Module 2 General principles of metabolism. Мetabolism of carbohy-drates, lipids, amino acids and its regulation

Test questions in text form

  1. ______is a cosubstrate.
  2. * Tetrahydrofolate.
  3. NADH
  4. Biotin
  5. Thiamin pyrophosphate.
  6. Pyridoxol phosphate

2.  ______can bind to the free enzyme.

  1. * A competitive inhibitor
  2. A uncompetitive inhibitor
  3. A non-competitive inhibitor
  4. a and c
  5. b and c

3.  ______is the coenzyme involved in decarboxylation reactions.

  1. Tetrahydrofolate.
  2. NADH
  3. Biotin
  4. Thiamin pyrophosphate.
  5. * Pyridoxol phosphate.

4.  ______alters the Vmax of an enzyme.

  1. A competitive inhibitor
  2. * A uncompetitive inhibitor
  3. A non-competitive inhibitor
  4. A and c
  5. B and c

5.  ______binds to the enzyme at sites other than the substrate binding site.

  1. An allosteric inhibitor
  2. * A uncompetitive inhibitor
  3. A non-competitive inhibitor
  4. A and c
  5. All of the above

6.  ______is the term that describes a theoretical value achieved when all enzyme substrate binding sites are occupied by the substrate.

  1. Km
  2. Kcat
  3. Vmax
  4. * kcat/ Km
  5. mg
  6. (k-1 + kcat)/k1 = ______.
  7. Vmax
  8. * Km
  9. Kcat
  10. Kcat/Km
  11. All of the above

8.  A catalyst can promote product formation during a chemical reaction by _____.

A.  Lowering the activation energy barrier.

  1. Stabilizing the transition state.

C.  Positioning reactants in the correct orientation.

  1. * Bringing reactants together.
  2. All of the above

9.  A catalyst can promote product formation during a chemical reaction by _____.

A.  Lowering the activation energy barrier.

  1. Stabilizing the transition state.

C.  Positioning reactants in the correct orientation.

  1. * Bringing reactants together.
  2. All of the above

10.  A column packed with the sieved particles are used in which of the following techniques to separate smaller and larger protein molecules

  1. Affinity chromatography
  2. Electrophoresis
  3. * Molecular exclusion chromatography
  4. Selective adsorbtion
  5. All of these
  6. A competitive inhibitor binds to
  7. Substrate
  8. * Active site
  9. Allosteric site
  10. Enzyme-substrate complex
  11. Coenxyme

12.  A reaction is designated as exergonic rather than endergonic when ______.

A.  Activation energy exceeds net energy release

  1. Activation energy is necessary
  2. No kinetic energy is released

D.  * The potential energy of the products is less than the potential energy of the reactants

  1. It absorbs more energy

13.  A reversible inhibitor that can bind to either E alone or the ES complex is referred to as a _____.

  1. Competitive inhibitor.
  2. * Non-competitive inhibitor
  3. Uncompetitive inhibitor
  4. Suicide inhibitor
  5. Irreversible inhibitor

14.  A reversible inhibitor that only binds to the ES complex is referred to as a _____.

  1. Competitive inhibitor
  2. Non-competitive inhibitor
  3. Uncompetitive inhibitor
  4. Suicide inhibitor
  5. * Irreversible inhibitor
  6. A thermodynamic pit occurs when
  7. ES is not very stable

B.  ES forms faster than it dissociates

  1. * ES is highly stable

D.  S is not bound tightly to an enzyme

E.  S is positioned incorrectly to the enzyme

16.  According to the second law of thermodynamics, which of the following is true?

A.  The total amount of energy in the universe is constant.

B.  Energy conversions increase the order in the universe.

C.  The ordering of one system depends on the disordering of another.

D.  The entropy of the universe is constantly decreasing.

E.  * All reactions produce some heat.

17.  Active holoenzymes are formed from ______in the presence of ______.

  1. Cofactors; proteins
  2. Proteins; cofactors
  3. * Apoenzymes; cofactors
  4. Apoenzymes; proteins
  5. Apoenzymes; inactive holoenzymes

18.  An allosteric inhibitor of an enzyme usually

A.  Binds to the active site.

  1. * Participates in feedback regulation.
  2. Denatures the enzyme.

D.  Causes the enzyme to work faster.

  1. Is a hydrophobic compound.

19.  An enzyme is said to be catalytically perfect when ______.

  1. It has a large Km
  2. It has a small kcat

C.  * Its kcat/Km value is close to that of the diffusion limit

D.  It has very high affinity for the transition state

  1. All of the above

20.  An enzyme is specific. This means

A.  It has a certain amino acid sequence.

B.  It is found only in a certain place.

C.  It functions only under certain environmental conditions.

D.  It speeds up a particular chemical reaction.

E.  * It occurs in only one type of cell.

21.  An update of Fischer's lock and key theory of enzyme specificity view the ______as the lock and ______as the key.

  1. Enzyme; substrate
  2. Substrate; enzyme
  3. * Enzyme; transition state
  4. Transition state; enzyme
  5. Substrate; transition state

22.  By efektors can forward some substance, except:

  1. Hormones
  2. Mediators of the nervous system
  3. Metals
  4. Products of enzymatic reactions
  5. * Vitamins

23.  Ca++ or Mg++ are most likely to be part of ______, while Zn++ or Fe++ are present in ______.

  1. * Metal-activated enzymes; metalloenzymes
  2. Metalloenzymes; metal-activated enzymes
  3. Cofactors; coenzymes
  4. Coenzymes; cofactors
  5. Apoenzymes; holoenzymes

24.  Conserved serine, histidine and aspartate residues are present in the catalytic center of all serine proteases. Which of the following describes the role of the histidine residue in the mechanism of this reaction?

  1. * Covalent binding of acyl groups
  2. Hydrophobic stabilization of the substrate
  3. Proton transfer
  4. Cation binding
  5. Anion transport

25.  Consider a hypothetical metabolic pathway for the synthesis of the amino acid arginine: precursor A intermediate B arginine. Each reaction is catalyzed by a different enzyme. This metabolic pathway is controlled by feedback inhibition with arginine inhibiting the conversion of precursor A to intermediate B. In this case, arginine almost certainly acts as a _____ of the first enzyme in the pathway.

  1. * Substrate
  2. Competitive inhibitor
  3. Catalyst
  4. Cofactor
  5. None of the above

26.  Covalent modifications that increase the activity of allosterically regulated enzymes do so by ______.

A.  * Adding phosphate groups to essential amino acids in the active site

B.  Causing the enzyme to fold into a more active configuration

C.  Increasing the amount of total enzyme present

  1. None of the above
  2. All of the above

27.  During allosteric, or feed back, inhibition

A.  Transcription of mRNA specific for the enzymes involved in the pathway is repressed by the pathway's end product.

B.  Enzyme concentrations in the cell remain relatively constant.

C.  * The pathway's end product represses the activity of the first enzyme in the pathway

D.  All of the above apply to feedback inhibition.

E.  More than one of the above, but not all, apply to feedback inhibition.

  1. During electrophoretic research of LDG in the blood serum found out predominance of content of LDG1 and LDG2. Pathology of what organ does these information testify?
  2. Lungs
  3. * Heart
  4. Liver
  5. Musculs
  6. Spleen
  7. During enzyme repression

A.  The pathway's end product represses the activity of the first enzyme in the pathway.

B.  B.Enzyme concentrations in the cell remain relatively constant.

C.  Transcription of mRNA specific for the enzymes involved in the pathway is repressed by the pathway's end product.

D.  * More than one of the above, but not all, apply to feedback inhibition.

E.  All of the above apply to feedback inhibition.

30.  During feedback inhibition, the effector molecule binds to the enzyme's ______site

  1. Permissive
  2. Alternative
  3. Allosteric
  4. * Conformational
  5. Active

31.  Energy-requiring reactions can occur in biological systems because enzymes allow their coupling to other reactions with:

A.  The activation energy of the reaction is doubled.

B.  The activation energy of the reaction is lowered.

C.  It's optimal conditions for temperature of the enzyme are doubled.

D.  * The shape of the enzyme molecule is changed.

  1. All of above

32.  Enzymes that are allosterically regulated ______.

  1. Are multimeric proteins
  2. * Possess regulatory and catalytic domains

C.  Do not behave according to the Michaelis-Menton equation

  1. All of the above
  2. Are monomeric proteins
  3. Enzymes:

A.  Are composed primarily of polypeptides, which are polymers of amino acids.

B.  * Can bind prosthetic groups such as metal ions that participate in enzyme reactions.

  1. Have defined structures.

D.  Bind their substrates at active sites.

  1. All statements are true.
  2. Ethanol (CH3CH2OH) is the alcohol found in beverages. It is oxidized in the body to acetaldehyde by the enzyme alcohol dehydrogenase. Methanol (CH3OH), also known as wood alcohol, is converted to formaldehyde by the same enzyme. Acetaldehyde is toxic, but formaldehyde is far more toxic to humans, which is why the ingestion of relatively small amounts of methanol can cause blindness or death. One treatment for mild methanol poisoning is the administration of ethanol. Why might a doctor choose this treatment?

A.  Ethanol must act as a competitive inhibitor for the alcohol dehydrogenase and therefore slows the formation of formaldehyde.

B.  Ethanol likely irreversibly binds to alcohol dehydrogenase which prevents the formation of formaldehyde.

C.  * The ethanol is likely an uncompetitive inhibitor and binds to a site other than the active site of the enzyme.

D.  The doctor has given up on the patient and administers ethanol for sedation

  1. B and C

35.  If it is known that the only two ionizable residues in the active site are both glutamates, which conclusion can be drawn?

A.  * The glutamates have different microenviroments which cause their pKa's to differ.

B.  One of the glutamates must be amidated.

C.  Both glutamates have a pKa equal to 5.0.

D.  Both glutamates are deprotonated during the reaction.

  1. B and C

36.  If the tertiary structure of an enzyme is changed _____.

A.  * Its substrate may not fit properly in the active site

B.  It will be missing one of its polypeptides

C.  The helical coil will be stretched out

D.  The product of the reaction will be a different molecule

E.  Its substrate will bond covalently with the wrong part of the molecule

37.  In a multienzyme complex the process of directly transferring a product of one reaction to the next active site without allowing it to enter the bulk solvent is termed ______.

  1. a ping-pong reaction
  2. * metabolite channeling
  3. the activity pathway
  4. the sequential mode
  5. All of the above

38.  In a ping-pong reaction which does not occur?

A.  One product is released before a second substrate is bound.

B.  The enzyme covalently binds a portion of the first substrate.

C.  * The enzyme is permanently converted to an altered form by the first substrate.

D.  A group is transferred from one substrate to another.

  1. All of the above

39.  Izoenzymes differ between itself some physical and chemical properties, except:

  1. Electrophoretic mobility
  2. Molecular activity
  3. Stability
  4. * Present in different tissues
  5. Difference their primary structure

40.  Mg2+ is used as a(n) by metal activate enzymes that utilize negatively charged substrates like ATP.

  1. Metalloenzyme
  2. * Activator ion
  3. Prosthetic group
  4. Co-substrate
  5. Ingibitor ion

41.  R-CH2OH + O2 > R-CHO + H2O2 which of the following types of enzymes catalyzes this reaction

  1. Dehydrogenase
  2. Oxidase
  3. * Peroxidase
  4. Aldolase
  5. Catalase

42.  Some antibody molecules are enzymatic if they are formed against

  1. Enzymes
  2. Enzymes bound to other proteins

C.  * Transition state analogs bound to other proteins

  1. Transition state analogs
  2. All of the above

43.  Specificity of enzyms is conditioned by the following factors, except:

  1. Conformation complementare
  2. Electrostatic complementare

C.  The feature structure of active center of enzyme

D.  * The feature structure of allosteric center

  1. Proteins nature

44.  ?The active site of an enzyme differs from an antibody-antigen binding site in that the enzyme active site

  1. Contains modified amino acids
  2. Catalyzes a chemical reaction

C.  Is complementary to a specific ligand

  1. * Contains amino acids without sidechains

E.  None of the above are correct

45.  The assumptions made in calculating the Michaelis-Menten Equation include

A.  That the formation and decomposition of ES is the same for a period of time

B.  That the concentration of the substrate is much greater than the concentration of E

C.  That the value of k-2 can be ignored

  1. * a, b and c
  2. a and b

46.  The catalytic triad of chymotrypsin and other serine proteases are

A.  Three subunits of the enzyme.

B.  Three adjacent amino acid residues which act to make serine a strong nucleophile.

C.  * Three amino acid residues close enough together to make serine a strong nucleophile.

D.  Three enzymes with very similar structural features.

  1. All of the above

47.  The concentrations of enzymes is determined by using pseudo first-order conditions in which

A.  concentration is kept the same and the rate is measured

B.  concentration is kept the same and the rate is measured

C.  * concentration is constant, E concentration varied and the rate is measured

D.  concentration is constant, S concentration varied and the rate is measured

  1. All of the above
  2. The data shown on the graph were obtained for a kinetic experiment. What type of inhibition is it?
  3. Competitive
  4. Uncompetitive
  5. * Noncompetitive
  6. Irreversible
  7. A and B

49.  The enzyme has an active site which

  1. Fits the substrate exactly
  2. Fits the transition state

C.  May contain hydrogen bonds which are covalent like

  1. a and c
  2. * b and c
  3. The equilibrium constant for the reaction, glucose 6-phosphate + waterTglucose + phosphate, is 260. What can you conclude about this reaction:
  4. It is a closed system
  5. It never reached equilibrium.

C.  Starting with glucose 6-phosphate, it is not spontaneous.

D.  * At equilibrium, the concentration of glucose is much higher than the concentrations of glucose 6-phosphate.

E.  At equilibrium, the concentration of glucose is much higher than the concentrations of phosphate

51.  The mechanism of enzyme action is _____.

A.  * To create an energy barrier between substrates

B.  To lower the energy of the activation of a reaction

C.  To change the direction of thermodynamic equilibrium

D.  To change endergonic into exergonic reactions

E.  To allow substrates to move more freely in solution

  1. The Michaelis constant, Km, is

A.  The maximum velocity that any given enzyme reaction can achieve

B.  The substrate concentration which gives the best enzyme assay for an enzyme reaction

C.  * The substrate concentration when the reaction is half the way toward the maximal velocity