Microbiology HW 8

Why might some cells uncouple the electron transport chain?

Cells can use the energy from the proton gradient for functions other than producing ATP, such as heat generation.

In which of the following organelles does photosynthesis take place?

Chloroplast

Which of the following statements regarding competitive inhibitors is true?

Competitive inhibitors decrease the rate of enzyme activity.

What enables competitive inhibitors to bind to a specific enzyme?

Competitive inhibitors have structures that resemble the enzyme's substrate.

Which of the following factors may influence an enzyme's activity by altering its three-dimensional structure?

pH and temperature only

The main goal of fermentation is to sustain ATP production by glycolysis. This is accomplished by

passing the electrons on NADH to pyruvic acid, regenerating NAD+ so glycolysis can continue.

Enzymes can lower the activation energy of a chemical reaction by

properly positioning reactants and stabilizing the transition state

Glycolysis makes ATP using ______.

substrate-level phosphorylation

Glycolysis literally means

sugar splitting.

During an oxidation reaction,

the donor molecule loses an electron and becomes oxidized.

Why is reduction the term used to describe the gain of an electron?

The electron acceptor's net charge decreases.

What two molecules are produced by the light reactions and used to power the Calvin cycle?

ATP and NADPH

What are the products made during glycolysis?

4 ATP (net gain of 2) and 2 NADH and 2 pyruvic acid

Which of the following equations represents photosynthesis?

6CO2 + 6H2O → C6H12O6 + 6O2

Choose the true statement(s) about ATP. To be marked correct, you'll need to select all true statements, as there may be more than one correct answer.

ATP is made by phosphorylating ADP. Catabolizing one lipid molecule would produce more ATP for a cell than catabolizing one glucose molecule.

Why is ATP required for glycolysis?

ATP makes it easier to break apart glucose into two three-carbon molecules.

Which is the key difference between aerobic and anaerobic respiratory chains?

Aerobic respiratory chains always use oxygen as the final electron acceptor while anaerobic respiratory chains may use a variety of inorganic substances other than oxygen as the final electron acceptor.

Where would you expect to find electron transport chains in a prokaryote?

Along the plasma membrane

What connects the two photosystems in the light reactions?

An electron transport chain

What is the function of GTP?

An energy carrier

What is the correct general equation for cellular respiration?

C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP energy

What provides the carbon atoms that are incorporated into sugar molecules in the Calvin cycle?

Carbon dioxide (CO2)

Cyanide is a poison which prevents the last carrier in the electron transport chain (cytochrome C oxidase) from transferring the electron to the final electron acceptor. Which of the following would not be a consequence of exposure to this poison?

Carbon dioxide would continue to be generated.

Which of the following could serve as a final electron acceptor in an anaerobic respiratory chain?

Carbonate (CO3 2-)

Where does the energy required for anabolic reactions come from?

Catabolic reactions

How does cyanide poisoning result in the decrease of ATP production?

Cyanide permanently reduces cytochrome a3, preventing other components to change into the oxidized state. This causes the proton gradient to break down, stopping ATP synthesis.

Sulfate-reducing bacteria such as Desulfovibrio vulgaris use sulfate as a final electron acceptor in their respiratory chain. Based on this information, choose the true statement about D. vulgaris.

D. vulgaris should, on average, make less ATP from one molecule of glucose than a microorganism that uses an aerobic electron transport.

What occurs at the bridge step?

Decarboxylation of pyruvic acid

Why do all enzymatic reactions need activation energy?

Energy is required to disrupt a substrate's stable electron configuration.

Why are enzymes important to biological systems?

Enzymes decrease the amount of activation energy required for chemical reactions to occur.

What is meant by the statement "Enzymes are biological catalysts"?

Enzymes speed up the chemical reactions in living cells.

Which of the following is one way that enzymes decrease activation energy?

Enzymes stabilize the reaction's transition state.

Ethylene glycol is an ingredient in antifreeze. If antifreeze is swallowed, the enzyme alcohol dehydrogenase binds to the ethylene glycol and converts it to toxic oxalic and glycolyic acid. One of the treatments for ethylene glycol poisoning is the administration of the enzyme's natural substrate, ethanol. Based on this information, what is the best way to describe how ethanol protects against ethylene glycol poisoning?

Ethanol competes with ethylene glycol to limit oxalic and glycolyic acid formation.

Why does FADH2 yield less ATP than NADH?

FADH2 electrons enter the electron transport chain at a lower energy level.

Rank the following metabolic strategies from least potential ATP gain to greatest potential ATP gain.

Fermentation, anaerobic respiration, aerobic respiration

Based on the animation, how many electron carriers are reduced in the Krebs cycle only?

Four

Which step is the step for which glycolysis is named?

Fourth

Fluoride and triclosan are compounds that inhibit the oral pathogen Streptococcus mutans, which can cause dental caries (cavities). These compounds inhibit pyruvate kinase, an enzyme that uses substrate level phosphorylation to convert phosphoenolpyruvate to pyruvic acid and ATP. Based on your knowledge of cellular respiration, fluoride and triclosan specifically prevent the final step in which metabolic pathway?

Glycolysis

Which of the following statements about glycolysis is true?

Glycolysis is also called the Embden-Meyerhof pathway.

What provides electrons for the light reactions?

H2O

Select the true statement(s) about chemiosmosis in eukaryotes.

In eukaryotes, chemiosmosis requires that protons (H+ ions) diffuse through ATP synthase in the inner mitochondrial membrane. In aerobic eukaryotes, chemiosmosis leads to the production of water and up to 34 ATP.

How does a noncompetitive inhibitor reduce an enzyme's activity?

The inhibitor binds to the enzyme in a location other than the active site, changing the shape of the active site.

Arsenic is a toxic metalloid that is known to interfere with cellular metabolism. Your patient (a 3-year old female) ingested a toxic amount of arsenic, and you find the below metabolites in her blood. Based on these metabolite levels, which part of cellular respiration can you conclude that arsenic directly inhibits?

Intermediate step

How is nevirapine used to treat HIV infections?

It alters the active site of reverse transcriptase, decreasing that enzyme's activity.

Which of the following statements about fermentation is true?

It is an alternative way to return electron carriers to their oxidized state.

Iron is considered an essential element for many bacteria. Based on the animation, how would lack of iron affect energy production of a bacterium?

Lack of iron would mean lack of heme, and thus lower amounts of functioning cytochrome proteins. This would mean lower energy yields.

Lactate dehydrogenase converts lactate to pyruvic acid. In this reaction the enzyme also converts NAD+ to NADH. Choose the statement that best describes lactate dehydrogenase's actions.

Lactate dehydrogenase reduces NAD+ to NADH and oxidizes lactate to pyruvic acid.

Select the best definition of metabolism.

Metabolism refers to all of the chemical reactions in a cell that impact energy use and release.

Which of the following can be used as a final electron acceptor for aerobic respiration?

Molecular oxygen

Glycolysis produces energy in which form?

NADH and ATP

According to the animation, which compounds provide electrons to the system?

NADH and FADH2

How do electrons get from glycolysis, the intermediate step, and the Krebs cycle to the electron transport chain?

NADH and FADH2 transport electrons to the electron transport chain.

What transports electrons from the light reactions to the Calvin cycle?

NADPH

What would be the likely outcome if you increased the concentration of substrate for an enzyme in the presence of a noncompetitive inhibitor?

No change in enzyme activity would be observed.

Which of the following pathways are operational in a cell growing via fermentation?

glycolysis

Which of the following is needed as a reactant for the first step of the citric acid cycle?

Oxaloacetic acid

What is the final electron acceptor in aerobic cellular respiration?

Oxygen

If high amounts of sulfanilamide are in the presence of an enzyme whose substrate is PABA, what outcome is expected?

PABA will not be catalyzed.

What is meant by substrate-level phosphorylation?

Production of ATP by transferring phosphates directly from metabolic products to ADP

How does the proton gradient help ATP synthase to make ATP?

Protons move from outside the membrane to inside the membrane.

What carbon molecules remain at the end of glycolysis?

Pyruvic acid

Which of the following statements regarding redox reactions is true?

Redox reactions involve an oxidation reaction coupled with a reduction reaction.

Sauerkraut is a product of homolactic fermentation of cabbage sugars by various lactic acid bacteria, such as Pediococcus. In this scenario, which of the following mechanisms does Pediococcus most likely use to make ATP?

Substrate-level phosphorylation

Which phosphorylation mechanism for recharging ADP to ATP is incorrectly matched with its description?

Substrate-level phosphorylation: A phosphate is transferred to ADP from a high-energy substrate after passing through an electron transport chain.

Where does the energy come from to power the formation of GTP?

Succinyl CoA

Why does lack of oxygen result in the halt of ATP synthesis?

The chain shuts down and can no longer pump hydrogen ions across the membrane, and the proton gradient cannot be maintained.

According to the animation, what does the electron transport chain do to the concentration of hydrogen ions (protons)?

The concentration of protons is higher outside the membrane than inside.

Choose the true statement about the Krebs cycle.

The major energy benefit of the Krebs cycle is the mass production of reduced cofactors, such as NADH and FADH2.

What is the driving force of energy production in steps 6 and 7?

The oxidation of three-carbon compounds

Which step(s) of the Krebs cycle does (do) not produce any usable energy?

The second and seventh steps

Which step involves the release of carbon dioxide?

The third and fourth steps

What is the fate of metabolites during respiration?

They are oxidized completely to carbon dioxide and water.

How does a competitive inhibitor slow enzyme catalysis?

They compete with the substrate for the enzyme's active site.

Which statement describes the citric acid cycle?

This process produces some ATP and carbon dioxide in the mitochondrion.

Which statement describes glycolysis?

This process splits glucose in half and produces 2 ATPs for each glucose.

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.

How many molecules of ATP can be generated from one molecule of NADH?

Three

How many net ATPs can be made from one molecule of glucose in glycolysis?

Two

What is the net production of ATP in glycolysis?

Two ATP

What is one difference between ubiquinones and cytochromes?

Ubiquinones are not made of protein; cytochromes are.

Which of the following situations does not result in a breakdown of the proton gradient?

Uncoupling proteins

According to the animation, what does oxygen get reduced to at the end of the electron transport chain?

Water

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

glycolysis

A reaction that involves the transfer of electrons from one molecule to another is referred to as

a redox reaction.

Oxidation of nutrients by cells results in

a release of energy, which can be used to recharge ADP to ATP.

Which molecule is the product of the intermediate step which is a direct input into the Krebs cycle?

acetyl CoA

The reactions involved in producing larger compounds from smaller compounds is called

anabolism

Anabolic reactions

are endergonic and involve dehydration synthesis.

Catabolic reactions

are hydrolytic and involve breaking down larger molecules into smaller molecules.

The process of generating ATP using a proton gradient is referred to as

chemiosmosis.

Which structural and functional feature(s) listed are key to an enzyme's activity?

contains an active site where the enzyme can interact with a specific substrate

Enzymes are necessary for cells because

enzymes allow chemical reactions to occur under physiological conditions and within a time frame conducive to life.

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

glycolysis → acetyl CoA → citric acid cycle → electron transport chain

The immediate result of electron movement through the electron transport chain is the pumping of protons across the bacterial cell membrane, creating a _____ outside the cell than inside the cell.

higher concentration of protons

The use of amino acids to make proteins

is an example of anabolism.

In metabolism, energy that is not used

is given off as heat.

Of the following fermentation pathways, which can be carried out by human muscle cells?

lactic acid: homolactic

The main function of the Krebs cycle during cellular respiration is to ______.

make NADH and FADH2 through redox reactions

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

mitochondrion

The light reactions take place in the _________ and the Calvin cycle takes place in the _________.

thylakoids; stroma