Exam 3

Microfilaments are approximately (A)___ in diameter, while microtubules are around (B)____ in diameter.

7 nm, 25 nm

In a motile cilium or flagellum, _______ microtubules are arranged _______.

9 doublet; in a circle around a central pair of microtubules

Which comparison of a hemidesmosome and a desmosome is correct?

A hemidesmosome uses integrins as transmembrane connectors to the ECM; a desmosome uses desmosomal cadherins to connect to another cell.

Integrins bind to:

All of the above

The physical characteristics of extracellular matrix can be modified by

All of the above.

The physical characteristics of extracellular matrix can be modified by:

All of the above.

Branching of actin filaments can be initiated by:

Arp2/3

Which comparison of collagen and elastin is correct?

Both proteins are connected into large complexes by hydroxylysine crosslinks.

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

Catenins

Which movement is not due mainly to actin or actin-myosin interactions?

Chromosome movement during mitosis

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

Collagens

Loss of _____ can contribute to the development of a cancer by _____

E-cadherin; freeing cells to migrate to new locations

Keratin filaments are found in which of the following cell types?

Epithelial cells

Which of the following is not an intermediate filament protein?

Fibronectin

Actin exists in cells in two major forms called:

G actin and F actin.

Space-filling extracellular matrix contains a large, strong fibrils composed primarily of type _______ collagen.

I or II

Basal laminae contains a meshwork of fibrils composed primarily of type _______ collagen.

IV

Which statement about collagen is false?

It forms a double helix, with two collagen molecules wrapped around each other.

Which of these comparisons between microfilaments and microtubules is correct?

Microtubules only add and remove monomers from the "+" end, while microfilaments can add and remove from both ends.

Collagen is prevented from assembling into insoluble fibrils inside the cell by:

N- and C-terminal regions that are not cleaved until it is secreted

If developing pre-nerve cells expressing only N-cadherin on their surfaces were mixed with epithelial cells expressing only E-cadherin, what would be the most likely result?

Nerve cells would adhere to one another, and epithelial cells would adhere to one another.

Are the two halves of a fibronectin dimer identical? Why or why not?

No; the two chains may be alternatively spliced to refine how cells bind to ECM.

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?

Type I procollagen is synthesized with nonhelical segments at each end of the polypeptide chain, limiting their ability to form collagen fibrils in cells.

Laminin is a t-shaped complex of three proteins, with ___, and ___.

a tail domain that binds to cells; arms that bind to collagen and ECM materials.

Adherens junctions are linked to cytoplasmic:

actin filaments.

Actin filaments are anchored at junctions called:

adherens junctions.

ATP is hydrolyzed by actin:

after assembly but before disassembly.

Gap junctions between two adjacent cells can form _______ between the two cells.

all of the above

Which of the following can pass through gap junctions?

cAMP and calcium ions

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

cadherins.

The basal bodies of cilia and flagella are similar in structure to (and can form from):

centrioles.

The major microtubule-organizing center in most animal cells is the:

centrosome

The major protein of the extracellular matrix of animal cells is:

collagen.

What is the function of plectin?

connects intermediate filaments to desmosomes or hemidesmosomes

Microtubules are not involved in:

cytokinesis of animal cells.

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

desmoglein and desmocollin.

A junctional complex consists of a tight junction associated with both adherens junctions and:

desmosomes.

Keratin filaments are anchored to junctions called:

desmosomes.

Microtubules are assembled from:

dimers of α- and β-tubulin

The microtubule behavior in which individual microtubules alternate between cycles of growth and shrinkage is called:

dynamic instability

A male patient at a medical clinic presents with infertility due to nonmotile sperm and an inability to clear mucous from his respiratory tract. Other tissues are normal. You suspect that these symptoms may be caused by mutation in:

dynein.

The beating of cilia and flagella occurs by means of _______-based _______.

dynein; microtubule sliding

Vimentin is the major intermediate filament protein of _______ cells

fibroblast

Connective tissue cells are connected to the extracellular matrix by receptors that bind to an adhesive protein called:

fibronectin.

The GTP bound to β-tubulin hydrolyzes to GDP and Pi :

following polymerization but before depolymerization

Transgenic mice that express a shortened skin keratin protein in place of the normal keratin protein would be most likely to have a phenotype that includes:

fragile, easily blistered skin.

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

gap junctions.

Collagens commonly have very high concentrations of three amino acids: proline, _____

glycine, and hydroxyproline

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

glycosaminoglycans (GAGs).

Integrins are ______ of ______ polypeptide subunits

heterodimers; two different transmembrane

The only glycosaminoglycan that occurs as a single long polysaccharide chain is:

hyaluronan.

Assembly of microfilaments is driven by ____, while assembly of microtubules is driven by _____.

hydrolysis of ATP; hydrolysis of GTP

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

integrins.

Desmosomes are linked to cytoplasmic:

intermediate filaments.

The major function of adhesion proteins such as fibronectin is to:

link collagen, proteoglycans, and cells containing integrins

Glycosaminoglycans (GAGs) are highly (A)_____, due to the presence of (B)____.

negatively charged, sulfate groups

The primary function of tight junctions is to:

prevent the free passage of molecules between cells of an epithelial sheet.

The function of gap junctions is to:

provide direct communication between cells.

Intermediate filaments function mainly in:

providing mechanical strength for cells.

Cell adhesion mediated by selectins, integrins, and most cadherins is similar in that they all:

require divalent cations

Intermediate filaments are typically composed of (A)___ protein monomers, while microtubules are typically composed of (B)___ protein monomers.

rod-like, globular

A major function of tight junctions is to:

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

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

selectins

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

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

Integrins are:

transmembrane receptors for ECM molecules

In actin filament assembly, the process in which ATP-actin monomers are added to the barbed end of the filament while ADP-actin monomers are concurrently dissociating from the pointed end of the filament is referred to as:

treadmilling

Actin filaments are stabilized by:

tropomyosin

Kinesin I is a motor protein molecule consisting of (A)____ that transports (B)____ along microtubules.

two heavy chains and two light chains, All of the above

Thin, sheetlike basal laminae are found:

under epithelia.

Rings of the protein _______ in the pericentriolar material nucleate microtubule assembly.

γ-tubulin