Deck 16: Cell Walls, the Extracellular Matrix, and Cell Interactions

Question 1

The cell walls of bacteria are made of a copolymer of

A) proteins and lipids.
B) proteins and polysaccharides.
C) polysaccharides and peptides.
D) cellulose and lignin.

Answer 1

C

Question 2

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

A) Penicillin
B) Streptomycin
C) Tetracycline
D) Actinomycin D

Answer 2

A

Question 3

The polysaccharide chains of bacterial cell walls are made of alternating

A) N-acetylgalactose and N-acetylmuramic acids.
B) N-acetylglucosamine and N-acetylmuramic acids.
C) N-acetylglucosamine and N-acetylneuraminic acids.
D) N-acetyl galactose and N-acetylneuraminic acids.

Answer 3

B

Question 4

Plant cell walls consist of cellulose fibrils in a matrix of

A) chitin and pectin.
B) pectin and hemicellulose.
C) Pectin and lignin.
D) lignin and chitin.

Question 5

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

A) exoskeletons.
B) endoskeletons.
C) eyes.
D) cartilage.

Question 6

Pectins form a _______ network in plant cell walls.

A) fibrous
B) gel-like
C) solid, rigid
D) waxy

Question 7

Cellulose synthase in plants is located

A) in the Golgi apparatus.
B) in the cytosol.
C) in the plasma membrane.
D) outside the cell.

Question 8

The direction of cellulose microfibril synthesis in elongating plant cells is

A) parallel to the direction of cell elongation.
B) perpendicular to the direction of cell elongation.
C) perpendicular to the direction of microtubules under the plasma membrane.
D) parallel to the endoplasmic reticulum under the plasma membrane.

Question 9

The thin, sheetlike basal laminae are found

A) under epithelia.
B) in the cytoplasm just below the plasma membrane.
C) in the extracellular space surrounding all eukaryotic cells.
D) in between adjacent cells connected by gap junctions.

Question 10

The major protein of the extracellular matrix of animal cells is

A) keratin.
B) fibronectin.
C) collagen.
D) chondroitin sulfate.

Question 11

Collagens commonly contain the three repeating amino acids: proline,

A) glutamine, and hydroxyproline.
B) glycine, and hydroxyproline.
C) glycine, and hydroxylysine.
D) glutamine, and hydroxylysine.

Question 12

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

A) I
B) II
C) III
D) IV

Question 13

The smallest amino acid is

A) glycine.
B) proline.
C) cysteine.
D) asparagine.

Question 14

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

A) a critical structural component of collagen.
B) required for the enzymatic activity of prolyl hydroxylase.
C) required for the enzymatic activity of cellulose synthase.
D) required for the enzymatic activity of hydroxyproline.

Question 15

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

A) fibronectin.
B) aggrecan.
C) integrin.
D) lamin.

Question 16

Integrins are

A) transmembrane proteins.
B) peripheral membrane proteins.
C) components of the extracellular matrix.
D) components of a desmosome.

Question 17

Integrins bind to

A) collagen, laminin, and fibronectin.
B) plectin and proteoglycans.
C) α-actinin, vinculin, and talin.
D) All of the above

Question 18

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

A) hemidesmosomes.
B) desmosomes.
C) integrins.
D) laminin.

Question 19

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

A) Selectins
B) Integrins
C) Collagens
D) Immunoglobulin superfamily

Question 20

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

A) calmodulins.
B) calsequestrins.
C) cadherins.
D) fibronectins.

Question 21

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?

A) All cells would mix and adhere to one another equally.
B) Nerve cells would adhere to one another, and epithelial cells would adhere to one another.
C) Nerve cells would adhere to one another in the center, and epithelial cells would surround them.
D) Epithelial cells would adhere to one another in the center, and nerve cells would surround them.

Question 22

Adherens junctions are linked to cytoplasmic

A) actin filaments.
B) intermediate filaments.
C) microtubules.
D) myosin filaments.

Question 23

Desmosomes are linked to cytoplasmic

A) actin filaments.
B) intermediate filaments.
C) microtubules.
D) myosin filaments.

Question 24

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

A) Plakoglobulins
B) Plectins
C) Talins
D) $\alpha$ - and $\beta$ -catenin

Question 25

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

A) desmoglein and desmocollin.
B) desmoglein and desmoplakin.
C) desmoglobin and desmocollin.
D) desmoglobin and desmoplakin.

Question 26

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

A) desmosomes.
B) gap junctions.
C) hemidesmosomes.
D) focal adhesions.

Question 27

The function of gap junctions is to

A) hold epithelia together.
B) seal the space between cells.
C) provide direct communication between cells.
D) maintain the spacing of the basal laminae beneath epithelial cells.

Question 28

Which of the following can pass through gap junctions?

A) cAMP and calcium ions
B) Insulin and calcium ions
C) cAMP and glucose
D) Insulin and glucose

Question 29

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

A) Charcot-Marie-Tooth disease.
B) deafness.
C) cataracts.
D) scurvy.

Question 30

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

A) external lamina.
B) middle lamella.
C) intermediate lamella.
D) plasmodesmata.

Question 31

The communicating junctions between plant cells are called

A) gap junctions.
B) plasmodesmata.
C) plasmotubules.
D) lamellar junctions.

Question 32

Within the plant cell wall, cellulose microfibrils are embedded in a matrix consisting of proteins and two other types of polysaccharides: _______ and _______.

Question 33

In plant cell walls, _______ are highly branched polysaccharides that are hydrogen-bonded to cellulose microfibrils.

Question 34

Responsible for much of the rigidity of plant tissues, _______ is the internal hydrostatic pressure that builds up within the cell and equalizes its osmotic pressure.

Question 35

The hydroxyl groups on the modified amino acids of collagen form _______ that stabilize the collagen triple helix.

Question 36

The amino acid sequence of a collagen triple helix domain consists of Gly-X-Y repeats, in which X is frequently _______ and Y is frequently _______.

Question 37

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

Question 38

Glycosaminoglycans (GAGs) consist of repeating disaccharide units. With the exception of hyaluronan, the sugars frequently contain _______.

Question 39

Gap junctions allow passage of molecules that have a molecular weight of less than _______ daltons.

Question 40

The individual units of gap junctions are composed of _______ molecules.

Question 41

Gap junctions between nerve cells form _______ synapses.

Question 42

Basal laminae are formed primarily from type IV collagen and other proteins.

Question 43

The fibrous proteins of the extracellular matrix are embedded in polysaccharide gels formed of glycosaminoglycans.

Question 44

Aggrecan is a large proteoglycan consisting of about 100 hyaluronan chains extending from a core protein.

Question 45

Integrins are homodimers of two transmembrane polypeptide subunits.

Question 46

Integrin was first localized to sites of cell adhesion to the extracellular matrix by immunofluorescence microscopy.

Question 47

Cell adhesion mediated by selectins, integrins, and most cadherins requires divalent cations.

Question 48

Loss of E-cadherin can lead to the development of a cancer.

Question 49

Adherens junctions and desmosomes both link to intermediate filaments in cells.

Question 50

Tight junctions provide strong adhesions between cells.

Question 51

Tight junctions involve a fusion between the outer leaflets of two membranes in the region of the junction.

Question 52

Tight junctions are located around the entire circumference of the cell.

Question 53

Charcot-Marie-Tooth disease is a tight junction disease.

Question 54

Plasmodesmata contain a single microtubule running from cell to cell down their center.

Question 55

Plasmodesmata can open and close in response to signals.

Question 56

What prevents collagen from assembling into fibrils inside the cell?

Question 57

Why is the term "basal lamina" preferred over the term "basement membrane"?

Question 58

Describe the structure of laminins.

Question 59

What is the function of plectin?

Question 60

Describe two ways in which a hemidesmosome differs from a desmosome.

Question 61

Which proteins attach integrins to actin filaments at focal adhesions?

Question 62

Describe the structure of an integrin, as determined from the cDNA sequence isolated from fibroblasts by Hynes et al.

Question 63

Describe the process of adhesion between leucocytes and endothelial cells that allows leucocytes to leave the circulation and enter an inflamed tissue.

Question 64

What are the four classes of cell adhesion molecules?

Question 65

What are the three cell-to-cell junctions found in the junctional complex between two intestinal epithelial cells?

Question 66

What is the primary function of tight junctions?

Question 67

What is a secondary function of tight junctions?

Question 68

How many molecules of the gap junction protein form one open channel between two cells?

Question 69

How do the hexagonal units of connexin form a junction through which molecules can diffuse?

Question 70

What is the function of gap junctions in heart muscle?

Question 71

What are the three most common disease consequences of connexin gene mutations?

Question 72

Why does a mutation in a gene for the gap junction protein not affect gap junction function in all tissues that have gap junctions?

Question 73

Why does any mutation in a gap junction protein produce defects in gap junction functions in sensitive tissues? Give two possible explanations.

Question 74

How do plasmodesmata form?

Question 75

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

A) Spherical
B) Rod-shaped
C) Curved or spiral-shaped
D) Filamentous

Question 76

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

A) cellulose.
B) chitin.
C) collagen.
D) hemicellulose.

Question 77

Cellulose, chitin, and hyaluronan are all deposited extracellularly by

A) secretion.
B) exocytosis.
C) ABC transporters.
D) plasma membrane enzyme complexes.

Question 78

Animal cells are embedded in a(n)

A) cell wall.
B) extracellular matrix.
C) hemicellulose-rich hyaluronan layer.
D) pectin-rich basal lamina.

Question 79

Which statement about collagen is false?

A) It is the most abundant protein in animal tissues.
B) It forms a double helix, with two collagen molecules wrapped around each other in a ropelike structure.
C) It contains an amino acid called hydroxyproline.
D) It is a secreted protein.

Question 80

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) Type I procollagen is synthesized with nonhelical segments at each end of the polypeptide chain, limiting their ability to form collagen fibrils in cells.
B) Procollagen is soluble and small enough to fit within the intracellular transport machinery.
C) Type I collagen consists of about 1000 amino acids or 330 Gly-X-Y repeats.
D) Type I procollagen contains hydroxylated proline and lysine residues that prevent polypeptide chain formation within the cell.