Cell Structure & Function Exam IV

cytoskeleton

gives structure and form to cells, primary way that cells generate force

What are some of the processes that the cytoskeleton is used to drive? (5)

cell division, trafficking of organelles, cell contraction in muscle cells, cell movement & migration, beating of cilia

three types of cytoskeletal filaments

actin filaments, microtubules, intermediate filaments

actin filaments

• associated with cell cortex (PM)

• shorter, smaller, and more flexible than microtubules

• drive contraction movements (muscle and cell division)

microtubules

• in cytoplasm, often emanating out of a centrosome

• long, hollow cylinders

• rigid structure

• can serve as highways for organelle and chromosome movement

What does MTOC stand for? Give an example

microtubule organizing center, ex: centrosome

intermediate filaments

• in cytoplasm and nucleus

• act as fairly flexible ropes that are resistant to stretching

• function to help cells deal w/ mechanical stress and not be torn apart

Examples and short description of how cytoskeletal filaments form stable structures and direct polarity (2)

stereocilia: actin filaments in the ear that are formed once and hopefully last a lifetime

epithelial cells: has stable F-actin and microvili and microtubules that direct apical basal polarity

describe how smaller subunits assemble into cytoskeletal filaments

often assemble into a helical structure through non-covalent interactions

Why do cytoskeletal filaments assemble through non-covalent interactions?

the subunits are more weakly held together so they can break down and reassemble quickly

describe how protofilaments are made and what they do

subunits assemble into protofilaments that then can interact laterally to form filaments

How does the lateral interaction of protofilaments help filaments?

stabilizes interior of filaments while allowing dynamic change at ends

nucleation

very short polymers are unstable due to absence of stabilizing interactions, often the rate limiting step in filament formation

microtubule formation and organization

• made of heterodimers of alpha- and beta-tubulin proteins that can bind and hydrolyze GTP

• heterodimers assemble head-to-tail in protofilaments

• 13 protofilaments wrap into hollow tubes that provide rigidity

What does the assembly of heterodimers generate for microtubules?

microtubule polarity

f-actin formation and organization

• actin filaments made of actin protein monomers that can bind and hydrolyze ATP

• bends into a helical structure

• actin monomers bind in head-to-tail manner

• single and double stranded filament

What does the structure of f-actin allow for?

greater flexibility than microtubules, though can be crosslinked into stronger structures

What does the assembly of actin monomers generate for f-actin?

polarity with plus and minus ends

What may be different between the two ends of a cytoskeletal filament?

growth rates