Final Review

Question 1

1. Intermediate filaments are relatively stable structures because:
   A. their subunits are joined together by covalent bonds.
   B. they do not bind GTP.
   C. they attach to desmosomes and hemidesmosomes.
   D. their subunits form coiled-coils.
   E. they attach to the extracellular matrix

Answer 1

D. their subunits form coiled-coils.

Question 2

2. There are several differences between intermediate filaments and the other filaments of the cytoskeleton, actin filaments and microtubules. Which of the following statements is false?
   A. Only intermediate filament have intrinsic ability to assembly and require no nucleation or assembly proteins.
   B. Only intermediate filament do not require ATP for growth.
   C. Only intermediate filaments require protein contact between heterodimers of individual filament proteins.
   D. Intermediate filaments are much more resistant to strain than either actin filaments or microtubules.
   E. There is a much greater diversity of types of intermediate filaments than there is for actin filaments or microtubules.

Answer 2

C. Only intermediate filaments require protein contact between heterodimers of individual filament proteins.

Question 3

3. What does the term “structural” keratin refer to?
   A. The first keratins to be expressed in embryonic tissue
   B. The keratins that are found in simple epithelium
   C. The keratins that are found in the basal layer of most epithelium (K5, K14)
   D. The keratins that are found in the suprabasal layers of stratified epithelium and are tissue specific
   E. The keratins expressed in and around specialized structures such as hair or nails

Answer 3

E. The keratins expressed in and around specialized structures such as hair or nails

Question 4

4. What does the term “barrier” keratin refer to?
   A. The first keratins to be expressed in embryonic tissue
   B. The keratins that are found in simple epithelium
   C. The keratins that are found in the basal layer of most epithelium (K5, K14)
   D. The keratins that are found in the suprabasal layers of stratified epithelium and are tissue specific
   E. The keratins expressed in and around specialized structures such as hair or nails

Answer 4

C. The keratins that are found in the basal layer of most epithelium (K5, K14)

Question 5

5. Which one of the following statements about keratins is false?
   A. Over 50 different types of keratins are expressed in humans, and they are co-expressed as pairs in individual cells.
   B. Keratins form attachments to the cell membrane by binding to hemidesmosomes and desmosomes.
   C. The presence of keratins in a sheet-like organization is hallmark of epithelial cells.
   D. Though they are predominantly expressed in mammals, keratins are also found in all eukaryotes.
   E. Keratins and other intermediate proteins are classified into six groups based on sequence similarity; keratins make up the majority of type I and type II intermediate filaments.

Answer 5

D. Though they are predominantly expressed in mammals, keratins are also found in all eukaryotes.

Question 6

6. Which of the following is not a member of the endomembrane system responsible for endocytosis and exocytosis?
   A. The medial golgi
   B. The late endosome
   C. The plasma membrane
   D. The nuclear membrane
   E. The endoplasmic reticulum

Answer 6

D. The nuclear membrane

Question 7

7. The proper sequence of compartments visited by proteins destined to be secreted from eukaryotic cells is:
   A. Endoplasmic reticulum- Golgi complex- endosome- plasma membrane
   B. Endoplasmic reticulum- Golgi complex- cytosol- plasma membrane
   C. Endoplasmic reticulum- Golgi complex-lysosome- plasma membrane
   D. Endoplasmic reticulum- Golgi complex-TGN-plasma membrane
   E. Endoplasmic reticulum- TGN-Golgi complex-plasma membrane

Answer 7

D. Endoplasmic reticulum- Golgi complex-TGN-plasma membrane

Question 8

8. Which of the following statements about regulated exocytosis is false?
   A. It requires metabolic energy (ATP).
   B. It requires the secretory vesicle to contain a unique coat protein (COP) that binds the plasma membrane.
   C. It requires transport of proteins through the trans Golgi network (TGN).
   D. It requires specific t-SNARES and v-SNAREs.
   E. It only occurs following stimulation of a cell.

Answer 8

B. It requires the secretory vesicle to contain a unique coat protein (COP) that binds the plasma membrane.

Question 9

9. Retrograde transport refers to movement of vesicles
   A. from the plasma membrane to the endosome.
   B. from the Golgi to the endoplasmic reticulum.
   C. from the endoplasmic reticulum to the Golgi.
   D. through the trans Golgi network.
   E. from the trans Golgi network to the plasma membrane.

Answer 9

B. from the Golgi to the endoplasmic reticulum.

Question 10

10. Which of the following statements about transport vesicles exiting the endoplasmic reticulum is false?
    A. These vesicles are formed by clathrin.
    B. These vesicles are coated with COPII proteins.
    C. These vesicles require a small GTPase to drive vesicle budding.
    D. Cargo proteins are incorporated into these vesicles by bulk flow or sorting signals.
    E. These vesicles are destined for the Golgi complex.

Answer 10

A. These vesicles are formed by clathrin.

Question 11

11. What is the targeting signal used to retain resident Golgi protein?
    A. The amino acid sequence KDEL
    B. The sugar mannose-6-phosphate
    C. The membrane spanning domain and the flanking amino acids
    D. The diacidic sequence (Αsp-X-Glu)
    E. All of the above are targeting signals for retention of resident Golgi proteins.

Answer 11

C. The membrane spanning domain and the flanking amino acids

Question 12

12. Despite the fact that they possess no intrinsic signaling ability, integrins are still considered signaling receptors. How is this possible?
    A. Integrins associate with Focal Adhesion Kinase, which binds to heterotrimeric G proteins and thus initiates signaling.
    B. Integrins phosphorylate tyrosines on Focal Adhesion Kinase, and this attracts SH2-containing proteins such as Grb2, thereby initiating a signaling pathway.
    C. Integrins cluster Focal Adhesion Kinase, a cytoplasmic tyrosine kinase, and this initiates a FAK transautophosphorylation step analogous to that associated with tyrosine kinase-linked receptors.
    D. Integrins bind to both growth factors and extracellular matrix proteins, and when they bind to growth factors they behave like tyrosine kinase linked receptors.
    E. Integrins bind to growth factors in the extracellular matrix and present the growth factor to the cell surface receptors, acting as co-receptor.

Answer 12

C. Integrins cluster Focal Adhesion Kinase, a cytoplasmic tyrosine kinase, and this initiates a FAK transautophosphorylation step analogous to that associated with tyrosine kinase-linked receptors.

Question 13

13. Which statement about laminins and fibronectins is true?
    A. Both are found in the extracellular matrix, and both bind to collagens and to integrins.
    B. Both contain triple helical domains.
    C. Laminins are found primarily in the basal lamina (basement membrane).
    D. Both are found in soluble and insoluble forms.
    E. Mutations in either type of protein cause epidermolysis bullosa.

Answer 13

A. Both are found in the extracellular matrix, and both bind to collagens and to integrins.

Question 14

14. Choose the single best definition of the term extracellular matrix.
    A. All of the material found in a multicellular animal that lies outside of the plasma membrane of cells
    B. A network of flexible, fibrous proteins that weaves in and out of cells, holding the cells together
    C. Hard, calcified material that fills the space between cells (e.g., in teeth and bones)
    D. A network of flexible, hydrated proteins that binds to desmosomes and hemidesmosomes
    E. A collection of insoluble, flexible, fibrous proteins and highly charged proteoglycans that lies outside of the plasma membrane of cells.

Answer 14

E. A collection of insoluble, flexible, fibrous proteins and highly charged proteoglycans that lies outside of the plasma membrane of cells.

Question 15

15. During the process of vesicle fusion to target membrane, where is ATP hydrolysis required?
    A. ATP hydrolysis is required for v-SNARE to bind to cognate t-SNARE prior to fusion during docking.
    B. ATP hydrolysis is required to unwind and separate the cognate SNARE pair immediately after fusion.
    C. ATP hydrolysis is required for formation of the vesicle that will recycle the SNAREs
    D. ATP hydrolysis is required for the actual fusion of the two plasma membranes.
    E. None of the above, ATP hydrolysis is not required.

Answer 15

B. ATP hydrolysis is required to unwind and separate the cognate SNARE pair immediately after fusion.

Question 16

16. The role of coat proteins in vesicle trafficking is
    A. to facilitate formation of transport vesicle.
    B. to select the appropriate cargo, either by direct or indirect binding.
    C. to facilitate the fusion of the transport vesicle to the target membrane.
    D. A and B

Answer 16

D. A and B

Question 17

17. Which one of the following statements about hemidesmosomes is false?
    A. They contain transmembrane proteins.
    B. They initiate intracellular signaling pathways.
    C. They contain integrins.
    D. They linked to intermediate filaments in the cytoplasm.
    E. They bind to extracellular matrix proteins such as collagen.

Answer 17

E. They bind to extracellular matrix proteins such as collagen.

Question 18

18. Which of the following is NOT a feature of the basal lamina?
    A. It serves as a structural support to epithelial cells.
    B. It serves as a filter for large molecules.
    C. It contains collagen type IV, proteoglycans, laminins, and entactin.
    D. It can influence the migration of cells attached to it.
    E. Fibronectins are most abundant here.

Answer 18

E. Fibronectins are most abundant here.

Question 19

Tight junctions are composed of networks of…

Answer 19

Occludin, claudin, and junctional adhesion molecules

Question 20

The major structural protein of the extracellular matrix of animal cells is…

Answer 20

Collagen

Question 21

What is the localization of GAP junctions?

Answer 21

Small molecules between adjacent cell. Found in most animal cells.

Question 22

What are GAP junctions?

Answer 22

Specialized structures on the cell surface that facilitate the direct transfer of ions and small molecules between adjacent cells. Only known means of cell-to-cell transport for animal cells. Facilitate transmission of electrical signals during muscle contractions. Consists of two halves called connexons which consists of six protein subunits called connexins.

Question 23

Collagen exists as a coiled protein due to the presence of three repeating amino acids. What are they?

Answer 23

Glycine, hydroxyproline, and proline

Question 24

Adjacent plant cells are connected via _________ to equalize the ionic concentrations of their cytosol.

Answer 24

Plasmodesmata

Question 25

What are the molecular connections making GAP junctions?

Answer 25

Two halves called connexons which consist of 6 protein subunits called connexins.

Question 26

Both Adherens junctions and Hemidesmosomes contribute to the stability of a sheet of epithelial cells. Compare and contrast the location, function and composition of each.

Answer 26

Adheren junctions are a family of related cell surface domains that link together neighboring cells. Adheren junctions contain transmembrane cadherin receptors. The best known adherens junction, the zonula adherens, is located within the junctional complex that forms between neighboring epithelial cells in some tissues. Within the zonula adherens, adaptor proteins called catenins link cadherins to actin filaments
Hemidesmosomes, like desmosomes, provide structural stabililty to epithelial sheets. Hemidesmosomes are found on the basal surface of epithelial cells, where they link the ECM to the intermediate filament network via transmembrane receptors.

Question 27

Explain the difference between AVIDITY and AFFINITY MODULATION of integrin receptor binding.

Answer 27

AVIDITY- the number of contacts formed between intrgrins and ECM proteins changes. Strength of adhesion depends on NUMBER of receptors.
AFFINITY- change in receptor conformation results in altered affinity for its ligand. Strength of adhesion depends on receptor CONFORMATION.

Also: Slide 22 - Avidity is essentially how close the receptors are to each other. The closer together the stronger the signal.

Affinity is how strong an individual receptor is.

Both have to do with signaling strength just in differing forms.

A simpler way they explained it too was that avidity depends on the number of receptors, whereas affinity depends on the conformation of the receptors.