BCHM253 CYTOSKELETON - COMPARE AND CONTRAST MICROFILAMENTS,
MICROTUBULES, AND INTERMEDIATE FILAMENTS
STRUCTURE AND COMPOSITION
MICROFILAMENTS: thin solid rods composed of a twisted double chain with a diameter of 7nm,
made from G-actin monomers that polymerise into F-actin.
MICROTUBULES: hollow tubes with an outer diameter of 25nm, built from alpha- and
beta-tubulin heterodimers that stack end-to-end to form protofilaments.
INTERMEDIATE FILAMENTS: rope-like filaments with a diameter of 10nm have a twisted,
cable-like structure and are composed of monomers, coiled dimers, and antiparallel tetramers.
POLARITY AND DYNAMICS
MICROFILAMENTS: have distinct polarity with a plus (barbed) end that grows faster and a
minus (pointed) end that grows slower; monomers are added at the plus end and removed from
the minus end.
MICROTUBULES: have polarity with a plus end (faster growing, terminated by beta tubulin) and
a minus end (often anchored, terminated by alpha tubulin).
INTERMEDIATE FILAMENTS: have no polarity and no plus/minus ends, so they do not have
directional growth.
NUCLEOTIDE BINDING AND REGULATION
MICROFILAMENTS: each actin monomer binds ATP, which is hydrolysed to ADP after
incorporation, creating dynamic behaviour.
MICROTUBULES: tubulin dimers bind GTP; this nucleotide binding regulates dynamics and can
be hydrolysed.
INTERMEDIATE FILAMENTS: do not use ATP or GTP hydrolysis; not regulated by nucleotide
binding, making them much more stable.
ORGANISATION AND LOCATION
MICROFILAMENTS: form bundles, gels, and fibres; found throughout the cell, highly
concentrated in the cell cortex under the plasma membrane.
MICROTUBULES: form long, straight fibres in interphase cells, mitotic spindles during cell
division, and 9+2 arrangements in cilia and flagella, and emanate from microtubule organising
centres.
INTERMEDIATE FILAMENTS: form rope-like filaments organised as sheets along the cell
periphery and meshworks beneath the inner nuclear membrane.
MOTOR PROTEINS
MICROFILAMENTS: myosin motor proteins walk along the microfilaments towards the plus end
using ATP.
MICROTUBULES: kinesin moves toward the plus end, and dynein moves toward the minus
end, both using ATP.
INTERMEDIATE FILAMENTS: do not use motor proteins, and have no associated motor protein
movement.
MICROTUBULES, AND INTERMEDIATE FILAMENTS
STRUCTURE AND COMPOSITION
MICROFILAMENTS: thin solid rods composed of a twisted double chain with a diameter of 7nm,
made from G-actin monomers that polymerise into F-actin.
MICROTUBULES: hollow tubes with an outer diameter of 25nm, built from alpha- and
beta-tubulin heterodimers that stack end-to-end to form protofilaments.
INTERMEDIATE FILAMENTS: rope-like filaments with a diameter of 10nm have a twisted,
cable-like structure and are composed of monomers, coiled dimers, and antiparallel tetramers.
POLARITY AND DYNAMICS
MICROFILAMENTS: have distinct polarity with a plus (barbed) end that grows faster and a
minus (pointed) end that grows slower; monomers are added at the plus end and removed from
the minus end.
MICROTUBULES: have polarity with a plus end (faster growing, terminated by beta tubulin) and
a minus end (often anchored, terminated by alpha tubulin).
INTERMEDIATE FILAMENTS: have no polarity and no plus/minus ends, so they do not have
directional growth.
NUCLEOTIDE BINDING AND REGULATION
MICROFILAMENTS: each actin monomer binds ATP, which is hydrolysed to ADP after
incorporation, creating dynamic behaviour.
MICROTUBULES: tubulin dimers bind GTP; this nucleotide binding regulates dynamics and can
be hydrolysed.
INTERMEDIATE FILAMENTS: do not use ATP or GTP hydrolysis; not regulated by nucleotide
binding, making them much more stable.
ORGANISATION AND LOCATION
MICROFILAMENTS: form bundles, gels, and fibres; found throughout the cell, highly
concentrated in the cell cortex under the plasma membrane.
MICROTUBULES: form long, straight fibres in interphase cells, mitotic spindles during cell
division, and 9+2 arrangements in cilia and flagella, and emanate from microtubule organising
centres.
INTERMEDIATE FILAMENTS: form rope-like filaments organised as sheets along the cell
periphery and meshworks beneath the inner nuclear membrane.
MOTOR PROTEINS
MICROFILAMENTS: myosin motor proteins walk along the microfilaments towards the plus end
using ATP.
MICROTUBULES: kinesin moves toward the plus end, and dynein moves toward the minus
end, both using ATP.
INTERMEDIATE FILAMENTS: do not use motor proteins, and have no associated motor protein
movement.
