cell movement (L22)

what are microtubules

hollow tubes of alternating alpha + beta tubulin with embedded GTP/GDP)

24 nanometres in diameter with 13 protofilaments per cycle

what 3 things does a cell require to be motile

energy

guidance

mechanical interaction with somethings outside the cell (microtubules/actin filaments)

what do microtubules move

cells (sperm/protozoa) or fluids (respiritory/reproductive tract)

what are the similarities between cillia and flagella

same structure but different lengths (cillia: 2-10×0.25 micrometres/ flagella: 100-200×0.25 micrometres)

both contain axoneme at centre

different waveforms

describe the structure of the axoneme

9+2 microtubule assembly

9 outer doublets with dynein arms (motor proteins) and radial spokes + inner pair

13 complete A fibres + 10 incomplete B fibres (both protofilaments)

nexin crosslinks between outer doublets anchor adjacent doublets + prevent them completely sliding past each other- bend instead

inner dynein arm controls waveform while outer controls power

what are the structure of basal bodies

9×3 microtubule array (outer triplets)

0.2×0.4 micrometres

anchor microtubule to centriole attached to centrosome

what does actin-based motility move and where does motility come from

muscle: whole body

non muscle: cells/tissues

motility comes from motor proteins + turnover

what is the structure of an actin filament

plus + minus end, polarity along length (grows at + end, minimises at - end)

embedded ATP/ADP (when polymerised as filament ATP→ADP)

what do profilin and cofilin do

profilin binds to ATP actin to prevent binding, cofilin binds to ADP to break apart chains

what is the motor protein for actin filaments

myosin

name and describe 4 actin based motility structures

• Filopodia: Actin bundles extend as linear, parallel filaments, driven by formin proteins, enabling cell "exploration" and sensing of the environment.

• Lamellipodia: Branched actin networks push the cell membrane forward, regulated by Arp2/3 complexes, enabling cell migration.

• Stress Fibers: Actin filaments are bundled in contractile structures, providing mechanical support and enabling force generation for contraction and cell shape maintenance.

• Cortical Actin: Forms a dense network beneath the plasma membrane, maintaining cell shape, supporting membrane stability, and regulating dynamic processes like migration and division.