Chapter 5-6 Quiz 2

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 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 vesicle inside the cell fuses with the plasma membrane and releases its contents outside the cell.

Exocytosis

Which stage of cellular respiration appears to have evolved first?

Glycolysis Glycolysis can occur in the absence of oxygen and evolved prior to oxygenic photosynthesis.

Which of the following processes takes place in the cytosol of a eukaryotic cell?

Glycolysis Glycolysis, the breakdown of glucose into two molecules of pyruvic acid, takes place in the cytosol, outside the mitochondria.

In muscle cells, fermentation produces _____.

Lactate and NAD+ These are the products of fermentation as it occurs in muscle cells.

The final electron acceptor of cellular respiration is _____.

Oxygen Oxygen is combined with electrons and hydrogen to form water.

A muscle cell deprived of molecular oxygen will convert glucose to lactic acid to __________.

Recycle NADH through fermentation. During lactic acid fermentation, pyruvate is reduced directly by NADH to form lactate. This recycles NAD+, so the cycle continues.

In the citric acid cycle (also called the Krebs cycle), ATP molecules are produced by _____.

Substrate-level phosphorylation A phosphate group is transferred from GTP to ADP.

Which statement describes the citric acid cycle?

This process produces some ATP and carbon dioxide in the mitochondrion. The citric acid cycle breaks down carbon molecules, releasing carbon dioxide and forming some ATP.

Which of these is NOT a product of the citric acid cycle (also called the Krebs cycle)?

acetyl CoA Acetyl CoA enters the citric acid cycle.

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.

In cellular respiration, most ATP molecules are produced by _____.

oxidative phosphorylation This process utilizes energy released by electron transport.

Which statement describes the electron transport chain?

This process uses energy captured from electrons flowing to oxygen to produce most of the ATPs in cellular respiration. In the electron transport chain, electrons move from one electron carrier to another, eventually reaching oxygen. The released energy is used to make ATPs.

Antibiotics - for example, penicillin - cannot be used to treat viral infections, such as the common cold. Why?

Antibiotics inhibit enzymes that are essential to the survival of bacteria only, not enzymes important to humans. Antibiotics are designed specifically to fight bacterial infections. Many antibiotics, such as penicillin, inhibit a bacterial enzyme that is used to make protective cell walls. Neither animals nor viruses make such an enzyme and therefore are mostly unaffected by antibiotics.

Recent data suggests that heat-generating brown fat is most active in __________.

Lean people exposed to cold temperatures. The first study suggests that weight and temperature might have an effect on brown fat activity levels; the second study confirms that thin individuals exposed to cold temperatures had the highest brown fat activity levels.

The plasma membrane is selectively permeable. Which of the following can pass freely through the membrane with no assistance?

Oxygen and carbon dioxide Oxygen and carbon dioxide, as well as other small, hydrophobic molecules, can move freely across the membrane.

Which statement describes glycolysis?

This process splits glucose in half and produces 2 ATPs for each glucose. In glycolysis, glucose is split into two molecules of pyruvic acid. The released energy is stored in ATP and the electron carrier NADH.

What is the correct general equation for cellular respiration?

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP energy Cellular respiration extracts energy from glucose (C6H12O6) to produce smaller energy packets (ATP).

In an experiment, mice were fed glucose (C6H12O6) containing a small amount of radioactive carbon. The mice were closely monitored, and in a few minutes, radioactive carbon atoms showed up in __________.

Carbon dioxide Cellular respiration, or the oxidization of glucose, involves the release of CO2.

During electron transport, energy from _____ is used to pump hydrogen ions into the _____.

NADH and FADH2 ... intermembrane space The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and used to pump hydrogen ions into the intermembrane space.

You're on the pilot episode of a new game show called "The Transport Factor." The host hands you three different amino acids, four different sugars, and two different ions. Then the host shouts, "How many different proteins does the cell need to move these molecules across the plasma membrane using facilitated transport?" Quickly, you correctly respond: _____.

Nine The specificity of transport proteins for the materials they transport is exactly like the specificity of enzymes for their substrates. Therefore, if there are nine different substances to be transported by facilitated diffusion, this almost certainly involves nine different transport proteins.

For each glucose that enters glycolysis, _____ NADH enter the electron transport chain.

10 For each glucose molecule that enters glycolosis, a total of 10 NADH are produced -- 2 are produced in glycolysis, 2 are produced in acetyl CoA production, and 6 are produced in the citric acid cycle.

Which of these enters the citric acid cycle (also called the Krebs cycle)?

Acetyl CoA Acetyl CoA is a reactant in the citric acid cycle (also called the Krebs cycle).

Requires energy from the cell. Molecules move against their concentration gradient.

Active Transport

These are true for chemical reaction graph: By binding to reactant molecules, enzymes make it easier for the bonds in the molecules to break apart. Enzymes lower the overall energy input needed for a reaction to occur. Reactants cannot convert to products without an initial input of energy to start the reaction.

For a chemical reaction to begin, chemical bonds in the reactant molecules must be broken. This process requires that the molecules absorb energy from their surroundings. The energy that must be invested to start a reaction is called activation energy because it activates the reactants and triggers the chemical reaction. Enzymes enable metabolism to occur by reducing the amount of activation energy required to break the bonds of reactant molecules.

A scientist wants to study the enzymes of the citric acid cycle in eukaryotic cells. What part of the cell would she use as a source of these enzymes?

Mitochondrial matrix The water-soluble citric acid cycle intermediates and enzymes of a eukaryotic cell are found in the mitochondrial matrix, where the newly synthesized NADH and FADH2 diffuse to proteins of the electron transport chain held within the inner mitochondrial membrane. The matrix corresponds to the cytoplasm of the bacterium from which mitochondria are descended.

In what organelle would you find acetyl CoA formation, the citric acid cycle, and the electron transport chain?

Mitochondrion. All of the steps of cellular respiration except glycolysis take place in the mitochondrion.

The proximate (immediate) source of energy for oxidative phosphorylation is _____.

kinetic energy that is released as hydrogen ions diffuse down their concentration gradient Concentration gradients are a form of potential energy.

Drag the labels onto the flowchart to indicate how food molecules reach the body's cells and fuel cellular respiration. Start with the ingestion of food on the left.

1). Eating food provides fuel and building blocks for your body. 2). After food is broken down is the digestive system, it is transported to cells via the circulatory system 3). Fuel molecules are broken down further in glycolysis and the citric acid cycle (also called the Krebs cycle). 4). ATP is produced with the help of the electron transport chain

In cellular respiration, which of the following outcomes is the result of electrons moving through the electron transport chain (or its components)?

A proton gradient is formed. The energy released by the electron transport chain is used to create a proton gradient across the inner mitochondrial membrane. This allows the production of ATP by chemiosmosis.

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.

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.

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 _____.

B ... 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.

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.

Azidothymidine (AZT) is an antiretroviral drug used in the treatment of HIV. It shares a structural similarity to a nucleotide. What might be the mode of action for this drug?

Competitive inhibition. AZT and the nucleotide compete for the active binding site. When AZT binds to an enzyme known as reverse transcriptase, it blocks the replication of the genetic material of HIV.

A single glucose molecule produces about 38 molecules of ATP through the process of cellular respiration. However, this only represents approximately 34% of the chemical energy present in this molecule. The rest of the energy from glucose is __________.

Converted to heat. The majority of the energy in a molecule of glucose is lost as heat.

A form of passive transport. Molecules move across the plasma membrane by crossing the lipid bilayer.

Diffusion

Select the correct sequence of steps as energy is extracted from glucose during cellular respiration.

Glycolysis → acetyl CoA → citric acid cycle → electron transport chain Glycolysis produces pyruvic acid, which enters the mitochondrion. There, it is converted to acetyl CoA, which enters the citric acid cycle. Electron carriers bring electrons from the first three steps to the electron transport chain, and ATP is made.

A chemist has discovered a drug that blocks phosphoglucoisomerase, an enzyme that catalyzes the second reaction in glycolysis. He wants to use the drug to treat people with bacterial infections. However, he can't do this because _____.

Human cells also perform glycolysis; the drug might also poison them. The chemist's drug could have a devastating effect on human cells.

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.

Taq polymerase is an enzyme isolated from the organism Thermophilus 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.

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.

As shown below, an electron carrier, such as __________, acts as an energy-storage molecule when it is __________.

NADH ... reduced NADH is the reduced form of this molecule and it carries high energy electrons. This makes it an energy storage molecule.

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 and binds to the enzyme's active site.

Most NADH molecules generated during cellular respiration are produced during __________.

The citric acid cycle There are 6 NADH molecules produced by the citric acid cycle per molecule of glucose. Two molecules of FADH2 are also produced by this cycle, which makes it a big source of high energy electron carriers.