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Cortisol is a signaling molecule that regulates gene expression in the cells of a mammal.  Cortisol enters a cell and binds to a protein called a cortisol receptor. Binding of cortisol facilitates the phosphorylation of the cortisol receptor, which then can enter the nucleus and affect transcription.  The figure below shows a system of two genes whose transcription is regulated by cortisol. The IL10 gene codes for a protein called interleukin 10. The BGLAP gene codes for a protein called osteocalcin. A cortisol receptor can activate or repress the transcription of a gene by binding to a regulatory element. For example, a cortisol receptor activates transcription of the IL10 gene but represses transcription of the BGLAP gene.   When a person experiences stress, their adrenal gland releases cortisol, increasing the concentration of cortisol throughout the body. As a person sleeps, the concentration of cortisol in their blood decreases to nearly zero. After waking, the concentration of cortisol increases by four to seven times the concentration during sleep.   Complete the following sentence. During sleep, a cortisol receptor is _______ to be bound to the regulatory element of the IL10 gene.

The figure shows the movements of hydrogen ions (H+), potassium ions (K+), sucrose molecules, and calcium ions (Ca2+) through a cell membrane. The relative concentrations of each ion (high or low) are provided. From left to right, the proteins are labeled A, B, C and D. What type of protein is protein A?  

Thyroxine (T4) is a hormone that certain animals use to regulate the activity of cells. The production of T4 depends on the concentrations of two other hormones: thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH).  TRH comes from a part of the brain called the hypothalamus. This hormone can bind to receptors in another part of the brain, called the pituitary gland. Upon binding to a receptor, TRH activates a signaling pathway that causes a cell to release TSH.  The figure shows the signaling pathway that controls the production of T4. TSH binds to receptors in the thyroid gland, causing cells of this gland to produce T4. The production of T4 depends on an enzyme called thyroid peroxidase (TPO), which creates T4 by adding an iodide ion (I-) to a molecule.  A nonpolar structure enables T4 to diffuse through the phospholipid bilayer of any cell, including cells of the hypothalamus and the pituitary gland, where T4 inhibits the release of TRH and TSH, respectively. Choose the word or phrase that accurately completes the following sentence. If the concentration of iodide ions (I-) in the thyroid gland decreases, the concentration of T4 in a cell of the thyroid gland would ______.

Muscle cells require calcium ions (Ca2+) to contract. When the concentration of calcium in the intracellular fluid decreases, a muscle cell relaxes. When the concentration of calcium in the cytoplasm increases, a muscle cell contracts.  To prevent unwanted contraction, a muscle cell stores most of its Ca2+ in a specialized compartment within the cell, called an organelle. An organelle has its own membrane, similar in structure to the membrane that surrounds the cell. The concentration of Ca2+ in the intracellular fluid depends on the activity of transport proteins in the cell’s membrane and organelle’s membrane.  The figures show a system of transport proteins that regulate the movement of Ca2+ in a cell. The top figure illustrates the function of the transport proteins in this system. The lower left-hand portion of the bottom figure shows a muscle cell as the concentration of calcium in the intracellular fluid decreases, leading to relaxation. The lower right-hand portion of the bottom figure shows a muscle cell as the concentration of calcium in the intracellular fluid increases, leading to contraction. Which word or phrase accurately completes the following sentence? If the concentration of sodium ions (Na+) outside of a muscle cell increases, the rate at which calcium ions (Ca2+) are transported out of this cell would _______.

The figure shows a homeostatic system with four components labeled A, B, C, and “regulated variable.” What is the target value of a regulated variable?

Thyroxine (T4) is a hormone that certain animals use to regulate the activity of cells. The production of T4 depends on the concentrations of two other hormones: thyrotropin releasing hormone (TRH) and thyroid stimulating hormone (TSH).  TRH comes from a part of the brain called the hypothalamus. This hormone can bind to receptors in another part of the brain, called the pituitary gland. Upon binding to a receptor, TRH activates a signaling pathway that causes a cell to release TSH.  The figure shows the signaling pathway that controls the production of T4. TSH binds to receptors in the thyroid gland, causing cells of this gland to produce T4. The production of T4 depends on an enzyme called thyroid peroxidase (TPO), which creates T4 by adding an iodide ion (I-) to a molecule.  A nonpolar structure enables T4 to diffuse through the phospholipid bilayer of any cell, including cells of the hypothalamus and the pituitary gland, where T4 inhibits the release of TRH and TSH, respectively. About 1 in 200 people have a genetic condition called Graves’ disease. A person with this condition produces an excess of proteins that bind to TSH receptors, activating more of these receptors than usual. The next figure shows four hypothetical relationships between the number of TSH receptors activated by proteins and the concentration of T4 in a cell, labeled A through D. Which relationship accurately describes the expected relationship in a patient with Graves’ disease?

Plants use a homeostatic system to regulate the osmolarity of the fluid in xylem. As the osmolarity of this fluid increases, the cells of the roots produce proteins that transport solutes through the cell membrane. These proteins actively transport solutes from the roots into the soil, decreasing the osmolarity of the cells. As the osmolarity of root cells decreases, water moves from these cells into the xylem via osmosis, decreasing the osmolarity of the fluid in the xylem. The top figure shows a set of linear relationships among three variables involved in regulating the osmolarity of fluid in the xylem. The bottom figure shows four path models, labeled A through D, that represent possible homeostatic systems that regulate the osmolarity of fluid in the xylem. The regulated variable is represented by a dashed box. Other variables are represented by a solid black box. An arrow connecting one box to another indicates a relationship between two variables. The sign above an arrow (+ or -) indicates whether the variables are positively or negatively related.  Which path model accurately describes the relationships among the three variables?

The figure shows the movements of hydrogen ions (H+), potassium ions (K+), sucrose molecules, and calcium ions (Ca2+) through a cell membrane. The relative concentrations of each ion (high or low) are provided. From left to right, the proteins are labeled A, B, C and D. What type of membrane protein is protein A?  

The figure shows a signaling pathway for a signaling molecule called insulin, which binds to an insulin receptor. In the figure, phosphorylation of a protein by a kinase is represented by a “P” in a yellow circle. True or false? Upon binding insulin, an insulin receptor can directly phosphorylate a molecule of IRS. 

A cell responds to two types of signaling molecules. Estrogen is a signaling molecule that binds to an intracellular receptor known as an estrogen receptor (ER), ultimately causing gene expression. Insulin-like growth factor 1 (IGF-1) is a signaling molecule that binds to a membrane receptor (IGF-1R). Upon binding to IGF-1R, a molecule of IGF-1 activates a signaling pathway that can phosphorylate ER, enhancing the rate of gene expression caused by estrogen alone. The top figure shows the integration of the two signaling pathways. The bottom figure shows the rates of gene expression in a cell under four conditions, labeled 1 through 4.   In which condition was the cell most likely to be exposed to neither estrogen nor IGF-1?