Biology Chapter 11 and 12 Review

Questions and Answers

Define 'paracrine signaling' and give an example.

Paracrine signaling occurs when numerous cells simultaneously receive and respond to growth factors produced by a single cell in their vicinity. An example is local regulators in animals that stimulate nearby target cells to grow and multiply.

Explain how plant and animal hormones travel to target cells.

In animals, special endocrine cells release hormones into the circulatory system where they travel to target cells in other parts of the body. In plants, growth regulators (hormones) travel in vessels or from cell to cell or move through air by diffusion.

List and briefly define the three stages of cell signaling.

Reception is when a chemical signal binds to a cellular protein. Transduction is when binding leads to a change in the receptor, triggering a series of changes along the signal-transduction pathway. Response is when the transduced signal triggers a specific cellular activity.

Describe the nature of a ligand-receptor interaction and state how such interactions initiate a signal-transduction system.

This interaction is highly specific; one ligand will bind to one receptor type like a lock and key. When the proper ligand binds, the receptor changes conformation and initiates a specific reaction inside the cell. Signup and view all the answers

State where signal receptors may be located in target cells.

Plasma membrane proteins. Signup and view all the answers

Compare and contrast G-protein-linked receptors, tyrosine-kinase receptors, and ligand-gated ion channels.

G-protein-linked receptors respond to signaling molecules by activating a G protein. Tyrosine-kinase receptors trigger several pathways at once involving enzymatic activity. Ligand-gated ion channels open or close in response to a signaling chemical, regulating ion flow. Signup and view all the answers

List two advantages of using a multistep pathway in the transduction stage of cell signaling.

It allows the signaling molecules to be amplified to create a larger cellular response and provides regulation and coordination. Signup and view all the answers

Explain how an original signal molecule can produce a cellular response when it may not even enter the target cell.

The signaling molecule binds to the protein receptor on the outside of the cell, causing a chain of reactions inside the cell. Signup and view all the answers

Describe how phosphorylation propagates signal information.

A phosphorylation cascade involves one enzyme phosphorylating another, creating a chain reaction that leads to the phosphorylation of thousands of proteins. Signup and view all the answers

Define the term 'second messenger'. Briefly describe the role of these molecules in signaling pathways.

Second messengers are small, water-soluble molecules or ions that rapidly relay the signal from the membrane-receptor-bound 'first messenger' into a cell's interior. Signup and view all the answers

Describe how cyclic AMP is formed and how it propagates signal information in target cells.

After epinephrine binds to its receptor, the G-protein is activated, which in turn activates Adenyl cyclase, producing cAMP that triggers protein kinase A. Signup and view all the answers

Describe how the cytosolic concentration of Ca2+ can be altered and how the increased pool of Ca2+ is involved with signal transduction.

Both voltage-sensitive Ca2+ channels and voltage-sensitive Na+-Ca2+ exchange can increase [Ca2+]i during depolarization, which is vital for regulating cardiac excitation and contraction. Signup and view all the answers

Study Notes

Cell Signaling Overview

Paracrine signaling involves multiple nearby cells responding to growth factors released by a single cell, facilitating local cellular growth and multiplication.
Animal hormones are secreted into the bloodstream by endocrine cells, whereas plant hormones can travel through vessels, cell diffusion, or air.

Stages of Cell Signaling

Reception: A chemical signal binds to a specific cellular protein on the surface or inside the cell.
Transduction: The binding induces a conformational change in the receptor, triggering a cascade of relay molecules through the signal-transduction pathway.
Response: This cascade activates specific cellular activities, leading to a response from the cell.

Ligand-Receptor Interaction

Ligand-receptor interactions are highly specific; one ligand fits one receptor type like a lock and key.
Binding induces a conformational change in the receptor, starting a chain of intracellular responses which facilitate the signal transduction process.

Signal Receptor Locations

Receptors are typically located on plasma membrane proteins, allowing them to interact with external signaling molecules.

Types of Receptors

G-Protein-Linked Receptors: These plasma membrane proteins activate G proteins upon ligand binding, initiating the signaling process.
Tyrosine-Kinase Receptors: Enzymatic receptors that can activate multiple pathways simultaneously by transferring phosphate groups from ATP to tyrosine residues on proteins.
Ligand-Gated Ion Channels: Membrane proteins that open or close in response to ligand binding, regulating the flow of specific ions.

Advantages of Multistep Pathways

Multistep pathways amplify the signal strength, resulting in a more significant cellular response.
These pathways also provide finer regulation and coordination of cellular responses.

Signal Propagation Without Entry

Original signal molecules can elicit responses without entering the target cell by binding to external receptors, triggering internal signaling cascades through a series of reactions.

Phosphorylation Cascade

A phosphorylation cascade consists of sequential phosphorylation among enzymes that exponentially amplify the signal, resulting in extensive modifications of numerous proteins, common in hormone signaling transduction.

Second Messengers

Small, water-soluble molecules or ions that relay signals from membrane-bound receptors to the cell's interior, participating in pathways initiated by both G protein-coupled receptors and receptor tyrosine kinases.
Common second messengers include cAMP and calcium ions, which facilitate further signaling processes.

Cyclic AMP (cAMP) Role

cAMP is formed following epinephrine binding to its receptor, activating adenyl cyclase which produces cAMP.
cAMP activates protein kinase A and triggers glucose release from glycogen, responding to low glucose concentrations in liver or muscle cells.

Cytosolic Ca2+ Concentration

Increased cytosolic Ca2+ can result from voltage-sensitive Na+-Ca2+ exchange and Ca2+ channels, impacting cardiac excitation and contraction mechanics.
Altered cytosolic Ca2+ plays a significant role in signal transduction, linking extracellular signals to cellular responses.

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Test your knowledge of paracrine signaling and hormonal communication in plants and animals with these flashcards. These questions will help reinforce your understanding of how signaling and hormonal pathways influence growth and development.