admission. How can you notify each of these people? You are on the yearbook committee and would like to organize a fundraising car wash event. How could you get the word out to the community, so that there is a good turnout?

Modes of Communication How might some of these forms of communication be similar to how cells communicate with each other in your body? Can you think of any examples of short and long distance messages sent in your body? Can you think of any cellular messages that are general information for the whole body and others that are specific to certain cell? How can information that is general get to all the cells in the body efficiently?

An Overview of Cell Signaling Cell-to-cell communication is essential for multicellular organisms The combined effects of multiple signals determine cell response Example: the dilation of blood vessels is controlled by multiple molecules

P207

Cell Communication yeast cells Cells of the yeast - use chemical signaling to id cells and to initiate the mating process 1 st - cells of mating type A release a-factor, bind to receptors on nearby cells of mating type B. B cells release b-factor, which binds to specific receptors on A cells. Both "factors" are small proteins – (20 aa) Binding of these factors to the receptors induces changes in the cells that lead to their fusion, or mating. The resulting A/B cell combines in its nucleus all the genes from both A and B cells, (diploid).

Bacteria Communication Prokaryotic example --- p207 The concentration of signaling molecules allows bacteria to detect population density

Fig Individual rod- shaped cells Spore-forming Spore-forming structure (fruiting body)structur e (fruiting body) Aggregation in processegation in process Fruiting bodies 0.5 mm p207

Local & Long-distance Signaling Cells in a multicellular organism communicate by chemical messengers Cells in a multicellular organism communicate by chemical messengers Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells Animal and plant cells have cell junctions that directly connect the cytoplasm of adjacent cells In local signaling, animal cells may communicate by direct contact, or cell-cell recognition In local signaling, animal cells may communicate by direct contact, or cell-cell recognition

Fig p208 Plasma membranes Gap junctions between animal cells (a) Cell junctions Plasmodesmata between plant cells (b) Cell-cell recognition

In many other cases, animal cells communicate using local regulators, messenger molecules that travel only short distances In long-distance signaling, plants and animals use chemicals called hormones

Fig p190 Local signaling Target cell Secreting cell Secretory vesicle Local regulator diffuses through extracellular fluid (a) Paracrine signaling (b) Synaptic signaling Target cell is stimulated Neurotransmitter diffuses across synapse Electrical signal along nerve cell triggers release of neurotransmitter Long-distance signaling Endocrine cell Blood vessel Hormone travels in bloodstream to target cells Target cell (c) Hormonal signaling

Communicating cells may be close together or far apart Communicating cells may be close together or far apart Three stages of cell signaling are: Three stages of cell signaling are: –Reception –Transduction –Response

Figure 11.6 p 209

Communicating cells may be closer together or far apart A chemical signal that communicates between two nearby cells is called a local regulator. Two types of local signals have been described in animals: –PARACRINE SIGNALING –SYNAPTIC SIGNALING

Paracrine Signaling In paracrine signaling, one cell secretes a signal into the extracellular fluid and the signal acts on a nearby target cell Examples of paracrine signaling include growth factors, which stimulate cells to grow and divide

Fig p 208 Local signaling Target cell Secretory vesicle Secreting cell Local regulator diffuses through extracellular fluid (a) Paracrine signaling (b) Synaptic signaling Target cell is stimulated Neurotransmitter diffuses across synapse Electrical signal along nerve cell triggers release of neurotransmitter

Synaptic Signaling In synaptic signaling, a nerve cell releases a signal (neurotransmitter) into a synapse, the narrow space between the transmitting cell and a target cell, such as another nerve or muscle cell.

Hormones A chemical signal which communicates between cells some distance apart is called a HORMONE. Hormones have been described in both plants and animals

Video Clip #1

Three stages of cell signaling 1/9 Signal reception: The signal binds to a specific cellular protein called a receptor, which is often located on the surface of the cell. Signal transduction: The binding of the signal changes the receptor in some way, usually a change in conformation or shape, The change in the receptor initiates a process of converting the signal into a specific cellular response; this is signal transduction. Cellular response: The transduction system triggers a specific cellular response. The response can be almost any cellular activity…enzyme activation to gene expression!

Fig Reception 1 EXTRACELLULAR FLUID Signaling molecule Plasma membrane CYTOPLASM 1 Receptor

Signal Reception and the Initiation of Transduction A chemical signal binds to a receptor protein, causing the protein to change shape. The signal molecule is complementary to a specific region of the receptor protein The signal behaves as a ligand, a term for a small molecule that binds to another, larger molecule

Fig EXTRACELLULAR FLUID Signaling molecule Plasma membrane CYTOPLASM Transduction 2 Relay molecules in a signal transduction pathway Reception 1 Receptor

Signal Reception and the Initiation of Transduction Binding of the ligand to the receptor can lead to the following events: –Alteration in receptor conformation or shape; may lead to the activation of the receptor which enables it to interact with other cellular molecules –Aggregation of receptor complexes

Fig EXTRACELLULAR FLUID Plasma membrane CYTOPLASM Receptor Signaling molecule Relay molecules in a signal transduction pathway Activation of cellular response TransductionResponse 2 3 Reception 1

Signal Receptors Most signal receptors are plasma- membrane proteins Many signals molecules cannot pass freely through the plasma membrane. The receptors for such signal molecules are located on the plasma membrane.

p211

GDP and GTP The function of the G-protein is influenced by the nucleotide to which it is bound: –G-proteins bound to GDP are inactive –G-proteins bound to GTP are active When a ligand (signal) binds to a G-protein- linked receptor, the receptor changes its shape and interacts with a G-protein. This interaction causes the GDP bound to the inactive G-protein to be displaced by GTP, thereby activating the G-protein GTPase hydrolyses the bound GTP back to GDP

Video clip #2

p211

Tyrosine-kinase receptors – p212 The structure of a tyrosine-kinase receptor is characterized by an extracellular ligand- binding domain and a cytosolic domain These enzymes help control factors such as cell-cycle control systems

Ion-channel receptors p213 Some chemical signals bind to ligand- gated ion channels. These are protein pores in the membrane that open or close in response to a ligand binding, allowing or blocking the flow of specific ion (Na +, Ca 2 ).

Signal Transduction Pathways Pathways relay signals from receptors to cellular responses Ligand binding to a receptor triggers the first step in the chain of reactions—the signal transduction pathway—that leads to the conversion of the signal to a specific cellular response The transduction system does not physically pass along the signal molecule, rather the information is passed along. At each step in the process, the nature of the information is converted, or transduced into a different form.

Signal Transduction Pathways Protein phosphorylation is a major mechanism of signal transduction Protein phosphorylation the transferring of a phosphate group from ATP to a protein substrate (catalyzed by protein kinases). Cells turn off signal transduction pathways when the initial signal is no longer present.

Receptor Signaling molecule Activated relay molecule Phosphorylation cascade Inactive protein kinase 1 Active protein kinase 1 Active protein kinase 2 Active protein kinase 3 Inactive protein kinase 2 Inactive protein kinase 3 Inactive protein Active protein Cellular response ATP ADP ATP ADP ATP ADP PP P P P P i Figure 11.10

Small Molecules and Ions Not all the components of signal transduction pathways are proteins, some rely on small, nonprotein water soluble molecules or ions. These are called second messengers.

Calcium Ions Many signaling molecules induce their specific responses in target cells by increasing the cytoplasm’s concentration of Ca 2+. The Ca 2+ pool can affect signal transduction by affecting the activity or function of target proteins The Ca 2+ can bind to relay proteins and changing the relayed message

Cellular Responses to Signals In response to a signal, a cell may regulate activities in the cytoplasm or transcription in the nucleus In the cytoplasm, the signaling can affect the function or activity of proteins which carry out various processes: –Rearrangement of cytoskeleton –Opening or closing of an ion channel –Serve at key points in metabolic pathways –Modulate every aspect of gene expression

Signal Amplification The production of second messengers provides a built-in means of signal amplification. The binding of one ligand (first message) can lead to the production of many second messages. The degree of amplification is heightened when the second messenger system is linked to a phosphorylation cascade.

Signal Specificity Only target cells with the appropriate receptor bind to a particular signaling molecule However, a particular signal can bind to different cell types and result in different responses in each of the cell types p223 Apoptosis pp