Cell Bio Exam III

Which is true of intracellular signaling molecules?

They can be proteins.

How a newly synthesized protein will cross the membrane bound compartment: ER?

Transport across membrane

How a newly synthesized protein will cross the membrane bound compartment: Mitochondria and chloroplasts?

Transport across membrane

How a newly synthesized protein will cross the membrane bound compartment: Nucleus?

Transport through nuclear pore

How a newly synthesized protein will cross the membrane bound compartment: Golgi, plasma membrane, lysosomes?

Transport vesicles

Protein shape when transported: Folded or unfolded in the 'Mitochondria and Chloroplasts?'

Unfolded

Protein shape when transported: Folded or unfolded in the ER?

Unfolded

Which statement regarding G proteins is true? (When G protein inactive _______?)

When G protein is inactive, GDP bound to α.

Define "amplification" as it applies to the intracellular signaling pathway?

'Popeye's' signal-> few signals relayed through cascade

Other proteins involved in recognizing which compartment protein should be in: ER?

(SRP) binds to s.s. on new protein and to SRP receptor in ER membrane

Which best describes a pathway that a protein might follow from synthesis to secretion?

Cytosol → ER → transport vesicle → Golgi → transport vesicle → plasma brane

Researchers studying yeast discovered that, for some mutants, when the temperature at which the cells are grown is elevated from 25ºC to 37ºC, their secretory pathway no longer functions and the cells grow dense with unsecreted protein. When these cells are examined microscopically, they can be divided into groups that vary in terms of where the unsecreted proteins accumulate. In some of the mutants, proteins accumulate in the ER; in others, the Golgi; in others, they accumulate in vesicles near the plasma membrane. What is the likely explanation for this difference in appearance?

Different temp-sensitive mutations affect different transport stages

Which organelle is the major site of new membrane synthesis in a cell?

ER

Which of the following choices reflects the appropriate order through which a protein destined for the plasma membrane travels?

ER → Golgi → plasma membrane

Which statement about cell signaling is correct? (signal, molecule ratio)

Each receptor activated by one type of signal.

1. Prolactin is released from the pituitary gland and promotes breast gland development during pregnancy _____________

Endocrine

Cortisol is produced by the adrenal glands located at the top of the kidneys. Cortisol stimulates glucose production in the liver cells. This is an example of:

Endocrine signaling

Which statements are true of receptor-mediated endocytosis? (EVaCuate)

Extra material taken in by clathrin-coated vesicles Viruses hijack entry Cells can pickup cholesterol-carrying (LDLs)

Protein shape when transported: Folded or unfolded in the 'Golgi, Plasma Membrane and Lysosomes?'

Folded

Protein shape when transported: Folded or unfolded in the NUCLEUS?

Folded

As a polypeptide is being translocated across the membrane of the endoplasmic reticulum, a stop-transfer sequence can halt the process. What eventually becomes of this stop-transfer sequence?

Forms α-helical membrane bridge of protein.

Ribosomes synthesis of the protein is completed on: free or bound to ER in the 'Mitochondria and Chloroplasts?'

Free

Ribosomes synthesis of the protein is completed on: free or bound to ER in the 'nucleus?'

Free

1. Translation of the mRNA is started by ________________.

Free ribosomes in cytosol

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 GDP without significantly changing its affinity for GTP?

G protein more easily activated.

A certain membrane protein is found on the ER membrane with the N-terminus on the ER side of the membrane and the C-terminus on the cytosol side of the membrane. The protein contains three transmembrane domains. What would be the orientation of the protein across the ER membrane if the gene were mutated such that the third transmembrane domain coded for hydrophilic amino acids?

N + C-terminus on lumen side

Other proteins involved in recognizing which compartment protein should be in: Nucleus?

Nuclear import receptor binds to s.s. on new protein

Other proteins involved in helping move new protein into final compartment: Nucleus?

Nuclear pore

What is true of protein glycosylation in the ER?

Oligosaccharides added by enzyme, active site on the lumenal side

1. The protein is passed through the _______________ into the lumen of ER while it is being translated.

Protein Translocator

Other proteins involved in helping move new protein into final compartment: ER?

Protein Translocator across ER membrane

Other proteins involved in helping move new protein into final compartment: Mitochondria and Chloroplasts?

Protein Translocator across both membranes

ATP is important for chaperone protein function. Why would protein import into mitochondria be disrupted if ATP were depleted from inside mitochondria?

Protein could slip out of mito during transport.

Which of these actions occur(s) commonly at a nuclear pore complex? (Preppy Local girl Enters a New text from Car. Preppy Emo boy Exits house to Come over. Both Escape to Cali.)

Proteins with nuclear local signal enter (from cyto)+, nuclear export signal exit (to cyto). mRNA exported to cyto

Other proteins involved in recognizing which compartment protein should be in: Golgi, Plasma Membrane and Lysosomes?

Rab on vesicle + tethering protein on new compartment

IP3 signaling helps regulate sweating, which is important for regulating body temperature. Anhidrosis, the inability to sweat normally, can be caused by genetic and environmental factors. A rare mutation has been identified in a family with several children suffering from anhidrosis. The mutation inactivates the protein that IP3 binds on the ER membrane. Suppose cells were isolated from affected family members and exposed to different treatments. Which of the following treatments would be able to repair the signaling defect in cells isolated from these patients?

adding lots of Ca2+ in cytosol

An individual transport vesicle: (1:1)

fuses with one type of brane.

Botulism is a potentially fatal foodborne disease caused by the bacterium Clostridium botulinum. C. botulinum produces different toxins, several of which are proteases that cleave neuronal SNARE proteins. What normal process is blocked by cleavage and inhibition of SNARE proteins?

fusion of vesicles with target membranes

The ER signal sequence on a growing polypeptide chain is recognized by a signal-recognition particle (SRP) in the cytosol. What does this interaction accomplish?

guides ribosome and its polypeptide to ER.

Signal transduction pathways benefit the cell for all the following reasons? (no crosswalk, popeye's, hive, plankton's buckets)

help respond to signals that can't cross can amplify a signal help integrate signals = coordinated response help distribute signals to influence others

Acetylcholine acts at a G-protein-linked receptor on heart muscle to make the heart beat more slowly by the effect of the G protein on a K+ channel, as shown in figure 16-21 in your book. Which one of the following would enhance this effect of acetylcholine?

high concentration of GTP, can't be hydrolyzed.

Match the target of the G protein with the appropriate signaling outcome: adenylyl cyclase?

increase in cAMP levels

All members of the steroid hormone receptor family__________?

interact with signal molecules diffuse through membrane.

Which serve as direct targets for G proteins?

membrane-bound enzymes ion channels

The growth factor Superchick stimulates proliferation of cultured chicken cells. The receptor that binds Superchick is a receptor tyrosine kinase, and many tumor cell lines have mutations in the gene that encodes this receptor. Which of the following types of mutations would be expected to induce uncontrolled cell proliferation?

mutation, prevents receptor recog by phosphatases.

Choose ALL of the protein(s) that would be translated on ribosomes bound to the ER? (Brain, Sink, Degrades, ERC, Unzips)

neurotransmitters surface receptor protein lysosome hydrolytic enzymes ER chaperone protein RNA polymerase

Which type of receptors do steroid hormones generally employ?

nuclear receptors

Many of the extracellular signal molecules that regulate inflammation are released locally at the site of infection. What form of cell-cell signaling is being used?

paracrine

c. During limb development, Fibroblast Growth Factor (FGF) is released from cells of the mesoderm tissue layer to cause cells of the adjacent endoderm tissue layer develop limp specific patterns of gene expression_______________

paracrine

Lysosomal enzymes are directed to lysosomes by which of the following?

phosphorylated sugar group

Ricin is one of the most powerful toxins known. The protein consists of two subunits: the A chain is an enzyme that inhibits translation and the B chain is a lectin that binds to carbohydrates on the cell surface. What is the most likely mechanism by which ricin enters the cell?

protein internalized by endocytosis.

Which molecule performs the primary signal transduction step in cell signaling?

receptor protein

1. If the protein has an ER ________________ in its N-terminal end, translation will slow and the ribosome will move to the ER.

signal sequence

When cells respond to an extracellular signal, they most often convert the information carried by this molecule from one form to another. What is this process called?

signal transduction

1. GABA release from neurons in the brain inhibits firing of an action potential in adjacent neuronal cells_____________

synaptic

The signaling pathways shown below integrate information provided by signal 1 and signal 2 to activate the transcription of a target gene and trigger a cell response. The intracellular signaling molecules in the pathway are only active when they receive an activating signal (→) from an upstream signaling molecule and are not being inhibited (—I) by any upstream signaling molecule. Given this information, under what conditions will the target gene for this signaling network be expressed?

target gene expressed when either signal present

Most extracellular signal molecules act on cell-surface receptors rather than intracellular receptors. Which statements are true about these extracellular molecules?

too large, hydrophilic to cross membrane directly.

Which of the following statements about proteins destined for the ER is TRUE?

translated on cyto ribosomes, s.s. = targets to ER

Which of the following statements is true about translocation of proteins into the mitochondria? (Translocators _________:causing?)

translocators initiate: proteins cross outer/inner mito membranes.

What happens to the final products of the digestion of macromolecules?

txfr to cytosol via transporters in lysosomal membrane.

However, if Ras operates ________________________, a constantly active Ras would be unable to transmit a signal past the obstruction caused by the disabled protein.

upstream of the protein

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

α subunit exchanges GDP for GTP.

Signaling via a GPCR ceases when which condition occurs?

α unit hydrolyzes GTP.

c. Notch signal expressed on the surface of developing white blood cells causes adjacent cells with Notch receptor to become T cells_____________________

contact-dependent

Most mitochondrial and chloroplast proteins are made within which part of the cell?

cytosol

Where are proteins in the mitochondria synthesized?

cytosol, mitochondrial matrix

What protein can assemble into a basketlike network that gives budding vesicles their shape?

clathrin

Match the target of the G protein with the appropriate signaling outcome: phospholipase C?

cleavage of inositol phospholipids

Give one-two example(s) of a step where amplification occurs in the adenylyl cyclase signaling pathway?

1) Adenylate cyclase = cAMP. 1 signal binds to cell receptor. Turns on G-protein -> turns on adenylyl cyclase = cAMP 2) Phosphorylation of proteins by PKA

Put the steps in the phospholipase C signaling pathway in order?

1. Signal binds to GPCR 2. G- protein binds to GTP 3. PLC activated 4. inositol phospholipid hydrolyzed into IP3, DAG 5. Ca rushes out of ER through ion channel 6. PKC activated 7. proteins phosphorylated.

Phagocytosis is a process by which cells do which of the following?

eat large particles, like cell debris

Signal sequences that direct proteins to the correct compartment are __________________.

encoded in protein amino acid sequence

1. The adrenal gland secretes aldosterone which causes, among other effects, water uptake by the large intestine _______________

endocrine

Which cellular compartment acts as the main sorting station for extracellular cargo molecules taken up by endocytosis?

endosomes

What is the role of the nuclear localization sequence in a nuclear protein?

binds to cyto proteins, direct nuclear protein -> pore.

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? (a) addition of a drug that causes cyclic AMP phosphodiesterase to be hyperactive (b) addition of a drug that prevents GTP hydrolysis by Gα (c) addition of a drug that activates adenylyl cyclase (d) addition of a drug that mimics the ligand of ERC1

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

Put the following steps used to transport proteins into mitochondria into the proper order. Receptor on membrane binds s.s. to protein protein synthesized in cyto P moves through t. apparatus Protein delivered to mito t. apparatus S.S. removed by s.p, protein folds into final shape

1. protein synthesized in cyto 2. Receptor on membrane binds s.s. to protein 3. Protein delivered to mito t. apparatus 4. P moves through t. apparatus 5. S.S. removed by s.p, protein folds into final shape

The drug Viagra promotes blood vessel dilation by prolonging signaling through nitric oxide (NO). How does Viagra boost NO?

blocks enzyme that degrades cyclic GMP.

Oligosaccharide chains added in the ER can undergo further modification in which organelle(s)?

both cis and trans Golgi networks

Which of the following is true of lysosomes? (pump)

ATP-driven H+ pump in lysosomal brane maintains pH.

Which of the following signaling pathways would be likely to trigger the most rapid cell response?

Ach binds to anion-channel-coupled receptor, allows Na+ to flow down electro gradient

Ras and G protein are similar in all the following ways EXCEPT?

both result in second messengers.

Endocrine signaling _________ Paracrine signaling _________ Synaptic signaling __________ Contact-dependent ___________

Bloodstream, long-range tissue, receptors neurotransmitter, adhesion, causes x->x

Indicate which of the cell signaling pathways each of the following statements applies to: Adenylyl cyclase, phospholipase C, Neither or Both? The pathway is acivated by a G protein coupled receptor (GPCR) The pathway leads to activation of a kinase. cAMP is produced in the pathway. One step in the pathway involves Ca2+ release from the ER. After binding to the signal molecule the receptor phosphorylates itself.

Both Both Adenlyl Cyclase PLC Neither

What are the similarities and differences between the activation of G protein and the activation of Ras?

Both transmembrane proteins. Activation in both requires active GTP bound form, inactive GDP. Activated GPCRs do this directly for G proteins. In Ras, enzyme linked receptors assemble multiple proteins into a signaling complex through active phosphorylation

Ribosomes synthesis of the protein is completed on: free or bound to ER in the 'ER?'

Bound

Ribosomes synthesis of the protein is completed on: free or bound to ER in the 'Golgi, Plasma Membrane and Lysosomes?'

Bound

1. Translation of the mRNA will be completed by __________________.

Bound ribosomes bound to ER

Match the target of the G protein with the appropriate signaling outcome: Ion channels?

Changes in brane potential

Which of the following correctly describe steps required for protein transport into the rough ER? (CPR)

Cleavage of the s.s. by s.p. Passing P to P translocation channel in ER membrane Recog and binding of s.s. by SRP

Which is true of ribosomes?

Common pool used to synthesize cytosolic proteins + ER proteins.

The length of time a G protein will signal is determined by _______?

GTPase activity of Gα.

Which organelle receives proteins and lipids from the endoplasmic reticulum, modifies them, and then dispatches them to other destinations in the cell?

Golgi

Which of the following steps are required in the activation of the G-protein signaling pathway?

Gα exchanges GDP for GTP. Ligand binds to GPCR Active Gα influences target proteins.

Other proteins involved in recognizing which compartment protein should be in: Mitochondria and Chloroplasts?

Import receptor protein embedded in out-brane binds to s.s.

Alterations in signaling in the pituitary gland can lead to human disease. The GH-releasing hormone (GHRH) stimulates release of growth hormone (GH) from the pituitary gland by binding to GHRH receptors, which are G-protein-coupled receptors. Excessive activity of the GHRH signaling pathway leads to excessive release of growth hormone, which can lead to acromegaly, a form of gigantism. Some patients can reach more than 8 feet tall as they continue to grow even in adulthood. Consider steps that could be taken to reduce GH release. Sort each of the following interventions into the proper category. Decreases GH Release? Increases GH Release?

Inhibit Gα - receptor interaction Block ligand binding Activate receptor phosphorylation by GRK Block arrestin binding to receptor Block hydrolysis of GTP

Which proteins play a central role in the fusion of a vesicle with a target membrane?

SNAREs

Which of the following protein families are involved in helping transport vesicles fuse with the correct target membrane?

SNAREs Rabs tethering proteins

1. The signal recognition particle binds to the _____________ embedded in the ER membrane.

SRP receptor

1. When a protein has completed translation into the ER, _____________ cleaves off the signal sequence.

Signal peptidase

1. The ______________ binds to the signal sequence in the cytosol.

Signal recognition particle (SRP)

The receptor for androgen is found in the cytoplasm of many cells, especially in males. This suggests that androgen is

Small and hydrophobic

1. A double-pass transmembrane protein has an internal _________________ that is not cleaved off and is ultimately moved laterally into the ER membrane along with the stop-transfer sequence.

Start-transfer signal sequence

If a signal sequence is removed from an ER protein, what happens to the altered protein?

Stays in cyto

1. In a single-pass transmembrane protein,________________ is moved laterally out of the protein translocator channel into the ER membrane.

Stop-transfer sequence

Other proteins involved in helping move new protein into final compartment: Golgi, Plasma Membrane and Lysosomes?

T-Snares, V-snares fuse vesicle to new compartment

What is true of the GTP-binding proteins that act as molecular switches inside cells?

active when GTP bound.

As a second messenger Ca2+ must be rapidly removed from the cell after causing an effect. How is Ca2+ removed?

actively pumped into ER

Which of the following statements is true? a) Each extracellular signal molecule interacts with a single class of cell-surface receptor. b) Ion-channel-coupled receptors can rapidly alter the membrane potential in response to signal binding. c) G-protein-coupled receptors are GTP-binding proteins. d) Many ion-channel-coupled receptors have an intrinsic catalytic domain on the cytosolic side of the plasma membrane. e) All enzyme-coupled receptors have an intrinsic catalytic domain on the cytosolic side of the plasma membrane.

b) Ion-channel-coupled receptors can rapidly alter the membrane potential in response to signal binding.

Which of these organelles are surrounded by a double membrane?

chloroplast, nucleus, mitochondrion

What is required for PKC activation?

binding to DAG and constant Ca2+

Consider the pathway: epinephrine > G-protein coupled receptor > G protein > adenylyl cyclase > cAMP > protein kinase A > active enzyme. Identify the second messenger?

cAMP