biology tes 3

_____ aid in the coordination of the activities of adjacent animal cells.

Gap (communicating) junctions

In general, a signal transmitted via phosphorylation of a series of proteins _____.

results in a conformational change to each protein

In multiple sclerosis the myelin sheaths around the axons of the brain and spinal cord are damaged and demyelination results. How does this disease manifest at the level of the action potential? I) Action potentials move in the opposite direction on the axon. II) Action potentials move more slowly along the axon. III) No action potentials are transmitted

only II

In the sequence of permeability changes for a complete action potential, the first of these events that occurs is the _____.

opening of voltage-gated sodium channels

The transmission of a nerve impulse first triggers the _____.

opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron

Osteocytes are bone cells. Collagen fibers and calcium salts are found in abundance between and among the osteocytes. The collagen and calcium salts are _____.

part of the extracellular matrix

The receptors for steroid hormones and peptide hormons are fundamentally different because.

peptides are hydrophilic (lipophobic) and steroids are hydrophobic (lipophilic)

An inhibitory postsynaptic potential (IPSP) occurs in a membrane made more permeable to _____.

potassium ions

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

potassium leak channel

The surface on a neuron that discharges the contents of synaptic vesicles is the _____.

presynaptic membrane

A toxin that binds specifically to voltage-gated sodium channels in axons would be expected to _____.

prevent the depolarization phase of the action potential

One of the major categories of receptors in the plasma membrane reacts by forming dimers, adding phosphate groups, and then activating relay proteins. Which type does this?

receptor tyrosine kinases

Immediately after an action potential passes along an axon, it is not possible to generate a second action potential. Thus, we state that the membrane is briefly _____.

refractory

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

signal molecule

The opening of gated channels for _______ ions creats a dramatic electrical signal that alters the membrane potential in a mater of a few milliseconds.

sodium

A neuron has a resting potential of about _____ millivolts.

-70

The following steps refer to various stages in transmission at a chemical synapse. 1. Neurotransmitter binds with receptors associated with the postsynaptic membrane. 2. Calcium ions rush into neuron's cytoplasm. 3. An action potential depolarizes the membrane of the presynaptic axon terminal. 4. The ligand-gated ion channels open. 5. The synaptic vesicles release neurotransmitter into the synaptic cleft. Which sequence of events is correct?

3 → 2 → 5 → 1 → 4

Put the steps of the process of signal transduction in the order they occur: 1. A conformational change in the signal-receptor complex activates an enzyme. 2. Protein kinases are activated. 3. A signal molecule binds to a receptor. 4. Target proteins are phosphorylated. 5. Second messenger molecules are released.

3, 1, 5, 2, 4

The membrane potential with 50% of the K+ leak channels closed is close to negative _____________ mV.

56

Use the GHK equation to calculate the membrane potential using only Na+, K+ and Cl- ion concentrations. Your calculated value will not be exactly -70 mV but should be close. The membrane potential calculated is negative _____________ mV

64

Why does a hormone act only on specific cell types in an organism and not others?

A cell must have the appropriate receptor before it can bind to the hormone.

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.

Based on what you have learned about how cells ensure that proteins end up in the right place (Chapter 7), what type of signal would you expect to be exposed on a cytosolic receptor after a steroid hormone changes the receptor's conformation?

Amino acids required for transport through the nuclear pore complex

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.

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

FALSE

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

The membrane transporter that brings Glucose into the Beta Cell of the pancreas after a carbohydrate meal is called a __________ transporter. Give just the general acronym for this glucose transporter - it is not necessary to number the specific one.

GLUT

A mutation that disrupts the ability of an animal cell to add polysaccharide modifications to proteins would most likely cause defects in its _____.

Golgi apparatus and extracellular matrix

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

K+

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

Membrane potential.

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

Phospholipase C ... IP3 .... Ca2+

Which statement is most accurate concerning how the molecular composition of a plant cell wall compares with the ECM of animal cells?

Plant cell wall fibers consist primarily of carbohydrates; ECM fibers are dominated by proteins.

Which of the following statements most accurately describes the function of plasmodesmata in plant cells or gap junctions in animal cells?

Plasmodesmata allow passage of proteins and small molecules between adjacent cells.

For the experiment shown in Figure 11.9, which answer correctly states the prediction of the "hypothesis" or "null hypothesis"?

Prediction of hypothesis: Antibodies to some membrane proteins will block cell-cell adhesion.

How does the function of an intracellular receptor differ from that of a membrane receptor?

The intracellular receptor binds DNA or binds a Transcription Factor protein that binds DNA

Which of these is activated by calcium ions?

calmodulin

How can a hormone that is present in very small quantities within the bloodstream elicit such a large response within a cell?

The message from the hormone is amplified many times within the cell.

H. V. Wilson worked with sponges to gain some insight into exactly what was responsible for holding adjacent cells together. He exposed two species of differently pigmented sponges to a chemical that disrupted the cell-cell interaction (cell junctions), and the cells of the sponges dissociated. Wilson then mixed the cells of the two species and removed the chemical that caused the cells to dissociate. Wilson found that the sponges reassembled into two separate species. The cells from one species did not interact or form associations with the cells of the other species. How do you explain the results of Wilson's experiments?

The molecules responsible for cell-cell adhesion (cell junctions) differed between the two species of sponge.

What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?

The sodium channel opens, and Na+ ions flow in.

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

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

Acetylcholine is a neurotransmitter that binds to receptors on skeletal muscle cells. The receptor-signal complex brings about a series of events that result in contraction of skeletal muscle. Venom from black widow spiders causes an explosive release of acetylcholine. What would that do to its victims?

The victim's muscles would be unable to relax.

Acetylcholine released into the junction between a motor neuron and a skeletal muscle binds to a sodium channel and opens it. This is an example of _____.

a ligand-gated sodium channel

Not all intercellular signals require transduction. Which one of the following signals would be processed without transduction?

a lipid-soluble signal

Pemphigus vulgaris is an autoimmune disorder in humans in which antibodies are produced against the cadherins of desmosomes. The blistering of the skin and mucous membranes characteristic of this disorder is probably a result of _____.

a loss in cell-cell adhesion

Excitatory postsynaptic potentials (EPSPs) produced nearly simultaneously by different synapses on the same postsynaptic neuron can also add together, creating _____.

a spatial summation

Different body cells can respond differently to the same peptide hormones because _____.

a target cell's response is determined by the components of its signal transduction pathways

An example of ligand-gated ion channels is _____.

acetylcholine receptors at the neuromuscular junction

Protein kinase is an enzyme that _____.

activates or inactivates other proteins by adding a phosphate group to them

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

amplification

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

amplify the original signal many times

An action potential moves along a(n) _____.

axon

In the diagram, (a), (b), and (c) represent three points along a vertebrate axon where electrodes were implanted to detect action potentials. Under normal conditions, when this neuron produces an action potential, the action potential passes through point (a) first, followed by point (b), and then point (c).Suppose, however, that an action potential is artificially triggered at the point indicated by the red arrow. In what sequence would the action potential pass through points (a), (b), and (c)?

b,a,c

Steroid hormones bind to receptors inside the cell and alter their conformation. The hormone-receptor complex is then transported into the nucleus, where it can directly affect gene expression. To get from the location where the receptor binds the hormone to its site of action, the hormone-receptor complex must _____.

be transported through the nuclear pore complex

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. The second messenger in this pathway is _____.

cAMP

The most abundant protein found in the extracellular matrix of animal cells is _____.

collagen

Which of these acts as a second messenger?

cyclic AMP

Integrins are integral membrane proteins. They are often attached to _____.

cytoskeletal proteins and proteins in the extracellular matrix

The cleavage of glycogen by glycogen phosphorylase releases _____.

glucose-1-phosphate

The activity of acetylcholine in a synapse is terminated by its_____.

degradation on the postsynaptic membrane

The primary role of _____ is to bind animal cells together.

desmosomes

The activation of receptor tyrosine kinases is characterized by _____.

dimerization and phosphorylation

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

endoplasmic reticula

The release of acetylcholine from the terminal of a motor neuron is most directly linked to the _____.

entry of calcium into the axon terminal

Neurotransmitters are released from axon terminals via _____.

exocytosis

In a Beta pancreatic cell whose membrane has been depolarized, the secretory vesicles storing insulin are released by the process of __________ , which is driven by the influx of _____ ions.

exocytosis, calcium

Because cell walls consist of a cross-linked network of long filaments embedded in a stiff surrounding material, they can be called _____.

fiber composites

Ions can travel directly from the cytoplasm of one animal cell to the cytoplasm of an adjacent cell through _____.

gap junctions

Hormones are chemical substances produced in one organ that are released into the bloodstream and affect the function of a target organ. For the target organ to respond to a particular hormone, it must _____.

have receptors that recognize and bind the hormone molecule

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

Neurotransmitters categorized as inhibitory are expected to _____.

hyperpolarize the membrane

Neural transmission across a mammalian synapse is accomplished by _____.

impulses causing the release of a chemical signal and its diffusion across the synapse

Where would you expect to find tight junctions?

in the epithelium of an animal's stomach

Signal transduction pathways

include the intracellular events stimulated by an extracellular signal.

How could you increase the magnitude of inhibitory postsynaptic potentials (IPSPs) generated at a synapse?

increase K+ permeability

Signals from the extracellular matrix to the cytoskeleton may be transmitted by _____.

integrins

Which of the following is characteristic of a steroid hormone action?

internal receptor binding

A G-protein receptor with GTP bound to it _____.

is in its active state

The most common 'on' signal for activating proteins during the process of signal transduction is through the addition of a phosphate gourp by a _____________ enzyme.

kinase

The function of _________ enzymes is to add phosphates to proteins, whereas a _______ enzyme functions to remove the phosphates.

kinase, phosphatase

The resting membrane potential of an animal cell is made possible by the continuous opperation of the Na+/K+ pump, along with the very large number of __________ channels for K+ ions.

leak

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

ligand

Action potentials move along axons _____.

more rapidly in myelinated than in non-myelinated axons

The receptors for steroid hormones are located inside the cell instead of on the membrane surface like most other signal receptors. This is not a problem for steroids because _____.

steroid hormones are lipid soluble, so they can readily diffuse through the lipid bilayer of the cell membrane

The "undershoot" phase of after-hyperpolarization is due to _____.

sustained opening of voltage-gated potassium channels

When two excitatory postsynaptic potentials (EPSPs) occur at a single synapse so rapidly in succession that the postsynaptic neuron's membrane potential has not returned to the resting potential before the second EPSP arrives, the EPSPs add together producing _____.

temporal summation

After the depolarization phase of an action potential, the resting potential is restored by _____.

the opening of voltage-gated potassium channels and the closing of sodium channels

In a simple synapse, neurotransmitter chemicals are received by _____.

the postsynaptic membrane

In a simple synapse, neurotransmitter chemicals are released by _____.

the presynaptic membrane

At rest, which of these plays a role in establishing the charge differential across a neuron's plasma membrane?

the sodium-potassium pump moving sodium ions out of the neuron and potassium ions into the neuron

For a tissue or an organ to function as a unit, _____.

there must be cell-cell communication among the cells within a tissue or organ

The fastest possible conduction velocity of action potentials is observed in _____.

thick, myelinated neurons

Which of these cell junctions form a barrier to the passage of materials?

tight junctions

In this animation, which of the following, when activated by a signal transduction pathway, moved from the cytoplasm to the nucleus of a cell?

transcription factor

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

transduction

Action potentials are normally carried in only one direction: from the axon hillock toward the axon terminals. If you experimentally depolarize the middle of the axon to threshold, using an electronic probe, then _____.

two action potentials will be initiated, one going toward the axon terminal and one going back toward the hillock

Intercalated discs are cell-cell junctions found between cardiac muscle cells. One feature of these intercalated discs is that they contain a large number of gap junctions, which means that _____.

water ions and small molecules can readily pass from one cardiac muscle cell to the next