Bio II - Chapter 6

At what point in cellular respiration is the first molecule of CO2 produced? Hint: This occurs when a 3-carbon molecule is oxidized to a 2-carbon molecule.

in the reaction that creates acetyl CoA (coenzyme A) from pyruvate Carbon dioxide is produced in the transition between glycolysis and the citric acid cycle when each 3-carbon pyruvate is cleaved to a 2-carbon acetyl molecule with the remaining carbon of pyruvate released as carbon dioxide. This is the first step in cellular respiration where carbon dioxide is released. 6.8

A molecule that functions as the electron donor in a redox reaction __________.

loses electrons and becomes oxidized An electron "donor" donates (loses) electrons, thereby becoming oxidized. In cellular respiration, glucose is oxidized when it loses electrons in hydrogen atoms, and oxygen is reduced as it gains electrons in hydrogen atoms. 6.5A

In cellular respiration, glucose __________ electrons and oxygen __________ electrons.

loses, gains During cellular respiration, glucose loses electrons and oxygen gains electrons. Oxidation and reduction always go together, as electron transfer requires both a donor and an acceptor. 6.5A

What process regulates the rate of cellular respiration? Hint: This is a common principle throughout biology.

feedback inhibition When a metabolic end product accumulates, an enzyme (or enzymes) that would be used earlier in the pathway switches off, ensuring that the rate of metabolism is appropriate for the cell's needs. 6.15

A person's basal metabolic rate (BMR) is equal to about __________. Hint: Be sure you know the definition of BMR.

1,300-1,500 Calories/day This represents the number of kcal (Calories) needed to maintain the body's life-sustaining activities. 6.4

Each turn of the citric acid cycle generates one ATP molecule as well as which energy-rich molecules? Hint: Examine Figure 6.8A for a review of the products of the citric acid cycle.

3 NADH and 1 FADH2 The citric acid cycle generates three molecules of NADH and one molecule of FADH2. These reduced molecules carry high-energy electrons that will be delivered to the electron transport chain. 6.8A

About how much ATP is produced by the metabolism of one molecule of glucose in cellular respiration?

32 molecules This is the number of molecules of ATP that are produced by glycolysis, the citric acid cycle, and oxidative phosphorylation. 6.11

Given the relatively modest number of calories burned by any but the most vigorous activities, why can most people consume more than 2,000 kilocalories per day yet maintain a healthy body weight? Hint: Figure 6.4 only includes the extra calories (beyond the BMR) burned through physical activity.

A large proportion of the energy consumed in food is needed to maintain the body's functions, so only a fraction of food energy needs to be burned in exercise. This is fortunate for people who want to lose weight. If we had to burn 2,000 kilocalories per day in exercise, we'd need to run a marathon every day. 6.4

Each glucose molecule yields __________ molecule(s) of ATP during the citric acid cycle.

Each molecule of glucose yields two molecules of pyruvate, and each of these yields one molecule of acetyl CoA that enters the citric acid cycle. Each acetyl CoA molecule, in turn, yields 1 molecule of ATP as it moves through the cycle. Thus, a total of two ATP molecules are generated from 1 glucose molecule. 6.8B

Why are wine barrels and beer fermentation vats designed to keep air out? Hint: What metabolic pathways do yeasts "prefer"?

Facultative anaerobes prefer aerobic pathways. Exposing facultative anaerobes to anaerobic pathways only ensures that they will use these pathways, which yield alcohol. Because they are facultative rather than obligate anaerobes, they can use the more productive aerobic pathways, which, however, do not yield ethanol. 6.12

Which of the following statements about glycolysis is INCORRECT? - Early prokaryotes probably generated ATP exclusively via glycolysis. - Glycolytic pathways do not require membrane-bound organelles. - Glycolysis became a universal cellular process about the time that significant levels of O2 appeared in the atmosphere. - Glycolysis is the first stage of cellular respiration. Hint: Review the evidence for the evolution of glycolysis.

Glycolysis became a universal cellular process about the time that significant levels of O2 appeared in the atmosphere. This is the incorrect statement. Glycolysis is anaerobic and, hence, did not require oxygen. 6.13

Which of the following statements about glycolysis is correct? - Glycolysis releases carbon dioxide as a by-product. - Glycolysis requires ATP to make ATP. - Glycolysis does not require ATP to make ATP. - Glycolysis requires oxygen in order to occur. Hint: In glycolysis, energy is needed to split glucose molecules into two 3-carbon sugars. Recall the reactions in the investment phase of glycolysis.

Glycolysis requires ATP to make ATP. Glycolysis contains an "investment" phase and a "payoff" phase. Two ATP are "invested" to make two 3-carbon sugars that are oxidized to produce four ATP ("payoff") and water as a by-product. Glycolysis is anaerobic. 6.7C

What is the role of the dehydrogenase enzyme at the beginning of the electron transport chain in cellular respiration?

It transfers two electrons from the glucose molecule to NAD+, reducing it to NADH. NAD+ is reduced by its dehydrogenase to NADH, which is a molecule with two electrons to transfer to the next molecule in the electron transport chain. The chain "runs" by electron transfers by higher-energy molecules to lower-energy molecules, which releases energy used to synthesize ATP. 6.5B

During fermentation, __________ that was produced during glycolysis is converted back to __________. Hint: Examine Figures 6.13A and 6.13B to see what molecules needed during glycolysis are produced during fermentation.

NADH; NAD+ NADH molecules produced during glycolysis are converted back to NAD+ during fermentation. This NAD+ is used again in a new round of glycolysis, where it will be reduced to NADH. 6.12 and 6.13 A & B

TRUE or FALSE: Early prokaryotes probably generated ATP exclusively via glycolysis.

This is a correct statement. Early prokaryotes lived in an atmosphere in which oxygen was absent or present at low concentrations.

TRUE or FALSE: Glycolysis is the first stage of cellular respiration.

This is a correct statement. Glycolysis generates pyruvate, which enters the citric acid cycle and supplies the substrate for a series of redox reactions, which yield electrons for the electron transport chain of oxidative phosphorylation.

TRUE or FALSE: Glycolytic pathways do not require membrane-bound organelles.

This is a correct statement. It is likely that glycolysis evolved early in organisms that lacked membrane-bound organelles.

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

babies and lean people exposed to cold temperatures In addition to reiterating the information that babies use brown fat for insulation, two studies in adults are described in this section. The first found that brown fat, although present in relatively few adults, was more common in thinner patients studied in cold weather. The second found that the brown fat of lean people was more active than the brown fat of overweight or obese people after they were exposed to cold temperatures. 6.10 and 6.11 graph

Let's look at the big picture here: Fueled by the ATP generated during cellular respiration, the intermediates of glycolysis and the citric acid cycle, such as pyruvate and acetyl CoA, are siphoned off and used to __________. Hint: Examine Figure 6.15 to see the "fate" of those intermediates.

build proteins, fats, and carbohydrates The beauty of many metabolic pathways is that they can be used for both the breaking down of compounds for energy or to synthesize complex macromolecules, depending on the needs of the cell and the availability of energy. 6.15

Glycolysis begins with __________ and ends with __________.

one molecule of glucose, two molecules of pyruvate Several intermediates are formed in a series of redox reactions, each of which is catalyzed by a different enzyme. Each molecule of glucose contains six C atoms, and each molecule of pyruvate contains three atoms. 6.7 A and C

In oxidative phosphorylation, electrons are passed from one electron carrier to another. The energy released is used to __________. Hint: What ion increases in concentration as electrons are passed from one carrier to the next?

pump protons (H+) across the mitochondrial membrane The energy harvested from many redox reactions is used to power proton pumps that span the inner mitochondrial membrane. The pumps move H+ across the inner mitochondrial membrane to the intermembrane space. 6.9

Sunlight is essential for the varied life on Earth because it provides __________. Hint: Consider the starting products and the end products of photosynthesis.

the energy necessary to power the rearrangement of chemical bonds in H2O and CO2 This is what photosynthesis accomplishes in the conversion of water and carbon dioxide to sugars. 6.1

What "powers" ATP synthase, allowing it to catalyze the conversion of ADP to ATP in the presence of phosphate?

the flow of H+ ions down their concentration gradient. H+ is pumped across the inner mitochondrial membrane by electron transport chains, resulting in a higher concentration of H+ in the intermembrane space than in the mitochondrial matrix. As H+ diffuses down its concentration gradient back into the mitochondrial matrix, the flow of ions "turns the rotor" of ATP synthase, activating sites within the enzyme that result in the phosphorylation of ADP to ATP. 6.9

Oxidative phosphorylation could not occur without glycolysis and the citric acid cycle because __________. Hint: Why does oxygen "wait" at the end of the electron transport chain?

these two stages supply the electrons needed for the electron transport chain. The main function of glycolysis and the citric acid cycle is to supply oxidative phosphorylation, the last stage of cellular respiration, with electrons carried by NADH and FADH2. 6.6

Which of the following is the role of cellular respiration?

to harvest energy from organic molecules Cellular respiration is a series of chemical reactions that harvest energy in the form of ATP from glucose and other organic molecules. CO2 and water are also released. 6.2

Fat is the most efficient fuel molecule because __________. Hint: Compare the energy contained in 1 gram of glucose with that contained in 1 gram of fat.

with their numerous hydrogen atoms, fats provide an abundant source of high-energy electrons Because oxidative phosphorylation depends on a source of electrons (all of which are extracted from hydrogen atoms), fats, which contain many hydrogen atoms, are an abundant source of high-energy electrons that can be harvested for energy production. 6.14