Chapter 11 Mastering Biology

What is apoptosis?

controlled cell suicide

Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor on target cells is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine. Which statements are true about the binding of histamine to the histamine H1 receptor?

-Histamine binds extracellularly to the H1 receptor. -When histamine binds to the H1 receptor. the receptor undergoes a conformation change and binds the inactive G protein. -Once the G protein is active, it binds to the enzyme phospholipase C, activating it. -Histamine is likely hydrophilic. When histamine encounters a target cell, it binds extracellularly to the H1 receptor, causing a change in the shape of the receptor. This change in shape allows the G protein to bind to the H1 receptor, causing a GTP molecule to displace a GDP molecule and activating the G protein. The active G protein dissociates from the H1 receptor and binds to the enzyme phospholipase C, activating it. The active phospholipase C triggers a cellular response. The G protein then functions as a GTPase and hydrolyzes the GTP to GDP. The G protein dissociates from the enzyme and is inactive again and ready for reuse.

Cell signaling involves converting extracellular signals to specific responses inside the target cell. Different molecules are involved at each stage of the process. Which items are involved in reception, transduction, or response?

-Reception: G protein-coupled receptor, receptor tyrosine kinase, signaling molecule -Transduction: phosphorylation cascade, second messenger, adenylyl cyclase, Ca2+, cAMP, IP3 -Response: protein synthesis Receptor proteins (located in the plasma membrane or inside the cell) bind signaling molecules. The reception of the signal causes a shape change in the receptor molecule, to which other molecules inside the cell respond. The message is then relayed through signal transduction, which may involve a phosphorylation cascade or second messengers such as cAMP, Ca2+, or IP3. Possible responses to the signal may include synthesis of a particular protein or regulation of a particular enzyme.

Cortisol is a steroid hormone that can pass through the plasma membrane. Complete the flowchart describing the interaction of cortisol with intracellular receptors.

1. Cortisol passes through the plasma membrane into the cytoplasm. 2. Cortisol-receptor complex forms in the cytoplasm. 3. Cortisol-receptor complex enters the nucleus where it binds to genes. 4. Cortisol-receptor complex acts as a transcription factor 5. The transcribed mRNA is translated into a specific protein. Cortisol is a small, hydrophobic steroid hormone that can pass through the plasma membrane of cells. In target cells, cortisol binds to the intracellular receptor protein in the cytoplasm, forming a hormone-receptor complex. The hormone-receptor complex then moves into the nucleus and acts as a transcription factor, binding to specific genes and activating their transcription into mRNA. The mRNA that is produced is eventually translated into specific proteins. Proteins produced in response to the cortisol signal function in the stress response. For example, some of these proteins aid in elevating glucose levels in the blood, helping an animal to meet the demands of starvation or intense physical activity

Histamine is a chemical substance released in inflammatory and allergic responses. The histamine H1 receptor is a G protein-coupled receptor that activates phospholipase C in response to the binding of histamine. Show the process of histamine signal transduction from the H1 receptor.

1. Enzyme cleaves PIP2, forming DAG and IP3. 2. IP3 binds to a ligand-gated ion channel in the ER membrane. 3. Calcium ions flow through the ligand-gated ion channel. 4. Calcium ion concentration increases in the cytosol. 5. Calcium ions activate a protein, leading to a cellular response. After the reception of the histamine signaling molecule, the active G protein activates the enzyme phospholipase C. Phospholipase C cleaves PIP2 into DAG and IP3. IP3 diffuses through the cytosol and binds to an IP3-gated calcium channel in the ER membrane, causing it to open. As a result, Ca2+ ions flow out of the ER and into the cytosol. The increase in the calcium ion concentration in the cytosol helps activate the cellular response. Signal transduction pathways that involve phosphorylation cascades or multiple second messengers, such as histamine's signal transduction pathway, enable a signal to be amplified and regulated at different points. Similarly, multistep pathways can facilitate the coordination of cellular responses to multiple signals.

The process by which a signal is converted to a specific cellular response involves three stages:

1.reception of a signaling molecule 2.transduction of the signal 3.response to the signal

Which is a logical signal transduction pathway?

A G-protein-linked receptor activates G protein, which activates phospholipase C, which cleaves a membrane lipid to form IP3, which binds to a calcium channel on the ER, which opens to release calcium ions into the cytoplasm, which bind to an intracellular enzyme that carries out a response.

Unlike steroid hormones, signaling molecules that are large and/or hydrophilic cannot pass through the cell's plasma membrane and therefore must bind extracellularly to receptor molecules in the plasma membrane. Two types of signal receptors embedded in the cell's plasma membrane are G protein-coupled receptors and receptor tyrosine kinases. Classify each phrase by whether it applies to G protein-coupled receptors only, receptor tyrosine kinases only, both receptors, or neither receptor.

G-protein: interact directly with G proteins Receptor tryosine kinases: catalyzes the transfer of a phosphate group t o the receptor, binding of the signaling molecule forms a dimer Both: binding site for signaling molecule is located on the extracellular side of cell, receptor is locate in plasma membrane Neither: binding of the signaling molecule allows ions to flow through a channel in the receptor Both G protein-coupled receptors and receptor tyrosine kinases are transmembrane receptors that have a binding domain located on the extracellular side of the plasma membrane. The binding of a signaling molecule to these receptors is the first step in a signaling pathway. However, what happens after a signaling molecule binds is different for each receptor. An activated G protein-coupled receptor activates a G protein inside the cell, which involves the release of GDP and the binding of GTP. The activated G protein then activates an associated enzyme, leading to a cellular response. Receptor tyrosine kinases form dimers after binding signaling molecules. The tyrosines are then phosphorylated, fully activating the receptor. Each phosphorylated tyrosine can bind a relay protein, each of which can trigger a transduction pathway. In this way, a single signaling-molecule binding event can trigger multiple signal transduction pathways and thus multiple cellular responses.

Which provides molecular evidence that signal transduction pathways evolved early in the history of life?

The molecular details of cell signaling are quite similar in organisms whose last common ancestor was a billion years ago.

What are among the most common second messengers?

calcium ion and cAMP

What substance acts at a long distance from the site at which it is secreted?

hormone (Both animals and plants use them to signal at greater distances.)

The histamine H1 receptor is one of several existing histamine G protein-coupled receptors. Depending on many factors, including the type of receptor, histamine can trigger a variety of responses, including vasodilation, smooth muscle contraction, stimulation of gastric secretion, cardiac stimulation, and increased vascular permeability. What could account for the different cellular responses to histamine?

•the type of histamine receptor •the type of cell in which the receptor is located •the enzyme that is activated by the G protein associated with the receptor •the types of second messengers involved in the signal transduction pathway •the proteins activated by the second messengers Signaling molecules can trigger a multitude of cellular responses, which may ultimately affect the transcription of genes, the activity of proteins, or cell growth and division.