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Motion is enabled by two elements: __ and __
Many of the proteins that play key roles in __ are members of the same protein family, the __
molecular-motor proteins and complex networks of filamentous proteins termed the cytoskeleton
converting chemical energy into kinetic energy
Molecular motors operate by small increments, converting __ into __
Orderly motion across distances requires __
The motor proteins cycle between __
changes in protein conformation into directed motion
a track that steers the motion of the motor assembly
forms having high or low affinity for the filament tracks in response to ATP binding and hydrolysis, enabling a bind, pull, and release mechanism that generates motion
A set of flagella act as __, rotated by a __in the bacterial cell membrane. This rotary motor is driven by a __ across the membrane, rather than by __. The mechanism for coupling the __ to __ is analogous to that used by the F0 subunit of ATP synthase.
- proton gradient
- ATP hydrolysis
- proton gradient to rotatory motion
Eukaryotic cells contain three major families of motor proteins: __, __, and __. Members of each of these classes move along __, but, at first glance, these protein families appear to be quite different from one another
Myosin moves along __
§ Structure of myosin
- myosins, kinesins, and dyneins.
- components of the cytoskeleton
- filaments of the protein actin
Each molecule of muscle myosin consists of two copies each of a heavy chain with a molecular mass of 220 kd, an essential light chain, and a regulatory light chain
__, which have __ as well as __, are generally __
__ power the __, and a general __contributes to a variety of motions in all cells, including __ and various transport events in mitosis
- roles in protein, mRNA, and vesicle transport
- construction of the mitotic spindle and chromosome segregation
- dimers of two polypeptides
- motion of cilia and flagella
- cytoplasmic dynein
- vesicle transport
__ and __ families have remarkable similarities in that they contain __
Sequence analysis of the __ reveals it to be a member of the __
__has __sequences encoding such __ arrayed along its length, although only __ actually appear to bind __
- Myosin and kinesin
- P-loop NTPase cores
- dynein heavy chain
- AAA subfamily of P-loop NTPases
- P-loop NTPase domains
Molecular motors are generally __ with an __ and an extended structure
Myosin structure: __
The treatment of myosin with __ and __ results in the formation of four fragments: __
- oligomeric proteins
- ATPase core
- is a two-headed structure linked to a long stalk.
- trypsin and apain
- two S1 fragments; heavy meromyosin (HMM) which consists of the S1 fragments and an additional region termed S2; and a fragment called light meromyosin (LMMM)
Each S1 fragment corresponds to __and includes __ from one of the __ as well as one copy of each of the __.
A __ is present that is the __
- one of the heads of the intact structure
- 850 amino-terminal amino acids
- two heavy chains
- light chains
- P-loop NTPase-domain core
- site of ATP binding and hydrolysis
Extending away from the structure is a __, which does what?
These proteins do what?
The remaining fragments of myosin—__ and __—are largely __, forming __ created by the remaining lengths of the two heavy chains wrapping around each other
- long alpha helix from the heavy chain
- binds the two light chains, which are members of the EF-hand family
- wrap around an alpha helix, thickening and stiffening it.
- S2 and light meromyosin
- alpha helical
- two-stranded coiled coils
Conventional kinesin (kinesin 1) has several structural features in common with myosin.
What are the commonalities?
Myosin domain is __than kinesin’s domain because of __
Conventional kinesin (kinesin 1)
A dimer that has two heads connected by an extended structure, which is 1/3 the size of myosin; the head is also built around a P-loop NTPase core
- two large insertions in the myosin domain that bind to actin filaments
A region of about __ extends from the __
Extended part forms an __
Has __ that bind near the __ of the heavy chain and are thought to do what?
- 500 amino acids
- head domain
- alpha helical coiled coil
- light chains
- link the motor to intracellular cargo
Dynein has a __ that has __ homologous to the __
Head is appended to region of __ that forms an __that does what
to form __and __.
- heavy chain
- six regions
- AAA subfamily of ATPase domains
- approximately 1300 amino acids
- extended structure
links dynein units together
- interacts with other proteins
Common features of the molecular motors:
§ Each is dimeric with two head domains, has regions of extended but rigid structures, and has regions for interacting with other proteins·
The regions for interacting with other proteins represents __, the extended structures represent the __, and the head domains are the __.
- grasping hands
- arms that act as levers to promote large-scale motion
- engines that provide the necessary mechanical energy
Structure of myosin in association with ADP and ATP
The long helix that binds the light chains (lever arm) protrudes outward from the head domain
§ Rotated by 90 degrees in the ADP-VO43- complex compared with its position in the nucleotide-free form.
How does the species in the nucleotide-binding site cause this dramatic transition?
Two regions around the nucleotide-binding site (switch I and switch II) tightly conform to the shape of the gamma-phosphoryl group of the ATP analog and adopt a looser conformation when the gamma-phosphoryl group is absent.
What does this conformational change allow?
This conformational change allows a long alpha helix (the relay helix) to adjust its position. The carboxyl-terminal end of the relay helix interacts with structures at the base of the lever arm, and so a change in the position of the relay helix leads to a reorientation fo te lever arm
Kinesins change similarly when binding different nucleotides, except they lack an __ and instead have a __, which responds to __
It does what
when ATP is bound but is __when the nucleotide-binding site is vacant or occupied by ADP
- alpha-helical lever arm
- neck linker
- nucleotide binding
- binds to the head domain