GUIDED READING AND TEXTBOOK QUESTIONS 5-6

You are sailing on Lake Superior from Copper Harbor, Michigan, to Isle Royale National Park. A sudden storm causes your sailboat to spring a leak. You immediately grab a bucket and begin bailing water out of the boat. Briefly explain how your predicament could be used as an analogy to help explain both active and passive transport.

If you simply let the water flow into the boat, then water will travel down its concentration gradi- ent (into your boat) until the gradient is abolished (your boat sinks). If you want your boat to stay afloat, then you simply bail water out of the boat. In effect, you are moving water against its con- centration gradient in order to maintain that gradient (keeping your boat afloat).

For a short time in the 1930's, some physicians prescribed low doses of a compound called dinitrophenol (DNP) to help patients lose weight. This unsafe method was abandoned after some patients died. DNP uncouples the chemiosmotic machinery by making the inner mitochondrial membrane leaky to H+. Explain how this drug could cause profuse sweating, weight loss, and possibly death.

In a person treated with uncoupling agents like DNP, the proton gradient established during electron transport is no longer tied to ATP synthesis. As a result, oxidation of glucose during cellular respiration yields very little ATP since ATP is normally produced as H+ ions flow back through ATP synthase in the inner mitochondrial membrane. Without large amounts of ATP available, biosynthesis cannot take place and new organic molecules cannot be synthesized. Low ATP levels would signal the body to continue breaking down its own molecules and feeding them into cellular respiration pathway, leading to excessive weight loss and severe overheating, sweating, and dehydration. One or a combination of these factors can cause death.

Movement across a cell membrane that requires no energy from a cell:

Passive transport

Every cell membrane has a(n) ___________________ that allows it to maintain a cellular environment that is separate from the environment in which it is found.

Plasma membrane

In what stage (s) of cellular respiration does FADH2 shuttle electrons to the electron transport chain?

oxidative phosphorylation

In what stage (s) of cellular respiration uses the potential energy of a H+ gradient?

oxidative phosphorylation

Fermentation is essentially glycolysis because glycolysis does not require _________________ to function.

oxygen

Penicillin is a drug that affects bacterial cells and not human cells. How is this possible?

This is possible because the drug is targeting a structure not found in eukaryotic cells.

The driving force behind oxidative phosphorylation is ____________. a. oxygen b. carbon dioxide c. NADH d. H2O

a. oxygen

Which of the following statements regarding transport across a plasma membrane is false? a. passive transport requires an input of energy from the cell. b. osmosis is the diffusion of water across a selectively permeable membrane. c. substances always travel down their concentration gradient in passive transport. d. facilitated diffusion requires a specific transport protein found in the membrane.

a. passive transport requires an input of energy from the cell.

In lactic acid fermentation, __________ becomes the target of reduction by NADH. a. pyruvate b. lactate c. glucose d. ATP

a. pyruvate

The synthesis of ATP from ADP and P a. stores energy in a form that can drive cellular work b. involves the hydrolysis of a phosphate bond c. transfers a phosphate, priming a protein to do work d. is an exergonic process

a. stores energy in a form that can drive cellular work

A biochemist wanted to study how various substances were used in cellular respiration. In one experiment, she allowed a mouse to breathe air containing O2 "labeled" by a particular isotope. In the mouse, the labeled oxygen first showed up in a. ATP b. NADH c. CO2 d. H2O

d. H2O

Nonpolar is to diffusion as ____________ is to facilitated diffusion.

polar

The relationship between an enzyme's active site and its substrate is most like which of the following? a. a comb and hair b. a car and a driver c. a scarf and a hand d. a key and a lock

d. a key and a lock

Diffusion across a semi-permeable membrane:

Osmosis

An average adult human requires 2,200 kcal of energy per day. Suppose your diet provides an energy of 2,300 kcal per day. How many hours per week would you have to walk to burn off the extra calories? Swim? Run?

100 kcal per day is 700 kcal per week. Walking 3 mph would require about 2.8 hours (700/245); swimming, 1.7 hours; running, 0.7 hour.

The phosphorylation of ADP creates ____________.

ATP

________________________ uses the energy found within a proton gradient to drive the syn- thesis of ATP.

ATP synthase

Cells lining kidney tubules function in the reabsorption of water from urine. In response from chemical signals, they reversibly insert additional aquaporins into their plasma membranes. In which of these situations would your tubule cells have the most aquaporins: after a long run on a hot day, right after a large meal, or after drinking a large bottle of water? Explain.

Aquaporins are water transport channels that allow for very rapid diffusion of water through a cell membrane. It would be most important for your body to reabsorb water form the urine, thus preventing dehydration, after a run on a hot day.

Explain how your body can convert excess carbohydrates in the diet to fats. Can excess carbohydrates be converted to protein? What else must be supplied?

As carbohydrates are broken down in glycolysis and the oxidation of pyruvate, glycerol can be made from G3P and fatty acids can be made from acetyl CoA. Amino groups, containing N atoms, must be supplied to various intermediates of glycolysis and the citric acid cycle to produce amino acids.

Oxidative phosphorylation involves the flow of both electrons and H+. Explain the roles of these movements in the synthesis of ATP.

As electrons from fuel molecules are passed from NADH or FADH2 through the electron transport chain to oxygen, the energy released from some of these redox reactions is used to pump H+ across the inner mitochondrial membrane into the inner membrane space. When hydrogen ions flow back through ATP synthase down their concentration gradient, they power the phosphorylation of ADP to ATP.

What initial observation led scientists to hypothesize that brown fat may be activated by cold temperatures?

Brown fat tissue was found at higher levels when the scans were taken during cold weather.

Outputs of cellular respiration

CO2 + H2O

How do the components and structure of cell membranes relate to the functions of membranes?

Cell membranes are composed of diverse proteins suspended in a fluid phospholipid bilayer. The hydrophilic heads of the phospholipids face the aqueos environment on both sides of the membrane and the fatty acid tails cluster in the hydrophobic center of the membrane. The membrane forms a selectively permeable boundary between cells and their surroundings (or between organelles and their cytosol). The proteins perform many of the functions of membranes, such as enzyme action, transport, attachment, and signaling.

When there exists a difference in the amount of a substance across a distance:

Concentration gradient

A reaction that requires an input of energy:

Endergonic reaction

______________ is always lost during photosynthesis and cellular respiration.

Energy

Relate the laws of thermodynamics to living organisms.

Energy is neither created nor destroyed but can be transferred and transformed. Plants transform the energy of sunlight into chemical energy stored in organic molecules. Almost all organisms rely on the products of photosynthesis for the source of their energy. In every energy transfer or transformation, disorder increases as some energy is lost to the random motion of thermal energy and released as heat.

Why is the barrier of the activation energy beneficial for cells? Explain how enzymes lower activation energy.

Energy is stored in the chemical bonds of a cell's organic molecules. The activation energy barrier prevents these molecules from spontaneously breaking down and releasing that energy. When a substrate fits into an enzyme's active site with an induced fit, its bonds may be strained and thus easier to break, amino acids or cofactors in the active site may facilitate or participate in the catalysis, or the active site may orient two substrates in such a way that expedites the conversion to products.

A reaction that gives off energy:

Exergonic reaction

____________ generates fewer molecules of ATP because it contributes its electrons further along the electron transport chain.

FADH

True or false: The transfer of H atoms from glucose to oxygen does not represent redox reactions. If false, make it a correct statement.

False, it does represent redox reactions, as oxygen gas is reduced.

True or false: Blood traveling from your leg muscles to the lungs would be high in oxygen. If false, make it a correct statement.

False, it would be low in oxygen.

True or false: A substance that makes the inner mitochondrial membrane leaky to H1 (H1 would be able to leak across the membrane at points other than ATP synthase) increases ATP production in mitochondria. If false, make it a correct statement.

False, it would decrease ATP production as ATP synthase efficiency would be reduced.

Isotonic solution effect on plant cell:

Flaccid

Which of the three stages of cellular respiration is considered the most ancient? Explain your answer.

Glycolysis is considered the most ancient because it occurs in virtually all cells (including prokaryotic cells, which evolved before eukaryotic cells) and doesn't require oxygen or membrane-enclosed organelles.

List two sources of evidence that indicate glycolysis is extremely old.

Glycolysis is universal, and it does not occur within a membrane-bound organelle.

Compare and contrast fermentation as it occurs in your muscle cells and in yeast cells.

In lactic acid fermentation (in muscle cells), pyruvate is reduced by NADH to form lactate, and NAD+ is recycled. In alcohol fermentation, pyruvate is broken down to CO2 and ethanol as NADH is oxidized to NAD+. Both types of fermentation allow glycolysis to continue to produce 2 ATP per glucose by recycling NAD+.

In pole vaulting, the higher the bar is placed, the more difficult it is to clear it. Explain why this is a good analogy to help students understand enzymes and activation energy.

In this analogy, the bar represents the activation energy necessary for the reaction to occur. The higher the bar, the harder it is to jump. The more activation energy that is required, the harder it will be for the reaction to occur.

Sometimes inhibitors can be harmful to a cell; often they are beneficial. Explain.

Inhibitors that are toxins or poisons irreversibly inhibit key cellular enzymes. Inhibitors that are designed as drugs are beneficial, such as when they interfere with the enzymes of bacterial or viral invaders or cancer cells. Cells use feedback inhibition of enzymes in metabolic pathways as important mechanisms that conserve resources.

You are taking a road trip from Chicago to Denver. The trip is going to take roughly 15 hours. At the start of your trip, you get a 96-oz Mega Gulp from 11-seven of Mountain Mist. This beverage will have roughly 1,360 kcal. How long into your trip will you have burned the calo- ries from this drink? Refer to Figure 6.4 in your textbook on page 91.

It would actually take longer than your trip, a bit over 22 hours.

Briefly explain why a teeter-totter is a good analogy for describing how reductions and oxida- tions always go together.

It's a good analogy because, for every reduction, there is an oxidation, and vice versa. This is similar to a teeter-totter: When one side goes up, the other has to go down.

In the following reaction, which is the enzyme?Lactose --> Glucose + Galactose

Lactose

Hypotonic solution effect on animal cell:

Lyse

A series of reactions that either build or break down a molecule:

Metabolic pathway

The sum of all chemical reactions in an organism:

Metabolism

Your body makes NAD+ and FAD from two B vitamins, niacin and riboflavin. The Recommended Dietary Allowance for niacin is 20 mg and for riboflavin, 1.7 mg. These amounts are thousands of times less than the amount of glucose your body needs each day to fuel its energy needs. Why is the daily requirement for these vitamins so small?

NAD+ and FAD are coenzymes that are not used up during the oxidation of glucose. NAD+ and FAD are recycled when NADH and FADH2 pass the electrons they are carrying to the electron transport chain. We need a small additional supply to replace those that are damaged.

Is energy required for the cell for facilitated diffusion?

No

Is energy required for the cell for osmosis?

No

Is energy required from the cell for diffusion?

No

Sucrase is the enzyme that breaks down sucrose into glucose and fructose. Will sucrose also catalyze the breakdown of the disaccharide maltose? Briefly explain your answer.

No, because maltose will have a different structure than sucrose and so it will not fit into the active site of sucrase

If you opened a wine vat, would the yeast inside continue to perform alcoholic fermentation? Briefly explain your answer with some details about what would happen.

No, because they would be exposed to atmospheric oxygen and they would preferentially per- form aerobic respiration.

Isotonic solution effect on animal cell:

Normal

Inputs of cellular respiration

O2 + C6H12O6

Hypertonic solution effect on an animal cell:

Shrivel

Hypertonic solution effect on plant cell:

Shriveled

Movement of a substance from high to low concentration:

Simple diffusion

Organophosphates (organic compounds containing phosphate groups) are commonly used as insecticides to improve crop yield. Organophosphates typically interfere with nerve signal transmision by inhibiting the enzymes that degrade transmitter molecules. They affect humans and other vertebras as well as insects. Thus, the use of organophosphate pesticides poses some health risks. On the other hand, these molecules break down rapidly upon exposure to air and sunlight. As a consumer, what level of risk are you willing to accept in an exchange for an abundant and affordable food supply?

Some issues and questions to consider: Is improving crop yields of paramount importance in a world where many people can't get enough food? Does the fact that these compounds rapidly breaks down indicate that the risk to humans is low? How about the risks to people who work in agriculture or to other organisms, such as bees and other pollinating insects, birds, and small mammals? Might their be negative effects on ecosystems that are impossible to predict?

CO2 is a gaseous by-product of cellular respiration that you exhale with each breath. Briefly explain where the CO2 comes from.

The CO2 comes from the organic molecules (food) that you consume and is a by-product of cellular respiration.

Mercury is known to inhibit the permeability of water channels. To help establish that the protein isolated by Agre's group was a water channel, the researchers incubated groups of RNA-injected oocytes (which this made aqualorin proteins) in four different solutions: plain buffer, low concentration and high concentration of mercury chloride (HgCl2) solution, and low concentration of a mercury solution followed by an agent (ME) known to reverse the effects of mercury. The water permeability of their osmotic swelling. Interpret the results of this experiment, which are presented in the graph.Control oocytes not injected with an aquaporin RNA were also incubated with buffer and the two concentrations of mercury. Predict what the result of these treatments would be.

The aquaporin RNA-injected oocytes had a high rate of water permeability. Treatment with mercury chloride inhibited the aquaporins, and the water permeability of the oocytes was reduced. As expected, the higher concentration of mercury, the greater the inhibition and reduction in water permeability. When that inhibition was reversed by treatment with the chemical ME, the channels once again functioned and water permeability was increased to almost the level of the uninhibited oocytes. The control oocytes were not injected with aquaporin RNA and thus did not have aquaporins. Thus, their water permeability should be very low and not affected by the mercury treatment. Indeed, their water permeability was much lower than any of the RNA-injected oocytes.

The overall chemical equation for cellular respiration is: C6H12O6 + 6O2 → → → → 6CO2 + 6H2O Briefly explain why the equation has multiple arrows.

The arrows represent the fact that cellular respiration consists of multiple chemical reactions.

Explain how the mechanisms of brown fat metabolism is similar to the effect that the drug DNP has on mitochondria. Pharmaceutical companies may start targeting brown fat for weight loss drugs. How might such drugs help patients lose weight? What dangers might such drugs propose?

The mitochondria of brown fat cells have protein channels that make the inner mitochondrial membrane leaky to H+ ions, producing the same effect that the drug DNP has on mitochondria. When these channels are activated, brown fat burns fuel without producing ATP. Drugs that could activate brown would help a patient burn more calories. Thus, excess calories from the diet would not be converted to fat, and fat stores of the body could be reduced. If these drugs somehow affected the mitochondria of all body cells, however, the results could be as disastrous as they were with DNP.

Several cells have found a correlation between the activity levels of brown fat tissue in research participants following exposure to cold and their percentage of body fat. What would the graph look like from the results of the study? Propose two hypotheses that could explain these results.

The percentage of body fat is the independent variable and is plotted on the x axis. The activity of brown fat is the dependent variable, and it is plotted on the y axis. The graph should show a negative correlation between body fat percentage and activity of brown fat (data points = higher for lower body fat percentage and decrease as the body fat percentage increases). One hypothesis could be that thin individuals have more active brown fat and thus burn more calories, which contributes to their thins (lower percentage of body fat). A second hypothesis is that the higher percentage of body fat insulated the bodies of the more overweight subjects, thus their brown fat did not have to be as active to maintain their body temperatures when exposed to cold.

ATP synthase enzymes are found in the prokaryotic plasma membrane and in the inner membrane of a mitochondrion. What does this suggest about the evolutionary relationship of this eukaryotic organelle to prokaryotes?

The presence of ATP synthase enzymes in prokaryotic plasma membranes and the inner membrane of mitochondria provides support for the theory of endosymbiosis-that mitochondria evolved from an engulfed prokaryote that used aerobic respiration.

What are the main types of cellular work? How does ATP provide the energy for this work?

The work of cells falls into three main categories: chemical, transport, and mechanical. ATP provides the energy for cellular work. During the hydrolysis of ATP, a phosphate group is often transferred to a substrate (chemical) or to a protein (transport and mechanical).

What feature does diffusion, osmosis, and facilitated diffusion all share?

They are all types of passive transport

How are photosynthesis and cellular respiration linked on a molecular level?

They are linked in that the products of one are the reactants of the other.

Biologists have described a cell's plasma membrane as being a fluid mosaic. Briefly explain why this is an accurate description.

This is an accurate description because a plasma membrane is made of multiple types of molecules with many different functions (the mosaic) and the molecules are in constant motion around each other (fluid).

Students frequently have the misconception that plant cells don't perform cellular respiration. Briefly explain the basis of this misconception.

This misconception arises because plant cells perform photosynthesis, which creates the as- sumption that plant cells do not perform cellular respiration.

A cell pumps certain ions against their concentration gradient in order to maintain those gradients. What type of cellular work is this?

This would be considered transport work.

True or false: Aquaporins form the specific protein channel through which water diffuses. If false, make it a correct statement.

True

True or false: Brown fat contains mitochondria. If false, make it a correct statement.

True

True or false: The fact that all cells have a plasma membrane supports the evolutionary linkage of all life. If false, make it a correct statement.

True

Hypotonic solution effect on plant cell:

Turgid

A cell is placed into a beaker containing a 4% sucrose solution. The cell contains a 1% sucrose solution. Use an arrow to illustrate the direction in which water will diffuse in the figure below. Assume that the cell's membrane is not permeable to the sucrose.

Water will move out of the cell

The food we eat has chemical energy. Is it possible for a candy bar to have potential energy for two different reasons at the same time? Briefly explain your answer.

Yes, it is. The candy bar has potential energy due to the bonds within the molecule, but it could also have potential energy if you placed it near the edge of a table.

The graph on page 83 in your textbook illustrates the difference between a chemical reaction with and without an enzyme. Can the reaction represented by the black line still occur without the enzyme? Briefly explain your answer.

Yes, it would just take more energy to get the reaction started.

A chemical reaction is determined to be endergonic. If you were trying to get that reaction to occur using a separate reaction, what would you do?

You would couple it to an exergonic reaction.

Which of the following is a distinction between cellular respiration and fermentation? a. NADH is oxidized by passing electrons to the electron transport chain in respiration only. b. Only respiration oxidizes glucose. c. Substrate-level phosphorylation is unique to fermentation; cellular respiration uses oxidative phosphorylation. d. Fermentation is the metabolic pathway found in prokaryotes; cellular respiration is unique to eukaryotes.

a. NADH is oxidized by passing electrons to the electron transport chain in respiration only.

Plants release what gaseous by-product as a result of photosynthesis? a. O2 b. CO2 c. H2O d. Solar energy

a. O2

The energy needed to initiate a chemical reaction is the ____________. a. activation energy b. substrate energy c. active site d. inhibition site

a. activation energy

A buildup of ____________ initiates the inhibition of an enzyme that functions early in glycolysis. a. ADP b. ATP c. glycerol d. amino acids

b. ATP

Which of the following is the correct order of the main stages of cellular respiration? a. Citric acid cycle, glycolysis, oxidative phosphorylation b. Glycolysis, citric acid cycle, oxidative phosphorylation c. Citric acid cycle, oxidative phosphorylation, glycolysis d. Oxidative phosphorylation, glycolysis, citric acid cycle

b. Glycolysis, citric acid cycle, oxidative phosphorylation

Any substance that inhibits the transportation of oxygen from the lungs affects _____________. a. photosynthesis b. cellular respiration c. chloroplasts d. none of the above

b. cellular respiration

Which best describes the structure of a cell membrane? a. proteins between two bilayers of phospholipids b. proteins embedded in a bilayer of phospholipids c. bilayer of protein coating a layer of phospholipids d. cholesterol embedded in a bilayer of phospholipids

b. proteins embedded in a bilayer of phospholipids

Which of the following best describes the structure of a plasma membrane? a. proteins sandwiched between two layers of phospholipids b. proteins embedded in two layers of phospholipids c. a layer of protein on top of a layer of phospholipids d. phospholipids sandwiched between two layers of protein

b. proteins embedded in two layers of phospholipids

In which of the following is the first molecule becoming reduced to the second molecule? a. pyruvate --> acetylCoA b. pyruvate --> lactate c. glucose --> pyruvate d. NADH+H+ --> NAD+ + 2H

b. pyruvate --> lactate At the same time NADH is oxidized to NAD+

Anything that inhibits ATP synthesis in a cell most likely a. forces the cell to use ADP as an energy source. b. results in the death of the cell. c. makes the cell start using lipids as energy. d. causes the cell to stop doing mechanical work but not transport work.

b. results in the death of the cell.

Which of the following is the most immediate source of energy for making most of the ATP in your cells? a. the transfer of P from intermediate substrate to ADP b. the movement of H+ across a membrane down its concentration gradient c. the splitting of glucose into two molecules of pyruvate d. electrons moving through the electron transport chain

b. the movement of H+ across a membrane down its concentration gradient

Facilitated diffusion across a membrane requires ________________ and moves a solute _______________ its concentration gradient. a. transports proteins... up (against) b. transport proteins... (down) c. energy and transport proteins... (up) d. energy and transport proteins... (down)

b. transport proteins... (down)

Fats are hydrophobic and carbohydrates are hydrophilic. Use this information to explain why humans store the majority of their excess energy as fat and not carbohydrates.

because fats will not require water for storage.

The poison cyanide binds to an electron carrier within the electron transport chain and blocks the movement of electrons. When this happens, glycolysis and the citric acid cycle soon grind to a halt as well. Why do you think these two stages of cellular respiration stop? Explain answer. a. They run out of ATP. b. Unused O2 interferes with cellular respiration. c. They run out of NAD+ and FAD d. Electrons are no longer available

c. They run out of NAD+ and FAD, which are recycled by electron transport, are in limited supply in the cell.

The sodium concentration in a cell is 10 times less than the concentration in the surrounding fluid. How can the cell move sodium out of the cell? (Explain your answer) a. passive transport b. receptor-mediated endocytosis c. active transport d. facilitated diffusion

c. active transport because only active transport can move solute against a concentration gradient.

Energy is never created or destroyed. What happened to the energy that was stored in your gas tank after your lawnmower comes to a stop as a result of running out of gas? a. the energy was lost. b. entropy decreased in the universe. c. it was converted to heat. d. the lawnmower gained energy.

c. it was converted to heat.

Most of the CO2 from cellular respiration is released during a. stage 1: glycolysis b. stage 2: pyruvate oxidation c. stage 2: citric acid cycle. d. stage 3: oxidative phosphorylation

c. stage 2: citric acid cycle.

The only portion of cellular respiration that is cyclic is ____________. a. glycolysis b. the electron transport chain c. the citric acid cycle d. the oxidation of pyruvate

c. the citric acid cycle

In what stage (s) of cellular respiration produces CO2?

citric acid cycle

In what stage (s) of cellular respiration produces molecules of FADH2?

citric acid cycle

In what stage (s) of cellular respiration occurs in the mitochondria?

citric acid cycle and oxidative phosphorylation

The formation of NaCl (table salt) involves an atom of Na giving an electron to an atom of Cl. a. This would be considered a redox reaction. b. Na got oxidized. c. Cl got reduced. d. All of the above are true statements regarding the formation of NaCl.

d. all of the above are true statements regarding the formation of NaCl.

A plant cell placed in distilled water will ___________; an animal cell placed in distilled water will _____________. a. burt... burst b. become flaccid... shrivel c. become turgid... be normal in shaped d. become turgid... burst

d. become turgid... burst

In glycolysis, _____________ is oxidized and _____________ is reduced. a. NAD+... glucose b. glucose... oxygen c. ATP... ADP d. glucose... NAD+

d. glucose... NAD+

In what stage (s) of cellular respiration involves the splitting of glucose?

glycolysis

In what stage (s) of cellular respiration occurs in the cytosol?

glycolysis

In what stage (s) of cellular respiration does substrate-level phosphorylation occur?

glycolysis and citric acid cycle

In what stage (s) of cellular respiration produces molecules of NADH?

glycolysis and citric acid cycle

In what stage (s) of cellular respiration occurs in a plant cell?

glycolysis, citric acid cycle, and oxidative phosphorylation

In what stage (s) of cellular respiration occurs in an animal cell?

glycolysis, citric acid cycle, and oxidative phosphorylation

In what stage (s) of cellular respiration produces ATP?

glycolysis, citric acid cycle, and oxidative phosphorylation

Example of kinetic energy

solar energy

What must proteins be broken down into before they can be burned as energy?

they must be broken down into amino acids.

True or false: Glycolysis and the citric acid cycle both function as metabolic interchanges where the products of their chemical reactions can also be used for biosynthesis. If false, make it a correct statement.

true

In contrast to passive transport, active transport pumps a substance ____________ its gradient.

up