Cellular And Molecular Biology

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Cellular And Molecular Biology - Quiz

Have you studied cellular and molecular biology well? Take this cellular and molecular biology quiz, and see how much you know about these topics. It is basically the study of the structure and function of organisms and biological processes at the level of cells and the macromolecules that define them. You can either practice or test your knowledge here, and your scores will say it all. All the best! Do not forget to share the quiz results with other medical people.


Questions and Answers
  • 1. 

    The sodium-potassium pump makes the cell interior more ______ by pumping ____ sodium ions out of the cell for every ____ potassium ions pumped in.

    • A.

      Negative, 3, 2

    • B.

      Negative, 2, 3

    • C.

      Positive, 3, 2

    • D.

      Positive, 2, 3

    • E.

      Negative, 4, 3

    Correct Answer
    A. Negative, 3, 2
    Explanation
    The sodium-potassium pump is an active transport mechanism that helps maintain the electrochemical gradient across the cell membrane. It uses ATP energy to pump three sodium ions out of the cell for every two potassium ions pumped into the cell. This creates an imbalance of positive charges outside the cell and negative charges inside the cell, making the cell interior more negative.

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  • 2. 

    What is the distinguishing characteristic of a P-type pump?

    • A.

      It must be pumped during the cycle.

    • B.

      It must be phosphorylated during the cycle.

    • C.

      It must be protonated during the cycle.

    • D.

      It must be deprotonated during the cycle.

    • E.

      It must be potassiumated during the cycle.

    Correct Answer
    B. It must be phosphorylated during the cycle.
    Explanation
    The distinguishing characteristic of a P-type pump is that it must be phosphorylated during the cycle. Phosphorylation is a process in which a phosphate group is added to a molecule, typically a protein, which can alter its structure and function. In the case of a P-type pump, phosphorylation is necessary for the pump to undergo conformational changes that allow it to transport ions across a membrane. This phosphorylation-dephosphorylation cycle is essential for the proper functioning of P-type pumps.

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  • 3. 

    In the Na+/glucose cotransporter, _____ moving down its/their gradient drive the transport of _____ against its/their gradient.

    • A.

      Na+ ions, K+ ions

    • B.

      Na+ ions, glucose

    • C.

      Glucose, Na+ ions

    • D.

      K+ ions, glucose

    • E.

      Glucose, K+ ions

    Correct Answer
    B. Na+ ions, glucose
    Explanation
    In the Na+/glucose cotransporter, the movement of Na+ ions down their gradient drives the transport of glucose against its gradient. This means that Na+ ions move from an area of higher concentration to lower concentration, while glucose moves from an area of lower concentration to higher concentration. This process is known as secondary active transport, where the energy stored in the Na+ ion gradient is used to transport glucose against its concentration gradient.

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  • 4. 

    Which enzyme of the Krebs (TCA) cycle is different from the others with respect to its location, and where is it located?

    • A.

      Succinate dehydrogenase, mitochondrial matrix

    • B.

      Malate dehydrogenase, mitochondrial matrix

    • C.

      Succinate dehydrogenase, inner mitochondrial membrane

    • D.

      Malate dehydrogenase, inner mitochondrial membrane

    • E.

      Succinate dehydrogenase, intermembrane space

    Correct Answer
    C. Succinate dehydrogenase, inner mitochondrial membrane
    Explanation
    Succinate dehydrogenase is the only enzyme of the Krebs (TCA) cycle that is located in the inner mitochondrial membrane. The other enzymes, including malate dehydrogenase, are located in the mitochondrial matrix.

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  • 5. 

    The movement of water through a semipermeable membrane from a region of higher water concentration to a region of lower water concentration is called ________.

    • A.

      Diffusion

    • B.

      Osmosis

    • C.

      Denaturation

    • D.

      Metabolism

    • E.

      Solubility

    Correct Answer
    B. Osmosis
    Explanation
    Osmosis is the correct answer because it refers to the movement of water molecules across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration. This process occurs in order to equalize the concentration of solutes on both sides of the membrane. Diffusion, on the other hand, refers to the movement of particles (not just water) from an area of higher concentration to an area of lower concentration. Denaturation, metabolism, and solubility are unrelated to the movement of water through a semipermeable membrane.

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  • 6. 

    The phosphorylation of glucose to generate glucose-6-phosphate is catalyzed by the enzyme hexokinase. This enzyme, however, is inhibited by its own product, glucose-6-phosphate. This is an example of

    • A.

      Allosteric regulation

    • B.

      Irreversible inhibition

    • C.

      Non-covalent modification

    • D.

      Feedback regulation

    • E.

      Covalent modification

    Correct Answer
    D. Feedback regulation
    Explanation
    The inhibition of hexokinase by its own product, glucose-6-phosphate, is an example of feedback regulation. In feedback regulation, the end product of a metabolic pathway inhibits an earlier step in the pathway, thereby regulating the overall rate of the pathway. In this case, the accumulation of glucose-6-phosphate inhibits the activity of hexokinase, preventing further phosphorylation of glucose and regulating the flow of glucose through the pathway.

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  • 7. 

    A protein extract containing an enzyme of interest is prepared from a tissue. The enzyme activity is tested using a panel of suspected substrates. However, the enzyme is not active, leading to the conclusion that none of the compounds is the enzyme’s substrate. One student of Biol218-003 suggests adding ATP to the enzyme mixture. Suddenly a reaction is observed in one of the tubes. After adding ATP, the enzyme was purified, and one of its amino acids had a phosphate group. This is an example of

    • A.

      Lucky guess

    • B.

      Covalent modification of enzymes

    • C.

      Activation of the enzymatic activity by a kinase

    • D.

      B and c

    Correct Answer
    D. B and c
    Explanation
    The correct answer is b and c, covalent modification of enzymes and activation of the enzymatic activity by a kinase. This is because the addition of ATP, which is a source of phosphate groups, resulted in the enzyme becoming active and one of its amino acids having a phosphate group. This suggests that the enzyme was modified through the covalent attachment of a phosphate group, which can be catalyzed by a kinase enzyme.

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  • 8. 

    A transport system that moves two solutes into the cell during a single cycle accompanied by no expenditure of energy could be called a(n) ________

    • A.

      Active antiport

    • B.

      Active uniport

    • C.

      Passive antiport

    • D.

      Active symport

    • E.

      Passive symport

    Correct Answer
    E. Passive symport
    Explanation
    A transport system that moves two solutes into the cell during a single cycle without using any energy is called a passive symport. In a symport, both solutes are transported in the same direction across the cell membrane. The term "passive" indicates that the transport process does not require energy expenditure. Therefore, the correct answer is passive symport.

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  • 9. 

    Feedback inhibitors bind to the

    • A.

      Allosteric site

    • B.

      Active site

    • C.

      Substrate

    • D.

      Cofactor

    • E.

      A and b

    Correct Answer
    A. Allosteric site
    Explanation
    Feedback inhibitors are molecules that regulate enzyme activity by binding to a site on the enzyme other than the active site, known as the allosteric site. This binding causes a conformational change in the enzyme's structure, which can either inhibit or enhance its activity. By binding to the allosteric site, feedback inhibitors can effectively regulate enzyme activity and control metabolic pathways. Therefore, the correct answer is the allosteric site.

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  • 10. 

    Which type of RNA brings the amino acids to the ribosomes during protein synthesis?

    • A.

      SRNA

    • B.

      RRNA

    • C.

      TRNA

    • D.

      MRNA

    Correct Answer
    C. TRNA
    Explanation
    tRNA, or transfer RNA, is responsible for bringing the amino acids to the ribosomes during protein synthesis. It acts as a carrier molecule, binding to specific amino acids and delivering them to the ribosomes where they are assembled into a protein chain. tRNA molecules have an anticodon sequence that is complementary to the codon sequence on the mRNA, allowing them to recognize and bind to the appropriate amino acid. This process ensures that the correct amino acids are added to the growing protein chain in the ribosome.

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  • 11. 

    The inner membrane of the mitochondria has a high protein tolipid ratio because it contains ____________.

    • A.

      Electron transport chain

    • B.

      ATP synthase

    • C.

      Cardiolysin

    • D.

      A and b

    • E.

      A and c

    Correct Answer
    D. A and b
    Explanation
    The inner membrane of the mitochondria has a high protein to lipid ratio because it contains both the electron transport chain and ATP synthase. The electron transport chain is responsible for generating ATP, while ATP synthase is the enzyme that actually produces ATP. Both of these processes require a high concentration of proteins in the inner membrane to function effectively. Therefore, the high protein to lipid ratio is necessary for the proper functioning of these crucial processes in the mitochondria.

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  • 12. 

    What is the purpose of uncoupling proteins in mammalian brown adipose tissue (baby fat)?

    • A.

      They help the tissue expand and contract when needed.

    • B.

      They function as a source of heat production during exposure to cold temperatures.

    • C.

      They allow the production of a larger number of ATPs per glucose.

    • D.

      They allow muscles to contract more efficiently.

    • E.

      They give the tissue its color.

    Correct Answer
    B. They function as a source of heat production during exposure to cold temperatures.
    Explanation
    Uncoupling proteins in mammalian brown adipose tissue, also known as baby fat, function as a source of heat production during exposure to cold temperatures. These proteins uncouple the process of ATP synthesis from the electron transport chain, leading to the generation of heat instead of ATP. This heat production helps to regulate body temperature and keep the body warm in cold conditions.

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  • 13. 

    Which molecule below plays a key role in regulating the rate of glycolysis and Krebs cycle by regulating the activity of key enzymes?

    • A.

      ADP

    • B.

      ATP

    • C.

      Inorganic Phosphate

    • D.

      Molecular oxygen

    • E.

      None of the above

    Correct Answer
    B. ATP
    Explanation
    ATP plays a key role in regulating the rate of glycolysis and the Krebs cycle by regulating the activity of key enzymes. ATP is the primary energy currency of the cell and is involved in energy transfer within cells. It acts as a substrate for enzymes involved in glycolysis and the Krebs cycle, providing the necessary energy for these processes to occur. Additionally, ATP can also act as an allosteric regulator, binding to enzymes and altering their activity. Therefore, ATP is essential in regulating the rate of these metabolic pathways.

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  • 14. 

    Metabolic pathways that make available raw materials from which other molecules can be synthesized and that provide chemical energy required for many cell activities are known as ______.

    • A.

      Anabolism

    • B.

      Catabolism

    • C.

      Manabolism

    • D.

      Allosterism

    Correct Answer
    B. Catabolism
    Explanation
    Catabolism refers to the metabolic pathways that break down complex molecules into simpler ones, releasing energy in the process. These pathways provide the chemical energy required for various cell activities and also produce raw materials that can be used for the synthesis of other molecules. Anabolism, on the other hand, is the opposite process, involving the synthesis of complex molecules from simpler ones, requiring energy input. Manabolism and allosterism are not recognized terms in the context of metabolic pathways.

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  • 15. 

    A reaction involving the gain of one or more electrons is a(n) _________ reaction.

    • A.

      Oxidation

    • B.

      Reduction

    • C.

      Inclusion

    • D.

      Elimination

    • E.

      None of the above

    Correct Answer
    B. Reduction
    Explanation
    A reaction involving the gain of one or more electrons is called a reduction reaction. In a reduction reaction, the species involved accepts electrons, resulting in a decrease in its oxidation state. This process is often associated with the addition of hydrogen or the removal of oxygen from a compound. Reduction reactions are commonly observed in many chemical and biological processes, such as the conversion of an oxidized metal to its reduced form or the reduction of carbon dioxide to produce glucose during photosynthesis.

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  • 16. 

    In order to take full advantage of the energy released during an exergonic reaction, it is ______________.

    • A.

      Done in small steps

    • B.

      Used to drive the temperature of the cells up

    • C.

      Coupled to an endergonic reaction

    • D.

      Coupled to another exergonic reaction

    Correct Answer
    C. Coupled to an endergonic reaction
    Explanation
    In order to take full advantage of the energy released during an exergonic reaction, it is coupled to an endergonic reaction. This means that the energy released from the exergonic reaction is used to drive the endergonic reaction, which requires an input of energy. By coupling the two reactions together, the energy released from the exergonic reaction can be effectively utilized to power the endergonic reaction, maximizing the overall energy efficiency of the system.

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  • 17. 

    Which of the following is the primary function of fermentation?

    • A.

      Completely break down a glucose molecule to carbon dioxide and water

    • B.

      Produce ATP by chemiosmosis

    • C.

      Oxidize NAD+ to NADH

    • D.

      Oxidize NADH to NAD+

    • E.

      All of the above

    Correct Answer
    D. Oxidize NADH to NAD+
    Explanation
    Fermentation is a metabolic process that occurs in the absence of oxygen. One of its primary functions is to regenerate NAD+ from NADH. During glycolysis, glucose is partially broken down into pyruvate, producing NADH in the process. In order for glycolysis to continue, NADH must be converted back to NAD+ so that it can accept more electrons in subsequent reactions. This is achieved through fermentation, which oxidizes NADH to NAD+. Therefore, the correct answer is "oxidize NADH to NAD+".

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  • 18. 

    Which reaction below might be a suitable coupled reaction for the reaction A + B <—> C + D (ÄG = +6.7 kcal/mole)?

    • A.

      E + F G + H (ÄG = -5.4 kcal/mole)

    • B.

      C + F G + H (ÄG = -5.4 kcal/mole)

    • C.

      E + F G + H (ÄG = -8.3 kcal/mole)

    • D.

      E + F G + H (ÄG = -9.7 kcal/mole)

    • E.

      None of them

    Correct Answer
    E. None of them
  • 19. 

    The outer membrane of the mitochondria has large channels surrounded by a Beta barrel called _________________.

    • A.

      Proton pump

    • B.

      Cardiolipin

    • C.

      Porins

    • D.

      Cytochrome complex

    • E.

      ATP synthesis

    Correct Answer
    C. Porins
    Explanation
    The outer membrane of the mitochondria contains large channels surrounded by a Beta barrel, which are called porins. These porins allow the passage of small molecules, such as ions and metabolites, across the membrane. They play a crucial role in regulating the transport of molecules into and out of the mitochondria, contributing to the overall function and communication of the organelle with the rest of the cell.

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  • 20. 

    The redox centers of most of the proteins of the respiratory chain are made up of _________________.

    • A.

      Flavoproteins

    • B.

      Vitamins

    • C.

      Prosthetic groups

    • D.

      Cytochromes

    • E.

      Ubiquinone

    Correct Answer
    C. Prosthetic groups
    Explanation
    Prosthetic groups are non-protein molecules that are tightly bound to proteins and play a crucial role in their function. In the context of the respiratory chain, prosthetic groups are responsible for carrying and transferring electrons during the process of cellular respiration. They are essential for the redox reactions that occur in the respiratory chain, allowing the proteins to accept and donate electrons. Therefore, the redox centers of most proteins in the respiratory chain are made up of prosthetic groups.

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  • 21. 

    An electrochemical gradient is caused by __________________.

    • A.

      Energy distribution

    • B.

      Voltage gradient

    • C.

      Concentration gradient

    • D.

      A and b

    • E.

      B and c

    Correct Answer
    E. B and c
    Explanation
    An electrochemical gradient is caused by both a voltage gradient and a concentration gradient. A voltage gradient refers to a difference in electrical potential between two points, while a concentration gradient refers to a difference in the concentration of a substance between two points. In the context of electrochemical gradients, both of these factors play a role in the movement of ions or molecules across a membrane. The voltage gradient provides the driving force for charged particles to move, while the concentration gradient determines the direction of movement based on the principle of diffusion. Therefore, both a voltage gradient and a concentration gradient are necessary for the establishment of an electrochemical gradient.

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  • 22. 

    Which molecule is the final electron acceptor in the electron transport chain?

    • A.

      ATP

    • B.

      Water

    • C.

      NADH

    • D.

      Oxygen

    • E.

      FADH2

    Correct Answer
    D. Oxygen
    Explanation
    In the electron transport chain, oxygen serves as the final electron acceptor. After electrons flow through the chain, they combine with oxygen to form water molecules. This process is crucial for the production of ATP, as it generates a proton gradient that drives ATP synthesis. Without oxygen as the final electron acceptor, the electron transport chain would not be able to continue functioning properly, leading to a decrease in ATP production.

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  • 23. 

    Diffusion during which the substance to be transported binds selectively to a membrane-spanning protein, which helps the process along, is called ________.

    • A.

      Osmosis

    • B.

      Facilitated Osmosis

    • C.

      Simple Diffusion

    • D.

      Facilitated Diffusion

    • E.

      Active Transport

    Correct Answer
    D. Facilitated Diffusion
    Explanation
    Facilitated diffusion is the correct answer because it involves the substance being transported binding selectively to a membrane-spanning protein. This protein helps to facilitate the movement of the substance across the membrane, but does not require any energy input from the cell. This process is different from simple diffusion, where substances passively move across the membrane without the aid of a protein, and active transport, which requires energy expenditure by the cell. Osmosis refers specifically to the movement of water across a membrane, and facilitated osmosis is not a recognized term.

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  • 24. 

    An important aspect of transport by facilitated transporters and pumps is

    • A.

      Conformational shifts

    • B.

      Rigidity softness

    • C.

      á-helix

    • D.

      B-pleated sheet

    Correct Answer
    A. Conformational shifts
    Explanation
    Transport by facilitated transporters and pumps involves conformational shifts, which refers to the changes in the shape or conformation of the transporter or pump protein. These conformational shifts are crucial for the transport process as they allow the protein to undergo specific structural changes that enable the binding and movement of molecules across the cell membrane. The conformational shifts can be triggered by various factors such as the binding of the transported molecule, changes in the membrane potential, or the presence of specific ions. Overall, conformational shifts play a key role in facilitating the transport of molecules across biological membranes.

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  • 25. 

    The site of aerobic respiration (electron transport chain) and ATP formation is in the _________________ of the Mitochondria.

    • A.

      Outer membrane

    • B.

      Matrix

    • C.

      Inner membrane

    • D.

      Intermembrane space

    Correct Answer
    D. Intermembrane space
    Explanation
    The correct answer is the intermembrane space. This is where the electron transport chain takes place, which is a series of protein complexes that transfer electrons and generate a proton gradient. This proton gradient is then used by ATP synthase, located in the inner membrane, to produce ATP. The intermembrane space is the region between the outer and inner membranes of the mitochondria, allowing for the efficient transfer of protons during aerobic respiration.

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  • 26. 

    One mechanism (or class of molecules) by which ions are specifically transported into the cell is the

    • A.

      Induced fit model

    • B.

      Gated channels

    • C.

      Carrier protein transport

    • D.

      Uniport transport

    • E.

      All of the above

    Correct Answer
    B. Gated channels
    Explanation
    Gated channels are a mechanism by which ions are specifically transported into the cell. Gated channels are protein channels that open and close in response to specific signals or stimuli, allowing ions to pass through the cell membrane. This mechanism ensures that only specific ions are transported into the cell, maintaining ion homeostasis and regulating cellular processes. The induced fit model, carrier protein transport, and uniport transport are other mechanisms for ion transport, but they are not specifically mentioned in the question. Therefore, the correct answer is gated channels.

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  • 27. 

    During strenuous exercise, you may notice that your muscles burn. Which of the following statements best explains this phenomenon?

    • A.

      Proteins are being digested to provide energy

    • B.

      ADP is accumulating, which produces a burning sensation

    • C.

      Without oxygen, pyruvate is converted to lactic acid.

    • D.

      Pyruvic acid causes muscle pain.

    • E.

      Carbon dioxide is building up in muscle and changing the pH.

    Correct Answer
    C. Without oxygen, pyruvate is converted to lactic acid.
    Explanation
    During strenuous exercise, when the body cannot supply enough oxygen to the muscles, pyruvate, a product of glucose breakdown, is converted into lactic acid through anaerobic respiration. This process is known as lactic acid fermentation. The accumulation of lactic acid in the muscles leads to a burning sensation or muscle pain. Therefore, the statement "Without oxygen, pyruvate is converted to lactic acid" best explains the phenomenon of muscles burning during strenuous exercise.

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  • 28. 

    Of the following molecules, which would NOT be expected to be moved across a membrane by simple diffusion?

    • A.

      Fatty acids

    • B.

      Glucose

    • C.

      Oxygen

    • D.

      Water

    Correct Answer
    B. Glucose
    Explanation
    Glucose would not be expected to be moved across a membrane by simple diffusion because it is a large polar molecule. Simple diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, without the need for a transport protein. However, glucose is a large molecule and it is polar, meaning it has a charge imbalance. These characteristics make it difficult for glucose to pass through the hydrophobic interior of the lipid bilayer of the cell membrane. Therefore, glucose requires the assistance of specific transport proteins to facilitate its movement across the membrane.

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  • 29. 

    You are trying to figure out an electron transport pathway including the following electron transport molecules: B, K, T, and X. You do so by employing inhibitors for various steps in the process. When you do, you get the following results:Inhibitor                                Electron Transport Molecules Trapped in                                              Reduced FormTicin                                    Q& KDigitin                                  KEstin                                   T, K, Q & BLucin                                   Q, K & TWhat is the order of the molecules (the pathway) in the electron transport chain suggested by the above data from the most reduced to the least reduced molecule?

    • A.

      K¨ T ¨ B¨ Q ¨ X

    • B.

      K ¨ X ¨ B ¨ Q ¨ T

    • C.

      K ¨ Q ¨ T ¨ B ¨ X

    • D.

      X ¨ B ¨ T ¨ Q ¨ K

    • E.

      T ¨ B ¨ K ¨ Q ¨ X

    Correct Answer
    C. K ¨ Q ¨ T ¨ B ¨ X
    Explanation
    The given results show that Ticin traps Q and K, Digitin traps K and Estin traps T, K, and Q. From this information, we can deduce the order of the molecules in the electron transport chain from the most reduced to the least reduced. Based on the inhibitors and the molecules they trap, the correct order is K ¨ Q ¨ T ¨ B ¨ X.

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  • 30. 

    A researcher is interested in the mode of transport across the cell membrane of three different substances: A, B, and C. His data are reported in the graphs associated with the following questions. The graph above shows the initial rate of transport for each substance when the cells are placed in solutions of different concentrations of A, B, and C. Based on this data, substance A is transported via

    • A.

      Simple diffusion

    • B.

      Active transport

    • C.

      Facilitated diffusion

    • D.

      Passive transport

    • E.

      A, b and c

    Correct Answer
    A. Simple diffusion
    Explanation
    The graph shows that the initial rate of transport for substance A increases as the concentration of substance A in the solution increases. This indicates that substance A is being transported across the cell membrane in a manner that is not dependent on any external energy source or transport proteins. This is consistent with simple diffusion, where substances move from an area of higher concentration to an area of lower concentration without the need for energy or specialized transport proteins. Therefore, substance A is transported via simple diffusion.

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  • 31. 

    Based on the same graph, substances B and C

    • A.

      Are transported by a transporter protein

    • B.

      Do not move by simple diffusion

    • C.

      Show saturation kinetics

    • D.

      A and B only

    • E.

      All of the above

    Correct Answer
    E. All of the above
    Explanation
    The correct answer is "all of the above". Based on the graph, substances B and C are transported by a transporter protein, as indicated by the presence of a specific curve for their transport. Additionally, they do not move by simple diffusion, as simple diffusion would result in a linear relationship between concentration and rate of transport. Finally, the graph shows saturation kinetics for substances B and C, as the rate of transport plateaus at higher concentrations, indicating that all available transporter proteins are being utilized. Therefore, all three statements - substances B and C being transported by a transporter protein, not moving by simple diffusion, and showing saturation kinetics - are supported by the graph.

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  • 32. 

    The statement, "The total amount of energy in the universe is constant," is a tenet (part or implication) of

    • A.

      Thermodynamic spontaneity

    • B.

      The second law of thermodynamics

    • C.

      Enthalpy

    • D.

      The first law of thermodynamics

    • E.

      Entropy

    Correct Answer
    D. The first law of thermodynamics
    Explanation
    The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. This means that the total amount of energy in the universe remains constant.

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  • 33. 

    In a chemical reaction, the standard free energy change (¢G‹') is calculated to be 3.67 cal/mol. What can be said of the chemical reaction?

    • A.

      The reaction is not spontaneous under standard conditions.

    • B.

      There can be no reaction.

    • C.

      The reaction is at equilibrium under standard conditions.

    • D.

      Products predominate over reactants at equilibrium under standard conditions.

    • E.

      The reaction goes spontaneously to the right under standard conditions.

    Correct Answer
    A. The reaction is not spontaneous under standard conditions.
    Explanation
    The positive value of the standard free energy change (¢G‹') indicates that the reaction is not spontaneous under standard conditions. Spontaneous reactions have a negative ¢G‹' value, indicating that they can occur without the input of external energy. In this case, the positive value suggests that the reaction requires an input of energy to proceed.

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  • 34. 

    A negative free energy change indicates that

    • A.

      The reactant is predominant in equilibrium

    • B.

      The reaction is not possible

    • C.

      The reaction is at equilibrium

    • D.

      Energy must be added to the reaction before it can proceed.

    • E.

      The reaction is exothermic.

    Correct Answer
    E. The reaction is exothermic.
    Explanation
    A negative free energy change indicates that the reaction is exothermic. This means that the reaction releases energy in the form of heat. In an exothermic reaction, the products have lower energy than the reactants, resulting in a negative change in free energy. Therefore, the statement "the reaction is exothermic" is the correct explanation for a negative free energy change.

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  • 35. 

    A spontaneous reaction

    • A.

      Has to occur immediately.

    • B.

      Is associated exclusively with homeothermic organisms

    • C.

      Has an overall positive free energy change

    • D.

      Will never occur

    • E.

      Could occur but might take a very long time.

    Correct Answer
    E. Could occur but might take a very long time.
    Explanation
    A spontaneous reaction refers to a reaction that can occur without any external influence or intervention. While it is true that a spontaneous reaction can occur immediately, it is not a requirement. Spontaneous reactions can also occur over a longer period of time, although they may be slower. This is because the overall free energy change of the reaction is positive, meaning that the products have a higher energy state than the reactants. Therefore, although a spontaneous reaction could occur, it might take a very long time to reach completion.

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  • 36. 

    When the TG°' of a chemical reaction is positive (K'eq < 1.0) under standard conditions,

    • A.

      Work can be done under these conditions.

    • B.

      Reactants predominate over products.

    • C.

      Reactants and products are at equilibrium.

    • D.

      The reaction is exothermic.

    • E.

      The reaction is spontaneous to the right.

    Correct Answer
    B. Reactants predominate over products.
    Explanation
    When the standard Gibbs free energy change (ΔG°) of a chemical reaction is positive, it indicates that the reaction is not favorable under standard conditions. This means that the reactants have a higher free energy than the products, and therefore the reactants predominate over the products. In other words, the reaction tends to proceed in the reverse direction, favoring the formation of reactants rather than products.

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  • 37. 

    When TG' = 0 in a chemical reaction, under normal conditions

    • A.

      Reactants and products are at equilibrium.

    • B.

      The reaction is spontaneous to the left.

    • C.

      Work can be done; energy is required.

    • D.

      No work can be done; no energy is required.

    • E.

      Both A and D

    Correct Answer
    E. Both A and D
    Explanation
    When TG' = 0 in a chemical reaction, it means that the change in Gibbs free energy is zero. This indicates that the reaction is at equilibrium, where the forward and reverse reactions occur at the same rate. At equilibrium, the concentrations of reactants and products remain constant over time. Additionally, since there is no change in Gibbs free energy, no work can be done and no energy is required. Therefore, both options A and D are correct.

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  • 38. 

    Which of the following is NOT an example of facilitated diffusion?

    • A.

      Aquaporins

    • B.

      Anion exchange protein

    • C.

      Channel proteins

    • D.

      Oxygen transport

    • E.

      GluT1 glucose transporter

    Correct Answer
    B. Anion exchange protein
    Explanation
    Anion exchange proteins are not an example of facilitated diffusion because facilitated diffusion involves the passive transport of molecules across a membrane with the help of specific transport proteins. Aquaporins, channel proteins, oxygen transport, and GluT1 glucose transporter all facilitate the diffusion of specific molecules across a membrane, while anion exchange proteins are involved in active transport, which requires energy expenditure.

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  • 39. 

    Which of the following is NOT a characteristic of passive transport?

    • A.

      The energy for transport is generated by the gradient of the substance being transported.

    • B.

      The energy for transport is generated by the molecular bonds of the substance being transported.

    • C.

      Transport of the substance is the result of a conformational change.

    • D.

      It is specific to the molecule being transported.

    • E.

      It requires the binding of the molecule to be transported.

    Correct Answer
    B. The energy for transport is generated by the molecular bonds of the substance being transported.
    Explanation
    Passive transport refers to the movement of substances across a cell membrane without the input of energy. This process occurs down a concentration gradient, meaning that molecules move from an area of higher concentration to an area of lower concentration. The other characteristics listed in the options are all true for passive transport: the energy for transport is generated by the gradient of the substance being transported, transport is the result of a conformational change, it is specific to the molecule being transported, and it requires the binding of the molecule to be transported. However, the statement that the energy for transport is generated by the molecular bonds of the substance being transported is incorrect, as passive transport does not rely on the energy stored in the molecular bonds.

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  • 40. 

    Which of the following is/are TRUE with regard to water movement in osmosis?

    • A.

      Hypertonic ¨ hypotonic

    • B.

      Hypertonic ¨ isotonic

    • C.

      Hypotonic ¨ hypertonic

    • D.

      Isotonic ¨ hypotonic

    • E.

      Both choices C and D

    Correct Answer
    C. Hypotonic ¨ hypertonic
  • 41. 

    Covalent modification

    • A.

      Can inactivate an enzyme

    • B.

      Can activate an enzyme.

    • C.

      Affects the activity of an enzyme by adding or removing a chemical group.

    • D.

      Can involve the addition of phosphate groups.

    • E.

      All of the above

    Correct Answer
    E. All of the above
    Explanation
    Covalent modification refers to the alteration of an enzyme's activity by adding or removing a chemical group. This modification can either activate or inactivate the enzyme. Additionally, it can involve the addition of phosphate groups. Therefore, the correct answer is "all of the above," as covalent modification can have various effects on the activity of an enzyme.

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  • 42. 

    The process of glucose synthesis is called

    • A.

      Glucogeneration

    • B.

      Glycolysis.

    • C.

      Gluconeogenesis.

    • D.

      Aglycolysis.

    • E.

      Both B and C

    Correct Answer
    C. Gluconeogenesis.
    Explanation
    Glucose synthesis is the process by which glucose is formed from non-carbohydrate sources, such as amino acids or glycerol. This process is called gluconeogenesis. Glycolysis, on the other hand, is the breakdown of glucose into pyruvate to produce energy. Aglycolysis is not a recognized term in biology. Therefore, the correct answer is gluconeogenesis.

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  • 43. 

    Which of the following is NOT a product of the TCA cycle? 

    • A.

      Acetyl CoA

    • B.

      FADH2

    • C.

      ATP

    • D.

      NADH

    • E.

      Carbon dioxide (CO2)

    Correct Answer
    A. Acetyl CoA
    Explanation
    Acetyl CoA is not a product of the TCA cycle. It is actually a reactant that enters the TCA cycle to be oxidized and produce energy. The TCA cycle, also known as the citric acid cycle or Krebs cycle, is a series of chemical reactions that occur in the mitochondria of cells. It is responsible for the oxidation of acetyl CoA, derived from carbohydrates, fats, and proteins, to produce energy in the form of ATP, FADH2, NADH, and carbon dioxide. Therefore, acetyl CoA is not a product but a starting molecule in the TCA cycle.

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  • 44. 

    Facilitated diffusion implies that energy in which form is NOT required.

    • A.

      ATP

    • B.

      Light

    • C.

      Oxygen

    • D.

      Glucose

    Correct Answer
    A. ATP
    Explanation
    Facilitated diffusion is a type of passive transport where molecules move across a cell membrane with the help of transport proteins. Unlike active transport, facilitated diffusion does not require the input of energy in the form of ATP. Instead, it relies on the concentration gradient of the molecules being transported. Therefore, the correct answer is ATP, as it is not required for facilitated diffusion.

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  • 45. 

    A sick person often runs a fever, and this fever can inhibit the growth of bacteria because

    • A.

      Sweating removes prosthetic groups from biological enzymes.

    • B.

      Enzymes do not function as well at temperatures other than the optimal temperature.

    • C.

      Bacteria reproduce more rapidly at higher body temperature.

    • D.

      The higher temperature increases the activity of lysases.

    • E.

      Fever blocks the synthesis of proteins in the bacterial nucleus.

    Correct Answer
    E. Fever blocks the synthesis of proteins in the bacterial nucleus.
    Explanation
    When a person has a fever, the higher body temperature can inhibit the growth of bacteria because it blocks the synthesis of proteins in the bacterial nucleus. Proteins are essential for the growth and reproduction of bacteria, so when their synthesis is blocked, it hinders their ability to multiply and survive.

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  • 46. 

    Enzyme regulation may occur by several methods. Which of the following is NOT a means of enzyme regulation?

    • A.

      Allosteric regulation

    • B.

      Covalent modification

    • C.

      Feedback inhibition

    • D.

      Substrate-level phosphorylation

    • E.

      Saturation

    Correct Answer
    D. Substrate-level phosphorylation
    Explanation
    Substrate-level phosphorylation is not a means of enzyme regulation. Enzyme regulation refers to the control of enzyme activity in response to cellular needs. Allosteric regulation occurs when a molecule binds to a site on the enzyme, causing a change in its activity. Covalent modification involves the addition or removal of a chemical group, such as a phosphate group, to regulate enzyme activity. Feedback inhibition occurs when the end product of a metabolic pathway inhibits an earlier enzyme in the pathway. Substrate-level phosphorylation, on the other hand, is a metabolic process where a phosphate group is directly transferred from a substrate molecule to ADP to form ATP, and it does not regulate enzyme activity.

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  • 47. 

    Which of the following statements best describes the role of NAD+/NADH in glycolysis?

    • A.

      NAD+ is used to carry electrons.

    • B.

      NADH is used primarily in substrate-level phosphorylation.

    • C.

      NADH is capable of pumping ions during glycolysis.

    • D.

      NADH is used to produce energy by directly creating the phosphoanhydride bonds in ATP.

    • E.

      All of the above

    Correct Answer
    B. NADH is used primarily in substrate-level phosphorylation.
    Explanation
    NADH is used primarily in substrate-level phosphorylation. In glycolysis, NAD+ accepts electrons from glucose and becomes reduced to NADH. This NADH molecule then carries the electrons to the electron transport chain for further energy production. However, it is important to note that NAD+ also plays a role in carrying electrons during glycolysis, and NADH is not involved in directly creating the phosphoanhydride bonds in ATP or pumping ions. Therefore, the statement that best describes the role of NAD+/NADH in glycolysis is that NADH is used primarily in substrate-level phosphorylation.

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  • 48. 

    How does the sodium-potassium pump help to make the cell interior negative?

    • A.

      It pumps negative ions into the cell.

    • B.

      It pumps 3 sodium ions out of the cell for every 2 potassium ions pumped in.

    • C.

      It pumps 3 potassium ions out of the cell for every 2 sodium ions pumped in

    • D.

      It pumps 3 sodium ions out of the cell for every 2 sodium ions pumped in.

    • E.

      It pumps 3 potassium ions out of the cell for every 2 potassium ions pumped in.

    Correct Answer
    B. It pumps 3 sodium ions out of the cell for every 2 potassium ions pumped in.
    Explanation
    The sodium-potassium pump helps to make the cell interior negative by pumping 3 sodium ions out of the cell for every 2 potassium ions pumped in. This creates an imbalance of positive and negative ions, with more positive ions being pumped out of the cell than being pumped in, resulting in a negative charge inside the cell.

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  • 49. 

    The _____________ is when the reactants are ready to be converted to product

    • A.

      Activation barrier

    • B.

      Enzyme-substrate complex

    • C.

      Transition state

    • D.

      Steady state

    Correct Answer
    C. Transition state
    Explanation
    The transition state is the point at which the reactants are in the highest energy state and are ready to be converted into products. It represents the peak of the energy barrier that must be overcome for the reaction to occur. At this state, the reactant molecules have undergone sufficient rearrangement and bond breaking/forming to form the products. The transition state is a fleeting and highly unstable state, and it is crucial for the reaction to proceed towards product formation.

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  • 50. 

    What kind of inhibitor binds tightly to the enzyme, often forming a covalent bond with an amino acid in the active site?

    • A.

      Irreversible

    • B.

      Uncompetitive

    • C.

      Reversible

    • D.

      Allosteric

    Correct Answer
    A. Irreversible
    Explanation
    Irreversible inhibitors bind tightly to the enzyme and often form a covalent bond with an amino acid in the active site. This means that once the inhibitor binds, it cannot be easily removed, resulting in a long-lasting inhibition of the enzyme's activity. Unlike reversible inhibitors, irreversible inhibitors do not easily dissociate from the enzyme, making their effects more permanent.

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