Mastering Bio #1
Choose the organelle on the left that best matches the activity on the right. Drag the terms on the left to the appropriate blanks on the right to complete the sentences.
- N-linked glycosylation =rough endoplasmic reticulum - cytochrome P-450 = smooth endoplasmic reticulum - turgor pressure = plant vacuole - drug detoxification = smooth endoplasmic reticulum - acid hydrolases = lysosome - catalase = peroxisomes - glycosyl transferases = Golgi
Because ions carry a charge (positive or negative), their transport across a membrane is governed not only by concentration gradients across the membrane but also by differences in charge across the membrane (also referred to as membrane potential). Together, the concentration (chemical) gradient and the charge difference (electrical gradient) across the plasma membrane make up the electrochemical gradient. Consider the plasma membrane of an animal cell that contains a sodium-potassium pump as well as two non-gated (always open) ion channels: a Na+ channel and a K+ channel. The effect of the sodium-potassium pump on the concentrations of Na+ and K+ as well as the distribution of charge across the plasma membrane is indicated in the figure. Which of the following statements correctly describe(s) the driving forces for diffusion of Na+ and K+ ions through their respective channels? Select all that apply.
- The diffusion of Na+ ions into the cell is facilitated by the Na+ concentration gradient across the plasma membrane. -The diffusion of K+ ions out of the cell is impeded by the electrical gradient across the plasma membrane. -The electrochemical gradient is larger for Na+ than for K+. explanation: - The concentration gradient of Na+ ions across the membrane (higher Na+ concentration outside) facilitates the diffusion of Na+ into the cell. At the same time, the electrical gradient across the membrane (excess positive charge outside) drives Na+ into the cell. - The concentration gradient of K+ ions across the membrane (higher K+ concentration inside) facilitates the diffusion of K+ out of the cell. However, the electrical gradient across the membrane (excess positive charge outside) impedes the diffusion of K+ out of the cell. - The electrochemical gradient for an ion is the sum of the concentration (chemical) gradient and the electrical gradient (charge difference) across the membrane. For Na+ ions, diffusion through the Na+ channel is driven by both the concentration gradient and the electrical gradient. But for K+ ions, the electrical gradient opposes the concentration gradient. Therefore, the electrochemical gradient for Na+ is greater than the electrochemical gradient for K+.
Active transport by the sodium-potassium pump follows this cycle.
1. Three Na+ ions from the cytosol bind to the pump. 2. The binding of Na+ stimulates the phosphorylation of the pump protein by ATP. 3. Phosphorylation causes a conformational change in the pump that moves the three Na+ ions against their concentration gradient and releases them outside the cell. 4. The release of the Na+ ions permits two K+ ions from outside the cell to bind to the pump, and the phosphate group is released. 5. Release of the phosphate group causes another conformational change in the pump. 6. The conformational change in the pump moves the two K+ ions against their concentration gradient and releases them into the cytosol. The net result is that the concentration of Na+ is higher outside the cell and the concentration of K+ is higher inside the cell. In addition, one more positive charge has been transported out of the cell than into the cell, leaving the outside of the cell with an excess positive charge and the inside with an excess negative charge. Thus, the sodium-potassium pump creates both chemical gradients and charge differences across the plasma membrane. The function of the sodium-potassium pump in animal cells (and the proton pump in bacteria and plant cells) is essential to many cell functions. It prevents chemical and electrical gradients across the plasma membrane from reaching equilibrium (at which point the cell would be dead) and powers many types of active transport across the plasma membrane.
All cells contain ion pumps that use the energy of ATP hydrolysis to pump ions across the plasma membrane. These pumps create an electrochemical gradient across the plasma membrane that is used to power other processes at the plasma membrane, including some transport processes. In animal cells, the main ion pump is the sodium-potassium pump. Complete the diagram below using the following steps.: - Drag the correct white label to the white target, indicating how many ions move through the pump and in which directions. - Drag the pink labels to the pink targets, indicating the relative concentrations of Na+ and K+ inside and outside the cell. - Drag the blue labels to the blue targets, indicating the relative charges inside and outside the cell.
1.a.) 3 Na+ out 2 K+ in b.) Na+ concentration= high K+ concentration=low c.) Na+ concentration= low K+ concentration=high d.) excess + charge e.) excess - charge
Oxygen shows cooperative binding to hemoglobin. Cooperative binding has the following effects on the binding and release of oxygen: Oxygen binding to hemoglobin: When one molecule of oxygen binds to one of hemoglobin's four subunits, the other subunits change shape slightly, increasing their affinity for oxygen. Oxygen release from hemoglobin: When four oxygen molecules are bound to hemoglobin's subunits and one subunit releases its oxygen, the other three subunits change shape again. This causes them to release their oxygen more readily. These two graphs show how cooperative binding differs from a hypothetical situation where binding is not cooperative. The x-axis shows the partial pressure of oxygen (PO2). This is a measure of the amount of oxygen present in a tissue. The blue arrows on the x-axis show the partial pressure of oxygen in various tissues of the body. The y-axis shows the oxygen saturation of hemoglobin (O2 saturation). This is the percentage of oxygen-binding sites on hemoglobin molecules that are actually bound to oxygen. As you can see from the table, the cooperative binding of oxygen to hemoglobin is an important adaptation for gas exchange. Cooperativity allows hemoglobin to release much more oxygen to an animal's body tissues. Compare the numbers for cooperative binding (circled in red) to those for noncooperative binding (circled in gold). In a resting tissue, hemoglobin releases 50% of its oxygen. If there were no cooperativity, it would release only 30% of its oxygen. In an exercising tissue, hemoglobin releases 80% of its oxygen. If there were no cooperativity, it would release only 50% of its oxygen.
2. What is the O2 saturation in lungs at rest? (find value on y-axis on graph). Cooperative= 50% Non cooperative= 70% 3. what percent of O2 is delivered to tissues at rest? (to find these values subtract the percent of O2 saturation in the lungs from previous question from 100%) cooperative= 100%- 50%= 50% Non cooperative= 100%- 30%= 70% so on and so forth...
What can pass through the cell membrane?
Some solutes pass readily through the lipid bilayer of a cell membrane, whereas others pass through much more slowly, or not at all. Small nonpolar (hydrophobic) molecules, such as dissolved gases (O2, CO2, N2) and small lipids, can pass directly through the membrane. They do so by interacting directly with the hydrophobic interior of the lipid bilayer. Very small polar molecules such as water and glycerol can pass directly through the membrane, but much more slowly than small nonpolar molecules. The mechanism that permits small polar molecules to cross the hydrophobic interior of the lipid bilayer is not completely understood, but it must involve the molecules squeezing between the hydrophobic tails of the lipids that make up the bilayer. Polar molecules such as glucose and sucrose have very limited permeability. Large molecules such as proteins cannot pass through the lipid bilayer. Ions and charged molecules of any size are essentially impermeable to the lipid bilayer because they are much more soluble in water than in the interior of the membrane.
Eukaryotic cells have an integrated network of organelles, including the endoplasmic reticulum (ER), the Golgi apparatus, and lysosomes, which is collectively referred to as the endomembrane system. The endomembrane system serves a variety of functions within the cell, including protein synthesis and transport, metabolism of lipids, and detoxification. a.) The various parts of the endomembrane system serve different functions in the cell. In this activity, you will identify the roles of each part of the endomembrane system. Drag each function to the appropriate bin. b.)All proteins are synthesized by ribosomes in the cell. Some ribosomes float freely in the cytosol, while others are bound to the surface of the endoplasmic reticulum. Most proteins made by free ribosomes function in the cytosol. Proteins made by bound ribosomes either function within the endomembrane system or pass through it and are secreted from the cell. Which of the following proteins are synthesized by bound ribosomes? c.) Proteins that are secreted from a eukaryotic cell must first travel through the endomembrane system. Drag the labels onto the diagram to identify the path a secretory protein follows from synthesis to secretion. d.) Scientists can track the movement of proteins through the endomembrane system using an approach known as a pulse-chase experiment. This experiment involves the "pulse" phase: Cells are exposed to a high concentration of a radioactively labeled amino acid for a short period to tag proteins that are being synthesized. the "chase" phase: Any unincorporated radioactively labeled amino acids are washed away and large amounts of the same, but unlabeled, amino acid are added. Only those proteins synthesized during the brief pulse phase are radioactively tagged. These tagged proteins can be tracked through the chase period to determine their location in the cell. The data below were obtained from a pulse-chase experiment in which cells were examined at different times during the chase period. The numbers represent the radioactivity (measured in counts per minute) recorded at each of the indicated sites. The higher the number, the greater the radioactivity. (gives a chart. Note that the radioactivity of lysosome increase the most drastically over time!)
a.) - smooth Er: lipid synthesis, calcium ion storage, poison detoxification - rough Er: protein synthesis - Golgi apparatus: protein modification and sorting, cisternal maturation - lysosome: macromolecule digestion, autophagy The endomembrane system is critical for the synthesis, processing, and movement of proteins and lipids in the cell. The smooth ER functions mainly in lipid synthesis and processing. The rough ER is the site of secretory protein synthesis. These proteins are processed further in the Golgi apparatus, from where they are dispatched in vesicles to the plasma membrane. Lysosomes, whose enzymes and membranes are made and processed by the rough ER and Golgi apparatus, function in the hydrolysis of macromolecules, such as in phagocytosis and autophagy. b.) lysosomal enzyme, ER protein, and insulin. c.) A= endoplasmic reticulum B= cis golgi cisternae C= medial golgi cisternae D= Trans golgi cisternae E= plasma membrane explanation: As they are being synthesized, secretory proteins enter the lumen of the endoplasmic reticulum. From the ER, vesicles transport these proteins to the Golgi, where they are sequentially modified and concentrated in a cis-to-trans direction. Secretory vesicles bud from the Golgi and move along cytoskeletal filaments to eventually fuse with the plasma membrane, secreting their protein cargo. Each of these transport steps requires specialized proteins to ensure that the cargo is sent to the proper location and is able to fuse with the target membrane. d.) Phagocytosis: The cells in this experiment were macrophages. These immune system cells have many lysosomes for the destruction of bacteria and other invaders brought into the cell via phagocytosis. The enzymes (hydrolases) that carry out this catabolic activity are synthesized in the endoplasmic reticulum, modified in the Golgi, and transported to the lysosomes.
The plasma membrane separates a living cell from its surroundings. Phospholipids are one of the key components of the plasma membrane, making up its basic fabric. Click on the figure at left to review the structure of a phospholipid. Click on the figure at right to see the structure of the plasma membrane. (charts for these problems): a.) Drag the terms on the left to the appropriate blanks on the right to complete the sentences. b.)Phospholipids form the main fabric of the plasma membrane. One feature of phospholipids is that when they are placed in an aqueous solution, they will self-assemble into a double layer (bilayer) that resembles the bilayer of the plasma membrane. This self-assembly occurs because phospholipids are hydrophilic at one end (the phospholipid head) and hydrophobic at the other end (the phospholipid tails). Drag the labels to their appropriate locations in the figure. First, drag labels to targets (a) and (b) to indicate whether these environments are hydrophilic or hydrophobic. Next, drag the phospholipid layers to targets (c) and (d) to indicate how they are oriented in the plasma membrane. Finally, drag labels to targets (e), (f), and (g) to indicate which portions of the membrane protein are hydrophilic and which are hydrophobic. (chart for this part c.) A critical feature of the plasma membrane is that it is selectively permeable. This allows the plasma membrane to regulate transport across cellular boundaries--a function essential to any cell's existence. How does phospholipid structure prevent certain molecules from crossing the plasma membrane freely? (there is a chart for this part)
a.) 1. A phospholipid has a "head" made up of a glycerol molecule attached to a single phosphate group, which is attached to another small molecule. 2. Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a choline group attached to phosphate. 3. Because the phosphate group and its attachments are either charged or polar, the phospholipid head is hydrophilic, which means it has an affinity for water. 4. A phospholipid also has two "tails" made up of two fatty acidmolecules, which consist of a carboxyl group with a long hydrocarbon chain attached. 5. Because the C-H bonds in the fatty acid tails are relatively nonpolar, the phospholipid tails are hydrophobic, which means they are excluded from water. b.) a,b,e, and g are hydrophilic. F is hydrophobic. Finally the phospholipid bilayer arranges itself in a manner that the FA tails face eachother while the head groups face out. c.) a- hydrophobic, b- can cross easily, c- no transport protein required, d-hydrophilic , e- have difficulty crossing the hydrophobic part , f- transport protein required to cross efficiently , g-hydrophilic, h- have difficulty crossing the hydrophobic part, i-transport protein required to cross efficiently
Muscle cells use calcium ions to regulate the contractile process. Calcium is both released and taken up by the sarcoplasmic reticulum (SR). Release of calcium from the SR activates muscle contraction, and ATP-driven calcium uptake causes the muscle cell to relax afterward. When muscle tissue is disrupted by homogenization, the SR forms small vesicles called microsomes that maintain their ability to take up calcium. In the experiment shown in the figure below, a reaction medium was prepared to contain 5 mM ATP and 0.1 M KCl at pH 7.5. An aliquot of SR microsomes containing 1.0 mg protein was added to 1 mL of the reaction mixture, followed by 0.4 μmol of calcium. Two minutes later, a calcium ionophore was added. (An ionophore is a substance that facilitates the movement of an ion across a membrane.) ATPase activity was monitored during the additions, with the results shown in the figure. a.) What is the ATPase activity, calculated as micromoles of ATP hydrolyzed per milligram of protein per minute? Express your answer to one decimal place. (Answer will be the total amount of ATP hydrolyzed in the period between addition of Ca++ and the ionophore. Thus, average ATPase activity = area of the region in the chart/ time). b.) The ATPase is calcium-activated, as shown by the increase in ATP hydrolysis when the calcium was added and the decrease in hydrolysis when all the added calcium was taken up into the vesicles 1 minute after it was added. How many calcium ions are taken up for each ATP hydrolyzed? c.) The final addition is an ionophore that carries calcium ions across membranes. Why does ATP hydrolysis begin again?
a.) ATP ase activity = 0.2 μmoles/mgprotein−min b.) 2 calcium ions (from graph 0.4/0.2= 2 Ca2+ ions) c.) When the ionophore is added, the calcium ions that activate the ATPase leak out.
Acholeplasma laidlawii is a small bacterium that cannot synthesize its own fatty acids and must therefore construct its plasma membrane from whatever fatty acids are available in the environment. As a result, the Acholeplasma membrane takes on the physical characteristics of the fatty acids available at the time. a.) If you give Acholeplasma cells access to a mixture of saturated and unsaturated fatty acids, they will thrive at room temperature. Can you explain why? b.) If you transfer the bacteria of part A to a medium containing only saturated fatty acids but make no other changes in culture conditions, they will stop growing shortly after the change in medium. Explain why. c.)What is one way you could get the bacteria of part B growing again without changing the medium? Explain your reasoning. d.) If you were to maintain the Acholeplasma culture of part B under the conditions described there for an extended period of time, what do you predict will happen to the bacterial cells? Explain your reasoning. e.) What result would you predict if you were to transfer the bacteria of part A to a medium containing only unsaturated fatty acids without making any other changes in the culture conditions? Explain your reasoning.
a.) Acholeplasma cells will incorporate an appropriate combination of saturated and unsaturated fatty acids into their membranes to provide the cell with the optimum level of membrane fluidity. b.) Saturated fatty acids make a membrane less fluid. If only saturated fatty acids are available, the transition temperature of the membrane increases until the transition temperature is equal to the ambient temperature, at which point the membrane will become a gel. c.)The temperature of the culture could be raised to preserve membrane fluidity. d.)A cell will not be able to survive, because all cell functions that depend on the mobility of membrane proteins or lipids will be disrupted. e.) Unsaturated fatty acids increase membrane fluidity, thus increasing the permeability of the membrane to ions and other solutes and making it impossible to maintain concentration gradients that are vital to life.
a.) Inhalation and exhalation move air into and out of the lungs. What happens when you inhale and exhale? b.)Gas exchange involves the transport of two respiratory gases, oxygen and carbon dioxide. Review how each gas is transported between the atmosphere and the cells of your body by completing this exercise. Drag each statement into the appropriate bin depending on whether it applies to oxygen only, carbon dioxide only, or both oxygen and carbon dioxide.
a.) During inhalation, the diaphragm and rib muscles contract, increasing the volume of the lungs. Air enters the nose or mouth and flows down the trachea, bronchi, and bronchioles, and into the alveoli. During exhalation, the diaphragm and rib muscles relax, decreasing the volume of the lungs. Air leaves the alveoli and flows up the bronchioles, bronchi, and trachea, and exits through the nose or mouth. b.) Oxygen only: 1. required for cellular respiration 2. net diffusion from alveoli to lung capillaries Carbon dioxide only: 1. net diffusion from body tissues to blood 2. waste product of cellular respiration 3. sometimes transported as bicarbonate 4. net diffusion from lung capillaries to alveoli Both oxygen to carbon dioxide: 1. enters alveoli during inhalation 2. transported by hemoglobin
a.) All molecules have energy that causes thermal motion. One result of thermal motion is diffusion: the tendency of substances to spread out evenly in the available space. Although the motion of each individual molecule is random, there can be directional motion of an entire population of molecules. Consider a chamber containing two different types of dye molecules, purple and orange. The chamber is divided into two compartments (A and B) by a membrane that is permeable to both types of dye. Initially (left image), the concentration of the orange dye is greater on side A, and the concentration of the purple dye is greater on side B. With time, the dye molecules diffuse to a final, equilibrium state (right image) where they are evenly distributed throughout the chamber. b.) Some solutes are able to pass directly through the lipid bilayer of a plasma membrane, whereas other solutes require a transport protein or other mechanism to cross between the inside and the outside of a cell. The fact that the plasma membrane is permeable to some solutes but not others is what is referred to as selective permeability. Which of the following molecules can cross the lipid bilayer of a membrane directly, without a transport protein or other mechanism? Select all that apply. c.) The majority of solutes that diffuse across the plasma membrane cannot move directly through the lipid bilayer. The passive movement of such solutes (down their concentration gradients without the input of cellular energy) requires the presence of specific transport proteins, either channels or carrier proteins. Diffusion through a transport protein in the plasma membrane is called facilitated diffusion. Sort the phrases into the appropriate bins depending on whether they are true only for channels, true only for carrier proteins, or true for both channels and carriers.
a.) Each dye molecule and the water molecules that surround it are in constant motion due to their thermal energy. Any individual molecule's motion is random because of the frequent collisions among all of the molecules. If a concentration gradient exists for a population of molecules, the motion of the individual molecules in that population will result in a net (directional) movement from higher to lower concentration. For example, in the initial condition, there is a concentration gradient for the orange dye. As a result, the orange dye molecules diffuse down the concentration gradient, with net movement from side A to side B. Once diffusion has eliminated the concentration gradient and equilibrium is reached, net movement stops, but the random motion of each molecule continues b.) oxygen, water, carbon dioxide, and lipids. c.) only channels: allow water molecules and small ions to flow quickly across the membrane. provide a continuous path across the membrane only carriers: undergo a change in shape to transport solutes across the membrane. transport primarily small polar organic molecules both channels and carriers: provide a hydrophilic path across the membrane. transport solutes down a concentration or electrochemical gradient. are integral membrane proteins
a.) At one time, membrane biologists thought that transport proteins might act by binding a solute molecule or ion on one side of the membrane and then diffusing across the membrane to release the solute molecule on the other side. We now know that this transverse carrier model is almost certainly wrong. Suggest two reasons that argue against such a model. One of your reasons should be based on our current understanding of membrane structure and the other on thermodynamic considerations.
a.) Integral membrane proteins are embedded stably in the membrane and protrude from one or both sides based on their hydrophobic and hydrophilic regions. For a protein to traverse a membrane, movement of its hydrophilic region(s) through the hydrophobic interior of the membrane would be required, which would be highly endergonic and hence thermodynamically improbable.
In addition to their role in cellular secretion, the rough ER and the Golgi complex are also responsible for the biosynthesis of integral membrane proteins. More specifically, these organelles are the source of glycoproteins commonly found in the outer phospholipid monolayer of the plasma membrane. a.) Describe the synthesis and glycosylation of glycoproteins of the plasma membrane. b.) Explain why the carbohydrate groups of membrane glycoproteins are always found on the outer surface of the plasma membrane. c.) What assumption did you make about biological membranes in order to answer the queston in Part B?
a.) Integral membrane proteins are synthesized on the rough ER, with oligosaccharide side chains added in part on the lumenal side of the rough ER (core glycosylation) and in part on the lumenal side of the Golgi complex (terminal glycosylation). Side chains therefore face the interior of both organelles as well as the interior of transport vesicles and become oriented toward the exterior of the cell when the vesicles fuse with the plasma membrane. b.) Outer monolayer originally faced the interior of the rough ER and Golgi, where the enzymes involved in glycosylation are located. c.) Membrane asymmetry is maintained throughout the rough ER, Golgi, and plasma membrane.
Silicosis is a debilitating miner's disease that results from the ingestion of silica particles (such as sand or glass) by macrophages in the lungs. Asbestosis is a similarly serious disease caused by inhalation of asbestos fibers. In both cases, the particles or fibers are found in lysosomes, and fibroblasts, which secrete collagen, are stimulated to deposit nodules of collagen fibers in the lungs, leading to reduced lung capacity, impaired breathing, and eventually death. a.) How do you think the fibers get into the lysosomes? b.) What effect do you think fiber or particle accumulation has on the lysosomes? c.) How might you explain the death of silica-containing or asbestos-containing cells? d.) What do you think happens to the silica particles or asbestos fibers when such cells die? e.) How can cell death continue almost indefinitely, even after prevention of further exposure to silica dust or asbestos fibers? f.) Cultured fibroblast cells will secrete collagen and produce connective tissue fibers after the addition of material from a culture of lung macrophages that have been exposed to silica particles. What does this tell you about the deposition of collagen nodules in the lungs of silicosis patients?
a.) The fibers or particles are probably taken up by endocytosis, followed by transport via early and late endosomes to a heterophagic lysosome. b.) The fibers or particles may physically abrade the lysosomal membrane, causing it to become leaky. c.) Cell death is probably due to the digestion of cellular components by acid hydrolases that escape from damaged lysosomes. d.) The fibers or particles released on cell death presumably are available for ingestion by macrophages, with the same end result. e.) Because the fibers and particles are not digestible and there is no mechanism to remove them from the lungs, a cycle of uptake, lysosomal damage, cell death, and fiber or particle release is set up that can continue indefinitely, killing more and more cells. f.) Exposure of silica particles apparently causes the macrophages to release a soluble factor that stimulates fibroblast cells in the lung to deposit collagen fibers, probably in an attempt to seal off the silica in the lung.
Imagine a new type of cell was discovered on Mars in an organism growing in benzene, a nonpolar liquid. The cell had a lipid bilayer made of phospholipids, but its structure was very different from that of our cell membranes. a.) Describe what might be a possible structure for this new type of membrane. b.)What might be characteristic features of the phospholipid head groups? c.) What properties would you expect to find in membrane proteins embedded in this membrane? d) How might you isolate and visualize these unusual membranes?
a.) This membrane would have the nonpolar groups on the two surfaces facing the nonpolar solvent, and it would have a hydrophilic interior. b.) The phospholipid head groups would likely have equal numbers of positively and negatively charged groups that would pack well and not be bulky. c.) Membrane proteins embedded in the membrane would likely have hydrophilic regions spanning the membrane with hydrophobic groups protruding from both sides. Protein transporters would be required for hydrophobic compounds that could not otherwise pass through the hydrophilic membrane interior. d.) It may require hydrophilic solvents to solubilize these membranes and release embedded proteins prior to visualization by conventional means.
One type of active transport is called cotransport. In cotransport, the energy available from an ion moving through a transport protein down its electrochemical gradient is coupled with the movement of another solute (small polar molecule or ion) through the same protein but against its concentration or electrochemical gradient. The solute that is being transported against its gradient may move into the cell or out of the cell (but not both), depending on the type of transport protein that catalyzes this process. In many animal cells, the uptake of glucose into the cell occurs by a cotransport mechanism, in which glucose is cotransported with Na+ ions: Complete the diagram below.
a.) concentration of glucose low b.) Na+ and glucose down to the cell c.) concentration of glucose high 1. Na+ moves down its concentration gradient 2. Glucose moves against its concentration gradient. explanation: In cotransport, the energy required to move one solute against its concentration or electrochemical gradient is provided by an ion moving into the cell down its electrochemical gradient. The ion that moves into the cell down its gradient is usually the same ion that is pumped out of the cell by an active transport pump: for example, Na+ in animal cells using the sodium-potassium pump, or H+ in plants and prokaryotes using the proton pump. In the case of the glucose-sodium cotransporter in animals, Na+ moves back into the cell down its electrochemical gradient, providing the energy for glucose to move into the cell against its concentration gradient. The energy for glucose transport into the cell is supplied indirectly by the sodium-potassium pump's hydrolysis of ATP, and directly by the Na+ electrochemical gradient created by the pump.