cytoskeleton I Flashcards
what is the function of the cytoskeleton?
spatial and mechanical function
what makes up the cytoskeleton?
protein filaments and tubules
what is the purpose of the cytoskeleton?
cell shape, cell movement, internal structure, intracellular transport, intercellular communication, organelle and cell anchoring
what are the three types of cytoskeletal proteins?
actin, microtubules, intermediate filaments
what 4 functions does actin have?
cell surface shape, whole cell locomotion, links transmembrane proteins to cytosolic proteins, pinches cell shut after division
what 3 functions do microtubules have?
positions organelles, intracellular transport, needed for cell division
what 2 functions do intermediate tubules have?
provide mechanical strength, line inside of nuclear envelope
which accessory proteins are associated with microtubules?
Motor proteins (dynein, kinesin)
where is actin highly concentrated?
cortex of cytoplasm
which 2 proteins interact during cell division?
actin and microtubules
why must cytoskeleton be dynamic and adaptable? when is this most prevalent?
because of constant changes in cells, esp. during development, cell cycle, phagocytosis or other specific cellular function
what does it mean to have strength in numbers? why is this important?
Single filaments are prone to easy breaking so multiples are needed; multiple protofilaments needed to make microtubule thermally stable
why can’t microtubules just have strong covalent bonds within a single protofilament? what kind of bonds do they have instead?
it wouldn’t allow them to disassemble quickly; hydrophobic interactions and noncovalent bonds
how do motor proteins and microtubules interact? how is it done? what protein is responsible for this?
dynein and kinesin attach to microtubules and “walk” along it; repeated rounds of ATP hydrolysis; tubulin
what makes up an actin subunit?
G-actin , carrying an ATP or ADP
how are actin subunits assembled? what do they form?
assemble head to tail to form F-actin
how do actin subunits demonstrate directionality?
Actin subunits are polar and have structurally different ends (plus end and minus end)
how would you describe minus end of an actin subunit?
Slower-growing minus end (pointed end)
how would you describe plus end of an actin subunit?
Faster-growing plus end (barbed end), subunits are added here
where do actin filaments form a complex?
actin filaments and the motor protein myosin
what is filament nucleation? where is it used? how?
process of initial aggregation (clustering); actin filaments; Subunit assembly and disassembly where needed
How does branching nucleation work and how does it form the actin web?
Formation Arp2 and 3 (protein complex) serve as nucleation hubs, binding to
a preexisting actin filament to form a web, it then acts as a plus end for monomer addition
Give an example of how specialized cells can use cytoskeletal elements to perform their functions.
Myofibrils in striated skeletal muscle cells consist of sarcomeres, here actin and myosin interact
what is each band in one sarcomere made of?
light bands= actin only dark bands = actin and myosin
what is myosin and how does it function? how does it do this?
motor protein that “slides” along actin polymers for muscle contraction; Uses ATP hydrolysis
Why and where is the protein complex troponin important?
Critical for control of muscle contraction; skeletal and cardiac muscles
what steps does troponin take to cause a muscle to contract?
Calcium binds troponin, which causes tropomyosin (an accessory muscle protein) to move away from actin, so it can bind to myosin to shorten sarcomere and contract muscle
why is troponin measured clinically in cardiac muscles?
If troponin levels are high in the blood, it could be a sign that a heart attack has occurred
