Chapter 10: Microbial Metabolism

Question 1

What does metabolism refer to?

A) Only physical workings of the cell
B) Only chemical reactions in the cell
C) Both chemical reactions and physical workings of the cell
D) The process of breaking down macromolecules into smaller molecules

Answer 1

C) Both chemical reactions and physical workings of the cell

Explanation: Metabolism encompasses all chemical reactions as well as the physical workings of the cell, which includes both the synthesis of molecules (anabolism) and their breakdown (catabolism).

Question 2

Fill in the Blank: _______ is a process that results in the synthesis of cell molecules and structures, usually requiring the input of energy.

A) Metabolism
B) Catabolism
C) Anabolism
D) ATP

Answer 2

C) Anabolism

Explanation: Anabolism refers to the part of metabolism that builds up larger molecules from smaller ones, often requiring energy in the form of ATP.

Question 3

True or False: Catabolism typically requires energy input to break down molecules.

A) True
B) False

Answer 3

B) False

Explanation: Catabolic reactions break the bonds of larger molecules into smaller ones and often release energy, rather than requiring it.

Question 4

What is critical to the metabolism process?

A) Protein synthesis
B) Electron transfer
C) Oxygen
D) Water

Answer 4

B) Electron transfer

Explanation: Electrons play a critical role in metabolism; they are transferred from external sources to internal carriers and eventually used to produce energy through a series of proteins that harvest energy.

Question 5

Fill in the Blank: During metabolism, energy is collected and spent in the form of _____ or heat.

A) Glucose
B) ATP
C) Lipids
D) Proteins

Answer 5

B) ATP

Explanation: ATP (adenosine triphosphate) is the main energy currency of the cell. Metabolism involves the collection and expenditure of energy in the form of ATP or heat.

Question 6

What role do enzymes play in a microbial cell?

A) They serve as a blueprint for running metabolic reactions.
B) They act as catalysts to speed up the rate of chemical reactions.
C) They provide the basic building materials for the cell.
D) They store energy for cellular processes.

Answer 6

B) They act as catalysts to speed up the rate of chemical reactions.

Explanation: Enzymes are catalysts that increase the rate of chemical reactions in the cell without being consumed by the reaction.

Question 7

True or False: Enzymes create new chemical reactions in the cell.

A) True
B) False

Answer 7

B) False

Explanation: Enzymes do not create reactions; they accelerate existing chemical reactions by lowering the activation energy required.

Question 8

Enzymes can increase the rate of a reaction, such as the breakdown of urea, by a factor of _____ times compared to an uncatalyzed reaction.

A) 100
B) 1000
C) 1 million
D) 100 trillion

Answer 8

D) 100 trillion

Explanation: Enzymes can significantly increase the rate of chemical reactions, as exemplified by the enzyme urease which can accelerate the breakdown of urea by a factor of 100 trillion.

Question 9

Which of the following is NOT a characteristic of enzymes?

A) They can be recycled and function in low concentrations.
B) They are much smaller in size than their substrates.
C) They have an active site for target molecules.
D) They are not used up or permanently changed by the reaction.

Answer 9

B) They are much smaller in size than their substrates.

Explanation: Enzymes are typically much larger in size than their substrates, which allows them to have active sites where substrates can bind.

Question 10

True or False: Enzymes are permanently changed after they catalyze a reaction.

A) True
B) False

Answer 10

B) False

Explanation: Enzymes are not permanently changed or used up by the reaction they catalyze; they can be reused multiple times.

Question 11

Enzymes are greatly affected by _____ and _____.

A) Temperature; pressure
B) Temperature; pH
C) pH; concentration
D) Concentration; pressure

Answer 11

B) Temperature; pH

Explanation: The activity of enzymes is highly sensitive to changes in temperature and pH, which can alter their structure and function.

Question 12

What is required to initiate a chemical reaction, which is lowered by enzymes to speed up the reaction rate?

A) Enzymatic energy
B) Activation energy
C) Kinetic energy
D) Potential energy

Answer 12

B) Activation energy

Explanation: Activation energy is the initial energy needed to start a reaction. Enzymes lower the activation energy, allowing the reaction to proceed more quickly.

Question 13

True or False: Increasing the concentration of reactants is the most practical way to speed up reactions in living systems.

A) True
B) False

Answer 13

B) False

Explanation: In most living systems, increasing the temperature or the concentration of reactants is not feasible or practical. Catalysts, like enzymes, are used instead to lower the activation energy of reactions.

Question 14

Enzymes work by _______ the rate of molecular collisions without the need for increasing thermal energy or reactant concentration.

Answer 14

Increasing

Explanation: Enzymes speed up reactions by increasing the rate of molecular collisions, acting as a catalyst.

Question 15

What is NOT a method to overcome the activation energy in a reaction?

A) Heating the system
B) Increasing reactant concentration
C) Using a catalyst
D) Cooling the system

Answer 15

D) Cooling the system

Explanation: Cooling the system would typically slow down the reactions rather than overcoming the activation energy. Heating, increasing reactant concentration, and using a catalyst are methods that can overcome activation energy.

Question 16

True or False: An enzyme becomes part of the reaction products after the reaction occurs.

A) True
B) False

Answer 16

B) False

Explanation: Although an enzyme binds to the substrate and participates in the reaction, it is not consumed or becomes a part of the products; it can be reused.

Question 17

Fill in the Blank: The enzyme catalase can convert its substrates at a rate of several ______ per second.

Answer 17

Million

Explanation: Enzymes like catalase can operate at very high speeds, converting substrates at the rate of several million per second.

Question 18

What are the two main types of enzymes?

A) Simple and Complex
B) Simple and Conjugated
C) Active and Inactive
D) Protein and RNA

Answer 18

B) Simple and Conjugated

Explanation: Simple enzymes consist of protein alone, while conjugated enzymes are composed of protein and nonprotein molecules or ions, known as cofactors.

Question 19

True or False: All enzymes are made of proteins.

A) True
B) False

Answer 19

B) False

Explanation: While most enzymes are proteins, there exists a type of enzyme made of RNA, known as ribozymes.

Question 20

Fill in the Blank: The protein component of a conjugated enzyme is called an _______.

Answer 20

Apoenzyme

Explanation: The protein part of a conjugated enzyme is referred to as the apoenzyme.

Question 21

What is the role of cofactors in conjugated enzymes?

A) They provide energy for the enzyme action.
B) They stabilize the enzyme structure.
C) They act as the active site for substrates.
D) They are nonprotein molecules that help the enzyme function.

Answer 21

D) They are nonprotein molecules that help the enzyme function.

Explanation: Cofactors are nonprotein molecules or ions that bind to the apoenzyme to form the active enzyme (holoenzyme) and help in its function.

Question 22

True or False: Catalase, an enzyme that breaks down hydrogen peroxide, requires a metallic cofactor.

A) True
B) False

Answer 22

A) True

Explanation: Catalase is an example of an enzyme that requires a metallic cofactor, specifically iron, to function properly.

Question 23

Fill in the Blank: _______ are enzymes made of RNA that catalyze reactions on other RNA molecules.

Answer 23

Ribozymes

Explanation: Ribozymes are RNA molecules with catalytic properties, which are thought to be remnants of the earliest molecules on Earth.

Question 24

What historical hypothesis is supported by the discovery of ribozymes?

A) Protein World Hypothesis
B) DNA World Hypothesis
C) RNA World Hypothesis
D) Lipid World Hypothesis

Answer 24

C) RNA World Hypothesis

Explanation: The discovery of ribozymes supports the RNA World Hypothesis, which posits that RNA was the first genetic material in ancient cells.

Question 25

What is the range of molecular weight for apoenzymes?

A) 100 to 1,000
B) 1,000 to 12,000
C) 12,000 to 1 million
D) 1 million to 10 million

Answer 25

C) 12,000 to 1 million

Explanation: Apoenzymes can range from small polypeptides with a molecular weight of about 12,000 to large polypeptide conglomerates with a molecular weight of over 1 million.

Question 26

True or False: Apoenzymes only exhibit primary and secondary structures.

A) True
B) False

Answer 26

B) False

Explanation: Apoenzymes, like all proteins, exhibit multiple levels of molecular complexity, including primary, secondary, tertiary, and quaternary structures.

Question 27

The actual site where the substrate binds on an apoenzyme is called the _______ site.

Answer 27

B) Active

Explanation: The active site, also known as the catalytic site, is the specific region on an apoenzyme where the substrate binds.

Question 28

How many active sites can an apoenzyme have?

A) Only one
B) One or several
C) Always two
D) More than ten

Answer 28

B) One or several

Explanation: An apoenzyme can have one or several active sites where substrates bind to undergo a chemical reaction.

Question 29

True or False: The primary structure of an enzyme does not affect its active site.

A) True
B) False

Answer 29

B) False

Explanation: The primary structure of an enzyme, which is the unique sequence and number of amino acids, directly affects the folding and thus the unique active sites of the enzyme.

Question 30

Fill in the Blank: The three-dimensional shape of an enzyme’s active site is formed by the way the _______ chains are folded.

Answer 30

Amino acid

Explanation: The three-dimensional shape of an enzyme, including its active sites, is determined by the folding of amino acid chains.

Question 31

The fit between an enzyme and its substrate is often described as:

A) Slip-and-slide
B) Lock-and-key
C) Push-and-pull
D) Hit-and-miss

Answer 31

B) Lock-and-key

Explanation: The “lock-and-key” model describes the high specificity of the enzyme’s active site as a perfect fit for the substrate, similar to a key fitting into a lock.

Question 32

True or False: Enzyme-substrate interactions can happen very slowly, often taking several minutes per reaction.

A) True
B) False

Answer 32

B) False

Explanation: Enzyme-substrate interactions can occur very quickly, up to millions of times per second, facilitating rapid biological processes.

Question 33

Fill in the Blank: Once the enzyme-substrate complex is formed, the enzyme participates directly in breaking or making bonds, and this state is known as the _______ state.

Answer 33

Transition

Explanation: The transition state refers to the temporary but tight union between the enzyme and substrate during which the enzyme actively participates in the chemical reaction.

Question 34

What happens after the enzyme completes the reaction with the substrate?

A) The enzyme is consumed.
B) The enzyme becomes inactive.
C) The enzyme releases the products and can bind to another substrate.
D) The enzyme permanently bonds with the product.

Answer 34

C) The enzyme releases the products and can bind to another substrate.

Explanation: After the reaction, the enzyme releases the newly formed products and remains unchanged, ready to catalyze another reaction with a new substrate molecule.

Question 35

True or False: For a reaction to occur, the substrate must change the shape of the enzyme’s active site to fit.

A) True
B) False

Answer 35

B) False

Explanation: The enzyme’s active site is already a specific shape to fit the substrate, not the other way around, following the lock-and-key model.

Question 36

Fill in the Blank: The enzyme can attach to another substrate molecule and repeat the action after the _______ is formed and released.

Answer 36

Product

Explanation: After the enzyme-substrate complex leads to the reaction and the product is formed and released, the enzyme is free to attach to another substrate molecule and catalyze a new reaction.

Question 37

What is the role of metal cofactors in enzyme activity?

A) They decrease the enzyme’s activity.
B) They provide structural stability to enzymes.
C) They help with precise functions between the enzyme and its substrate.
D) They store energy for enzyme reactions.

Answer 37

C) They help with precise functions between the enzyme and its substrate.

Explanation: Metal cofactors, such as iron, copper, magnesium, and others, activate enzymes, help bring the active site and substrate together, and participate in chemical reactions.

Question 38

True or False: Coenzymes are the only type of cofactor that enzymes require.

A) True
B) False

Answer 38

B) False

Explanation: Coenzymes are one type of cofactor, and enzymes may also require metal ions as cofactors to assist in their functions.

Question 39

Fill in the Blank: _______ are one of the most important kinds of coenzymes and are vital for nutrition and growth in living organisms.

Answer 39

Vitamins

Explanation: Vitamins are crucial coenzymes that assist enzyme function and are required for nutrition and may be necessary as growth factors for living things.

Question 40

What is the general function of a coenzyme?

A) To provide energy for enzyme reactions.
B) To remove and transfer a chemical group from one substrate to another.
C) To make the enzyme’s active site more specific.
D) To bind permanently to enzymes.

Answer 40

B) To remove and transfer a chemical group from one substrate to another.

Explanation: Coenzymes typically act as transient carriers, removing a chemical group from one substrate molecule and adding it to another, thus aiding the enzyme in performing its function.

Question 41

True or False: Vitamin deficiencies have no effect on the formation of holoenzymes.

A) True
B) False

Answer 41

B) False

Explanation: Vitamin deficiencies can prevent the complete holoenzyme from forming since vitamins are essential coenzymes that contribute to the active enzyme structure.

Question 42

Metal cofactors, such as iron and copper, activate enzymes and help bring the active site and substrate close together, ensuring that _______.

Answer 42

chemical reactions proceed efficiently

Explanation: Metal cofactors are critical in activating enzymes and facilitating the efficient proceeding of chemical reactions between enzymes and substrates.

Question 43

What do oxidoreductases enzymes do?

A) Transfer electrons from one substrate to another.
B) Transfer functional groups from one substrate to another.
C) Cleave bonds on molecules with the addition of water.
D) Catalyze the formation of bonds with the input of ATP.

Answer 43

A) Transfer electrons from one substrate to another.

Explanation: Oxidoreductases are enzymes that catalyze the transfer of electrons from one molecule (the reductant) to another (the oxidant), which is a type of redox reaction.

Question 44

True or False: Isomerases catalyze the rearrangement of bonds within the same molecule.

A) True
B) False

Answer 44

A) True

Explanation: Isomerases are enzymes that convert a molecule from one isomeric form to another, which involves the rearrangement of bonds within that molecule.

Question 45

_______ enzymes catalyze the breaking of various chemical bonds by means of water addition.

Answer 45

Hydrolases

Explanation: Hydrolases are a class of enzymes that cleave bonds on molecules by the addition of water, such as in the digestion of food.

Question 46

What is the function of ligases?

A) To change a substrate into its isomeric form.
B) To add or remove groups from double-bonded substrates.
C) To catalyze the formation of bonds with the input of ATP and removal of water.
D) To transfer functional groups from one substrate to another.

Answer 46

C) To catalyze the formation of bonds with the input of ATP and removal of water.

Explanation: Ligases are enzymes that can join two large molecules together, often requiring energy from ATP and typically accompanied by the removal of water.

Question 47

True or False: Transferases are enzymes that transfer functional groups from ATP to substrates.

A) True
B) False

Answer 47

B) False

Explanation: Transferases are enzymes that transfer functional groups from one substrate to another, not necessarily involving ATP.

Question 48

Fill in the Blank: The enzyme that digests fats is known as _______.

Answer 48

Lipase

Explanation: Lipases are enzymes that break down fats and lipids, often working in the digestive system to process dietary lipids.

Question 49

An enzyme that digests carbohydrates is called a(n):

A) Protease
B) Amylase
C) Lipase
D) DNAse

Answer 49

B) Amylase

Explanation: Amylase is a type of carbohydrase enzyme that acts on starch (amylose) and breaks it down into simpler sugars.

Question 50

What is the action of the enzyme lactase?

A) It synthesizes lactose from glucose and galactose.
B) It breaks lactose down into glucose and galactose.
C) It hydrolyzes the beta-lactam ring of lactose.
D) It catalyzes the reduction of lactose.

Answer 50

B) It breaks lactose down into glucose and galactose.

Explanation: Lactase, a hydrolase enzyme, specifically breaks the disaccharide lactose into its monosaccharide components, glucose and galactose.

Question 51

True or False: Penicillinase catalyzes the formation of penicillin.
A) True
B) False

Answer 51

B) False

Explanation: Penicillinase, also known as beta-lactamase, is a hydrolase enzyme that breaks down penicillin by hydrolyzing its beta-lactam ring, not forming it.

Question 52

Fill in the Blank: DNA polymerase is an enzyme that synthesizes a strand of DNA using _______ as a model.

Answer 52

The complementary DNA strand

Explanation: DNA polymerase is a transferase enzyme that synthesizes DNA by adding nucleotides to a new strand using the complementary strand as a template.

Question 53

What is the function of lactate dehydrogenase?

A) It converts lactate to pyruvic acid.
B) It converts pyruvic acid to ethanol.
C) It converts pyruvic acid to lactate.
D) It converts glucose to lactate.

Answer 53

C) It converts pyruvic acid to lactate.

Explanation: Lactate dehydrogenase is an oxidoreductase enzyme that catalyzes the conversion of pyruvic acid to lactic acid in the process of fermentation.

Question 54

True or False: Oxidase is responsible for the addition of oxygen to substrates.

A) True
B) False

Answer 54

B) False

Explanation: Oxidase, specifically cytochrome oxidase, is an oxidoreductase that catalyzes the reduction of molecular oxygen (O2) by adding electrons and hydrogen, not by adding oxygen to other substrates.

Question 55

What is the role of oxidoreductase enzymes in the cell?

A) They remove electrons from one substrate and add them to another.
B) They catalyze the transfer of oxygen atoms.
C) They synthesize new molecules.
D) They break down molecules without changing electron states.

Answer 55

A) They remove electrons from one substrate and add them to another.

Explanation: Oxidoreductase enzymes are involved in oxidation-reduction (redox) reactions within the cell, where they transfer electrons from one molecule (oxidation) to another (reduction).

Question 56

True or False: In a redox reaction, the compound that gains electrons is said to be oxidized.

A) True
B) False

Answer 56

B) False

Explanation: In redox reactions, the compound that gains electrons is reduced, not oxidized. Oxidation refers to the loss of electrons.

Question 57

Fill in the Blank: _______ and _______ are common coenzyme carriers involved in redox reactions in the cell.

A) ATP and ADP
B) NAD+ and FAD
C) Glucose and fructose
D) Amino acids and nucleotides

Answer 57

B) NAD+ and FAD

Explanation: Nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD) are coenzymes that act as electron carriers in oxidation-reduction reactions.

Question 58

What does the compound that loses electrons in a redox reaction become?

A) Reduced
B) Hydrolyzed
C) Oxidized
D) Ligated

Answer 58

C) Oxidized

Explanation: In redox reactions, the compound that loses electrons undergoes oxidation, hence it is termed as being oxidized.

Question 59

True or False: Redox reactions are uncommon and insignificant in cellular metabolism.

A) True
B) False

Answer 59

B) False

Explanation: Oxidation-reduction (redox) reactions are common and critically important in the cell, playing a major role in the metabolism.

Question 60

Where do exoenzymes perform their functions?

A) Inside the cell where they were produced.
B) Outside the cell where they were produced.
C) On the cell surface only.
D) In the cell nucleus.

Answer 60

B) Outside the cell where they were produced.

Explanation: Exoenzymes are transported extracellularly to perform their tasks, such as breaking down large food molecules or harmful chemicals outside the cell.

Question 61

True or False: Endoenzymes function outside the cell.

A) True
B) False

Answer 61

B) False

Explanation: Endoenzymes function inside the cell. They are involved in most of the metabolic pathways that occur within the cell.

Question 62

Fill in the Blank: Enzymes that are always present and produced in relatively constant amounts regardless of the cellular environment are called _______ enzymes.

Answer 62

Constitutive

Explanation: Constitutive enzymes are produced continuously in a cell and are not influenced by changes in the cellular environment.

Question 63

What happens to the concentration of regulated enzymes in response to changes in substrate concentration?

A) It remains constant.
B) It increases or decreases.
C) It is always induced.
D) It is always repressed.

Answer 63

B) It increases or decreases.

Explanation: Regulated enzymes can be turned on (induced) or turned off (repressed) depending on the concentration of the substrate they act upon.

Question 64

True or False: The addition of more substrate will always increase the number of constitutive enzymes in a cell.

A) True
B) False

Answer 64

B) False

Explanation: The levels of constitutive enzymes remain constant in a cell regardless of the amount of substrate present.

Question 65

Fill in the Blank: Enzymes that are produced at variable rates and amounts, depending on the cellular conditions, are known as _______ enzymes.

Answer 65

Regulated

Explanation: Regulated enzymes are synthesized in amounts and rates that can change in response to the needs of the cell, often as a result of changes in substrate concentration.

Question 66

What is the role of exoenzymes secreted by pathogens?

A) They help in cell respiration.
B) They aid in digestion.
C) They help the pathogen avoid host defenses or promote multiplication in tissues.
D) They repair damaged tissues.

Answer 66

C) They help the pathogen avoid host defenses or promote multiplication in tissues.

Explanation: Pathogenic microorganisms secrete exoenzymes that function as virulence factors, helping them evade host defenses and facilitating their proliferation within host tissues.

Question 67

True or False: All microbial enzymes are harmful and cause tissue damage.

A) True
B) False

Answer 67

B) False

Explanation: While many microbial enzymes act as virulence factors causing tissue damage, not all microbial enzymes are harmful; some, like penicillinase, inactivate antibiotics such as penicillin to protect the microbe.

Question 68

Fill in the Blank: The enzyme streptokinase, produced by Streptococcus pyogenes, is notable because it _______.

Answer 68

digests blood clots

Explanation: Streptokinase is an exoenzyme that digests blood clots and helps the bacterium invade wounds, functioning as a virulence factor.

Question 69

What is the function of the enzyme streptolysin?

A) It synthesizes elastin and collagen.
B) It hydrolyzes lactose into glucose and galactose.
C) It damages blood cells and tissues.
D) It induces the immune response.

Answer 69

C) It damages blood cells and tissues.

Explanation: Streptolysin, an exoenzyme produced by Streptococcus pyogenes, is responsible for damaging blood cells and tissues, which contributes to the bacterium’s pathogenicity.

Question 70

True or False: Competitive inhibition of enzymes involves the use of molecules that resemble the enzyme’s normal substrate.

A) True
B) False

Answer 70

A) True

Explanation: Competitive inhibition occurs when a molecule similar to the enzyme’s normal substrate competes for the active site, thereby inhibiting enzyme activity. Many drugs work on this principle to treat diseases.

Question 71

Fill in the Blank: The enzyme _______ from Clostridium perfringens is known to cause tissue death associated with gas gangrene.

Answer 71

lecithinase C

Explanation: Lecithinase C is a lipase exoenzyme produced by Clostridium perfringens that can cause significant cell membrane damage and tissue death, which is characteristic of gas gangrene.

Question 72

What is the term for the process where high temperatures cause enzymes to lose their structure?

A) Hydrolysis
B) Phosphorylation
C) Denaturation
D) Saturation

Answer 72

C) Denaturation

Explanation: Denaturation refers to the process where high temperatures break the weak bonds in an enzyme, causing it to lose its native structure and function.

Question 73

True or False: Enzymes are stable and active over a wide range of temperatures and pH levels.

A) True
B) False

Answer 73

B) False

Explanation: Enzymes are highly sensitive to their environment and generally operate within a narrow range of temperature, pH, and osmotic pressure. Deviations from these conditions can make them labile and inactive.

Question 74

Fill in the Blank: Enzymes tend to be chemically unstable, or _______, when subjected to changes in their normal conditions of temperature, pH, and osmotic pressure.

Answer 74

Labile

Explanation: Labile means that enzymes are chemically unstable and their activity can be easily disrupted when exposed to changes in their normal environmental conditions.

Question 75

What can cause the distortion of an enzyme’s shape and prevent the substrate from attaching to the active site?

A) Low temperatures only
B) High temperatures only
C) Both low and high temperatures
D) Neutral pH only

Answer 75

C) Both low and high temperatures

Explanation: Both low temperatures, which inhibit catalysis, and high temperatures, which denature the apoenzyme, can disrupt the enzyme’s shape and prevent substrate attachment.

Question 76

True or False: Low or high pH and certain chemicals do not affect enzyme functionality.

A) True
B) False

Answer 76

B) False

Explanation: Extreme pH levels and certain chemicals, like heavy metals and alcohol, can denature enzymes, affecting their functionality.

Question 77

When enzymes are nonfunctional due to denaturation, _______ reactions can be blocked, leading to cell death.

A) Metabolic
B) Digestive
C) Respiratory
D) Excretory

Answer 77

A) Metabolic

Explanation: Nonfunctional enzymes due to denaturation can lead to the blockage of metabolic reactions, which is essential for cell survival, and may result in cell death.

Question 78

How are metabolic pathways typically organized?

A) As single-step reactions.
B) As a multistep series or pathways.
C) Randomly without any specific order.
D) Only in a linear form.

Answer 78

B) As a multistep series or pathways.

Explanation: Metabolic pathways are usually organized as multistep sequences, where each step is catalyzed by a different enzyme.

Question 79

True or False: Metabolic pathways operate in isolation without any interconnections.

A) True
B) False

Answer 79

B) False

Explanation: Metabolic pathways do not stand alone; they are interconnected and often merge at many sites, indicating a complex web of biochemical reactions within a cell.

Question 80

Fill in the Blank: Metabolic pathways can be _______, with the starting molecule being regenerated to initiate another turn of the cycle.

Answer 80

Cyclic

Explanation: Cyclic pathways, like the Krebs cycle, involve a series of reactions where the end product of one reaction is used to initiate another, regenerating the starting molecule.

Question 81

Competitive inhibition occurs when a molecule _______.

Answer 81

Resembles the enzyme’s normal substrate and competes for the active site.

Explanation: Competitive inhibition involves a molecule that mimics the enzyme’s substrate, competing for the active site and preventing the actual substrate from binding.

Question 82

True or False: Noncompetitive inhibition involves the binding of a regulatory molecule at the active site of an enzyme.

A) True
B) False

Answer 82

B) False

Explanation: In noncompetitive inhibition, the regulatory molecule binds to a site other than the active site, causing a change in the enzyme’s conformation and preventing substrate binding.

Question 83

_______ enzymes have two binding sites: one for the substrate at the active site and another called the regulatory site.

Answer 83

Regulated

Explanation: Regulated enzymes are capable of being turned on or off through the binding of molecules at their regulatory sites, not just the active site, providing a means to control enzymatic activity.

Question 84

What is enzyme repression?

A) A process that enhances enzyme activity
B) A mechanism to stop further synthesis of an enzyme
C) A method to permanently deactivate all enzymes
D) A type of competitive inhibition

Answer 84

B) A mechanism to stop further synthesis of an enzyme

Explanation: Enzyme repression occurs when the synthesis of an enzyme is halted due to the sufficient presence of an end product, which acts as a feedback mechanism to conserve cellular resources.

Question 85

True or False: Enzyme induction and repression are mechanisms that bacteria use to waste energy.

A) True
B) False

Answer 85

B) False

Explanation: Enzyme induction and repression are genetic control mechanisms that help bacteria adapt to varying nutrient conditions and prevent the waste of energy by synthesizing enzymes only when needed.

Question 86

Fill in the Blank: The synthesis of an enzyme is induced by its _______.

Answer 86

Substrate

Explanation: Enzyme induction occurs when the synthesis of an enzyme is triggered by the presence of its specific substrate.

Question 87

What happens to an enzyme when the end product of a reaction is in excess?

A) It is synthesized more rapidly.
B) It undergoes competitive inhibition.
C) It is synthesized less due to repression.
D) It becomes more active.

Answer 87

C) It is synthesized less due to repression.

Explanation: When the end product of a reaction builds up to excess, it binds to a site on DNA that regulates the enzyme’s synthesis, leading to enzyme repression and thus less enzyme is produced.

Question 88

True or False: Enzymes are constantly produced at the same rate regardless of the cellular environment.

A) True
B) False

Answer 88

B) False

Explanation: Enzyme synthesis is regulated according to the cell’s needs. Enzymes can be produced at different rates and amounts, controlled by mechanisms such as repression and induction, depending on the presence of substrates or products.

Question 89

Fill in the Blank: A classic example of enzyme induction is the lac operon in Escherichia coli, where the presence of lactose induces the production of _______.

Answer 89

Lactase

Explanation: The lac operon is an example of enzyme induction where the enzyme lactase is produced in response to the presence of lactose, its substrate.

Question 90

Exergonic reactions in cellular metabolism are characterized by:

A) Absorbing energy from the surroundings.
B) Releasing energy to the surroundings.
C) No exchange of energy.
D) Only occurring in photosynthetic organisms.

Answer 90

B) Releasing energy to the surroundings.

Explanation: Exergonic reactions release energy as they proceed, which can be harnessed by the cell for various activities. This energy release is a crucial aspect of metabolism, providing the necessary power for cellular functions.

Question 91

True or False: ATP can store energy from endergonic reactions for later use.

A) True
B) False

Answer 91

B) False

Explanation: ATP actually stores energy released during exergonic reactions. This stored energy is then used to drive endergonic reactions, which require an input of energy to proceed.

Question 92

Fill in the Blank: In cellular metabolism, glucose is broken down in a process called ________, which generates ATP, CO2, and H2O as end products.

Answer 92

Glycolysis and oxidative phosphorylation

Explanation: Glycolysis, followed by oxidative phosphorylation (which includes the Krebs cycle and electron transport chain), is the process by which glucose is oxidized to extract energy for ATP synthesis, resulting in CO2 and H2O as by-products.

Question 93

What molecule is commonly used by cells to store and transfer energy for endergonic reactions?

A) Glucose
B) ATP
C) CO2
D) NADH

Answer 93

B) ATP

Explanation: ATP, or adenosine triphosphate, acts as the primary energy currency in the cell. It captures chemical energy from exergonic reactions and releases it to fuel endergonic processes, making it a critical component of energy transfer within the cell.

Question 94

In redox reactions, the molecule that loses electrons is known as the:

A) Reducing agent
B) Oxidizing agent
C) Reduced agent
D) Oxidized agent

Answer 94

A) Reducing agent

Explanation: The reducing agent donates electrons in a redox reaction, becoming oxidized in the process.

Question 95

True or False: Oxidoreductases are enzymes that facilitate the transfer of electrons between molecules in redox reactions.

A) True
B) False

Answer 95

A) True

Explanation: Oxidoreductases are a class of enzymes that catalyze the transfer of electrons from one molecule (the reductant) to another (the oxidant), which is fundamental in cellular redox reactions.

Question 96

NAD+ is reduced to NADH in a process that involves the addition of a hydrogen ion and ___________.

Answer 96

Two electrons

Explanation: During the reduction of NAD+, it gains two electrons along with a hydrogen ion (proton) to become NADH, which is then used as an electron carrier in cellular metabolism.

Question 97

The energy captured in redox reactions is used to phosphorylate which molecule?

A) Glucose
B) NAD+
C) ATP
D) ADP

Answer 97

D) ADP

Explanation: The energy from redox reactions is often used to add an inorganic phosphate to ADP, thus creating ATP, an energy-rich molecule that powers many cellular processes.

Question 98

True or False: In cellular redox reactions, the removal of hydrogens from a compound is called dehydrogenation.

A) True
B) False

Answer 98

A) True

Explanation: Dehydrogenation is the process of removing hydrogen atoms from a molecule, which effectively means the removal of electrons, as hydrogen atoms consist of a proton and an electron.

Question 99

Which molecule is the most common electron carrier in cells that transfers both electrons and hydrogens?

A) ATP
B) NAD+
C) FAD
D) NADP+

Answer 99

B) NAD+

Explanation: NAD+ is the most common electron carrier in cells, functioning as an oxidizing agent that accepts electrons and a hydrogen ion to become NADH.

Question 100

True or False: In aerobic metabolism, the final electron acceptor is always an inorganic compound other than oxygen.

A) True
B) False

Answer 100

B) False

Explanation: In aerobic metabolism, the final electron acceptor is molecular oxygen, which is reduced to water.

Question 101

Fill in the Blank: The high energy of ATP is due to the strain in the bond between the last two phosphate groups, and when the terminal phosphate is removed, _____ energy is released.

Answer 101

free

Explanation: ATP contains high energy in the bonds between its phosphate groups, particularly the terminal bonds. When these bonds are broken, free energy is released which can be used for cellular work.

Question 102

ATP hydrolysis drives biosynthesis by providing what to individual substrates?

A) A nucleotide
B) A hydrogen atom
C) An activating phosphate
D) A ribose sugar

Answer 102

C) An activating phosphate

Explanation: The hydrolysis of ATP releases a phosphate group that can be transferred to other substrates, providing the activation energy necessary for various biosynthetic processes.

Question 103

True or False: ATP can be regenerated from ADP by the addition of an inorganic phosphate through a process known as substrate-level phosphorylation.

A) True
B) False

Answer 103

A) True

Explanation: Substrate-level phosphorylation is one way that cells regenerate ATP from ADP, by transferring a phosphate group directly from a phosphorylated substrate to ADP.

Question 104

The main energy currency of the cell, which stores and transfers energy for cellular processes, is ____________.

Answer 104

ATP

Explanation: ATP, or Adenosine Triphosphate, is often referred to as the energy currency of the cell. It stores energy when it is not needed and releases it during cellular activities.

Question 105

True or False: In a redox reaction, the oxidizing agent gains electrons and the reducing agent loses electrons.

A) True
B) False

Answer 105

A) True

Explanation: Redox reactions are characterized by the transfer of electrons from the reducing agent, which loses electrons and is oxidized, to the oxidizing agent, which gains electrons and is reduced.

Question 106

Which of the following are electron carriers used by cells?

A) Hemoglobin
B) Insulin
C) NAD+, FAD, NADP+
D) Cholesterol

Answer 106

C) NAD+, FAD, NADP+

Explanation: NAD+, FAD, and NADP+ are coenzymes that function as electron carriers. They play a critical role in redox reactions, facilitating the transfer of electrons in metabolic pathways.

Question 107

What is metabolism?

A) The breakdown of complex molecules into simpler ones.
B) The synthesis of complex molecules from simpler ones.
C) The sum of all chemical processes that occur in a living organism to maintain life.
D) The process by which enzymes are synthesized.

Answer 107

C) The sum of all chemical processes that occur in a living organism to maintain life.

Explanation: Metabolism encompasses both catabolism and anabolism, which involve the breakdown and synthesis of organic molecules, respectively.

Question 108

True or False: Enzymes are consumed during the chemical reactions they catalyze.

A) True
B) False

Answer 108

B) False

Enzymes act as catalysts and are not consumed in the reactions they facilitate; they can be used repeatedly to catalyze many reactions.

Question 109

Fill in the Blank: A holoenzyme is the ________ form of an enzyme and consists of an apoenzyme plus its cofactors.

Answer 109

Active

Explanation: A holoenzyme is the complete, active form of an enzyme, including its apoenzyme (protein component) and necessary non-protein cofactors.

Question 110

Which type of enzyme works outside the cell to degrade large molecules?

A) Endoenzymes
B) Exoenzymes
C) Constitutive enzymes
D) Regulated enzymes

Answer 110

B) Exoenzymes

Explanation: Exoenzymes are secreted by cells and work outside the cell to break down large molecules, often for nutrient acquisition or to protect against pathogens.

Question 111

True or False: Regulated enzymes are produced at a constant rate, regardless of the cellular environment.

A) True
B) False

Answer 111

B) False

Explanation: Regulated enzymes are synthesized in response to the cell’s needs and environmental changes, unlike constitutive enzymes, which are produced at a constant rate.

Question 112

True or False: Enzymes are biological catalysts that speed up biochemical reactions without being consumed in the process.

A) True
B) False

Answer 112

A) True

Explanation: Enzymes are indeed biological catalysts, meaning they accelerate the rate of reactions. They are not consumed in the chemical reactions they catalyze and can be used repeatedly.

Question 113

What is the term used to describe the fit of a substrate into an enzyme’s active site?

A) Induced fit
B) Active lock
C) Enzyme puzzle
D) Lock-and-key fit

Answer 113

D) Lock-and-key fit

Explanation: The term “lock-and-key fit” is used to describe the highly specific interaction between an enzyme and its substrate, where the substrate fits precisely into the active site of the enzyme.

Question 114

Fill in the Blank: Coenzymes are organic molecules that function as _______ for enzymes.

Answer 114

cofactors

Explanation: Coenzymes are a type of cofactor, which are non-protein molecules that assist enzymes in catalyzing reactions.

Question 115

What class of enzymes adds groups to or removes groups from double-bonded substrates?

A) Transferases
B) Hydrolases
C) Lyases
D) Isomerases

Answer 115

C) Lyases

Explanation: Lyases are enzymes that add functional groups to or remove them from double-bonded substrates, often forming new double bonds or rings in the process.

Question 116

Which of the following is NOT a true statement about enzymes?

A) They lower the activation energy of reactions.
B) They are used up during the reaction.
C) They can be highly specific for their substrates.
D) They can be regulated by inhibitors.

Answer 116

B) They are used up during the reaction.

Explanation: Enzymes are not consumed in the reactions they catalyze; they remain unchanged after the reaction and can be reused.

Question 117

Fill in the Blank: The process by which enzymes are regulated by molecules that resemble their substrates is known as _______ inhibition.

Answer 117

competitive

Explanation: Competitive inhibition occurs when a molecule similar in structure to the enzyme’s substrate binds to the active site, preventing the substrate from binding.

Question 118

True or False: ATP is the primary energy currency of the cell, and its hydrolysis drives many cellular processes.

A) True
B) False

Answer 118

A) True

Explanation: ATP (adenosine triphosphate) is indeed the primary molecule for storing and transferring energy in cells. The hydrolysis of ATP releases energy that can be used for various biological processes.

Question 119

Which molecule carries electrons from the Krebs cycle to the electron transport chain?

A) ATP
B) ADP
C) NADH
D) Glucose

Answer 119

C) NADH

Explanation: NADH is a coenzyme that carries electrons from the Krebs cycle to the electron transport chain, where they are used to produce ATP.

Question 120

Fill in the Blank: Anaerobic respiration uses a _______ other than oxygen as the final electron acceptor.

Answer 120

compound

Explanation: Anaerobic respiration involves the use of an electron acceptor other than oxygen, such as sulfate (SO₄²⁻), nitrate (NO₃⁻), or carbon dioxide (CO₂).

Question 121

True or False: Glycolysis is the process by which glucose is broken down into pyruvate and occurs in the absence of oxygen.

A) True
B) False

Answer 121

A) True

Explanation: Glycolysis is a series of reactions that convert glucose into pyruvate, and it can occur with or without oxygen, making it an anaerobic process.

Question 122

What is the primary function of enzymes within a cell?

A) To provide structural support.
B) To speed up chemical reactions.
C) To store genetic information.
D) To generate cellular energy.

Answer 122

B) To speed up chemical reactions.

Explanation: Enzymes are catalysts that significantly increase the rate of reactions by lowering the activation energy.

Question 123

True or False: The apoenzyme is the active form of an enzyme.

A) True
B) False

Answer 123

B) False

Explanation: The apoenzyme is the inactive protein part of an enzyme to which a cofactor must bind to form the active holoenzyme.

Question 124

Fill in the Blank: _____ are enzymes that function inside the cell, while _____ are enzymes that function outside the cell.

Answer 124

Endoenzymes, Exoenzymes

Explanation: Endoenzymes work within the cell, and exoenzymes are secreted to perform their functions outside the cell.

Question 125

Which type of enzyme expression is regulated based on the presence of certain substrates?

A) Constitutive enzymes
B) Regulated enzymes
C) Apoenzymes
D) Holoenzymes

Answer 125

B) Regulated enzymes

Explanation: Regulated enzymes are produced only under certain conditions, such as the presence of a specific substrate, to meet the needs of the cell.

Question 126

True or False: The Krebs cycle occurs in the mitochondrial matrix of eukaryotic cells.

A) True
B) False

Answer 126

A) True

Explanation: The Krebs cycle, part of cellular respiration, occurs in the mitochondrial matrix of eukaryotic cells.

Question 127

Fill in the Blank: The _____ cycle is a series of reactions that produce energy and building blocks for biosynthesis from compounds like glucose.

Answer 127

Krebs

Explanation: The Krebs cycle is a central metabolic pathway that generates energy and precursor molecules for various biosynthetic pathways.

Question 128

What is the final destination for electrons in the electron transport system (ETS)?

A) Oxygen
B) Carbon dioxide
C) Water
D) ATP

Answer 128

A) Oxygen

Explanation: In the electron transport system, the final electron acceptor is oxygen, which combines with hydrogen ions to form water.

Question 129

True or False: Cytochromes in the electron transport chain do not contain a metal atom at their center.

A) True
B) False

Answer 129

B) False

Explanation: Cytochromes are a group of heme proteins central to electron transport and they contain a tightly bound metal atom at their center which is actively involved in accepting and donating electrons.

Question 130

Fill in the Blank: In the electron transport system, the carriers and enzymes are embedded in the _________ membrane in bacteria.

Answer 130

Cytoplasmic

Explanation: In bacteria, the electron transport carriers and enzymes are embedded in the cytoplasmic membrane, whereas in eukaryotes, they are located in the inner mitochondrial membrane.

Question 131

Which of the following is not a principal compound that carries out complex reactions in the respiratory chain?

A) NADH dehydrogenase
B) Flavoproteins
C) Coenzyme Q (ubiquinone)
D) Hemoglobin

Answer 131

D) Hemoglobin

Explanation: Hemoglobin is not involved in the respiratory chain. The compounds that are involved include NADH dehydrogenase, flavoproteins, coenzyme Q (ubiquinone), and cytochromes.

Question 132

True or False: The electron transport chain is not compartmentalized in the cell.

A) True
B) False

Answer 132

B) False

Explanation: The highly compartmentalized structure of the respiratory chain is an important factor in its function, allowing for efficient electron transfer and ATP production.

Question 133

What is the term for the process by which a concentration gradient of hydrogen ions is used to produce ATP?

A) Glycolysis
B) Krebs cycle
C) Chemiosmosis
D) Electron transport chain

Answer 133

C) Chemiosmosis

Explanation: Chemiosmosis refers to the movement of ions across a semipermeable membrane, down their electrochemical gradient. In the context of cellular respiration, it is the process that generates ATP as hydrogen ions (protons) pass through ATP synthase due to a proton motive force across the membrane.

Question 134

True or False: ATP synthase is an enzyme that generates ATP as hydrogen ions flow through the center of the enzyme by diffusion.

A) True
B) False

Answer 134

A) True

Explanation: ATP synthase is indeed a complex enzyme that utilizes the flow of protons (hydrogen ions) through its structure to synthesize ATP from ADP and inorganic phosphate, a process central to chemiosmosis.

Question 135

Fill in the Blank: The __________ motive force consists of a difference in charge across the membrane and is essential for ATP synthesis during chemiosmosis.

Answer 135

Proton

Explanation: The proton motive force is created by the active transport of hydrogen ions across a membrane during electron transport, establishing a gradient that ATP synthase uses to power the synthesis of ATP.

Question 136

What is the final electron acceptor in the electron transport chain during aerobic respiration?

A) Hydrogen peroxide (H₂O₂)
B) Superoxide ion (O₂⁻)
C) Oxygen (O₂)
D) Carbon dioxide (CO₂)

Answer 136

C) Oxygen (O₂)

Explanation: Oxygen acts as the final electron acceptor in the electron transport chain during aerobic respiration. It combines with electrons and protons to form water.

Question 137

True or False: Cyanide is harmful to bacteria because it blocks cytochrome oxidase, thereby completely blocking aerobic respiration.

A) True
B) False

Answer 137

B) False

Explanation: Cyanide causes rapid death in humans and other eukaryotes because it blocks cytochrome oxidase, but it is harmless to certain bacteria that lack cytochrome oxidase, such as Klebsiella and Enterobacter.

Question 138

Fill in the Blank: The enzyme complex that catalyzes the last step of the electron transport chain, where oxygen accepts electrons, is known as ___________.

Answer 138

Cytochrome aa₃ or cytochrome oxidase

Explanation: Cytochrome aa₃, also known as cytochrome oxidase, is the large enzyme complex adapted to receive electrons from another cytochrome, pick up hydrogens from the solution, and react with oxygen to form water in the terminal step of the electron transport chain.

Question 139

Which of the following is not a component of the electron transport chain?

A) NADH dehydrogenase
B) Flavin mononucleotide (FMN)
C) Cytochrome c
D) Hemoglobin

Answer 139

D) Hemoglobin

Explanation: Hemoglobin is not a component of the electron transport chain. It is a protein found in red blood cells that carries oxygen. The electron transport chain components mentioned include NADH dehydrogenase, flavin mononucleotide (FMN), and cytochrome c.

Question 140

True or False: Superoxide dismutase and catalase are enzymes that help aerobes deal with toxic oxygen products.

A) True
B) False

Answer 140

A) True

Explanation: Superoxide dismutase and catalase are enzymes that help aerobic organisms neutralize toxic oxygen species like superoxide ions and hydrogen peroxide, which can be byproducts of the electron transport chain.

Question 141

Fill in the Blank: The process that creates a proton motive force (PMF) across a membrane by actively pumping protons to generate ATP is called ____________.

Answer 141

Chemiosmosis

Explanation: Chemiosmosis is the process where electron transport leads to the active pumping of hydrogen ions (protons) across a membrane, creating a concentration gradient known as the proton motive force, which is then used to produce ATP.

Question 142

The inorganic phosphate and the substrate form a bond with high potential energy in a reaction catalyzed by what enzyme to produce ATP?

A) ATP synthase
B) Cytochrome oxidase
C) NADH dehydrogenase
D) Succinyl dehydrogenase

Answer 142

A) ATP synthase

Explanation: ATP synthase is the enzyme that facilitates the formation of ATP by using the energy from the proton motive force created during electron transport.

Question 143

True or False: Eukaryotic and bacterial cells utilize the same structure for the electron transport system.

A) True
B) False

Answer 143

B) False

Explanation: Eukaryotic cells have electron transport components located in the inner mitochondrial membranes, while bacteria use the cytoplasmic membrane for housing these components.

Question 144

What are the two general categories of fermentation products?

A) Alcoholic and lactic
B) Alcoholic and acidic
C) Acidic and basic
D) Alcoholic and solvent-based

Answer 144

B) Alcoholic and acidic

Explanation: Fermentation products can be broadly classified into alcoholic and acidic categories. Alcoholic fermentation is typically carried out by yeast or bacterial species and results in the production of ethanol, while acidic fermentation results in the production of organic acids like lactic acid.

Question 145

True or False: During alcoholic fermentation, NAD+ is regenerated, allowing glycolysis to continue.

A) True
B) False

Answer 145

A) True

Explanation: In alcoholic fermentation, the oxidation of NADH to NAD+ occurs when acetaldehyde is reduced to ethanol, which allows glycolysis to continue by providing the necessary NAD+ for glycolysis reactions.

Question 146

Fill in the Blank: In alcoholic fermentation, pyruvic acid is first converted to _________, which is then reduced to ethanol.

Answer 146

acetaldehyde

Explanation: The first step in alcoholic fermentation involves the conversion of pyruvic acid to acetaldehyde. This decarboxylation step is followed by the reduction of acetaldehyde to ethanol, which regenerates NAD+ from NADH, allowing glycolysis to continue.

Question 147

What is the primary chemical in which energy is stored in cells?

A) Glucose
B) ATP
C) NADH
D) CO2

Answer 147

B) ATP

Explanation: ATP, or adenosine triphosphate, is known as the energy currency of the cell. It stores energy in its high-energy phosphate bonds, which can be released to fuel cellular processes.

Question 148

True or False: In the absence of oxygen, cells cannot produce ATP.

A) True
B) False

Answer 148

B) False

Explanation: Cells can still produce ATP in the absence of oxygen through processes such as fermentation. Although less efficient than aerobic respiration, fermentation allows cells to generate ATP without oxygen.

Question 149

Fill in the Blank: During aerobic respiration, the final electron acceptor in the electron transport chain is _______.

Answer 149

oxygen (O2)

Explanation: In aerobic respiration, electrons are transferred through a series of carriers to the final electron acceptor, which is oxygen. Oxygen accepts electrons and protons to form water, completing the electron transport chain.

Question 150

What by-product of aerobic metabolism can contribute to cellular damage if not neutralized?

A) Oxygen (O2)
B) Carbon dioxide (CO2)
C) Superoxide ion (O2−)
D) Ethanol (C2H5OH)

Answer 150

C) Superoxide ion (O2−)

Explanation: Superoxide ions are a by-product of aerobic metabolism and can cause significant damage to cells if not neutralized by enzymes like superoxide dismutase.

Question 151

True or False: The Krebs cycle only occurs in the presence of oxygen.

A) True
B) False

Answer 151

B) False

Explanation: The Krebs cycle itself does not require oxygen; however, it is part of aerobic respiration because it is linked to the electron transport chain, which does require oxygen. In the absence of oxygen, cells may undergo fermentation, bypassing the electron transport chain.

Question 152

Fill in the Blank: The energy stored in acetyl CoA is transferred to NAD+ and FAD by reducing them, producing NADH and FADH2 during the _______ cycle.

Answer 152

Krebs

Explanation: The Krebs cycle involves a series of reactions where acetyl CoA is oxidized, transferring its energy to electron carriers NAD+ and FAD, which are reduced to NADH and FADH2, respectively. These carriers then transport electrons to the electron transport chain.

Question 153

What are the three main catabolic pathways, and what is the estimated ATP yield for each?

A) Glycolysis (2 ATP), Krebs cycle (2 ATP), Electron transport chain (34 ATP)
B) Glycolysis (2 ATP), Krebs cycle (2 ATP), Electron transport chain (36 ATP)
C) Glycolysis (4 ATP), Krebs cycle (2 ATP), Electron transport chain (32 ATP)
D) Glycolysis (4 ATP), Krebs cycle (2 ATP), Electron transport chain (38 ATP)

Answer 153

C) Glycolysis (4 ATP), Krebs cycle (2 ATP), Electron transport chain (32 ATP)

Explanation: Glycolysis produces 2 ATP directly and 2 NADH, which can yield approximately 2 ATP in the electron transport chain. The Krebs cycle produces 2 ATP and several NADH and FADH2, which can yield approximately 6 ATP in the electron transport chain.

Question 154

True or False: The Krebs cycle is identical in bacteria and eukaryotes.

A) True
B) False

Answer 154

B) False

Explanation: While the overall steps of the Krebs cycle are similar in bacteria and eukaryotes, there are some differences in the enzymes and intermediates involved. For example, some bacteria have variations in the enzymes used in the cycle and may produce different intermediates as byproducts.

Question 155

Which of the following statements describes the electron transport system?

A) It occurs in the cytoplasm of the cell.
B) It involves the transfer of electrons along a series of carriers, leading to the production of ATP.
C) It is independent of oxygen.
D) It occurs after glycolysis but before the Krebs cycle.

Answer 155

B) It involves the transfer of electrons along a series of carriers, leading to the production of ATP.

Explanation: The electron transport system is a series of membrane-bound protein complexes and cytochromes located in the inner mitochondrial membrane in eukaryotes (or the plasma membrane in prokaryotes). It involves the transfer of electrons from electron carriers (NADH and FADH2) to oxygen, generating ATP through oxidative phosphorylation.

Question 156

True or False: Anaerobic respiration yields more ATP than aerobic respiration.

A) Ture
B) False

Answer 156

B) False

Explanation: Anaerobic respiration typically yields less ATP than aerobic respiration because oxygen is not available as the final electron acceptor, resulting in the incomplete oxidation of glucose and a lower ATP yield.

Question 157

How are noncarbohydrate compounds catabolized?

A) They are converted directly into glucose for use in glycolysis.
B) They are first converted into intermediate metabolites that can enter glycolysis or the Krebs cycle.
C) They are broken down into fatty acids and glycerol.
D) They are stored as fat in adipose tissue.

Answer 157

B) They are first converted into intermediate metabolites that can enter glycolysis or the Krebs cycle.

Explanation: Noncarbohydrate compounds such as proteins and lipids are broken down into their constituent molecules (amino acids and fatty acids, respectively) and converted into intermediate metabolites that can enter central metabolic pathways such as glycolysis or the Krebs cycle for further catabolism and energy production.