Question

antigens are foreign proteins, typically from pathogens, that can induce an immune response in a host organism. antigens are targeted by antibodies that are produced by the organisms immune system in response to contact with the antigen. antibodies are specific to antigens. many different cell types are involved in immune responses. (***note: this question is bad)

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

(a) chemicals that are secreted from antigen - presenting cells then activate helper t cells.
(b) a macrophage cell engulfs a pathogen in the blood.
(c) antigens attaching to receptors on memory b cells stimulate the memory b cells to become plasma cells.
(d) antigen - presenting cells engulf antigens at the first exposure.

1. 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?

(a) they allow the movement of molecules from one cell to another, enabling communication between cells.
(b) they prevent the cell membrane from pulling away from the cell wall during periods of drought.
(c) they eliminate the need to produce signaling molecules and eliminate the need for cells to have receptors for signaling molecules.
(d) they increase the surface area available for attachment of ribosomes and thus increase protein synthesis.

1. 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?

(a) the hormone interacts with the nerves at the base of the brain and directs signals to the target cells through the nervous system.
(b) the hormone diffuses into target cells adjacent to the anterior pituitary gland, where the hormone is degraded.
(c) the hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.
(d) 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.

1. which of the following describes a critical role of camp during the transduction stage of a g protein signal transduction pathway?

(a) camp carries the signal to the nucleus of the cell and results in new sequences of nucleotides being added to the cells dna.
(b) camp binds the extracellular signal molecule and carries it to the intracellular target specified by the signal.
(c) camp modifies a specific monomer so that it can be added to an elongating structural macromolecule.
(d) camp results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.
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 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.

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

(a) it is a secondary messenger that amplifies a signal through a cascade reaction.
(b) it is a ligand that activates the signal transduction pathway of the activation of ampk.
(c) it is an allosteric regulator that binds to a crucial section of the dna that makes the enzymes needed for glucose uptake.
(d) it is a competitive inhibitor that binds to glucose and prevents it from entering the cell.

Answer:

1. Answer:

• A. Chemicals that are secreted from antigen - presenting cells then activate helper T cells.
• Explanation:
• Cell - to - cell communication in an immune response. Antigen - presenting cells (like dendritic cells) secrete cytokines (chemicals) that communicate with helper T cells.
• Option B is phagocytosis (a macrophage engulfing a pathogen) which is not cell - to - cell communication in the context of signaling between different cell types for an immune response.
• Option C is about antigen - antibody interaction on B cells, not cell - to - cell communication in the broader sense of different cell types communicating.
• Option D is about antigen - presenting cells engulfing antigens (phagocytosis - like process) not cell - to - cell communication.

1. Answer:

• A. They allow the movement of molecules from one cell to another, enabling communication between cells.
• Explanation:
• Plasmodesmata are channels that connect plant cells. Their main function is to allow for the passage of small molecules (such as signaling molecules, nutrients) between cells, which is a form of cell - to - cell communication.
• Option B is incorrect as plasmodesmata are not related to preventing the cell membrane from pulling away during drought.
• Option C is wrong because cells still produce signaling molecules and have receptors, plasmodesmata just provide an additional communication route.
• Option D is incorrect as ribosomes are attached to the endoplasmic reticulum (in rough ER) and plasmodesmata are not related to ribosome attachment.

1. Answer:

• C. The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.
• Explanation:
• Hydrophilic peptide hormones (like many pituitary hormones) are released into the bloodstream. The bloodstream is a common transport medium for hormones to reach target cells throughout the body.
• Option A is incorrect because hydrophilic peptide hormones do not interact with the nervous system in this way to reach all target cells.
• Option B only describes local action (diffusing to adjacent cells) which is not how a hormone reaches cells in many parts of the body.
• Option D is incorrect as cytoplasmic connections (like plasmodesmata in plants) are not a major way for hormones in the body (in animals) to reach target cells.

1. Answer:

• D. cAMP results in the activation of an enzyme that amplifies the signal by acting on many substrate molecules.
• Explanation:
• In G - protein signaling, cAMP (a second messenger) activates protein kinase A. Protein kinase A can phosphorylate (and thus activate or inactivate) many target proteins (substrate molecules), amplifying the initial signal.
• Option A is incorrect as cAMP does not directly carry the signal to the nucleus to add nucleotides to DNA.
• Option B is wrong because cAMP does not bind the extracellular signal molecule (the ligand binds the G - protein - coupled receptor).
• Option C is incorrect as cAMP does not modify a monomer for addition to a structural macromolecule in the context of signal transduction.

1. Answer:

• B. It is a ligand that activates the signal transduction pathway of the activation of AMPK.
• Explanation:
• Metformin activates AMPK (a cellular regulator). Since it cannot cross the plasma membrane (as stated), it likely binds to a receptor (acts as a ligand) on the cell surface to activate the AMPK signal transduction pathway.
• Option A is incorrect as metformin is not a secondary messenger (secondary messengers like cAMP are produced inside the cell in response to a ligand).
• Option C is wrong as there is no indication that metformin binds to DNA.
• Option D is incorrect as metformin is used to decrease glucose production, not to prevent glucose from entering the cell (and there is no mention of it binding to glucose).