Biochemistry, M&s – Semester 1, Mini 1

100 Questions | Total Attempts: 133

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Biochemistry Quizzes & Trivia

Questions and Answers
  • 1. 
    The rate of a typical enzyme-catalyzed reaction:
    • A. 

      Is independent of pH over a broad range of pH values

    • B. 

      Is roughly proportional to the substrate concentration as long as the substrate concentration is much lower than the Km

    • C. 

      Rises by a factor of about 4 when the temperature is raised by 10°C

    • D. 

      Is no longer affected by the enzyme concentration at saturating substrate concentrations

    • E. 

      Is virtually independent of the temperature, as long as heat denaturation is avoided

  • 2. 
    The maximal reaction rate Vmax is a kinetic property of an enzymatic reaction that depends on the incubation conditions, the enzyme concentration, and:
    • A. 

      The standard free energy change (^G0‘) of the reaction

    • B. 

      The entropy change that accompanies the reaction

    • C. 

      The ratio between the kinetic rate constants for the forward and backward reactions

    • D. 

      The Michaelis constant Km

    • E. 

      The turnover number of the enzyme

  • 3. 
    In which way is the transition state of an enzyme-catalyzed reaction different from the transition state of the corresponding uncatalyzed reaction?
    • A. 

      It has a higher free energy content

    • B. 

      It has less chemical stability and is therefore more reactive

    • C. 

      It is more similar to the conformation of the substrate, as a result of induced fit

    • D. 

      It is energetically more stable, because it makes favorable interactions with the enzyme

    • E. 

      It participates in the reaction by exchanging a proton with the substrate, in a process that is known as general acid-base catalysis

  • 4. 
    Two different subtypes of matrix metalloproteinase, enzymes MMP-2 and MMP-9, are released from a squamous cell carcinoma. The enzymes behave according to Michaelis-Menten kinetics by the measured parameters below, using the same substrate.   Enzyme                  Km (microMoles/L)              Turnover (s-1) MMP-2          5000                                  100 MMP-9              50                               2000   Based on the data given above, which of the following is a true statement?
    • A. 

      MMP-2 makes more product than MMP-9 at the same enzyme concentrations

    • B. 

      MMP-2 is more stable to proteolytic degradation than MMP-9

    • C. 

      MMP-2 will be denatured in the extracellular environment faster than MMP-9

    • D. 

      MMP-2 is more active at its maximal velocity than MMP-9

    • E. 

      MMP-2 reaches half-maximal velocity at a higher substrate concentration than does MMP-9.

  • 5. 
    Neviripine is a drug for HIV infection that is a noncompetitive inhibitor of reverse transcriptase. As a non-competitive inhibitor it:
    • A. 

      Binds to the same site on the enzyme as the substrate.

    • B. 

      Reduces the Km of the substrate.

    • C. 

      Forms a covalent bond with the enzyme.

    • D. 

      Does not bond to the enzyme in the absence of substrate.

    • E. 

      Moves the intercept on the 1/v axis of the Lineweaver-Burk plot farther away from the x-y intersection

  • 6. 
    A liver enzyme called two-substrase inactivates a drug by the following reaction:                  Drug   +   NADPH----------------->     Inactive product   +   NADP+   The Km and physiological substrate concentrations (both in millimoles per liter) are given in the table below for both substrates.                       Substrate            Km             Concentration in cell                       NADPH              0.22                  0.22                     Drug                    0.12                12.3   What is the rate-limiting substrate under these conditions, and what is the derived Michaelis-Menten equation that describes the velocity of product formation by the enzyme?
    • A. 

      Drug limiting; vo = Vmax

    • B. 

      NADPH limiting; 1/2 Vmax

    • C. 

      NADPH limiting; (Vmax x [NADPH]) / 0.22 mM

    • D. 

      Drug limiting; (Vmax x [Drug]) / 0.12 mM

    • E. 

      NADPH limiting; k2/Km

  • 7. 
    Thiol proteases cleave peptide bonds by a mechanism similar to that of serine proteases, such as trypsin and chymotrypsin, but they contain cysteine instead of serine. In which way does the sulfhydryl group of cysteine participate in the reaction?
    • A. 

      It participates in substrate binding, and thereby helps determining the substrate specificity of the enzyme

    • B. 

      It react covalently with the side chain of an acidic amino acid residue in the substrate

    • C. 

      It attacks the C=O portion of a peptide bond, and forms a thioester with it

    • D. 

      It relays electrons to the peptide bond of the substrate, thereby facilitating the formation of a tetrahedral intermediate

    • E. 

      It forms a transient disulfide bond with a cysteine side chain of the substrate

  • 8. 
     The enzyme that catalyzes the following reaction belongs to which broad enzyme class?              Protein + ATP------------------>         Phosphoprotein + ADP
    • A. 

      Isomerase

    • B. 

      Lyase

    • C. 

      Oxidoreductase

    • D. 

      Transferase

    • E. 

      Ligase

  • 9. 
    Aldehyde groups are present in some metabolites.  These aldehyde groups are most likely to be metabolized with the help of which type of enzyme?
    • A. 

      Monooxygenase

    • B. 

      Dehydrogenase

    • C. 

      Kinase

    • D. 

      Synthetase

    • E. 

      Hydrolase

  • 10. 
    The “catalytic triad” in the active site of the serine protease thrombin contains the three amino acids:
    • A. 

      Aspartate, glutamate, histidine

    • B. 

      Cysteine, arginine, serine

    • C. 

      Glutamate, histidine, tryptophan

    • D. 

      Serine, histidine, aspartate

    • E. 

      Threonine, asparagine, tyrosine

  • 11. 
    Most NAD-using enzymes are named as:
    • A. 

      Transferases

    • B. 

      Dehydrogenases

    • C. 

      Carboxylases

    • D. 

      Oxygenases

    • E. 

      Lyases

  • 12. 
    Racemase enzymes interconvert:
    • A. 

      Epimers

    • B. 

      Anomers

    • C. 

      Enantiomers

    • D. 

      Diasteriomers

    • E. 

      Aldoses and ketoses

  • 13. 
    Which of the following is characteristic for the active sites of enzymes?
    • A. 

      Nearly all amino acid side chains of the protein participate in catalysis

    • B. 

      The amino acid residues that form the active site are adjacent in the primary structure of the polypeptide

    • C. 

      The amino acid residues in the active site that bind the substrate are always the ones that catalyze the reaction

    • D. 

      In many cases the active site changes its conformation when the substrate binds

    • E. 

      In many cases, the initial binding of the substrate to the active site involves the formation of a covalent bond

  • 14. 
    Cialis (Tadalafil) is a competitive inhibitor of phosphodiesterase type 5. As a competitive inhibitor, you can expect cialis to:
    • A. 

      Covalently modify the enzyme

    • B. 

      Bind to allosteric sites on the enzyme

    • C. 

      Lower the maximum velocity of the reaction

    • D. 

      Increase the Km of the enzyme for the substrate

    • E. 

      Reduce the free energy of activation for the reaction

  • 15. 
    The term ligase refers to a class of enzymes that catalyzes
    • A. 

      Hydrogen transfer reactions

    • B. 

      The transfer of a functional group from one molecule to another

    • C. 

      The removal of a group, forming a C=C double bond in the substrate

    • D. 

      The joining together of two molecules

    • E. 

      Cleavage of a bond

  • 16. 
    Which is true for enzymes in general?
    • A. 

      They reduce the free energy of the product relative to that of the substrate

    • B. 

      They can catalyze their reaction over a wide pH range

    • C. 

      They increase the rate of the forward and backward reactions in proportion

    • D. 

      When the substrate is chiral, both isomeric forms can be used as substrates of the enzymatic reaction

    • E. 

      They alter the position of the equilibrium for a reaction

  • 17. 
    CHAPTER 17: Second Messengers. The second messenger cAMP induces its effects by binding to the regulatory subunits of protein kinase A. What is the immediate target of the second messenger IP3?
    • A. 

      A calcium channel in the ER membrane

    • B. 

      Phospholipase C

    • C. 

      Protein kinase C

    • D. 

      A nuclear DNA-binding protein

    • E. 

      Calmodulin

  • 18. 
    Glucagon can induce gene transcription in the liver.  How?
    • A. 

      It is translocated to the nucleus where it binds to response elements in the regulatory sequences of the genes.

    • B. 

      It triggers cAMP formation, and cAMP activates genes by binding to the catabolite activator protein

    • C. 

      It releases calcium from the ER, which activates protein kinase C in the nucleus

    • D. 

      It causes phosphorylation of nuclear transcription factors by protein kinase A

    • E. 

      It induces the formation of the second messenger IP3, which activates transcription by binding to nuclear transcription factors

  • 19. 
    What is the difference between nicotinic and muscarinic acetylcholine receptors?
    • A. 

      Nicotinic: has guanylate cyclase activity; muscarinic: ion channel

    • B. 

      Nicotinic: ion channel; muscarinic: coupled to G-proteins

    • C. 

      Nicotinic: coupled to G-proteins; muscarinic: has adenylate cyclase activity

    • D. 

      Nicotinic: coupled to G-proteins; muscarinic: ion channel

    • E. 

      Nicotinic: ion channel; muscarinic: has tyrosine-specific protein kinase activity

  • 20. 
    Inositol 1,4,5-trisphosphate (IP3) is a second messenger of many hormones. To form this second messenger, you need the enzyme:
    • A. 

      Phosphodiesterase

    • B. 

      Protein kinase C

    • C. 

      Protein kinase B

    • D. 

      Phospholipase C

    • E. 

      Ras

  • 21. 
    CAMP stimulates hormone production and cell proliferation in many endocrine tissues including the thyroid gland. Therefore a type of somatic mutation that is most likely to lead to the formation of a hormone-overproducing benign tumor in the thyroid gland (a "toxic nodule") is one that causes:
    • A. 

      Inability of the Gs protein to hydrolyze its bound GTP

    • B. 

      Inability of the Gi protein to hydrolyze its bound GTP

    • C. 

      Inability of the protein kinase A regulatory subunits to respond to cAMP

    • D. 

      Absence of the CREB (cyclic AMP response element binding) protein

    • E. 

      Degeneration of the TSH-producing thyrotrophs in the anterior pituitary gland

  • 22. 
    There is much overlap of the intracellular signaling cascades of growth factors such as EGF (epidermal growth factor) and PDGF (platelet-derived growth factor) with those triggered by:
    • A. 

      Neurotransmitters

    • B. 

      Hormones acting through cGMP

    • C. 

      Steroid hormones

    • D. 

      Insulin

    • E. 

      Hormones that are coupled to heterotrimeric G proteins

  • 23. 
    Many cytoplasmic enzymes become activated in response to an elevated calcium concentration.  In most cases these effects are mediated by the protein:
    • A. 

      Calmodulin

    • B. 

      Phospholipase A2

    • C. 

      Troponin

    • D. 

      Calsequestrin

    • E. 

      Calcineurin

  • 24. 
    One important feature of the insulin receptor is:
    • A. 

      It phosphorylates proteins on tyrosine side chains

    • B. 

      It is coupled to the Gi protein

    • C. 

      It is coupled to the Gq protein

    • D. 

      It has guanylate cyclase activity

    • E. 

      It mediates many of its effects through the production of nitric oxide (NO)

  • 25. 
    A linkage study has found that there is a gene for test taking skill in a particular region on the long arm of chromosome 4. A search of the human genome sequence shows that this chromosomal region contains a gene of unknown function. This gene encodes a protein that has not only a signal sequence, but also seven hydrophobic sequences, each about 20 amino acid residues long. The gene product is most likely:
    • A. 

      A voltage-gated ion channel

    • B. 

      A ligand-gated ion channel

    • C. 

      A cytoplasmic protein kinase

    • D. 

      A hormone receptor that is linked to G-proteins

    • E. 

      A hormone receptor with a tyrosine-specific protein kinase activity