BIO 2550 - Chapter 16 PRACTICE PROBLEMS Exam 3 Review

Circle the phrase in each pair that is likely to occur more rapidly in response to an extracellular signal A. changes in cell secretion / increased cell division B. changes in protein phosphorylation / changes in proteins being synthesized C. changes in mRNA levels / changes in membrane potential

A. changes in cell secretion B. changes in protein phosphorylation C. changes in membrane potential

Which of the following statements is false?

Dissolved gases such as nitric oxide (NO) can act as signal molecules, but because they cannot interact with proteins they must act by affecting membrane lipids

Which of the following statements is true?

Extracellular signal molecules that are hydrophilic must bind to a cell-surface receptor so as to signal a target cell to change its behavior

Akt promotes the survival of many cells by affecting the activity of Bad and Bcl2. Which of the following statements is false?

In the absence of a survival signal, Bad is phosphorylated

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. Explain your answers A. An extracellular signaling molecule binds and activates a GPCR

No. Each signaling molecule activates only one receptor molecule

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. Explain your answers D. cAMP activates protein kinase A

No. In unstimulated cells, protein kinase A is held inactive in a protein complex. Binding of cAMP to the complex induces a conformational change, releasing the active protein kinase A. Therefore, one cAMP cannot activate more than one molecule of protein kinase A

Which of the following statements about molecular switches is false?

Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off

Antibodies are Y-shaped molecules that have two identical binding sites. Suppose that you have obtained an antibody that is specific for the extracellular domain of an RTK. When the antibody binds to the RTK, it brings together two RTK molecules. If cells containing the RTK were exposed to the antibody, would you expect the kinase to be activated, inactivated, or unaffected? Explain your reasoning

The RTK will probably become activated on binding of the antibody molecule. This is because signal-induced dimerization usually activates RTKs. When RTK molecules are brought together, their cytoplasmic kinase domains become activated, and each receptor phosphorylates the other

When Ras is activated, cells will divide. A dominant-negative form of Ras clings too tightly to GDP. You introduce a dominant-negative form of Ras into cells that also have a normal version of Ras. Which of the following statements is true?

The cells you create will divide less frequently than normal cells in response to the extracellular signals that typically activate Ras

Which of the following statements about G-protein-coupled receptors (GPCRs) is false?

The different classes of GPCR ligands (proteins, amino acid derivatives, or fatty acids) bind to receptors with different numbers of transmembrane domains

Intracellular steroid hormone receptors have binding sites for a signaling molecule and a DNA sequence. How is it that the same steroid hormone receptor, which binds to a specific DNA sequence, can regulate different genes in different cell types?

The genes regulated by an activated steroid hormone receptor depend on two factors: the presence of the appropriate DNA sequence for receptor binding and the influence of various nuclear proteins that affect gene expression, which can differ among cell types

Can signaling via a steroid hormone receptor lead to amplificationof the original signal? If so, how?

The initial interactions between the signal molecule and its receptor, as well as the activated receptor and its target gene, occur on a one-to-one basis, meaning there is no amplification in this part of the signaling pathway. However, amplification can occur during gene transcription, as each activated gene produces multiple mRNA copies, which in turn are used to create many copies of the corresponding protein

Activated GPCRs activate G proteins by reducing the strength of binding of GDP to the α subunit of the G protein, allowing GDP to dissociate and GTP (which is present at much higher concentrations in the cell than GDP) to bind in its place. How would the activity of a G protein be affected by a mutation that reduces the affinity of the α subunit for GDPwithout significantly changing its affinity for GTP?

The mutant G protein would remain constantly active because, when the α subunit hydrolyzes GTP to GDP, the GDP would spontaneously dissociate, allowing GTP to bind again and reactivate the α subunit. This occurs due to the higher intracellular concentration of GTP compared to GDP. Normally, GDP is tightly bound to the α subunit, keeping the G protein inactive until an activated GPCR prompts the release of GDP

Explain why the signal molecules used in neuronal signaling work at a longer range than those used in contact-dependent signaling

The neurotransmitter released from a neuron in neuronal signaling must diffuse across the synaptic cleft to reach receptors on the target cell. In contrast, in contact-dependent signaling, the signal molecule is attached to the plasma membrane of the signaling cell and interacts with receptors located on the plasma membrane of the receiving cell; thus, the cells must be in direct contact for this type of signaling to occur

Which of the following statements is true?

The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling

The following happens when a G-protein-coupled receptor activates a G protein

The α subunit exchanges its bound GDP for GTP

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. Explain your answers B. The activated GPCRs cause Gα to separate from Gβ and Gγ

Yes. Each activated GPCR activates many G-protein molecules

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. Explain your answers C. Adenylyl cyclase produces cyclic AMP

Yes. Each activated adenylyl cyclase molecule can generate many molecules of cAMP

Indicate by writing "yes" or "no" whether amplification of a signal could occur at the particular steps described below. Explain your answers E. Protein kinase A phosphorylates target proteins

Yes. Each activated protein kinase A molecule can phosphorylate many molecules of each type of target protein

Rank the following types of cell signaling from 1 to 4, with 1 representing the type of signaling in which the signal molecule travels the least distance and 4 the type of signaling in which the signal moleculet ravels the largest distance _____ paracrine signaling _____ contact-dependent signaling _____ neuronal signaling _____ endocrine signaling

_3_ paracrine signaling _1_ contact-dependent signaling _2_ neuronal signaling _4_ endocrine signaling

The growth factor RGF stimulates proliferation of cultured rat cells. The receptor that binds RGF is a receptor tyrosine kinase called RGFR. Which of the following types of alteration would be most likely to prevent receptor dimerization?

a mutation that prevents RGFR from binding to RGF

You examine a cell line with a constitutively active Ras protein that is always signaling. Which of the following conditions will turn off signaling in this cell line?

addition of a drug that blocks protein Y from interacting with its target

You are interested in cell-size regulation and discover that signaling through a GPCR called ERC1 is important in controlling cell size in embryonic rat cells. The G protein downstream of ERC1 activates adenylyl cyclase, which ultimately leads to the activation of PKA. You discover that cells that lack ERC1 are 15% smaller than normal cells, while cells that express a mutant, constitutively activated version of PKA are 15% larger than normal cells. Given these results, which of the following treatments to embryonic rat cells should lead to smaller cells?

addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive

Acetylcholine binds to a GPCR on heart muscle, making the heart beat more slowly. The activated receptor stimulates a G protein, which opens a K+ channel in the plasma membrane. Which of the following would enhance this effect of the acetylcholine?

addition of a high concentration of a nonhydrolyzable analog of GTP

Match the target of the G protein with the appropriate signaling outcome. adenylyl cyclase _____ ion channels ______ phospholipase C _____ A. cleavage of inositol phospholipids B. increase in cAMP levels C. changes in membrane potential

adenylyl cyclase __B__ ion channels __C__ phospholipase C __A__

During nervous-system development in Drosophila, the membrane-bound protein Delta acts as an inhibitory signal to prevent neighboring cells from developing into neuronal cells. Delta is involved in______________ signaling

contact-dependent

The activation of the serine/threonine protein kinase Akt requires phosphoinositide 3-kinase (PI 3-kinase) to _________

create phosphorylated lipids that serve as docking sites that localize Akt to the plasma membrane

Which of the following mechanisms is not directly involved in inactivating an activated RTK?

dephosphorylation by serine/threonine phosphatases

The local mediator nitric oxide stimulates the intracellular enzyme guanylyl cyclase by ________________

diffusing into cells and stimulating the cyclase directly

When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________

hormone

All members of the steroid hormone receptor family__________________

interact with signal molecules that diffuse through the plasma membrane

Foreign substances like nicotine, morphine, and menthol exert their initial effects by _____

interacting with cell-surface receptors, causing the receptors to transduce signal inappropriately in the absence of the normal stimulus

A protein kinase can act as an integrating device in signaling if it ___________________

is activated by two or more proteins in different signaling pathways

The length of time a G protein will signal is determined by_______

the GTPase activity of Gα.

Adrenaline stimulates glycogen breakdown in skeletal muscle cells by ultimately activating glycogen phosphorylase, the enzyme that breaks down glycogen. Which of the following statements is false?

A constitutively active mutant form of PKA in skeletal muscle cells would lead to an excess in the amount of glycogen available