Mastering Biology Chapter 5

Which of the following is a difference between active transport and facilitated diffusion?

Active transport requires the expenditure of cellular energy, and facilitated diffusion does not.-- Active transport can move substances against the concentration gradient, but it requires energy, usually in the form of ATP.

Green olives may be preserved in brine, which is a 20-30% salt solution. How does this method prevent contamination by microorganisms?

Bacteria can't survive in a hypertonic solution because they lose water.-- If a cell is placed in a hypertonic solution, it will lose water to its environment, shrivel, and probably die.

In plant cells, carbon dioxide and water are joined to form carbohydrates. Plant cells can also break down carbohydrates such as glucose, releasing carbon dioxide, water, and energy. No one has ever observed such reactions between water and carbon dioxide outside of living cells. What allows simple molecules to assemble into more complex molecules, and also disassemble, in cells but not in other, nonbiological environments?

Cells couple energy-releasing reactions to energy-requiring reactions.-- One of the many things cells do well is the linking of metabolic reactions in ways that allow an energy-yielding reaction to be coupled to an energy-requiring reaction. ATP molecules are the key to energy coupling.

In a theoretical world where all things are possible, how could you increase the amount of energy that could be stored in a molecule of ATP?

Increase the negative charge of each phosphate group.-- Because the high energy of ATP hydrolysis depends on the strong charge repulsion between the negatively charged phosphates, anything that increases this repulsion would also increase the energy liberated when ATP is broken down to ADP + P.

A pharmaceutical company wishes to focus on an enzyme to develop new medications. What type of study would be of the greatest benefit?

Understanding the enzyme's structure would help pharmaceutical companies design molecules that fit to the binding site and alter activity.-- Enzymes are the most common targets of drugs. By understanding the details of enzyme structure, new drugs can be designed and existing drugs can be better understood and potentially modified.

Drag the labels onto the chart to match each process with its description.

a vesicle inside the cell fuses with the plasma membrane and relates its contents outside the cell- EXOCYTOSIS a form of passive transport. molecules move across the plasma membrane using a transport protein- FACILITATED DIFFUSION the plasma membrane forms a pocket that pinches inward, forming a vesicle that contains material from outside the cell- ENDOCYTOSIS a form of passive transport. molecules move across the plasma membrane by crossing the lipid bilayer.- DIFFUSION requires energy from the cell. molecules move against their concentration gradient- ACTIVE TRANSPORT

Utah's Great Salt Lake has an average salinity seven times higher than that of the oceans. Very few multicellular organisms live in this harsh environment. An example is the brine shrimp, which must devote a large portion of its metabolic energy to osmoregulation. These brine shrimp must _____.

actively pump water back into their cells to counter its loss due to osmosis-- A cell (in this case, cells within the body of a brine shrimp) will experience a net output of water in a hypertonic environment. For cells to prevent shriveling, they must actively recapture water from their surroundings.

A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via _____.

endocytosis-- Endocytosis is the procedure that cells use to import large molecules across their membranes.

A specific ______ speeds up each of a cell's chemical reactions.

enzyme

Through energy coupling, cells use _______, or energy-releasing, reactions to drive _________, or energy-requiring, reactions. The molecule ________ is the energy shuttle between these two types of reactions.

exergonic, endergonic, ATP

Mechanisms such as _________ enable precise control over a cell's metabolism -- all of its chemical reactions.

feedback inhibition

What condition might result from an excess of aquaporins?

fluid retention in pregnant women-- Aquaporins transport water. An excess of aquaporins during pregnancy can result in fluid retention.

New drugs are being developed to lower levels of circulating cholesterol. A successful drug would be one that _____.

increases the rate of LDL receptor-mediated endocytosis-- Because cholesterol levels in the blood reflect the balance of, addition to, and removal of cholesterol, anything that tips the balance in favor of removal will lower the concentration of circulating cholesterol. Increasing LDL receptor-mediated endocytosis will have exactly this effect.

There are three main types of cellular work: chemical, transport, and movement. Most of this work is powered by the transfer of a phosphate group from one molecule to another in a process known as

phosphorylation

Succinylcholine is structurally almost identical to acetylcholine, but if combined with the enzyme that normally hydrolyzes acetylcholine, the enzyme is no longer able to hydrolyze acetylcholine. This suggests that _____.

succinylcholine must be a competitive inhibitor of acetylcholine-- Competitive inhibition occurs when a molecule mimics the substrate.

In an oil-based, nonpolar environment, phospholipids would arrange themselves so that they __________.

would stay together but in a reverse orientation, with their tails projecting outward-- The fatty acid tails of a phospholipid remain nonpolar and the phosphate heads remain polar regardless of the surrounding environment. In an oily environment, the tables are turned relative to water; the polar heads will cluster together to avoid exposure to the oil, and the nonpolar tails will project outward into the nonpolar, oil-based surroundings.

Taq polymerase is an enzyme isolated from the organism Thermus aquaticus. This organism has been found living in the hot springs of Yellowstone National Park. This enzyme is used to copy human DNA from crime scenes. Most reactions are performed at ranges similar to those of the human body; however, what considerations should be made for optimum use of this enzyme?

The temperature should be raised.-- These enzymes are not denatured by high heat and work more efficiently at temperatures of around 70-75°C. If the temperature is not increased, then the reaction will occur at a much slower rate.

Cells A and B are the same size and shape, but cell A is metabolically quiet and cell B is actively consuming oxygen. Oxygen will diffuse more quickly into cell _____ because _____.

the diffusion gradient there is steeper-- As long as a metabolically active cell consumes oxygen as it enters, diffusion into the cell will continue because the concentration gradient favors movement in that direction.