Topic 6: Cytoskeleton & Cell Movement

Comprehensive flashcards covering Topic 6: Cytoskeleton & cell movement from BIOL 107, focusing on microtubules, microfilaments, intermediate filaments, motor proteins, cilia/flagella mechanics, and sarcomere contraction.

Which cytoskeletal functions are performed in eukaryotes but not in prokaryotes?

Moving things during regular physiological processes and propelling the cell or its surroundings.

What are the three broad functions of the eukaryotic cytoskeleton?

1. Maintain (and change) cell shape

2. Spatially organize the cell contents

3. Connect cells and environment

What are the three classes of cytoskeletal fibres in eukaryotes, along with their polarity and monomer types?

1. Microtubules (tubulin family): polar (directional), globular monomers

2. Microfilaments (actin family): polar, globular monomers

3. Intermediate Filaments: apolar, filamentous monomers

What are the structural characteristics, polarity, and mechanical strength properties of microtubules (MTs)?

They are stiff, hollow tubes made of tubulin heterodimers ($\alpha$-tubulin and $\beta$-tubulin) with polarity (a plus side and a minus side). They are strong under compression and maintain cell shape under pressure.

How do the motor proteins kinesin and dynein differ in their direction of movement along microtubules? what do they have in common?

• Kinesin moves toward the plus end (anterograde transport)

• Dynein moves toward the minus end (retrograde transport).

• Both are ATP-powered and walk in a hand-over-hand fashion.

How do transport vesicles attach to microtubule motor proteins?

Kinesins and dyneins attach to transport vesicles via cargo adaptors, which are cargo-specific proteins on the vesicle membrane.

what are cilia made of? What are the specific microtubule doublet and triplet arrangements found in a cilium's basal body and motile portion? what do they have in common?

• Made of microtubules

• Basal body: $9$ microtubule triplets with no central microtubule ($9+0$ configuration)

• Motile portion: $9$ microtubule doublets with a central microtubule pair ($9+2$ configuration)

• ATP powered share the same configuration

In the motile portion of a cilium, how do dynein motor proteins interact with adjacent microtubule doublets to produce movement?

Dynein arms extending from tubule A of one doublet attach to and walk along tubule B of the adjacent doublet, powered by ATP.

Why are cross-linking proteins and anchorage required for cilia to bend?

• Without restriction, dynein movement causes microtubule doublets to slide unrestrained past each other

• cross-linking proteins between outer doublets and anchorage in the cell restrict sliding to produce bending and wavelike motion.

How do cilia and eukaryotic flagella differ in their type of movement?

• A flagellum undulates symmetrically side to side

• a cilium beats asymmetrically with power stroke (fish the fluid) and recovery stroke (return to the starting point)

In reproductive physiology, how are the concepts of motility and mobility distinguished using sperm and ova?

• Sperm are motile because they propel themselves using a flagellum.

• Ova (eggs) are mobile because beating cilia on the epithelial cells of the oviducts ("Fallopian tubes") propel them and prevent backflow.

What paired cylindrical structures composed of microtubules are depicted in this image? What does this say about pants and fungi?

• Centrioles ((centrosome)

• Microtubule Organizing Center (MTOC)

How do plants and fungi organize their microtubules?

• in the absence of centrioles other non-centriole structures serve the purpose of a Microtubule Organizing Center (MTOC).

During mitosis, what structure do microtubules and what do they do?

• The spindle apparatus which is composed of microtubules

• Form to guide chromosomes to opposite sides of the cell

What are the structural monomer, polymer form, diameter, and energy requirement of microfilaments?

• The monomer is G-actin (globular actin)

• Polymerizes into F-actin (filamentous actin)

• Assembly into F-actin requires ATP.

What mechanical properties characterize microfilaments compared to microtubules? what is it’s main function?

• Microfilaments provide tensile strength (how much pulling force a material can withstand before it breaks) to parts of the cell

• Not strong under compression (unlike microtubules, which resist compression)

• Help with cell shape, cell movement, and muscle contraction

  
  

What cellular specializations rely on microfilaments for internal structural support?

• The cell cortex (sub-membrane shape support)

• microvilli (outfolds on intestinal epithelial cells) to increase SA

During sarcomere contraction, what happens to the thick filaments, actin, Z-line, and titin?

• Thick filaments don't budge

• Myosin heads tug on thin microfilaments; the actin filament is pulled which pulls the Z-line toward the M-line

• Compresses titin from its default extended shape.

Which motor protein system drives amoeboid crawling locomotion and cytoplasmic streaming in plants?

• The actin-myosin system (actin filaments interacting with myosin motor proteins).

• actin filaments —> protein fibers help change shape

• myosin—> use ATP to pull on actin filaments

• amoeboid movement: cell extend Pseudopodia (temporary extension of cytoplasm) and moves its body forward like crawling

Which Gram-negative obligate intracellular parasite manipulates host actin-based cytoskeletons, what cells does it infect, and what disease does it cause?

• Ehrlichia chaffeensis

• Hijacks the cytoskeleton of monocytes and macrophages

• is transmitted by the lone star tick

What are the key defining characteristics of intermediate filaments regarding what it’s made of, strength, and it does? what is it only in?

• made of various proteins

• high tensile strength

• help toughen parts of cell to morph the cell into specific shape

• animal structures only

What is the structural assembly hierarchy of intermediate filaments?

• monomers intertwine via coiled-coil interactions and disulfide bridges

• form dimers, dimers pair in a staggered fashion to form tetramers

• tetramers assemble into protofilaments; protofilaments assemble into the final filament cable.

what does Keratin do? What’s an example? what do they also form?

• Intermediate filament protein that provides high tensile strength to keep cells together

• Velcro portion of desmosomes are made of Keratin

• claws, horns, beaks, feather, hair and nails

Which specific intermediate filament protein forms a structural meshwork lining the inner nuclear membrane?

Lamin (which forms the nuclear lamina) —> in nucleus envelope