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. Which protein is an antiporter?  

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?  

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 protein transports Ca2+ from the intracellular fluid into the organelle?

A region of a protein consists of amino acids with polar R groups. A researcher needs to design a drug that can interact with these amino acids. Which type of R group would interact least strongly with amino acids that have polar R groups? 

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. When the concentration of cortisol increase after waking, a molecule of RNA polymerase is _______ to be bound to the promoter of the BGLAP gene.

An organism must regulate the concentration of solutes in its body fluids, called osmolarity. An extreme change in osmolarity will alter the diffusion of water through cell membranes, potentially disrupting the functions of cells.  In a healthy human, a homeostatic system ensures that the osmolarity of blood stays within a certain range. When the osmolarity increases, nerve cells in the hypothalamus detect the diffusion of water through channel proteins in their membranes (osmosis). These channels activate a signaling pathway that causes a nerve cell to secrete a hormone called vasopressin. A molecule of vasopressin can bind to receptors in the membranes of kidney cells, causing the kidneys to excrete less water as urine. Over time, the osmolarity of blood returns back to its expected range.  Alcohol inhibits the release of vasopressin by nerve cells. Typically, a person who has not consumed alcohol has a concentration of vasopressin between 0.5 pg ml-1 and 2 pg ml-1, but a person who has ingested alcohol has a much lower concentration of vasopressin.  The figure shows a path model of the homeostatic system that regulates the osmolarity of blood. This model also describes the effect of alcohol on the concentration of vasopressin in blood. 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 value above each arrow indicates the slope of the linear relationship between the variables connected by the arrow.  If the concentration of alcohol in the blood was 22 mmol L-1, how would the rate at which the kidneys excrete water change? The rate would ______.

An enzyme called phosphofructokinase binds a substrate called fructose-6-phosphate (F6P) and catalyzes a reaction to form a product. The activity of this enzyme depends on the presence of a molecule called adenosine triphosphate, or ATP.  The figure shows the relationship between the concentration of F6P and the activity of enzymes, in either the presence or absence of ATP. The activity of enzymes was measured as the rate at which products were formed (also called the rate of reaction). Which statement could explain the effect of ATP on the activity of this enzyme?

The top figure shows a path model of the homeostatic system that regulates the osmolarity of blood. This regulated variable is represented by a dashed box. Other variables are represented by solid black boxes. An arrow connecting one box to another indicates a relationship between two variables. The sign above an arrow (+ or -) indicates whether the variables are related positively or negatively.  The bottom figure is a set of plots. Which plot above shows the relationship between the volume of water ingested by a person (independent variable) and the osmolarity of blood (dependent variable)?

The figure shows a cell membrane with three different transport proteins (labeled A, B and C).  The type of transport (active vs. passive) is labeled above each protein. Given the functions of protein A and protein B, predict whether protein C is an ATPase engaged in active transport or a channel engaged in facilitated diffusion.  

Complete the following sentence: A _____ is a set of chemical instructions for producing a specific type of peptide.