Mastering 10

Which of these acts as a second messenger?

cyclic AMP

Cell biologists use the term "ligand" to refer to _____.

any small molecule that can bind in a specific manner to a larger one

A neuron's nucleus is located in its _____.

cell body

An example of antagonistic hormones controlling homeostasis is

insulin and glucagon in glucose metabolism.

The response of the heating system reduces the stimulus. This is an example of _______________ feedback.

negative

What type of cell makes up the myelin sheath of a motor neuron?

Schwann cells

Rank the axons from slowest to fastest conduction speed. If two axons have the same conduction speed, place one on top of the other.

(slowest to fastest) non-myelinated invertebrate axon, 20 um diameter non-myelinated invertebrate axon, 30 um diameter non-myelinated invertebrate axon, 40 um diameter myelinated invertebrate axon, 30 um diameter

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.

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 protein

Which of these is a signal molecule? The figure shows a cell membrane with integral molecule marked B. There is a specific recess in this molecule from the extracellular fluid side. The molecule in the intracellular fluid, which shape is identical to this recess, is marked A. Letter C marks the molecule which is connected to the integral molecule B and is located in the cytoplasm. Letter D marks the molecule in the cytoplasm near molecule C. Letter E marks the molecule in the cytoplasm, which is located below molecule D.

A

Which of these is responsible for initiating a signal transduction pathway? The figure shows the cell membrane with receptor and signal molecule. Each letter marks a definite structure. The molecule from the extracellular matrix, marked A, connects with the integral receptor, marked B. There is a molecule, marked C, near this receptor, close to the cell membrane. Letter D marks the molecule in the cytoplasm, near molecule C. Letter E marks the molecule, which is located near the nucleus.

A

Conduction of an action potential along an axon This diagram shows the changes in charge distribution that occur across an axon membrane as an action potential propagates from left to right. The region where the action potential is occurring is shown in orange. Seven locations along the axon are marked by the letters a through g. Diagram showing an action potential moving from left to right along an axon membrane. The axon membrane is labeled from left to right: a, b, c, d, e, f, g. The action potential starts at the leading edge, labeled (f), and ends at the trailing edge, labeled (a). Label g is at the right of the leading edge. Labels b, c, d, and e are within the action potential. At resting, the charge outside the cell is positive and the charge inside the cell is negative. As the action potential moves left to right, it temporarily reverses the charges inside and outside the cell. Match the letter of each location along the axon with the correct description of what is occurring at that position.

Action potential start to finish steps: 5. At location g, the axon membrane is at resting potential. 2. At location f , the axon membrane reaches threshold and the voltage-gated Na+ channels open. 7. At location e, the membrane potential changes sign (from a negative value to a positive value) and the voltage-gated Na+ channels are open. 4. At location d, the voltage-gated Na+ channels are inactivating and the voltage-gated K+ channels are opening. 1. At location c , the membrane potential changes sign (from a positive value to a negative value) and the voltage-gated K+ channels are open. 6. At location b, the voltage-gated K+ channels are closing. 3. At location a, the voltage-gated Na+ channels reactivate.

Which term describes an electrical signal generated by neurons?

Action potential.

Which statement correctly describes what causes the second voltage-gated Na+ channel to open?

After the first channel opens, the movement of many types of ions (both inside and outside the cell) alters the distribution of charges near the second channel, causing it to open. (When Na+ ions enter the cell through the first channel, the charge distribution across the membrane changes. Inside the cell, the increase in Na+ ions near the first channel makes that region more positive; as a result, negative ions are attracted to the region, while positive ions are repelled. Conversely, outside of the cell, the loss of Na+ ions makes the region near the first channel more negative; as a result, positive ions are attracted to that region, while negative ions are repelled. Together, all of these ion movements alter the charge (and thus the membrane potential) at the neighboring channel, allowing it to reach threshold.)

Suppose that an artificial non-gated K+ channel could be inserted into the plasma membrane of an axon at resting potential (membrane potential = -70 mV). Assume that the axon has not recently produced an action potential. What would happen when an artificial K+ channel is inserted into an axon membrane at resting potential?

At resting potential, the pumping of K+ ions into the cell by the sodium-potassium pump is balanced by the movement of K+ ions out of the cell through non-gated K+ channels. If an artificial K+ channel is inserted into the membrane at resting potential, K+ ions will also move out of the cell through that channel. The K+ ions moving through the artificial channel move along their concentration gradient, but against the membrane potential. The K+ movement further decreases the positive charge inside the cell, so the membrane potential becomes more negative (hyperpolarization).

Which of these is a membrane receptor? The figure shows the cell membrane with receptor and signal molecule. Each letter marks a definite structure. The molecule from the extracellular matrix, marked A, connects with the integral receptor, marked B. There is a molecule, marked C, near this receptor, close to the cell membrane. Letter D marks the molecule in the cytoplasm, near molecule C. Letter E marks the molecule, which is located near the nucleus.

B

Which of these is a receptor molecule? The figure shows a cell membrane with integral molecule marked B. There is a specific recess in this molecule from the extracellular fluid side. The molecule in the intracellular fluid, which shape is identical to this recess, is marked A. Letter C marks the molecule which is connected to the integral molecule B and is located in the cytoplasm. Letter D marks the molecule in the cytoplasm near molecule C. Letter E marks the molecule in the cytoplasm, which is located below molecule D.

B

What role does a transcription factor play in a signal transduction pathway?

By binding to DNA it triggers the transcription of a specific gene.

Which of these is NOT correct?

Cyclic AMP binds to calmodulin.

Which of these acts as a second messenger? The figure shows the signal transduction pathway. The molecule from the extracellular matrix, marked A, connects with the integral receptor, which passes the signal to the system, marked B. This system is linked with GTP. Then signal goes to the system, marked C, under the influence of which ATP activates the molecule, marked D. This molecule catalyzes the formation of substance, marked E.

D

Why are there often so many steps between the original signal event and the cell's response?

Each step in a cascade produces a large number of activated products, causing signal amplification as the cascade progresses.

Which one of the following statements about hormones or the endocrine system is correct?

Endocrine organs are sometimes derived from nervous tissue (For example, the posterior pituitary is derived from nervous tissue.)

True or false? For a signal transduction pathway to be activated, hormones must be present in the bloodstream at very high concentrations.

False (Only low concentrations of hormones are needed in the bloodstream to activate a signal transduction pathway, which works by producing second messengers inside the cell that amplify the hormonal signal.)

True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.

False (The potential energy of a membrane potential comes both from the difference in electrical charge and from the concentration gradient of ions across a membrane.)

True or false? Lipid-insoluble hormones affect their target cells by binding to receptors inside the cell.

False (Lipid-insoluble hormones cannot cross the plasma membrane and get into the cell, so they must bind to receptors on the cell surface and transduce their signals through signal transduction pathways.)

A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors.

G-protein-linked

Epinephrine acts as a signal molecule that attaches to _____ proteins.

G-protein-linked receptor

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?

Glycogen breakdown was observed only when epinephrine was administered to intact cells.

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? Select all that apply.

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.

Which of the following is a common feature of all hormones?

Hormones act as a chemical signal between cells.

Which of the following is not an accurate statement?

Hormones of the same chemical class usually have the same function

Which one of the following statements about the endocrine functions of the pancreas is correct?

Insulin triggers the uptake of glucose from the blood.

What is the role of cAMP in the signal transduction pathway activated by epinephrine?

It binds to and activates protein kinase A, which then phosphorylates other enzymes.

Resting neurons are most permeable to which of the following ions?

K+.

Which one of the following statements is correct?

Local regulators are signals that link neighboring cells. The series of changes in cellular proteins that convert the extracellular signal to a specific intracellular response is called signal transduction. Receptors for steroid hormones are located inside target cells. Many hormones elicit more than one type of response in the body. All of the above statements are true.

Which term describes the difference in electrical charge across a membrane?

Membrane potential

Gated ion channels

Once the membrane potential reaches threshold, the voltage-gated Na+ channels open and the Na+ ions move into the cell (moving down their electrochemical gradient). This influx of positive ions makes the inside of the cell less negative compared to the outside, and the membrane potential rises (depolarizes) rapidly.

_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell's cytoplasm.

Phospholipase C ... IP3 .... Ca2+ (Phospholipase C cleaves IP3 from a membrane protein, and IP3 then binds to a calcium channel on the ER.)

Which channel is mainly responsible for the resting potential of a neuron?

Potassium leak channel. (K+ ions flow along their concentration gradient to maintain the resting potential of a neuron.)

Blood sugar regulation

Process in photo

Which molecules determine the tissue specificity of hormones?

Receptors (Hormones bind to receptors on target cells and trigger a cellular response.)

Which statement about the lobes of the pituitary is correct?

The hypothalamus sends hormones to the anterior pituitary. (The hormones are secreted into capillaries that transport them into the endocrine cells of the anterior pituitary.)

Which of the following 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. (Yeast and mammal cells, for example, are very distantly related yet share many similarities in cell signaling.)

Which channel maintains the concentration gradients of ions across a neuronal membrane?

The sodium-potassium pump moving Na+ ions out and K+ ions in.

Which of the following statements about lipid-soluble hormones is true?

They act by affecting the transcription of genes (NOT TRUE: They bind to receptors on the plasma membrane. They act by producing second messengers. They bind to DNA as soon as they enter a cell.)

Which of the following is a structure that allows hormone-receptor complexes to bind to specific DNA sequences?

Zinc finger. (A zinc finger is a distinctive DNA-binding domain on some hormone receptors that is exposed when hormone-receptor complexes are formed.)

Voltage gated channels and the action potential

a. resting potential Na+ channels closed K+ channels closed b. rising phase Na+ channels open K+ channels closed c. falling phase Na+ channels closed k+ channels open d. undershoot Na+ channels closed K+ channels open e. resting potential Na+ channels closed K+ channels closed

Protein phosphorylation is commonly involved with all of the following except

activation of G protein-coupled receptors.

A protein kinase activating many other protein kinases is an example of _____.

amplification

Receptors for nonsteroid hormones are located in _____.

association with a cell's plasma membrane

A nerve impulse moves away from a neuron's cell body along _____.

axon

Diagram of a neuron, showing the cell body (left), axon (middle), and synaptic terminals (right). Points on the axon from left to right are labeled a, b, and c. An action potential is indicated by a red arrow between points (a) and (b), but closer to point (b).

b,a,c Under the artificial conditions, the axon membrane is initially at resting potential everywhere except at the location indicated by the red arrow (where the membrane is artificially brought to threshold). Voltage-gated Na+ channels at that location open and Na+ ions rush into the cell. The depolarization caused by this influx of Na+ ions is "felt" both to the right and left of the open channels. Voltage-gated Na+ channels on both sides open, resulting in an action potential that moves in both directions. It reaches nearby locations (on both sides) first, then locations farther away.

receptor tyrosine kinases

binding of the signaling molecule forms a dimer catalyzes the transfer of a phosphate group to the receptor

Which of the following sequences is correct?

binding of a growth factor to its receptor ® phosphorylation cascade ® activation of transcription factor ® transcription binding of a signaling molecule to its receptor ® G-protein activation ® phospholipase C activation ® IP3 production ® increase in cytoplasmic calcium concentration diffusion of a signaling molecule across the plasma membrane ® binding of the signaling molecule to its receptor ® movement of the signal molecule-receptor complex into the nucleus ® transcription binding of a signaling molecule to its receptor ® G-protein activation ® adenylyl cyclase activation ® cAMP production ® protein phosphorylation

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger.

cAMP

Two of the most common second messengers are _____.

calcium ion and cAMP

Which of these is activated by calcium ions?

calmodulin

Apoptosis is _____.

controlled cell suicide.

A nerve impulse moves toward a neuron's cell body along _____.

dendrites

The activation of receptor tyrosine kinases is characterized by

dimerization and phosphorylation.

Calcium ions that act as second messengers are stored in _____.

endoplasmic reticula

Tyrosine-kinase receptors are characterized by their _____.

enzymatic phosphorylation of tyrosine in the receptor protein

Which of these is a nonsteroid hormone?

epinephrine and oxytocin

Which of these extracellular signal molecules could diffuse through a plasma membrane and bind to an intracellular receptor?

estrogen

Which function below is not influenced by thyroid hormones?

fight-or-flight response (This is influenced by hormones secreted by the adrenal medulla.) (growth rate blood pressure maintenance rate of cellular respiration muscle tone all are)

The cleavage of glycogen by glycogen phosphorylase releases _____.

glucose-1-phosphate

The action of a local regulator is illustrated when _____.

growth factor stimulates the growth of embryonic cells prostaglandins released from the placenta alter the excitability of the muscle of the uterus cytokines play a role in immune responses there is relaxation of arterial smooth muscle caused by nitric oxide All of the choices are correct

The way this heating system maintains a stable room temperature is similar to the way an animal's body controls many aspects of its internal environment. The maintenance of a relatively constant internal environment is known as _______________________.

homeostasis

A substance that acts at a long distance from the site at which it is secreted is a ____.

hormone

Which of the following characteristics determines when the refractory period ends?

how long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential (During the refractory period, an action potential cannot be triggered even if the membrane potential reaches threshold because the voltage-gated Na+ channels are inactive. The Na+ channels must reactivate before Na+ ions can move into the cell again, and the rising phase of the second action potential can begin. In this way, the refractory period determines how closely one action potential can follow another.)

The heater turns on, and the temperature in the room ________________ until it returns to the original setting.

increases

G protein-coupled receptors

interact directly with G proteins

Lipid-soluble signal molecules, such as testosterone, cross the membranes of all cells but affect only target cells because

intracellular receptors are present only in target cells.

A signal molecule is also known as a(n) _____.

ligand

Binding of a signaling molecule to which type of receptor leads directly to a change in distribution of ions on opposite sides of the membrane?

ligand-gated ion channel

In their mechanism of action, a difference between lipid-soluble and water-soluble hormones is that _____.

lipid-soluble hormones bind to an intracellular receptor and this hormone-receptor complex binds to DNA (Most water-soluble signals bind to plasma membrane proteins, initiating signal-transduction pathways. Lipid-soluble hormones enter target cells and bind with intracellular receptors.)

Jet lag occurs when a person moves rapidly from one time zone to another, causing conflict between the body's biological rhythm and the new cycle of light and dark. Some scientists suspect that jet lag may result from disruption of a daily hormone cycle known as _____.

melatonin

Axons insulated by a(n) _____ are able to conduct impulses faster than those not so insulated.

myelin sheath

An impulse relayed along a myelinated axon "jumps" from _____ to _____.

node of Ranvier ... node of Ranvier

How do nonsteroid hormones differ from steroid hormones?

nonsteroid hormones act via signal transduction pathways; steroid hormones do not act via signal transduction pathways

response

protein synthesis

both types of receptors (receptor tyrosine kinases & G protein-coupled receptors)

receptor is located in the plasma membrane binding site for signaling molecule is located on the extracellular side of the cell

reception

receptor tyrosine kinase G protein-coupled receptor signaling molecule

Which of the following is an exocrine gland?

salivary gland (Endocrine glands are ductless glands that secrete their chemical messages directly into body fluids, such as blood. In contrast, exocrine glands secrete chemicals, such as sweat, mucus, and digestive enzymes, into ducts that convey their products to the appropriate locations.)

transduction

second messenger cAMP phosphorylation cascade adenylyl cyclase IP3 Ca2+

The thermostat is a __________ that detects the stimulus and triggers a response.

sensor

This heating system maintains room temperature at or near a particular value, known as the

set point

A signal transduction pathway is initiated when a _____ binds to a receptor.

signal molecule

Which type of hormone is lipid soluble? (DNA. Amino acid derivatives. Polypeptides. Steroids.)

steroids

You open the window, and a blast of icy air enters the room. The temperature drops to 17 degrees Celsius, which acts as a ______________ to the heating system.

stimulus

What part of a neuron relays signals from one neuron to another neuron or to an effector?

synaptic terminal

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 (causing runny nose and watery eyes). Which of the following could account for the different cellular responses to histamine? Select all that apply.

the enzyme that is activated by the G protein associated with the receptor the cell type in which the histamine receptor is located the types of relay molecules within the cell the type of second messengers involved in the signal transduction pathway

Molecular biologists think that signal transduction pathways evolved early in the history of life because ____. (Concept 11.1)

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

Steroid hormone-receptor complexes act in _____.

the nucleus

A signal molecule can cause different responses in different cells because _____.

the transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor

Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because

they amplify the original signal manyfold.

The primary reason steroid hormones usually act slowly is that _____.

they turn genes on or off and it takes time for gene products to build up or become depleted

Dioxin, produced as a by-product of various industrial chemical processes, is suspected of contributing to the development of cancer and birth defects in animals and humans. It apparently acts by entering cells by simple diffusion and binding to proteins in the cytoplasm, altering the pattern of gene expression. Among the cytoplasmic proteins to which dioxin binds are likely to be _____.

transcription factors

Which of these is the second of the three stages of cell signaling?

transduction