Deck 11: Cellcell Interactions

Question 1

Put the following events in the process of signal- transduction in order:
1) A conformational change in the signal- receptor complex activates an enzyme.
2) Protein kinases are activated.
3) A signal molecule binds to a receptor.
4) Target proteins are phosphorylated.
5) Second messenger molecules are released.

A) 3, 1, 5, 2, 4
B) 1, 3, 4, 2, 5
C) 3, 1, 2, 5, 4
D) 1, 2, 3, 4, 5

Answer 1

A

Question 2

A gap junction is a channel that connects adjacent cells. What kinds of substances can pass through a gap junction?

A) ions that can regulate heartbeat
B) subunits of nucleic acids
C) raw materials for protein synthesis
D) all of these substances

Answer 2

D

Question 3

Osteocytes are bone cells. Collagen fibers and calcium salts are found in abundance between and among the osteocytes. The collagen and calcium salts are

A) deposited by the circulatory system and are not associated with the osteocytes.
B) extensions of the endoplasmic reticulum.
C) part of the extracellular matrix.
D) components of the plasma membrane of osteocytes.

Answer 3

C

Question 4

Plasmodesmata in plant cells are most similar in function to which of the following structures in animal cells?

A) extracellular matrix
B) tight junctions
C) gap junctions
D) desmosomes
E) peroxisomes

Question 5

All of the following can be proteins found in the extracellular matrix of animal cells EXCEPT

A) collagen.
B) fibrillin.
C) fibronectin.
D) actin.

Question 6

Which component is a protein fibre of the extracellular matrix?

A) A
B) B
C) C
D) D
E) E

Question 7

What is a major difference in the extracellular matrix ECM) between plant and animal cells?

A) Plant ECM components are released extracellularly by the Golgi stacks, whereas lysosomes function in this capacity in animal cells.
B) Plant ECM is primarily carbohydrate in nature, whereas animal ECM is largely protein based.
C) Plant ECM is composed primarily of proteins, whereas animal ECM is mainly carbohydrates.
D) Plant and animal ECMs are quite similar in structure and function.

Question 8

Tight junctions are cell- cell junctions found between adjacent cells of the epithelium that lines the small intestine. What is the function of these cellular junctions?

A) to attach epithelial cells to a basement membrane
B) to recognize pathogenic organisms present in the lumen of the small intestine
C) to seal the epithelium and prevent movement of substances between cells
D) to release digestive enzymes into the intestinal lumen

Question 9

Integrins are integral membrane proteins. They are often attached to

A) glycogen molecules and other cellular inclusions.
B) pathogens.
C) membranes of intracellular organelles.
D) cytoskeletal proteins and molecules of the extracellular matrix.

Question 10

H. V. Wilson worked with sponges to gain some insight into exactly what was responsible for holding adjacent cells together. He exposed two species of differently pigmented sponges to a chemical that disrupted the
Cell- cell interaction. The cells of the sponges dissociated. Wilson mixed the cells of the two species and removed the chemical that caused the cells to dissociate. Wilson found the sponges reassembled into two separate species. The cells from one species did not interact or form associations with the cells of the other species. How do you explain the results of Wilson's experiments?

A) The disassembled cells formed bonds with any of the cells in the mixture. However, once the organism was completely assembled, an enzyme changed all cells to the same pigment.
B) The molecules responsible for cell- cell adhesion were different in the two different species of sponge.
C) There are enzymes involved in the assembly of the sponge organism, and the two different species had two different enzymes functioning in reassembly.
D) One cell functions as the nucleus for each organism, attracting only cells of the same pigment.

Question 11

Scientists have found that extracellular matrix components may induce specific gene expression in embryonic tissues such as the liver and testis. For this to happen, there must be direct communication between the extracellular matrix and the developing cells. Which kind of transmembrane protein would most likely be involved in this kind of induction?

A) actins
B) integrins
C) fibronectins
D) collagens

Question 12

Why are receptors for steroid hormones located inside the cell rather than on the membrane surface?

A) Cells with steroid hormone receptors inside the cell are not able to respond to steroid hormones.
B) The receptors are repressible, meaning they are actively altering cell function unless the target hormone is present.
C) Steroid hormones are lipid soluble and thus can readily diffuse through the lipid bilayer that makes up the cell membrane.
D) The receptors can be stimulated to exit to the membrane surface under conditions in which a cell needs to be regulated by the steroid hormone.

Question 13

Where would you expect to find tight junctions?

A) in the plasma membrane of prokaryotes
B) in the epithelium of an animal's stomach
C) in the lysosome membrane
D) between plant cells in a woody plant
E) between the smooth endoplasmic reticulum and the rough endoplasmic reticulum

Question 14

Signals from the extracellular matrix to the cytoskeleton may be transmitted by

A) integrins.
B) collagen.
C) fibronectin.
D) proteoglycans.
E) middle lamella.

Question 15

What is the function of the middle lamella in plant cells?

A) for gas and nutrient exchange between adjacent cells
B) to keep the cell walls of adjacent cells from dehydrating
C) to maintain the plant circulatory system
D) adhesion of adjacent cells

Question 16

One characteristic of life and living systems is that they are able to adapt. Toward this end, cells interact with other cells and their environment through the action of their

A) Golgi apparatus.
B) intracellular electrical currents.
C) microtubular tracks.
D) plasma membrane and extracellular matrix.

Question 17

For a tissue or an organ to function as a unit,

A) the cells within the tissue or organ must be able to depolarize to create cell signals.
B) there must be a signal molecule to which all cells in the tissue or organ can respond.
C) the tissue or organ must be composed of all of the same type of cells.
D) there must be cell- cell communication among the cells within a tissue or organ.

Question 18

Anorganic bone matrix ABM) is a material commonly used in bone grafts. Scientists compared ABM with ABM- peptide. The peptide that was bound to ABM was 15 amino acids long, derived from the extracellular matrix molecule, collagen. The researchers found that anchorage- dependent cells were more likely to adhere to and grow on the ABM- peptide than on ABM alone. What conclusion might be drawn from this research?

A) The peptide would have no effect on the success of the bone graft.
B) Attaching the peptide to ABM enhances the likelihood of success of the bone graft.
C) Anorganic bone matrix is not an effective material for use in bone grafts.
D) The immune system is more likely to reject the ABM- peptide than the ABM.

Question 19

What do the cell walls of plants and the extracellular matrix of animal cells have in common?

A) They are largely composed of phospholipids and glycoproteins.
B) They limit the passage of small molecules.
C) Their proteins are made by free cytoplasmic ribosomes.
D) They form rigid structures that provide structural support for cells but limit their expansion.
E) They have functional connections with the cytoskeleton inside the cell.

Question 20

Which of the following would not be found in a plant cell?

A) lignin
B) microfibrils
C) pectin
D) polysaccharides
E) collagen

Question 21

Which of the following statements about quorum sensing is FALSE? Quorum sensing

A) occurs only when cell numbers reach a threshold.
B) may result in biofilm formation.
C) is cell-cell communication only found in eukaryotes.
D) is species specific.
E) is particularly well studied because of its medical importance.

Question 22

What does it mean to say that a signal is transduced?

A) The physical form of the signal changes from one form to another.
B) The signal triggers a sequence of phosphorylation events inside the cell.
C) The signal is amplified, such that even a single molecule evokes a large response.
D) The signal enters the cell directly and binds to a receptor inside.
E) The signal molecule passes through the cell membrane.

Question 23

Steroid hormones bind to receptors inside the cell and alter their conformation. The hormone- receptor complex is then transported into the nucleus, where it can directly affect gene expression. To get from the location where the receptor binds the hormone to its site of action, the receptor- hormone complex must

A) enter the smooth endoplasmic reticulum.
B) become water soluble by binding to a carrier molecule.
C) be transported through the nuclear pore complex.
D) undergo another conformational change.

Question 24

Second messengers

A) are intracellular non- protein signalling molecules.
B) are intracellular kinases which lead to a cellular response.
C) can synthesize cAMP from AMP and ADP.
D) are signalling molecules which bind directly to the G- protein coupled receptor.

Question 25

Acetylcholine is a neurotransmitter that binds to receptors on skeletal muscle cells. The receptor- signal complex brings about a series of events that result in contraction of skeletal muscle. Venom from black widow spiders causes an explosive release of acetylcholine. What would that do to its victims?

A) Muscles would be unable to relax.
B) Cell receptors would no longer be able to bind regulatory hormones.
C) G- protein receptors would all be inactivated.
D) Muscles would be unable to contract.

Question 26

Pemphigus vulgaris is an autoimmune disorder in which antibodies are produced against the cadherins of desmosomes. The blistering seen in these individuals is probably a result of

A) loss of cell- cell adhesion.
B) inadequate production of cytoskeletal proteins.
C) a decrease in flexibility of the cell membrane.
D) inadequate numbers of G- protein receptors.

Question 27

The fact that a single signal- receptor complex results in the activation of several second messenger molecules enables the cell signal to be

A) terminated.
B) altered.
C) amplified.
D) reflected.

Question 28

Cells of capillaries that nourish the cells of the central nervous system are joined by tight junctions, whereas the capillaries to most other organs are characterized by having large openings or clefts between adjacent cells. How would the difference in cell- cell connections affect their functions?

A) There is more pressure on the blood passing through the central nervous system than to other organs.
B) The blood-brain barrier is more selective regarding the types of molecules that can pass out of circulation.
C) Capillaries of the blood-brain barrier are more likely to rupture.
D) Capillaries of the central nervous system are more tightly anchored to adjacent tissues.

Question 29

Blood sugar is regulated by two pancreatic hormones, namely insulin and glucagon. When blood sugar rises, insulin is released; it binds to receptors and, through signal transduction, results in an increase in glucose uptake by cells, effectively lowering blood glucose. When blood sugar decreases, glucagon is released, binds to cell receptors, and causes glucose to be released into circulation. Diabetes mellitus is a disorder that results from excessively high levels of blood glucose. Type II diabetics have normal to elevated levels of insulin. What, then, might be causing the elevated blood glucose levels?

A) defective receptors
B) inadequate insulin production
C) defective second messenger
D) inability to regulate gene expression

Question 30

Intercalated disks are cell- cell junctions found between cardiac muscle cells. A feature of intercalated disks is a large number of gap junctions. This means

A) an extension of smooth endoplasmic reticulum goes through the gap junction, making it continuous from one cardiac muscle cell to the next.
B) water and small ions can readily pass from one cardiac muscle cell to the next.
C) RNA from one cardiac muscle cell can be transported into an adjacent cell through the gap junction.
D) the plasma membrane encompasses multiple cardiac muscle cells.

Question 31

A kinase is an enzyme that

A) serves as a receptor for various signal molecules.
B) adds a phosphate group to target molecules.
C) produces second messenger molecules.
D) functions as a second messenger molecule.

Question 32

Hormones function as

A) signal molecules.
B) cell receptors.
C) second messengers.
D) neurotransmitters.

Question 33

Hormones are chemical substances produced in one organ that are released into the bloodstream and affect the function of a target organ. For the target organ to respond to a particular hormone, it must

A) be from the same cell type as the organ that produced the hormone.
B) have receptors that recognize and bind the hormone molecule.
C) have the same genetic makeup.
D) be experiencing a disruption in homeostasis.

Question 34

Pseudomonas aeruginosa is a bacterium that can settle on human lung cells. P. aeruginosa can secrete a signalling molecule that recruits other P. aeruginosa cells. The result of this secretion is the formation of a

A) slime layer.
B) biofilm.
C) capsule.

Question 35

Plasmodesmata are cell- cell junctions that can be found between

A) cells of connective tissue in animals.
B) skeletal muscle cells.
C) plant cells.
D) none of the above.

Question 36

Insulin is a hormone produced by the pancreas. When insulin binds to its receptor, which of the following will occur?

A) The G- protein will become active when GTP is replaced by GDP.
B) A receptor tyrosine kinase will change its conformation i.e. form a dimer) thereby allowing phosphorylation to occur.
C) A G- protein will change its conformation to the "on" position thereby allowing the effector to be activated.
D) A receptor tyrosine kinase will dissociate into two monomers thereby allowing phosphorylation to occur.

Question 37

Which of the following best describes the function of gap junctions?

A) They occur when peripheral membrane proteins from neighboring cells line up thereby permitting the exchange of water, small ions, and small molecules.
B) They are second messengers that activate protein kinases. The protein kinases then activate or deactivate other proteins.
C) They are intracellular receptors, which associate with signals entering the cell, and often regulate transcriptional processes.
D) They create direct connections between the cytoplasm of adjacent animal cells thereby permitting the exchange of water, small ions, and small molecules.

Question 38

A G- protein receptor with GTP bound to it

A) directly affects gene expression.
B) autophosphorylates its tyrosine residues.
C) will use cGMP as a second messenger.
D) is in its active state.