plant biology (PLBI 421) Question and
answers already passed 2026/2027
Plasmodesmata - correct answer channels through cell walls that connect the cytoplasms of adjacent
cells
Plants are known as ________ because their cells are connected - correct answer supracellular
How are vesicles delivered during pollen tube growth? - correct answer Actin & myosin
Structures unique to plant cells: - correct answer 1. cell wall
2. chloroplast
3. plasmodesmata
4. central vacuole
5. tonoplast
Components of the cytoskeleton - correct answer 1. Microtubules (MTs)- ~25 nm tubules
2. Actin filaments (AFs) AKA micofilaments- ~7nm filaments
* MTs & AFs have different functions in different cell types
cytoskeleton involved in: - correct answer - intracellular movement
- cell shape
- cell wall formation
- cell division
- organization of cell content
,- signalling & metabolism
Microtubules - correct answer - tubulin alpha & beta subunits make up protofilament.
- polymerization of tubulin dimers (a & B tubulin)
- polarized
- (+) end= addition of dimers
- (-) end= removal of dimers
- dynamic growth, catastrophe, severing, bundled, transported.
Self-assembly & dynamic instability of MTs depends on association with GDP/GTP - correct answer -
binding, hydrolysis & exchange of GTP
- B-tubulin GTP (assembled) or GDP (integrated form)
MT polymerization - correct answer - GTP bound B-tubulin the dimer has STRAIGHT conformation
- GDP bound B-tubulin is BENT conformation, causes internal pressure since they want to bend outwards
but are constrained.
* only GTP bound B-tubulin can be added to the (+) end *
Dynamics at the (+) end - correct answer - catastrophe is a rapid event (shrinking)
- GTP-tubulin drives polymerization
- GDP-tubulin drives depolymerization (dynamic instability that occurs at the (+) end)
- MT associated proteins (MAPs) eg. end-binding protein (EB1- binds to (+) end & stabilizes it).
MT nucleation - correct answer gamma-tubulin ring complex at (-) end
- gamma TuRC found on nuclear envelope & PM; it BRANCHES MT!
,What does the gamma tubulin ring complex do? - correct answer branches MT-
acts as a scaffold or template for α/β tubulin dimers during the nucleation process—speeding up the
assembly of the ring of 13 protofilaments that make up the growing microtubule. The γ-TuRC also acts
as a cap of the (−) end while the microtubule continues growth from its (+) end. This cap provides both
stability and protection to the microtubule (-) end from enzymes that could lead to its depolymerization,
while also inhibiting (-) end growth
Cellulose synthase - correct answer makes cellulose microfibrils, guided by cortical MTs
- many MAPs regulate MT dynamics
- many aspects of MT dynamics & functions unknown
know the figure on slide 10 under cytoskeleton powerpoint - correct answer cortical MTs nucleated by
y-TuRC associated w/ existing MTs.
Nucleation can branch away from parent MT (40 degree angle) or interact directly to form a bundle.
New MTs associate with the PM & are severed from yTuRC by katanin
Treadmilling at (+) end
Cortical MTs= sites for cellulose synthase complex insertion into the PM, guides movement for effective
cellulose placement in wall
Actin Filaments - correct answer - globular actin (G-actin)= monomer
- ATP required to make g-actin competent
- more flexible
- actin filament (f-actin) more flexible, bundling occurs
- Actin-binding proteins regulate f-actin dynaminc
- treadmilling occurs, but slower than that of MTs
- f-actin abundant throughout cell, including transvacuolar strand of cytoplasm
, F-actin important in: - correct answer - positioning organelles
- cytoplasmic streaming
- tip growth
Nucleation of AFs two main mechanisms: - correct answer 1. Formin
2. Arp 2/3 complex
1. Formin - correct answer FH1 domain: multiple binding sites for profilin (an abundant actin monomer
binding protein).
FH2 homodimers encircle the barbed end of a filament. Most FH2 domains inhibit actin filament
elongation, but FH1 domains concentrate multiple profilin-actin complexes near the end of the filament.
Actin transfers very rapidly from the FH1 domains onto the barbed end of the filament, allowing
elongation at rates that exceed elongation by the addition of free actin monomers diffusing in solution.
Binding of actin to the end of the filament provides the energy for the highly processive movement of
the FH2 as a filament adds thousands of actin subunits
Arp 2/3 complex - correct answer initiates branches off of existing actin filaments.
- grabs actin/profilin & builds a branch at 70 degree angle to existing AFs
- important in tip growth in polarized cells
Cytoskeleton motors - correct answer - ATP hydrolysis results in a conformational change to generate
force
- cycles between filament binding, conformational change, filament release, conformational relaxation &
filament binding again
Myosin & kinesin - correct answer - Head motor domain
- interacting tail domain
answers already passed 2026/2027
Plasmodesmata - correct answer channels through cell walls that connect the cytoplasms of adjacent
cells
Plants are known as ________ because their cells are connected - correct answer supracellular
How are vesicles delivered during pollen tube growth? - correct answer Actin & myosin
Structures unique to plant cells: - correct answer 1. cell wall
2. chloroplast
3. plasmodesmata
4. central vacuole
5. tonoplast
Components of the cytoskeleton - correct answer 1. Microtubules (MTs)- ~25 nm tubules
2. Actin filaments (AFs) AKA micofilaments- ~7nm filaments
* MTs & AFs have different functions in different cell types
cytoskeleton involved in: - correct answer - intracellular movement
- cell shape
- cell wall formation
- cell division
- organization of cell content
,- signalling & metabolism
Microtubules - correct answer - tubulin alpha & beta subunits make up protofilament.
- polymerization of tubulin dimers (a & B tubulin)
- polarized
- (+) end= addition of dimers
- (-) end= removal of dimers
- dynamic growth, catastrophe, severing, bundled, transported.
Self-assembly & dynamic instability of MTs depends on association with GDP/GTP - correct answer -
binding, hydrolysis & exchange of GTP
- B-tubulin GTP (assembled) or GDP (integrated form)
MT polymerization - correct answer - GTP bound B-tubulin the dimer has STRAIGHT conformation
- GDP bound B-tubulin is BENT conformation, causes internal pressure since they want to bend outwards
but are constrained.
* only GTP bound B-tubulin can be added to the (+) end *
Dynamics at the (+) end - correct answer - catastrophe is a rapid event (shrinking)
- GTP-tubulin drives polymerization
- GDP-tubulin drives depolymerization (dynamic instability that occurs at the (+) end)
- MT associated proteins (MAPs) eg. end-binding protein (EB1- binds to (+) end & stabilizes it).
MT nucleation - correct answer gamma-tubulin ring complex at (-) end
- gamma TuRC found on nuclear envelope & PM; it BRANCHES MT!
,What does the gamma tubulin ring complex do? - correct answer branches MT-
acts as a scaffold or template for α/β tubulin dimers during the nucleation process—speeding up the
assembly of the ring of 13 protofilaments that make up the growing microtubule. The γ-TuRC also acts
as a cap of the (−) end while the microtubule continues growth from its (+) end. This cap provides both
stability and protection to the microtubule (-) end from enzymes that could lead to its depolymerization,
while also inhibiting (-) end growth
Cellulose synthase - correct answer makes cellulose microfibrils, guided by cortical MTs
- many MAPs regulate MT dynamics
- many aspects of MT dynamics & functions unknown
know the figure on slide 10 under cytoskeleton powerpoint - correct answer cortical MTs nucleated by
y-TuRC associated w/ existing MTs.
Nucleation can branch away from parent MT (40 degree angle) or interact directly to form a bundle.
New MTs associate with the PM & are severed from yTuRC by katanin
Treadmilling at (+) end
Cortical MTs= sites for cellulose synthase complex insertion into the PM, guides movement for effective
cellulose placement in wall
Actin Filaments - correct answer - globular actin (G-actin)= monomer
- ATP required to make g-actin competent
- more flexible
- actin filament (f-actin) more flexible, bundling occurs
- Actin-binding proteins regulate f-actin dynaminc
- treadmilling occurs, but slower than that of MTs
- f-actin abundant throughout cell, including transvacuolar strand of cytoplasm
, F-actin important in: - correct answer - positioning organelles
- cytoplasmic streaming
- tip growth
Nucleation of AFs two main mechanisms: - correct answer 1. Formin
2. Arp 2/3 complex
1. Formin - correct answer FH1 domain: multiple binding sites for profilin (an abundant actin monomer
binding protein).
FH2 homodimers encircle the barbed end of a filament. Most FH2 domains inhibit actin filament
elongation, but FH1 domains concentrate multiple profilin-actin complexes near the end of the filament.
Actin transfers very rapidly from the FH1 domains onto the barbed end of the filament, allowing
elongation at rates that exceed elongation by the addition of free actin monomers diffusing in solution.
Binding of actin to the end of the filament provides the energy for the highly processive movement of
the FH2 as a filament adds thousands of actin subunits
Arp 2/3 complex - correct answer initiates branches off of existing actin filaments.
- grabs actin/profilin & builds a branch at 70 degree angle to existing AFs
- important in tip growth in polarized cells
Cytoskeleton motors - correct answer - ATP hydrolysis results in a conformational change to generate
force
- cycles between filament binding, conformational change, filament release, conformational relaxation &
filament binding again
Myosin & kinesin - correct answer - Head motor domain
- interacting tail domain
