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BCH403 > Exam 2 > Flashcards

Exam 2 Flashcards

1
Q

(Exam 2) The following table shows kcat/km values for one enzyme that has three different substrates. Based on this table, we can conclude that:
-The enzyme has its highest overall efficiency for Substrate 1
-The enzyme has its lowest overall efficiency for Substrate 2
-The enzyme has its highest affinity for Substrate 3
-The enzyme has its largest turnover number for Substrate 3

A

-The enzyme has its lowest overall efficiency for Substrate 2

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2
Q

(Exam 2) You experiment with a new inhibitor of Chymotrypsin. You find that no matter how much substrate you add, the Vmax of chymotrypsin is permanently lowered. Therefore, this is probably a competitive inhibitor.
-True
-False

A

-False

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3
Q

(Exam 2) A situation where the both the enzyme and the substrate alter their conformation when they bind together is an example of which of the following:
-Lock and key model of substrate binding
-Homoallosteric control of an enzyme
-Induced fit model of substrate binding
-General base catalysis, as long as the substrate becomes de-­protonated.

A

-Induced fit model of substrate binding

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4
Q

(Exam 2) The following Lineweaver Burk plot shows the result of adding an inhibitor (I) to an enzymatic reaction. What can you conclude from these data?
-The Vmax of the reaction has decreased due to the inhibitor.
-The inhibitor is an example of a competitive inhibitor.
-The inhibitor is an example of a noncompetitive inhibitor.
-This is an example of allosteric inhibition.

A

-The inhibitor is an example of a competitive inhibitor.

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5
Q

(Exam 2) An enzymatic reaction decreases in velocity as the pH increases, as shown below. Which of the following amino acid residues are most likely to be found in the active site?
-Methionine
-Tyrosine
-Alanine
-Glycine

A

-Tyrosine

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6
Q

(Exam 2) A decrease in the side chain pKa of tyrosine from 10.1 (free tyrosine) to 8.0 (when part of an active site) means that in the active site environment, tyrosine is a stronger acid.
-True
-False

A

-False

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7
Q

(Exam 2) The following protein is cleaved by chymotrypsin: SAAGTFEGSWEEDASFGAGYTSKG
How many separate peptides are formed?
-2
-3
-4
-5
-6

A

-5

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8
Q

(Exam 2) Chymotrypsin and Trypsin are examples of convergent evolution.
-True
-False

A

-False

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9
Q

(Exam 2) The role of Serine-­195 of trypsin can best be described as:
-An acid-­base catalyst
-A hydrogen bond donor that stabilizes the transition site
-A highly reactive nucleophile
-An electrostatic catalyst

A

-A highly reactive nucleophile

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10
Q

(Exam 2) In what way is Trypsin different than Carboxypeptidase A
-Trypsin displays selectivity for a certain “cut” site.
-Trypsin lowers the energy of activation of peptide bond cleavage.
-Trypsin does not undergo burst phase and steady state phase kinetics, while Carboxypeptidase A does.
-Trypsin is an endopeptidase, while Carboxypeptidase A is an exopeptidase.

A

-Trypsin is an endopeptidase, while Carboxypeptidase A is an exopeptidase.

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11
Q

(Exam 2) Triose phosphate isomerase (TPI) has been described as a near perfect enzyme due to its very high Kcat/Km.
-True
-False

A

-True

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12
Q

(Exam 2) Which of the following is the coenzyme for E1 (pyruvate dehydrogenase) in the pyruvate dehydrogenase (PDH) complex, and is it a prosthetic group?
-LA (lipoamide); prosthetic group
-LA (lipoamide); not a prosthetic group
-FAD (flavin adenine ribonucleotide); prosthetic group
-TPP (thiamine pyrophosphate); not a prosthetic group
-TPP (thiamine pyrophosphate); prosthetic group

A

-TPP (thiamine pyrophosphate); prosthetic group

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13
Q

(Exam 2) A coenzyme is always tightly bound to an enzyme.
-True
-False

A

-False

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14
Q

(Exam 2) An experiment is set to measure accumulation of CO2 during a reaction of the pyruvate dehydrogenase complex. However, you notice that CO2 levels are not increasing over time. Which enzyme:coenzyme pair has likely failed to work?
-E2:Lipoamide
-E3:FAD
-E1:TPP
-E2:Coenzyme A
-E3:NAD+

A

-E1:TPP

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15
Q

(Exam 2) The Fluid Mosaic Model of Biomembranes states that:
-Membranes are mostly static and have little lateral diffusion.
-Transverse diffusion occurs as frequently as lateral diffusion.
-The membrane is a “viscous solution” that has rapid lateral diffusion.
-Intrinsic membrane proteins are only found at the plasma membrane

A

-The membrane is a “viscous solution” that has rapid lateral diffusion.

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16
Q

(Exam 2) The following peptide is exposed to Carboxypeptidase A. How many fragments will result? TLRQNPYTSFANNFWSSR
-1
-2
-3
-4

A

-1

17
Q

(Exam 2) What nomenclature matches the following fatty acid?
-20:4 cΔ5,8,11,14
-20:4 cΔ6,9,12,15
-19:4 cΔ4,7,19,13
-19:4 tΔ4,7,19,13
-20:0

A

-20:4 cΔ5,8,11,14

18
Q

(Exam 2) Which of the following is NOT true regarding sphingolipids?
-Sphingolipids are components of membranes
-Sphingolipids contain a glycerol backbone
-Sphingolipids contain a fatty acid attached via an amide bond instead of an ester bond
-Some sphingolipids are also phospholipids

A

-Sphingolipids contain a glycerol backbone

19
Q

(Exam 2) Hydrogen bonding contributes to the spontaneous formation of a lipid bilayer.
-True
-False

A

-True

20
Q

(Exam 2) A bilayer is modified to replace the following phospholipid (PE 16:2/16:2) with a different phospholipid (PE 14:2/14:2). The new bilayer is less fluid and has a higher Tm.
-True
-False

A

-False

21
Q

(Exam 2) Cholesterol is added to a biological membrane to a final concentration of 20%. What effect does this have on the physical properties of the membrane?
-The Tm of the membrane has increased by 20%.
-The transition phase of the membrane between gel and liquid states has broadened.
-The lateral diffusion of proteins in this membrane has now decreased.
-The membrane now has multiple Tm values, one that matches the Tm of cholesterol.

A

-The transition phase of the membrane between gel and liquid states has broadened.

22
Q

(Exam 2) Which of the following DO NOT contribute to the favorable thermodynamics of membrane formation.
-Hydrogen bonding
-Van der Waals interac.ons
-The hydrophobic effect
-Disulfide bonds

A

-Disulfide bond

23
Q

(Exam 2) Lateral diffusion occurs within a lipid bilayer and requires help from an enzyme.
-True
-False

A

-False

24
Q

(Exam 2) Which of the following statements most accurately describes the role of the signal sequence in the Signal Hypothesis.
-A 15-­20 residue section of protein that is recognized by the SRP
-A 15-­20 residue section of protein that binds to a GTP molecule
-A 15-­20 residue section of protein that is recognized by the SRP receptor
-A 15-­20 residue section of protein that is located at the C-­terminal end is cleaved by a signal peptidase.

A

-A 15-­20 residue section of protein that is recognized by the SRP

25
Q

(Exam 2) Which of the following steps in the signal hypothesis requires thermodynamic coupling?
-Recognition of the signal sequence by the SRP
-Cleavage of the signal sequence by a signal peptidase
-Recruitment of the SRP-­ribosome complex to the ER membrane
-Opening of the translocon and dissociation of the SRP

A

-Opening of the translocon and dissociation of the SRP

26
Q

(Exam 2) The signal hypothesis explains why integral membrane proteins at the plasma membrane have an N-­terminus that is located on the extracellular side of the membrane.
-True
-False

A

-True

27
Q

(Exam 2) The sodium-­glucose transporter is an example of __________.
-Primary active antiport
-Primary active symport
-Secondary active antiport
-Secondary active symport

A

-Secondary active symport

28
Q

(Exam 2) Passive transport that does not require an interaction with a solute will display linear transport kinetics.
-True
-False

A

-True

29
Q

(Exam 2) Which of the following is a way to desensitized signal transduction?
-Phosphodiesterases convert cAMP into AMP
-Activation of adenylate cyclase
-Lateral diffusion of the G-­protein in the membrane bilayer
-Activation of kinase intracellular kinase enzymes

A

-Phosphodiesterases convert cAMP into AMP

30
Q

(Exam 2) Which bilayer containing the following lipids will have the lowest Tm.
-18:0
-18:1
-18:2
-cholesterol

A

-18:2

BCH403 (6 decks)

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