Biochemistry Exam (chemistry) Quiz

25 Questions

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Biochemistry Exam (chemistry) Quiz

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Questions and Answers
  • 1. 
    Which of the following is NOT a feature of enzymes ?
    • A. 

      Globular protein

    • B. 

      Faster than chemical catalysts

    • C. 

      Consumed in chemical reactions

    • D. 

      Each type of enzyme has optimal temperature and pH

    • E. 

      Can not change the equilibrium ratio

  • 2. 
    • A. 

      Enzyme binds the substrate reversibly to make ES complex

    • B. 

      ES is converted to EP

    • C. 

      The product dissociates

    • D. 

      The conformation of enzyme develops during reaction,even the substrates are absent

  • 3. 
    How does an enzyme's Km, compare to its affinity for substrate?
    • A. 

      The greater the Km, the higher the affinity

    • B. 

      The lower the Km, the higher the affinity

    • C. 

      The relationship depends on whether an inhibitor is present or not

    • D. 

      The relationship depends on the enzyme's Vmax.

  • 4. 
    Which of the following characters of acetylcholinestrase is mismatched?
    • A. 

      Peripheral site --> aromatic amino acids --> it guides the substrates

    • B. 

      Anionic site --> aspartic acid(- charged) --> attracts cholin(+ charged)

    • C. 

      Esteric site --> catalytic triad --> hydrolize acetylcholin

    • D. 

      Catalytic triad = Serine + Histidine + Glycine

  • 5. 
    • A. 

      Induced fit model is more specific than lock and key model

    • B. 

      In lock and key model the active site is more RIGID than induced fit model

    • C. 

      In induced fit model the active site can undergo conformational change

    • D. 

      In lock and key model--> enzyme considered as a lock and substrate considered as a key

  • 6. 
    According to classification of enzymes which of the following is false?
    • A. 

      Isomerase does not change the components of the substrates,but it changes the arrangement

    • B. 

      Hydrolase and lysase use H2O in claevage of bonds

    • C. 

      Lysase is not energy-dependent enzyme

    • D. 

      Ligase requires energy to make ligation

  • 7. 
    This diagram represents the relationship between enzyme activity and temperature,which of the following statements does not describe this diagram?
    • A. 

      It is biphasing diagram

    • B. 

      High temperature will decrease the activity due to denaturation of enzyme

    • C. 

      Increase of temperature will not affect on collisions between substrates and enzymes

  • 8. 
    According to this reaction,choose the incorrect statement:
    • A. 

      K1 indicates the association of ES

    • B. 

      K-1 & K2 indicate the dissociation of ES

    • C. 

      ES concentration changes during reaction

    • D. 

      The catalytic step (ES-->E+P) is almost irreversible

  • 9. 
    If the enzyme reaction activity reaches the maximal velocity,how can we increase rate of reaction?
    • A. 

      By decrease KM

    • B. 

      By increase enzyme concentration

    • C. 

      By increase substrates concentration

    • D. 

      By increase the temperature

  • 10. 
    According to Michalis-Menten equation and its plot, which statement is not true?
    • A. 

      Different enzymes reach Vmax at same [S]

    • B. 

      [S] = Km, substitution of Km for [S] in the Michaelis–Menten equation yields v = ½ Vmax

    • C. 

      When the velocity is plotted versus [S], a hyperbolic curve is produced

    • D. 

      As [S] is first increased, the initial rate or velocity (V0) increases with increasing substrate concentration ((V is proportional to [S]))

  • 11. 
    According to Lineweaver-Bruk transformation, which of the following is true?
    • A. 

      Slope of their equation = Vmax/Km

    • B. 

      Y-intercept = 1/Vmax

    • C. 

      X-intercept = 1/Km

    • D. 

      It is not linear equation

  • 12. 
    All of the following are true about activators except:
    • A. 

      They can be cofactors or hormones or second massengers

    • B. 

      They increase Vmax

    • C. 

      They increase Km

  • 13. 
    If we add irreversible inhibitors to enzymatic reaction,which of the following is not expected:
    • A. 

      They will bind to enzyme covalently

    • B. 

      The number of ES complex will not decrease

    • C. 

      Derivatized enzyme is no longer a catalyst

  • 14. 
    What is the type of this inhibitor?
    • A. 

      Competitive

    • B. 

      Non-competitive

    • C. 

      Uncompetitive

    • D. 

      Irreversible

  • 15. 
    Which of the following is not true about this type of inhibitors?
    • A. 

      They bind only to ES complex

    • B. 

      They form ESI complex

    • C. 

      They decrease Km

    • D. 

      They bind to the active site

  • 16. 
    Which of the following is mismatched ?
    • A. 

      Malonate --> competitive inhibitor

    • B. 

      Feedback inhibition --> noncompetitive inhibition

    • C. 

      Isoleucine --> uncompetitive inhibitor

    • D. 

      Methotrixate --> competitive inhibitor

    • E. 

      Aspirin & pencillin--> irreversible inhibitors

  • 17. 
    All of the following statements are true about isozymes except:
    • A. 

      They are different form of the enzyme that catalyze the same reaction

    • B. 

      They use the same substrate and produce the same product

    • C. 

      They have the same physical properties

    • D. 

      They are found in different tissues

  • 18. 
    Which of the following is NOT true about LDH?
    • A. 

      It is tetrameric

    • B. 

      It is composed of tow types of subunits

    • C. 

      LDH1 is found in heart & LDH5 in skeletal muscles

    • D. 

      At birth we have LDH1 in our heart

    • E. 

      It is used to diagnose myocardial infarction

  • 19. 
    Which one of the following is false about enzyme regulation?
    • A. 

      Gene expression --> control the quantity and the rate of enzymes --> slow mechanism

    • B. 

      Enzyme degradation --> by protelytic enzymes --> slow mechanism

    • C. 

      Covalent modification --> activation of zymogen(pro-enzyme) by protelytic cleavage --> rapid mechanism

    • D. 

      Allosteric regulation -->switches enzyme between tow conformations --> irreversible --> rapid mechanism

  • 20. 
    Which one of the following is not true about allosteric enzymes?
    • A. 

      It is difficult to monomeric enzymes

    • B. 

      All subunits can simultaneously change their structures

    • C. 

      R-subunits --> more avtive + higher affinity for substrate

    • D. 

      T-subunits--> less active + lower affinity for effectors

  • 21. 
    All of the following statements are true about inorganic cofactors except:
    • A. 

      They include metal ions

    • B. 

      They bind substrates to fix them at active site

    • C. 

      They mediate in redox reactions

    • D. 

      Most of them are negatively charged

  • 22. 
    Which one of the following is mismatched?
    • A. 

      Thiamine(B1) --> thiamine pyrophosphate --> decarboxylation

    • B. 

      Riboflavin(B2) --> FAD&FMN --> electrons carriers

    • C. 

      B12 --> tetrahydrofolate --> carries various forms of carbon unit during biosynthetic reactions

    • D. 

      Panthoic acid(B5) --> coenzyme A --> transfer acetyl or acyl groups

  • 23. 
    Which one of the following is NOt true ?
    • A. 

      Ascorbic acid acts as reducing agent

    • B. 

      NAD+,NADP+,FAD&FMN act as oxidizing agents

    • C. 

      Vitamin B12 need intrinsic factor to be absorbed in ileum

    • D. 

      Vitamins considered as organic coenzymes

  • 24. 
    Which of the following is true about enzymes deficiency?
    • A. 

      B12 deficiency is widespread between sailors

    • B. 

      Thiamine deficiency can cause beriberi

    • C. 

      Prenicious anemia caused by folic acid and vitamin c deficiency

    • D. 

      Riboflavin deficiency causes deramtitis,diarrhea and pellagra

  • 25. 
    One of the  following cofactors has one nucleotide 
    • A. 

      NAD+

    • B. 

      NADP+

    • C. 

      FAD

    • D. 

      FMN