Question 1

Discuss the characteristics of microtubules.​

Accepted Answer

Tubulin dimers polymerize to form microtubules, which are essentially helical structures, with 13 tubulin monomer "residues" per turn. Microtubules grown in vitro are dynamic structures that are constantly being assembled and disassembled. Because all tubulin dimers in a microtubule are oriented similarly, microtubules are polar structures. The end of the microtubule at which growth occurs is the plus end, and the other is the minus end. Microtubules in vitro carry out a GTP-dependent process called treadmilling, in which tubulin dimers are added to the plus end at about the same rate at which dimers are removed from the minus end.​

Question 2

Microtubules are ____ structures formed from ____.

Accepted Answer

A)  solid; myosin 
B)  self-assembling; phospholipids 
C)  hollow; membranes 
D)  self-assembling; tubulin 
E)  solid; tubulin 
A)  solid; myosin 
B)  self-assembling; phospholipids 
C)  hollow; membranes 
D)  self-assembling; tubulin 
E)  solid; tubulin D

Question 3

Discuss the cellular events that lead to a top-of-power stroke state.​

Accepted Answer

The myosin heads-with the hydrolysis products ADP and P_i bound-are mainly dissociated from the actin filaments in resting muscle. When the signal to contract is presented, the myosin heads move out from the thick filaments to bind to actin on the thin filaments. Actin binding closes the cleft in the myosin head, which causes a twist in the large β-sheet. The twist causes switch 1 and the P-loop of the ATP-binding site to "open," both of them moving away from the bound ADP and P_i. The β-sheet twist also straightens the kink in the relay helix. These conformational changes result in the top-of-power stroke state.

Question 4

All of the following are characteristics of microtubules EXCEPT:

Accepted Answer

A)  they are made up of two repeating subunits. 
B)  they grow at one end and are degraded at the other end. 
C)  they are static, helical structures. 
D)  they are hollow, cylindrical structures. 
E)  they are polar structures. 
A)  they are made up of two repeating subunits. 
B)  they grow at one end and are degraded at the other end. 
C)  they are static, helical structures. 
D)  they are hollow, cylindrical structures. 
E)  they are polar structures.

Question 5

The proposed sequence for kinesin movement along a microtubule is:
A.Leading head binds a new site on tubulin with ADP dissociation.
B.The kinesin head with ATP is bound to tubulin, and the kinesin head with ADP is ready to move aheaD.
C.Conformation change in the neck linkers flipping the trailing head to the next tubulin binding sitE.
D.ADP and Pi dissociation and ATP binds leading head.

Accepted Answer

A)  D, C, B, A 
B)  B, C, A, D 
C)  B, D, A, C 
D)  A, C, B, D 
E)  C, A, D, B 
A)  D, C, B, A 
B)  B, C, A, D 
C)  B, D, A, C 
D)  A, C, B, D 
E)  C, A, D, B

Question 6

In the β-sheet of the -α-β-α- segment of myosin, the ____ sequence likely binds ATP and is found in other nucleotide-binding proteins. The general sequence is:

Accepted Answer

A)  cys-X-X-cys-X-his 
B)  arg-X-X-his-X-gly 
C)  gly-X-X-gly-X-gly 
D)  ser-X-arg-X-lys-X-gly 
E)  lys-X-gly-X-X-ser 
A)  cys-X-X-cys-X-his 
B)  arg-X-X-his-X-gly 
C)  gly-X-X-gly-X-gly 
D)  ser-X-arg-X-lys-X-gly 
E)  lys-X-gly-X-X-ser

Question 7

Myofibrils are linear arrays of cylindrical ____, the basic structural unit in the contraction of striated muscle.

Accepted Answer

A)  foot structures 
B)  sarcomeres 
C)  sarcolemmas 
D)  sarcoplasmic reticulum (SR) 
E)  t-tubules 
A)  foot structures 
B)  sarcomeres 
C)  sarcolemmas 
D)  sarcoplasmic reticulum (SR) 
E)  t-tubules

Question 8

Discuss linear and rotating molecular motors.​

Accepted Answer

Molecular motors may be linear or rotati

Question 9

In E. coli, rotation of the flagella is powered by:

Accepted Answer

A)  phosphorylation of the motB protein by phosphoenolpyruvate. 
B)  a proton gradient across the plasma membrane of the bacterium. 
C)  the hydrolysis of ATP by the motB protein. 
D)  the hydrolysis of GTP by the flagella. 
E)  none of the above. 
A)  phosphorylation of the motB protein by phosphoenolpyruvate. 
B)  a proton gradient across the plasma membrane of the bacterium. 
C)  the hydrolysis of ATP by the motB protein. 
D)  the hydrolysis of GTP by the flagella. 
E)  none of the above.

Question 10

The protein in the troponin complex that shows 70% homology to calmodulin and involved in Ca2+ binding is:

Accepted Answer

A)  TnT. 
B)  TnC. 
C)  TnI. 
D)  TnA. 
E)  TnB. 
A)  TnT. 
B)  TnC. 
C)  TnI. 
D)  TnA. 
E)  TnB.

Question 11

All of the following affect microtubule polymerization and are used in cancer chemotherapy EXCEPT:

Accepted Answer

A)  Taxol. 
B)  colchicine. 
C)  vinblastine. 
D)  vincristine. 
E)  all are used. 
A)  Taxol. 
B)  colchicine. 
C)  vinblastine. 
D)  vincristine. 
E)  all are used.

Question 12

All are characteristics of molecular motors or motor proteins EXCEPT:

Accepted Answer

A)  They must be able to associate and dissociate reversibly with a polymeric protein array, a surface or substructure in the cell. 
B)  They use chemical energy (e.g., ATP) to orchestrate movement. 
C)  They transfer ATP energy into mechanical energy. 
D)  ATP hydrolysis is presumed to drive and control protein conformational changes that result in sliding or walking movement of one molecule relative to another. 
E)  All are true. 
A)  They must be able to associate and dissociate reversibly with a polymeric protein array, a surface or substructure in the cell. 
B)  They use chemical energy (e.g., ATP) to orchestrate movement. 
C)  They transfer ATP energy into mechanical energy. 
D)  ATP hydrolysis is presumed to drive and control protein conformational changes that result in sliding or walking movement of one molecule relative to another. 
E)  All are true.

Question 13

Intracellular movement of organelles in axons occurs through:

Accepted Answer

A)  axoneme motion through ATP-driven walking of dyneins along microtubules. 
B)  formation of ring-like structures around tubulin to move organelles. 
C)  progressive movement along DNA strands. 
D)  kinesin-mediated ATPase driven movement along microtubules. 
E)  all of the above. 
A)  axoneme motion through ATP-driven walking of dyneins along microtubules. 
B)  formation of ring-like structures around tubulin to move organelles. 
C)  progressive movement along DNA strands. 
D)  kinesin-mediated ATPase driven movement along microtubules. 
E)  all of the above.

Question 14

Which of the following best describes the conditions of switch 1, switch 2 and the actin-cleft during myosin rigor?

Accepted Answer

A)  switch 1 open, switch 2 open, actin-cleft open 
B)  switch 1 open, switch 2 open, actin-cleft closed 
C)  switch 1 closed, switch 2 open, actin-cleft open 
D)  switch 1 open, switch 2 closed, actin-cleft closed 
E)  switch 1 open, switch 2 closed, actin-cleft open 
A)  switch 1 open, switch 2 open, actin-cleft open 
B)  switch 1 open, switch 2 open, actin-cleft closed 
C)  switch 1 closed, switch 2 open, actin-cleft open 
D)  switch 1 open, switch 2 closed, actin-cleft closed 
E)  switch 1 open, switch 2 closed, actin-cleft open

Question 15

Order the reaction sequence for the involvement of free actin, free myosin and ATPase activity on each other.
A.Actin binds and activates ATPase activity by stimulating release of Pi and ADP.
B.In the absence of actin, the addition of ATP to myosin produces a rapid release of H+.
C.The binding of new ATP to the actomyosin complex.
D.Actomyosin dissociates into actin and myosin.
E.Low energy conformation change in myosin head.

Accepted Answer

A)  B, A, E, C, D 
B)  A, B, C, D, E 
C)  B, E, C, A, D 
D)  E, B, A, D, C 
E)  C, A, D, E, B 
A)  B, A, E, C, D 
B)  A, B, C, D, E 
C)  B, E, C, A, D 
D)  E, B, A, D, C 
E)  C, A, D, E, B

Question 16

Which of the following troponin subunits is responsible for inhibiting actin-myosin binding?

Accepted Answer

A)  troponin G 
B)  troponin I 
C)  troponin C 
D)  troponin M 
E)  troponin Y 
A)  troponin G 
B)  troponin I 
C)  troponin C 
D)  troponin M 
E)  troponin Y

Question 17

All of the following occur during muscle contraction EXCEPT:

Accepted Answer

A)  the length of the sarcomere is reduced. 
B)  the length of the thick filament is reduced. 
C)  the contraction produces an increased overlap of the actin and myosin filaments of the A band. 
D)  ATP hydrolysis occurs. 
E)  the length of the thin filaments is constant. 
A)  the length of the sarcomere is reduced. 
B)  the length of the thick filament is reduced. 
C)  the contraction produces an increased overlap of the actin and myosin filaments of the A band. 
D)  ATP hydrolysis occurs. 
E)  the length of the thin filaments is constant.

Question 18

Of the six polypeptides that make up the thick filament, the ATPase activity is in the:

Accepted Answer

A)  LC1 
B)  LC2 
C)  Myosin heavy chains 
D)  Essential light chains 
E)  Regulatory light chains 
A)  LC1 
B)  LC2 
C)  Myosin heavy chains 
D)  Essential light chains 
E)  Regulatory light chains

Question 19

Explain how negative cooperativity facilitates the hand-over-hand movement of Rep helicase.​

Accepted Answer

The Rep helicase from E. coli is monomer

Question 20

Self-assembly of microtubules occur by:

Accepted Answer

A)  helical twisting of strands of α-tubulin and β-tubulin. 
B)  intermolecular interactions of dimers of α-tubulin and β-tubulin. 
C)  polymerization of alternating α- and β-tubulin into a repeating α-β-α-β-... strand. 
D)  inter-subunit interaction to form α2β2-tetramers of tubulin. 
E)  ATP-dependent polymerization of tubulin monomers. 
A)  helical twisting of strands of α-tubulin and β-tubulin. 
B)  intermolecular interactions of dimers of α-tubulin and β-tubulin. 
C)  polymerization of alternating α- and β-tubulin into a repeating α-β-α-β-... strand. 
D)  inter-subunit interaction to form α2β2-tetramers of tubulin. 
E)  ATP-dependent polymerization of tubulin monomers.

Exam 16: Molecular Motors

Discuss the characteristics of microtubules.​

Microtubules are ____ structures formed from ____.

Discuss the cellular events that lead to a top-of-power stroke state.​

All of the following are characteristics of microtubules EXCEPT:

In the β-sheet of the -α-β-α- segment of myosin, the ____ sequence likely binds ATP and is found in other nucleotide-binding proteins. The general sequence is:

Myofibrils are linear arrays of cylindrical ____, the basic structural unit in the contraction of striated muscle.

Discuss linear and rotating molecular motors.​

In E. coli, rotation of the flagella is powered by:

The protein in the troponin complex that shows 70% homology to calmodulin and involved in Ca2+ binding is:

All of the following affect microtubule polymerization and are used in cancer chemotherapy EXCEPT:

All are characteristics of molecular motors or motor proteins EXCEPT:

Intracellular movement of organelles in axons occurs through:

Which of the following best describes the conditions of switch 1, switch 2 and the actin-cleft during myosin rigor?

Which of the following troponin subunits is responsible for inhibiting actin-myosin binding?

All of the following occur during muscle contraction EXCEPT:

Of the six polypeptides that make up the thick filament, the ATPase activity is in the:

Explain how negative cooperativity facilitates the hand-over-hand movement of Rep helicase.​

Self-assembly of microtubules occur by:

The Facts of Life: Chemistry Is the Logic of Biological Phenomena

Water: the Medium of Life

Thermodynamics of Biological Systems

Amino Acids and the Peptide Bond

Proteins: Their Primary Structure and Biological Functions

Proteins: Secondary, Tertiary, and Quaternary Structure

Carbohydrates and the Glycoconjugates of Cell Surfaces

Lipids

Membranes and Membrane Transport

Nucleotides and Nucleic Acids

Structure of Nucleic Acids

Recombinant Dna, Cloning, Chimeric Genes, and Synthetic Biology

Enzymeskinetics and Specificity

Mechanisms of Enzyme Action

Enzyme Regulation

Metabolism: an Overview

Glycolysis

The Tricarboxylic Acid Cycle

Electron Transport and Oxidative Phosphorylation

Photosynthesis

Gluconeogenesis, Glycogen Metabolism, and the Pentose Phosphate Pathway

Fatty Acid Catabolism

Lipid Biosynthesis

Nitrogen Acquisition and Amino Acid Metabolism

Synthesis and Degradation of Nucleotides

Metabolic Integration and Organ Specialization

Dna Metabolism: Replication, Recombination, and Repair

Transcription and the Regulation of Gene Expression

Protein Synthesis

Completing the Protein Life Cycle: Folding, Processing, and Degradation

The Reception and Transmission of Extracellular Information

Filters

Discuss the characteristics of microtubules.

Microtubules are structures formed from .

Discuss the cellular events that lead to a top-of-power stroke state.

Discuss linear and rotating molecular motors.

The protein in the troponin complex that shows 70% homology to calmodulin and involved in Ca²⁺ binding is:

Explain how negative cooperativity facilitates the hand-over-hand movement of Rep helicase.