AP BIO - Unit 4 AP Classroom

Which statement best predicts why a cell's progression through the cell cycle might be halted at the G1/S checkpoint?

There are not enough nucleotides available to construct new DNA.

The tumor suppressor protein p53 binds to DNA and activates target genes, which results in the synthesis of p21, CD95, and other proteins. The p21 protein promotes cell-cycle arrest, whereas the CD95 protein promotes apoptosis. Which of the following will most likely result from a loss of p53 function?

Uncontrolled cell proliferation

Metformin is a drug used to treat type 2 diabetes by decreasing glucose production in the liver. AMPAMP-activated protein kinase (AMPK)(AMPK) is a major cellular regulator of glucose metabolism. Metformin activates AMPKAMPK in liver cells but cannot cross the plasma membrane. By blocking AMPKAMPK with an inhibitor, researchers found that AMPKAMPK 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 ligand that activates the signal transduction pathway of the activation of AMPKAMPK.

GG 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 GG protein, the GG protein is activated. The GG protein then activates an enzyme that produces a second messenger called cAMPcAMP. Which of the following describes a critical role of cAMPcAMP during the transduction stage of a GG protein signal transduction pathway?

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

Researchers have discovered details about apoptosis (programmed cell death) by studying 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−9ced−9 and ced−3ced−3 . The ced−3ced−3 gene was found to promote cell death, and ced−9ced−9 to inhibit it. The ced−9ced−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−9ced−9 in C. elegans can affect regulation of apoptosis in the cell?

An experiment showed that a mutation in the ced−9ced−9 gene led to excessive cell death in C. elegans.

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 the 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?

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.

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?

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

Blood clots are formed by a positive feedback loop. Two pathways exist, the extrinsic and intrinsic pathways, which converge during clot formation. There are many clotting factors involved, most of which are proteins. Vitamin K is required for the formation of the active form of several of the clotting factors, including Factor X. A simplified model of the blood clotting process is shown in Figure 1. Warfarin is a drug used to treat certain blood clots. Warfarin blocks the formation of the active form of vitamin K-dependent clotting factors. Based on the model, which of the following best predicts the effects of warfarin on a patient?

Factor X will not be activated, which will prevent thrombin from forming.

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 SRYSRY 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 SRYSRY gene is absent or nonfunctional, the embryo will exhibit female sexual development.

A person's blood glucose level fluctuates during the day, as represented in Figure 1. Two hormones, insulin and glucagon, are directly involved in regulating the blood glucose level to maintain a healthy level. Insulin acts to lower the blood glucose level, and glucagon acts to increase the blood glucose level. Figure 1. Blood glucose fluctuations of an individual Which of the following best predicts what will happen to the blood glucose level if the person has another meal at 5 p.m.?

Immediately after the meal, the blood glucose level will increase, and then insulin will be secreted to counter the increase.

The epidermal growth factor receptor EGFR is a cell surface receptor. When a growth factor binds to EGFR, the receptor is activated. The activated EGFR triggers a signal transduction pathway, which leads to increased frequency of cell division. Which of the following best predicts the effect of a mutation that causes EGFR to be active in the absence of a growth factor?

Increased cell division will lead to the formation of a tumor

Phosphofructokinase (PFK) is a key enzyme in glycolysis. ATP is one of the two substrates for the reaction catalyzed by PFK. ATP is also an allosteric regulator of PFK. Figure 1 shows the enzyme-substrate interactions of PFK. Figure 1. The enzyme-substrate interactions of PFK A researcher found a mutation that resulted in the PFK enzyme being unable to bind ATP to the allosteric site. Which of the following best predicts the effect of the mutation?

Negative feedback regulation does not occur, so the enzyme will be active when glycolysis is not needed.

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

Fibroblast growth factor receptors (FGFRs) are transmembrane proteins that regulate cellular processes such as cell proliferation and differentiation. The extracellular domains of FGFR proteins bind specifically to signaling molecules called fibroblast growth factors. The intracellular domains of FGFR proteins function as protein kinases, enzymes that transfer phosphate groups from ATP to protein substrates. FGFR activation occurs when binding by fibroblast growth factors causes FGFR proteins in the plasma membrane to become closely associated with each other. The association of two FGFR proteins stimulates protein kinase activity, which triggers the activation of intracellular signaling pathways. A simplified model of FGFR activation is represented in Figure 1. Figure 1. A simplified model of FGFR activation Which of the following changes in the FGFR signaling pathway is most likely to result in uncontrolled cell proliferation?

The irreversible association of FGFRFGFR proteins

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

The ligand binds to the receptor

Figure 1. A simplified model of the signal transduction cascade triggered by epinephrine binding to the beta-2 adrenergic receptor Which of the following outcomes will most likely result from the inactivation of the beta-2 adrenergic receptor?

The rate of glycogen synthesis in the cell will increase.

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 GLUT4GLUT4, 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. Figure 1. A simplified model of the insulin receptor-signaling pathway Which of the following statements best predicts the effect of a loss of function of the insulin receptor's intracellular domain?

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

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