bio 1107 ch.9

• What is a ligand and how does it interact with ligand-gated ion channels?

Ligand-gated ion channels: channel proteins that allow specific ions, such as Na+ or Ca2+, into or out of the cell when a signaling molecule (ligand) binds to the receptor. Ligand is a general term for a molecule (e.g. neurotransmitters: glutamate, acetylcholine) that specifically binds to another molecule, often a larger one. Ligand-gated receptors change shape to allow molecules to pass through the channel, or stop molecules from passing through the channel, in response to the ligand binding.

• Describe how a signal transduction pathway with G proteins works.

Production of second messengers by enzymes in signal transduction pathways results in amplification of the signal, as a single activated enzyme can catalyze formation of many second messenger molecules. -->>>>> adenylyl cyclase

• What is a 'second messenger'? What is the second messenger in the G protein pathway example? Describe the role of these molecules in signaling pathways (e.g. how they may start a phosphorylation cascade).

Production of second messengers by enzymes in signal transduction pathways results in amplification of the signal, as a single activated enzyme can catalyze formation of many second messenger molecules. ex. cCAMP-->> derived from ATP

• Describe signal amplification and where it occurs in the signal transduction pathway.

Signal amplification occurs inside the cell. If some of the relay molecules in a multi-step pathway transmit the signal to numerous molecules at the next step, the result can be a large number of activated molecules by the end of the pathway (signal is amplified).

• What are the four steps of cell-cell signaling?

Signal reception Signal transduction (occur lipid insoluble hormones) Signal response Signal deactivation (termination) - not shown below

• What is the likely scenario for the evolution of signaling molecules?

Signaling pathway similarities between prokaryotes and eukaryotes suggest that ancestral signaling molecules evolved in prokaryotes. Likely that these pathways were later modified in single-celled and multicellular eukaryotes.

• What are signal receptors and what binds to them? What does it mean to be a target cell?

-Linking an external signal to the production of an intracellular signal in a G protein pathway involves several steps: -Hormone binds to the membrane receptor (G protein-coupled receptor), which changes shape and binds and activates the G protein -- G protein exchanges GDP for GTP. -Presence of appropriate receptor protein dictates whether cells respond to a particular hormone - those with appropriate receptors are called target cells.

• Explain the process of signaling reception and processing with lipid-insoluble hormones versus lipid-soluble hormones (and small signalers, e.g. NO) versus

-Lipid-soluble hormones (e.g. testosterone) that cross the plasma membrane involve different signal processing than lipid-insoluble hormones (e.g. insulin) that bind to membrane receptors. -Lipid-insoluble hormones cannot diffuse across the plasma membrane so they bind to membrane receptors.

• What types of organisms typically form physical connections between cells - unicellular or multicellular?

-Physical connections between cells form the basis of multicellularity. -Cells of multicellular organisms adhere to one another and have specific, distinct structures and functions. -Groups of similar cells performing similar functions in multicellular organisms are called tissues.

• What are the two general types of signal response that results from cell-cell signaling?

1.A change in which genes are being expressed in the target cell. 2.Activate or deactivate a particular target protein that already exists in the cell.

Name and describe the cell-cell gaps found in plant and animal cells. What types of molecules can pass through these gaps?

1.Plant cell walls are perforated with plasmodesmata, membrane-lined channels filled with cytoplasm. (water small solutes) 2.Gap junctions provide cytoplasmic channels between adjacent animal cells Ions, sugars, amino acids and other small molecules can pass through gap junctions.

1. What is the general composition and function of the ECM in animal cells? 2.How does collagen compare to cellulose? 3. How do integrins and fibronectins they related to links between the ECM and cytoskeleton?

1.The ECM contains a polysaccharide glue reinforced by cable-like proteins (e.g. collagen) that span the ECM. ECM can be used for structural support for a cell or as a "middle-lamella-like" layer that connects adjacent cells in many animal tissues, forming a continuous ECM. 2.The most common ECM protein fiber is collagen -- more elastic than cellulose and peptidoglycan 3.Integrins bind to ECM proteins such as fibronectins which then bind to collagen.

1.Name and describe the two types of cell junctions found in animal cells. 2.Which type have cadherins? Where would you typically find cells with each type of cell junction in body tissues?

1.Tight junctions seals cell together Desmosomes: connect the cytoskeletons of cells 2.Desmosomes 3.epitelial tussue

Describe how phosphorylation propagates signal information. What types of proteins are important to phosphorylation cascades?

A protein kinase

• Compare paracrine and endocrine signaling.

Cell signaling can be local with direct contact or local regulators (paracrine signaling) or long distance with hormonal regulators (endocrine signaling)

• Describe how cell signaling can be specific (e.g. cell specific and signal specific) and coordinated.

Different receptor proteins allow cells to detect and respond to different signals. The same signal can have different effects in cells with different receptor proteins and different relay molecules.

• Why might different tissues in different parts of the body have identical receptors?

Identical receptors in diverse cells and tissues allow long-distance signals to coordinate the activities of cells throughout a multicellular organism. Example: insulin will produce different, but coordinated responses in fat cells and liver cells.

• Describe three examples of local signaling.

cell cell gaps cep cell recognition local regulators

How do most cells communicate with each other?

chemical signals.

• What type of material composes the middle lamella of plant cells?

gelatinous pectins. Pectins are polysaccharides. They can be extracted and used as a gelling agent in foods like jams and jellies

• Describe signal transduction and where it occurs in the signal transduction pathway.

signal transduction pathway - an extracellular hormone signal is converted to an intracellular signal which is passed along by relay molecules until a response is triggered.

• Explain how bacteria cells communicate.

Bacteria release species-specific signaling molecules when their numbers reach a specific threshold. Quorum sensing allows bacteria populations to carry out activities that are only productive when performed by a critical mass of cells in synchrony

What activities are involved in signal transduction events that are not part of signaling with lipid-soluble hormones?

Lipid-insoluble hormones cannot diffuse across the plasma membrane so they bind to membrane receptors. This triggers a complex series of events, collectively called a signal transduction pathway - an extracellular hormone signal is converted to an intracellular signal which is passed along by relay molecules until a response is triggered.

• Compare and contrast lipid-soluble hormones and lipid-insoluble hormones.

Lipid-soluble hormones Typically steroid hormones (e.g. testosterone) Diffuse across the plasma membrane into the cytoplasm of target cells. -Lipid-insoluble hormones Typically peptide hormones (e.g. insulin) Are large or hydrophilic Do not cross the plasma membrane but instead bind to a receptor on the plasma membrane of a target cell.

• What types of hormones bind to membrane receptors versus intracellular receptors?

Lipid-soluble hormones (e.g. testosterone)

• Review overview of G protein signaling (diagram - slide 35)

OK

• What are the two main categories of cell-cell attachments and what are their general functions?

The structures that hold cells together vary among multicellular organisms. Plant vs animal structures Cell-cell connections help adjacent cells adhere to each other. Plant cells bind together with a middle lamella Animal cells adhere to one another with continuous ECM, tight junctions, and/or desmosomes Cell-cell gaps allow adjacent cells to communicate with each other, typically by exchanging small molecules. Adjacent plant cells can communicate via plasmodesmata Adjacent animal cells can communicate via gap junctions

What is selective adhesion? give ex

There are several classes of cell adhesion proteins in animal cells and they attach to each other in a specific fashion, referred to as selective adhesion ex.tight junctions

• How do cells communicate over long distances?

hormonal regulators (endocrine signaling)