BIOL 319 - Exam 4

The function of gap junctions is to

a. Seal the space between cells.

b. hold epithelial together

c. maintain the spacing of the basal laminae beneath epithelial cells

d. provide direct communication between cells

D

A junctional complex consists of tight junction associated with both adherent junctions and

a. gap junctions

b. hemidesmosomes

c. desmosomes

d. focal adhesions

C

Which of the following molecules mediate the association of actin filaments with the cadherins in an adheren junction?

a. a- and B- catenin

b. plectins

c. plakoglobulins

d. talins

A

Desmosomes are linked to cytoplasmic

a. myosin filaments

b. microtubules

c. actin filaments

d. intermediate filaments

D

Animal cells are embedded in a(n)

a. extracellular matrix

b. hemicellulose-rich hyaluronan layer

c. cell wall

d. pectin-rich basal lamina

A

Pectins form a ________ network in plant cell walls.

a. gel-like

b. solid, rigid

c. fibrous

d. waxy

A

Basal laminae are a meshwork of fibrils composed primarily of type ________ collagen.

a. III

b. IV

c. I

d. II

B

Adherens junctions and desmosomes may be distinguished from each other on the basis of

a. whether the linkage is between two cells of between a cell and the extracellular environment.

b. the linkage of cadherins either to actin filaments or to intermediate filaments, respectively.

c. the presence of cadherins versus ICAMs

d. whether the cadherins are linked directly or indirectly to cytoskeletal elements

B

Specific recognition between cell types such as leukocytes and endothelial cells of blood vessels is mediated by cel-surface glycoproteins called

a. spectrins

b. fibronectins

c. porins

d. selectins

D

The thin, sheetlike basal laminae are found

a. in between adjacent cells connect by gap junctions

b. in the extracellular space surrounding all eukaryotic cells

c. in the cytoplasm just below the plasma membrane

d. under epithelial

D

Tight junctions are located around the entire circumference of the cell. (T/F)

True

Integrins are homodimers of two transmembrane polypeptide subunits. (T/F)

False

The fibrous proteins of the extracellular matrix are embedded in polysaccharide gels formed of glycosaminoglycans. (T/F)

True

The major cell surface receptor(s) responsible for the attachment of cells to the extracellular matrix is(are)

a. desmosomes

b. integrins

c. laminin

d. hemidesmosomes

B

The direction of cellulose microfibril synthesis in elongating plant cells is

a. parallel to endoplasmic reticulum under the plasma membrane

b. perpendicular to the direction of cell elongation

c. parallel to the direction of cell elongation

d. perpendicular to the direction of microtubules inner the plasma membrane

B

Homophillic interactions between cells involve interactions

a. between cadherins and B-catenin

b. among adhesion molecules of different molecular classes

c. between integrins and ICAMs

d. among adhesion molecules of the same molecular class

D

Fungal cell walls are built primarily of

a. peptidoglycan

b. pectin

c. cellulose

d. chitin

D

The basic structural polysaccharide of fungal cell walls, crab shells, and insect exoskeletons is

a. chitin

b. cellulose

c. hemocellulose

d. collagen

A

The cell-cell interactions mediated by the selections, integrins, and most members of the Ig superfamily are _________ interactions in which the cytoskeleton of the adjacent cells are not linked to one another.

a. stable

b. transient

c. nonspecific

d. physiological unimportant

B

Collagen fibrils form extracellularly and not intracellularly, even though their components are synthesized within the cell and transported to the cell surface via the Golgi. Which statement explains why this happens?

a.

b.

c.

d.

Type I pro collagen is synthesized with non helical segments at each end of the polypeptide chain, limiting their ability to form collagen fibrils in cells

Adherens junctions are linked to cytoplasmic

a. actin filaments

b. microtubules

c. myosin filaments

d. intermediate filaments

A

The junctions between animal cells that allow the free passage of molecules smaller that approximately 1000 daltons are called

a. plasmodesmata

b. tight junctions

c. gap junctions

d. hemidesmosomes

C

Which statement about collagen is false?

a. it is a secreted protein.

b. it contains an amino acid called hydroxyproline.

c. it is the most abundant protein in animal tissues.

d. it forms a double helix, with two collagen molecules wrapped around each other in a rope like structure.

D

Integrins are

a. components of desmosomes

b. peripheral membrane proteins

c. transmembrane proteins

d. components of extracellular matrix

C

Adhesion of plant cells his mediated by a pectin-rich region of the cell wall called the

a. plasmodesmata

b. middle lamella

c. external lamina

d. intermediate lamella

B

Cellulose synthase in plants is located

a. in Golgi apparatus

b. outside the cell

c. in the plasma membrane

d. in the cytosol

C

Which of the following can pass through gap junctions?

a. insulin and glucose

b. cAMP and calcium ions

c. cAMP and glucose

d. insulin and calcium ions

B

Fibrous structural proteins of the extracellular matrix are embedded in gels formed from polysaccharides called

a. fibronectin

b. laminin

c. elastin

d. glycosaminoglycans (GAGs)

D

Cell adhesion mediated by selecting, integrins, and most cadherins requires divalent cations. (T/F)

Trie

All of the following can be due to a mutation in a gene for gap function protein except

a. deafness

b. cataracts

c. scury

d. Charcot-Marie-Tooth disease

C

A major function of tight junctions is to

a. create strong cell-cell adherence

b. sort cells on the basis of adhesion during migration in embryos

c. promote intermixing of proteins between the apical and basolateral surfaces of cells

d. seal the space between adjacent cells to provide, for example, a barrier to glucose diffusion across epithelial cell layer

D

Collagens commonly contain the three repeating amino acids: proline,

a. glutamine and hydroxyproline

b. glutamine and hydroxylysine

c. glycine and hydroxylysine

d. glycine and hydroxyproline

D

The cell walls of bacteria are made of a copolymer of

a. cellulose and lignin

b. polysaccharides and peptides

c. proteins and lipids

d. proteins and polysaccharides

B

The major protein of extracellular matrix of animal cells is

a. fibronectin

b. collagen

c. chondroitin sulfate

d. keratin

B

Major function of adhesion proteins such as fibronectin is to

a. link collagen, proteoglycans, and cells containing integrins

b. seal cell layers at tight junctions

c. link epithelial cell layers

d. support communication between adjacent cells

A

Which of the following antibiotics inhibits the synthesis of bacterial cell walls?

a. Tetracyclin

b. Streptomycin

c. Penicillin

d. Actinomycin D

C

Plasmodesmata can open and close in response to signals. (T/F)

False

Plasmodesmata contain a single microtubule running from cell to cell down their center. (T/F)

False

Cell adhesion molecules can be divided into four major groups. Which of the following is not one of those groups?

a. selectins

b. collagens

c. integrins

d. Ig superfamily

B

Integrins link extracellular matrix proteins either directly or indirectly to all of the following intracellular proteins except

a. actin.

b. α-actinin.

c. laminin.

d. talin.

C

A mutation in the bacterial gene encoding crescentic would likely have an effect on which type of bacteria?

a. rod-shaped

b. curved or spiral-shaped

c. spherical

d. filamentous

B

Vitamin C deficiency may lead to scurvy, a disease characterized by skin lesions and blood vessel hemorrhaged due to weakened connective tissue. Vitamin C deficiency has this effect because the vitamin is

required for the enzymatic activity of propyl hydroxylase

The structural polysaccharide of fungal cell walls is the same as the one found in insect

a. eyes

b. exoskeleton

c. endoskeleton

d. cartilage

B

The major family of calcium-mediated cell-surface adhesion molecules is

a. calmodulins

b. calsequestrins

c. cadherins

d. fibronectins

C

Charcot-Marie-Tooth disease is a tight junction disease. (T/F)

False

Desmosomes are held together by the adhesion fo the two desmosomal cadherins:

desmoglein and desmocollin

Neurotransmitters act by binding to receptors that area.

a. ligand-gated ion channels.

b. located in the cytoplasm.

c. tyrosine-kinase receptors.

d. not coupled to G proteins.

A

The medical usage of nitroglycerine in heart disease is based on its

a. inhibition of adenylate cyclase and blood vessel contraction.

b. conversion of NO and blood vessel dilation.

c. activation of NO-synthase and muscle cell contraction.

d. promotion of cyclooxygenase and prostaglandin synthesis.

B

Signaling molecules that activate cell surface receptors are essentially the same as those that activate intracellular receptors. (T/F)

False

Protein X is activated by protein kinase A. A mutation in protein X that replaces the protein's only serine residue with an arginine residue would be expected to

a. increase activation of protein X.

b. eliminate activation of protein X.

c. have no effect on activation of protein X.

d. prevent inactivation of protein X.

B

The TGF-β/Smad pathway is similar to JAK/STAT signaling in that a protein kinase associated with a receptor directly phosphorylates and activates a transcription factor. However, the receptors for transforming growth factor beta (TGF-) and related polypeptides are protein kinases that phosphorylate _______, rather than _______, residues on their substrate proteins.

a. serine or threonine; tyrosine

b. tyrosine; serine or threonine

c. proline or aspartate; tyrosine

d. tryptophan; tyrosine

D

A major function of cAMP in animal cells is to activate

a. adenylyl cyclase.

b. protein kinase A.

c. protein kinase C.

d. tyrosine kinases.

B

Which of the following signaling pathways allows for direct cell-cell signaling by transmembrane proteins?

a. Hedgehog

b. Notch

c. Wnt

d. NF-kB

B

NF-B can activate genes during the immune response by a protein kinase that

a. phosphorylates the transcription factor NF-B to activate it.

b. phosphorylates the inhibitory factor IB, causing it to be degraded and to release NF-B.

c. phosphorylates a MAP kinase to initiate its cascade.

d. activates a phosphorylase that removes an inhibiting phosphate from the NF-B.

B

B-arrestin binds to phosphorylated G protein-coupled receptors, binding Raf, MEK, and ERK into the complex and linking the G protein-coupled signal pathway to the ERK signaling pathway, This is an example of inhibitory crosstalk. (T/F)

False

Nitric oxide is a signal molecule that can

a. bind to surface receptors and activate second messengers.

b. bind to surface receptors and open ion channels.

c. diffuse across cell membranes and bind to receptors that regulate transcription.

d. diffuse across cell membranes and directly alter the activity of intracellular enzymes.

D

Protein kinase A regulates glycogen metabolism by phosphorylating glycogen synthase and

a. phosphorylase kinase.

b. glycogen phosphatase.

c. glycogen phosphorylase.

d. glucokinase.

A

Ras activation is mediated by guanine nucleotide exchange factors (GEFs) that stimulate the release of bound GDP and its exchange for GTP. (T/F)

True

The MEK kinase (MAP kinase/ERK kinase) is unusual in that it

a. is activated by a kinase.

b. lies downstream of G protein-coupled receptors.

c. is a dual-specificity kinase, having the ability to phosphorylate both threonines and tyrosines.

d. activates a kinase.

C

In plant cells, which signaling molecule induces cell elongation?a. Acetylcholine.

b. y-aminobutyric acid (GABA).

c. Auxin.

d. Retinoic acid.

C

How would inhibition of PI 3-kinase affect ERK activity in a growthfactor-stimulated cell?

a. ERK activity would be inhibited.

b. ERK activity would be unaffected.

c. ERK activity would be upregulated.

d. ERK protein would be targeted for destruction by proteolysis.

A

Statins, a class of drugs that are often administered to patients with high cholesterol, inhibit the biosynthesis of cholesterol. Statin drugs would not be expected to affect the biosynthetic pathway of which of the following signal molecules?

a. Thyroid hormone

b. Vitamin D3

c. Retinoic acid

d. Estrogen

C

Which molecule stimulates fibroblasts to proliferate and thus heal a wound?

a. EGF

b. NGF

c. NO

d. PDGF

D

The action effected by protein kinase A is terminated by

a. inactivation of the initial receptor.

b. inactivation of the stimulatory G protein.

c. degradation of cAMP.

d. dephosphorylation of phosphoproteins by protein phosphatase 1.

D

Cyclic AMP (cAMP) is synthesized from ATP by the action of

a. phosphodiesterase.

b. phosphorylase kinase.

c. adenylyl cyclase.

d. protein kinase A (PKA).

C

Heterotrimeric G proteins are not the only guanine nucleotide-binding proteins. Which of the following represents a family of GTP-binding proteins that act as monomers rather than heterotrimeric compounds?

a. Ras

b. ERK

c. Raf

d. Smad

A

The first step in growth factor pathway activation is

a. receptor dimerization.

b. receptor phosphorylation.

c. Ras activation.

d. the binding of SH2-containing proteins.

A

Went signaling molecules that binds to Frizzled/LRP, activating Dishevelied to inhibit a protein kinase. This results in longer lived B-catenin, which enters the nucleus and turns on target genes. (T/F)

True

During the odorant response in the cilia of olfactory neurons, the second messenger _______, leads to the opening of ion channels in the plasma membrane of olfactory neurons and the production of a nerve impulse.

a. Ca2+

b. cAMP

c. cGMP

d. IP3

B

Protein kinase A regulates glycogen metabolism by _______ glycogen synthase and _______ glycogen phosphorylase.

a. activating; activating

b. inactivating; inactivating

c. activating; inactivating

d. inactivating; activating

D

Which signal molecule diffuses through the plasma membrane to ultimately bind nuclear receptors and influence transcription?

a. Estrogen

b. Nitric oxide

c. Cadherins

d. Nerve growth factor

A

Hydrolysis of PIP2 by phospholipase C is stimulated by

a. G protein-linked receptors.

b. protein-tyrosine kinase receptors.

c. serine-threonine kinase receptors.

d. both G protein-linked receptors and protein-tyrosine kinase receptors.

D

A mutation that causes a G-protein to lose its ability to hydrolyze bound GTP would be expected to have constitutively

a. inactive subunits.

b. bound subunits.

c. active a subunits.

d. inactive subunits.

C

A researcher generated a mutant SH2-containing protein such that it binds tyrosine and phosphotyrosine with equal affinity. As a result, MEK activity would be expected to

a. increase with ligand binding-induced dimerization.

b. remain the same with receptor dimerization and autophosphorylation.

c. decrease due to changes in Raf activation.

d. decrease due to allosteric inhibition of SH2-domain binding.

B

SH2 domains are

a. protein domains that bind phosphotyrosine-containing peptides.

b. the domains on receptor tyrosine kinases that contain the phosphorylated tyrosine.

c. domains that mediate the dimerization of receptor tyrosine kinases.

d. the domains on receptor tyrosine kinases that possess the kinase activity.

A

Intracellular signaling pathways provide multiple opportunities for the amplification of a response to an extracellular signal. (T/F)

True

Which of the following hormones is(are) not synthesized from cholesterol?

a. Testosterone

b. Progesterone

c. Corticosteroids

d. Retinoic acid

D

Protein kinase A is activated by

a. phosphorylation of its catalytic subunit.

b. phosphorylation of its regulatory subunits.

c. binding of cAMP to its catalytic subunits.

d. binding of cAMP to its regulatory subunits.

D

Enkephalins and endorphins bind to the same receptors in the brain as

a. nerve growth factor.

b. aspirin.

c. morphine.

d. acetylcholine.

C

Which statement about protein kinase A (PKA) is false?

a. In the inactive state, PKA exists as a tetramer of two regulatory (R) and two catalytic (C) subunits.

b. PKA binds a total of four molecules of cAMP, one on each of the four subunits.

c. PKA binds a total of four molecules, two molecules on each of the two regulatory (R) subunits.

d. Once activated, the catalytic (C) subunits dissociate and activate target molecules.

B

A glucocorticoid binding to its receptor stimulates

a. phosphorylation of a transcription factor protein that activates a gene.

b. formation of a receptor dimer that triggers an intracellular signal pathway.

c. formation of a receptor dimer that binds to and activates a gene.

d. binding of the receptor monomer to a gene.

C

Signaling by neurotransmitters is an example of _______ signaling.

a. autocrine

b. endocrine

c. paracrine

d. direct cell-to-cell

C

Phosphorylation of G protein-coupled receptors by GRK

a. turns off G protein signaling.

b. hypersensitizes G protein signaling.

c. blocks the dissociation of the G protein from the receptor.

d. inhibits the GTPase activity of the alpha subunit of the G protein.

A

The alpha subunit of the G protein that is associated with the epinephrine receptor, Gs,

a. opens Ca2+ channels.

b. closes Na+ channels.

c. activates adenylate cyclase.

d. inhibits adenylate cyclase.

C

Studies on cell cycle mutants in budding and fission yeasts demonstrated that cdc2 and cdc28 both encode a

a. protein phosphatase

b. ubiquitin ligase

c. protein kinase

d. growth factor

C

The passage of a cell through the stages of the cell cycle is controlled by protein kinases that phosphorylate many different proteins at appropriate times. What are these protein kinases called?

a. Cdk activating kinases

b. Tyrosine kinases

c. Cyclin-dependent kinases

d. Cyclins

C

In the absence of growth factor, most animal cells will stop the cell cycle at a restriction point in what stage?

a. M phase

b. S phase

c. G2 phase

d. G1 phase

D

Which of the following is not one of the phases of mitosis?

a. anaphase

b. S phase

c. prophase

d. metaphase

B

Progression through the cell cycle in the yeast Saccharomyces cerevisiae is regulated by

a. internal signals such as growth factors and steroid hormones

b. external signals such as availability of nutrients and mating factors

c. internal signals such as the availability of glucose and ATP

d. simple organisms such as yeast do not have a cell cycle

B

The metaphase-to-anaphase transition in animal cells is triggered by the breakdown of cyclin B. (T/F)

False

Cells are restricted to one round of DNA replication per cycle by origin of replication proteins called

a. ATMs

b. Oris

c. MCMs

d. Akts

C

Cdks bind to cyclin and are activated by

a. the binding of Ink4

b. the binding of Cip

c. phosphorylation of Wee1

d. dephospho rylation by Cdc25 protein phosphatase

D

Which statement about cyclin B is false?

a. it cycles between active and inactive stated in the cell cycle

b. it is a component of MPF

c. it activated Cdc2 protein kinase

d. it accumulated throughout S and G2

A

The mechanism of cytokinesis in plants involved the formation of the

a. plasma membrane bridge

b. contractile ring

c. Aurora belt

d. cell plate

D

After development, liver cells stop cycling and stay in G1 phase. (T/F)

False

Cells in the quiescent phase of the cell cycle are said to be in the _______ phase.

a. M

b. G0

c. G1

d. G2

B

Rb is a member of the family of tumor suppressor genes. (T/F)

True

Which statement about cyclin D is false?

a. it is always present and its activity is regulated by fluctuating levels of Cdk4 and Cdk6.

b. it is activated by growth factors

c. it is rapidly degraded following removal of appropriate growth factors

d. it is required for cel cycle progression

A

You perform an experiment by incubating a radiolabeled nucleotide into the medium of a culture of cells. The cells that take up the radiolabel would be expected to be in what phase of the cell cycle?

a. M phase

b. G2 phase

c. S phase

d. G1 phase

C

interphase usually consists of G1, S, and G2 but in some cells it consists only of S. (T/F)

True