BIOL 4100 Exam 4 Petrov Summer 2024 Questions With
Complete Solutions
REVIEW QUESTIONS
Actin polymerization and assembly
Actin polymerization is reversible.
If assembly rate is higher than disassembly, filament grows
If assembly rate is lower, the filament will shrink
At the pointed end (-) assembly is disfavored; at the barbed end
(+) assembly is favored.
Arp 2/3 nucleation model
1. Arp2/3 Complex: binds to sides or - end of actin filaments
2. Nucleation promotion factors: deliver G-actin subunits to
anchored complex
3. G-actin monomers: added to + end of growing filament
Describe thermodynamics of filament depolarization for both
ends
ATP hydrolysis changes thermodynamics of dissociation.
Upon hydrolysis, most energy remains stored in the filament and
released upon depolymerization.
More energy is released upon filament dissociation, becomes
more negative (and thus KD goes up)
Describe functions and relationship between Thymosin and
profilin
,Thymosin: gene that encodes an actin sequestering protein
which will play a role in regulation of actin polymerization; also
involved in cell proliferation, migration, and differentiation.
Profilin: actin-binding protein that binds actin monomers and
stimulates the exchange of bound ADP for ATP; promotes actin
polymerization by increasing local conc. of ATP-actin.
Relationship: 2 major sequestering proteins that maintain pool
of monomeric actin (G-actin) within cells of higher eukaryotes.
Thymosin prevents G-actin from joining a filament, and Profilin
only supports barbed-end elongation
,BIOL 4100 Exam 4 Petrov Summer 2024 Questions With
Complete Solutions
Cells and organelles are what?
Cells are mobile (immune cells migrate)
Organelles form organelle networks (intricate)—networks are
dynamic and interact with each other. The cytoskeleton is
responsible for organelle placement and mobility
Describe the cytoskeleton
Cytoskeleton: complex network of interlinking filaments and
tubules that extend throughout the cytoplasm of a cell.
Cytoskeleton provides structural framework that determines cell
shape, positions of organelles, and general organization of the
cytoplasm
Cytoskeleton also responsible for movement of entire cells and
internal transport of organelles
Not rigid, but dynamic structure that is continually
reorganized as cells move and change shape
Describe the 3 main components of the cytoskeleton
Actin filaments: define cell shape and necessary for cell
locomotion
Microtubules: position membrane enclosed organelles, mediate
and form mitotic spindle during cell division
, Intermediate filaments: provide mechanical strength
What are molecular motors?
proteins that convert energy of ATP hydrolysis to mechanical
work
What are the main functions of the cytoskeleton?
1. Spatial organization of the contents of a cell: defines cell
shape, organelle trafficking, divides chromosomes during cell
division
2. Connects the components of the cell physically and
biochemically to each other and the cell surface: structural
support, mechanical stress
3. Generates coordinated forces that enable the cell to move
and/or change and/or keep shape: cell migration, chemotaxis
Describe actin filaments
Actin polymerizes to form actin filaments (microfilaments)
Microfilaments: flexible fibers organized into various
structures such as bundles and 3D networks; responds to local
signaling activity; polarized; myosin protein motors
Some actin filaments are alloys built out of several isoforms
Each actin monomer (globular [G] actin) has tight binding sites
that mediate head-to-tail interactions w/ two other actin
monomers to form filaments (filamentous [F] actin)
Complete Solutions
REVIEW QUESTIONS
Actin polymerization and assembly
Actin polymerization is reversible.
If assembly rate is higher than disassembly, filament grows
If assembly rate is lower, the filament will shrink
At the pointed end (-) assembly is disfavored; at the barbed end
(+) assembly is favored.
Arp 2/3 nucleation model
1. Arp2/3 Complex: binds to sides or - end of actin filaments
2. Nucleation promotion factors: deliver G-actin subunits to
anchored complex
3. G-actin monomers: added to + end of growing filament
Describe thermodynamics of filament depolarization for both
ends
ATP hydrolysis changes thermodynamics of dissociation.
Upon hydrolysis, most energy remains stored in the filament and
released upon depolymerization.
More energy is released upon filament dissociation, becomes
more negative (and thus KD goes up)
Describe functions and relationship between Thymosin and
profilin
,Thymosin: gene that encodes an actin sequestering protein
which will play a role in regulation of actin polymerization; also
involved in cell proliferation, migration, and differentiation.
Profilin: actin-binding protein that binds actin monomers and
stimulates the exchange of bound ADP for ATP; promotes actin
polymerization by increasing local conc. of ATP-actin.
Relationship: 2 major sequestering proteins that maintain pool
of monomeric actin (G-actin) within cells of higher eukaryotes.
Thymosin prevents G-actin from joining a filament, and Profilin
only supports barbed-end elongation
,BIOL 4100 Exam 4 Petrov Summer 2024 Questions With
Complete Solutions
Cells and organelles are what?
Cells are mobile (immune cells migrate)
Organelles form organelle networks (intricate)—networks are
dynamic and interact with each other. The cytoskeleton is
responsible for organelle placement and mobility
Describe the cytoskeleton
Cytoskeleton: complex network of interlinking filaments and
tubules that extend throughout the cytoplasm of a cell.
Cytoskeleton provides structural framework that determines cell
shape, positions of organelles, and general organization of the
cytoplasm
Cytoskeleton also responsible for movement of entire cells and
internal transport of organelles
Not rigid, but dynamic structure that is continually
reorganized as cells move and change shape
Describe the 3 main components of the cytoskeleton
Actin filaments: define cell shape and necessary for cell
locomotion
Microtubules: position membrane enclosed organelles, mediate
and form mitotic spindle during cell division
, Intermediate filaments: provide mechanical strength
What are molecular motors?
proteins that convert energy of ATP hydrolysis to mechanical
work
What are the main functions of the cytoskeleton?
1. Spatial organization of the contents of a cell: defines cell
shape, organelle trafficking, divides chromosomes during cell
division
2. Connects the components of the cell physically and
biochemically to each other and the cell surface: structural
support, mechanical stress
3. Generates coordinated forces that enable the cell to move
and/or change and/or keep shape: cell migration, chemotaxis
Describe actin filaments
Actin polymerizes to form actin filaments (microfilaments)
Microfilaments: flexible fibers organized into various
structures such as bundles and 3D networks; responds to local
signaling activity; polarized; myosin protein motors
Some actin filaments are alloys built out of several isoforms
Each actin monomer (globular [G] actin) has tight binding sites
that mediate head-to-tail interactions w/ two other actin
monomers to form filaments (filamentous [F] actin)
