Unit 4 - Cell Communication and Cell Cycle

An antigen can induce an immune response in a host organism. Antigens are targeted by antibodies that are produced by the organism’s immune system in response to contact with the antigen. Antibodies are specific to antigens. Many different cell types are involved in immune responses.

Which of the following best describes the role of cell-to-cell communication during a response to an invasion of antigens?

• A macrophage cell engulfs a pathogen in the blood.

• Chemicals that are secreted from antigen-presenting cells then activate helper T cells.

• Antigens attaching to receptors on memory B cells stimulate the memory B cells to become plasma cells.

• Antigen-presenting cells engulf antigens at the first exposure.

Adjacent plant cells have narrow channels called plasmodesmata that pass through the cell walls of the connected cells and allow a cytoplasmic connection between the cells.

Which of the following statements best describes a primary function of plasmodesmata?

• They increase the surface area available for attachment of ribosomes and thus increase protein synthesis.

• They prevent the cell membrane from pulling away from the cell wall during periods of drought.

• They eliminate the need to produce signaling molecules and eliminate the need for cells to have receptors for signaling molecules.

• They allow the movement of molecules from one cell to another, enabling communication between cells.

A hydrophilic peptide hormone is produced in the anterior pituitary gland located at the base of the brain. The hormone targets specific cells in many parts of the body.

Which of the following best explains a possible mechanism that would enable the hormone to efficiently reach all of the target cells in the body?

• The hormone interacts with the nerves at the base of the brain and directs signals to the target cells through the nervous system

• The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.

• The hormone diffuses into target cells adjacent to the anterior pituitary gland, where the hormone is degraded.

• The hormone moves through cytoplasmic connections between cells until it has reached all cells with the correct intracellular binding sites.

G proteins are a family of receptor proteins that are involved in transmitting signals from outside a cell to inside a cell. When a signaling molecule binds to a G

protein, the G protein is activated. The G

protein then activates an enzyme that produces a second messenger called cAMP.

Which of the following describes a critical role of cAMP during the transduction stage of a G protein signal transduction pathway?

• cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.

• cAMP modifies a specific monomer so that it can be added to an elongating structural macromolecule.

• cAMP binds the extracellular signal molecule and carries it to the intracellular target specified by the signal.

• cAMP carries the signal to the nucleus of the cell and results in new sequences of nucleotides being added to the cell’s DNA

  DNA.

Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. AMP

-activated protein kinase (AMPK)

is a major cellular regulator of glucose metabolism. Metformin activates AMPK

in liver cells but cannot cross the plasma membrane. By blocking AMPK

with an inhibitor, researchers found that AMPK

activation is required for metformin to produce an inhibitory effect on glucose production by liver cells.

Which of the following best describes the component that metformin represents in a signal transduction pathway that regulates glucose production in the liver?

• It is a secondary messenger that amplifies a signal through a cascade reaction.

• It is an allosteric regulator that binds to a crucial section of the DNA that makes the enzymes needed for glucose uptake.

• It is a ligand that activates the signal transduction pathway of the activation of AMPK

  AMPK.

• It is a competitive inhibitor that binds to glucose and prevents it from entering the cell.

Which of the following steps in a signaling pathway typically occurs first once a chemical messenger reaches a target cell?

• A second messenger molecule is produced.

• A ligand binds to a receptor.

• Specific genes are activated.

• Specific proteins are synthesized.

During a fight-or-flight response, epinephrine is released into the body’s circulatory system and transported throughout the body. Some cells exhibit a response to epinephrine while other cells do not.

Which of the following justifies the claim that differences in components of cell signaling pathways explain the different responses to epinephrine?

• D

  Cell signaling requires reception, transduction, and response. All cells can receive epinephrine, all cells respond with a pathway, but only select cells have the proper coding in their DNA to respond.

• Cell signaling depends on the signal being able to diffuse through the cell membrane. Epinephrine is incapable of diffusing through some plasma membranes because of the membrane’s phospholipid composition.

• Cell signaling depends on the transduction of a received signal by the nervous system. Not all cells are close enough to a synapse to receive the signal and respond.

• Cell signaling depends on the ability to detect a signal molecule. Not all cells have receptors for epinephrine. Only cells with such receptors are capable of responding.

Signal transduction may result in changes in gene expression and cell function, which may alter phenotype in an embryo. An example is the expression of the SRY gene, which triggers the male sexual development pathway in mammals. This gene is found on the Y chromosome.

Which statement provides the evidence to justify the claim that signal transduction may result in an altered phenotype?

• If the SRY gene is absent or nonfunctional, the embryo will exhibit male sexual development.

• An embryo with a male sex chromosome will always exhibit male sexual development.

• If the SRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.

• An embryo with two male sex chromosomes will always exhibit male sexual development.

Researchers have discovered details about apoptosis (programmed cell death) by studying the embryologic development of a nematode worm, Caenorhabditis elegans. Apoptosis is a normal developmental process in C. elegans. They found several genes involved in apoptosis, including ced−9

and ced−3. The ced−3 gene was found to promote cell death, and ced−9 to inhibit it. The ced−9 gene serves as a regulator that prevents apoptosis in the absence of a signal promoting apoptosis.

Which of the following statements best justifies the claim that changes in the expression of ced−9 in C. elegans can affect regulation of apoptosis in the cell?

• An experiment showed that a mutation in the

  ced−9 gene led to excessive cell death in C. elegans.

• An experiment showed that the ced−9 gene normally produces a protein that promotes excessive cell death in C. elegans.

• A mutation in ced−3 will cause ced−9 to be incorrectly transcribed.

• Apoptosis is dependent on a signal from the ced−9

  ced−9 gene in C. elegans.

The insulin receptor is a transmembrane protein that plays a role in the regulation of glucose homeostasis. The receptor’s extracellular domain binds specifically to the peptide hormone insulin. The receptor’s intracellular domain interacts with cellular factors. The binding of insulin to the receptor stimulates a signal transduction pathway that results in the subcellular translocation of GLUT4, a glucose transport protein that is stored in vesicles inside the cell. A simplified model of the insulin receptor–signaling pathway is shown in Figure 1.

Which of the following statements best predicts the effect of a loss of function of the insulin receptor’s intracellular domain?

• The stimulation of the signal transduction pathway will increase.

• The storage of GLUT4 in vesicles inside the cell will increase.

• The number of GLUT4 molecules in the plasma membrane will increase.

• The concentration of glucose inside the cell will increase.