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BCH 339M exam 1What are the three major types of motors in eukaryotic cells? How are they similar? How are they
different? What are three functions carried out by family members of each motor type? - correct answer
✔✔The three main types of motors in eukaryotic cells are myosin, kinesin, and dynein
They are similar that all three types of motor proteins uses ATP as a fuel and they all facilitate vesicle and
organelle transport within the cells.
They are different that one of them uses a different type of motor than the other two, they move in
different relative directions and on different tracks.
Myosin functions: muscle contraction, vesicle transport and organelle transport.
Kinesin functions: organelle transport, vesicle transport and chromosome movement.
Dynein functions: organelle transport, vesicle transport, cilia movement.
2. Define allostery and describe one example of allosteric behavior. - correct answer ✔✔Allostery is the
regulation/process when a macromolecule bind to a site of an enzyme that is not the active site to help
regulate the activity of the enzyme.
One example of allosteric behavior would be hemoglobin and it's binding activity to oxygen. There are
four binding sites on hemoglobin and binding on one site will affect the affinity for oxygen on the
allosteric sites. It increases other sites' affinity for oxygen.
What is a role of dimerization in kinesin and myosin V? - correct answer ✔✔Myosin V:
-Two dimers/head act independently
-Only one attaches to actin at a given time
-Role of two dimers is to perform walking action on actin
Kinesin:
-Process is faster than myosin V
-Advantages of dimerization
-Neck linker connects two coiled-coil dimerization domains
-Motion on one side of neck linker is connected to partner, driving motion of other head
, -Neck linker provides smaller conformation change.
At what stage of the ATP cycle does the power stroke occur for myosin? Kinesin? - correct answer
✔✔Myosin V: Myosin V does not bind to actin when it is bound to ATP. The power stroke occur when
ADP and Pi dissociate from the myosin head.
Kinesin: Kinesin bind tightly to tubulin when it is bound to ATP. The power stroke occur when ATP binds.
To change conformation between ATP and ADP bound states, motor proteins must sense the presence or
absence of the -phosphate. How do myosin and kinesin do this? - correct answer ✔✔They sense the
presence or absence of the phosphate using 𝛄-phosphate sensor. This sensor consisted of two loops and
they functio to make hydrogen bonds with the 𝛄-phosphate and catalytic water to facilitate the
attachment of the phosphate group to ADP.
What is the relay helix in myosin and what is its function? Does kinesin have a homologous helix? -
correct answer ✔✔Relay helix:
-Highly conserved long helix
Connects to switch II loop at NH2-terminus and COOH-terminus domain
-Important role in communication between catalytic site, polymer binding site, and mechanical elements
in myosin
-Not always at a particular nucleotide site
Kinesin:
-Has homologous helix structure to relay helix in myosin
X-ray crystallography and cryo-EM provide "snapshots" of molecules in fixed conformations. How do
scientists observe ATP-bound conformations of ATPases whose job it is to hydrolyze ATP and thus only
bind ATP transiently? - correct answer ✔✔Scientists are able to observe ATP-bound conformation of
ATPase by trapping it at specific conformation using an ATP analog that is not hydrolyzable. X-ray
crystallography and cryo-EM only provide snapshots of the conformations, but scientists are able to take
snapshots of multiple stages, they will be able to put together all the pictures and understand the
mechanisms of ATPase.
The step size of cargo-carrying myosins and kinesins invariably correspond to an integral number of
helical turns of the track (actin filaments or microtubules, respectively). Why? - correct answer ✔✔The
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