“
Microfilaments Are Thin Actin, Microtubules Are Big Tubulin, Intermediate Holds Tension
Picture This (Mental Hook): Imagine a skyscraper: Microfilaments (7 nm) are the thin steel guy-wires made of Actin. Microtubules (25 nm) are the giant hollow exhaust pipes made of Tubulin where Kinesin & Dynein trains run! Intermediate filaments (10 nm) are the tough braided cables holding the walls together!
📊 Visual Diagram & Mental Flow:
┌─────────────────────────┬──────────────┬────────────────────────┬─────────────────────────────┐ │ Filament System │ Diameter │ Monomeric Subunits │ Motor Proteins / Function │ ├─────────────────────────┼──────────────┼────────────────────────┼─────────────────────────────┤ │ Microfilaments │ 7 nm (Thin) │ G-Actin (ATP binding) │ Myosin motors; cytokinesis, │ │ │ │ │ lamellipodia, microvilli │ │ Intermediate Filaments │ 10 nm (Medium│ Keratin, Vimentin, │ NO MOTORS! Pure mechanical │ │ │ │ Desmin, Lamins, NF │ tensile strength, desmosomes│ │ Microtubules │ 25 nm (Thick)│ alpha & beta Tubulin │ Kinesin (+ anterograde) & │ │ │ │ (GTP cap, 13 protofil) │ Dynein (- retrograde) │ └─────────────────────────┴──────────────┴────────────────────────┴─────────────────────────────┘
🔍 The Decoded Sequence:
7-10-25 nm
Dimensions
Actin (7 nm) < Intermediate (10 nm) < Microtubules (25 nm)
Kinesin
Kicking Out (+)
Anterograde transport towards cell periphery (+) end
Dynein
Dying In (-)
Retrograde transport towards centrosome / nucleus (-) end
Examiner Trap / Never Forget: Intermediate filaments have NO structural polarity (both ends identical) and do NOT use motor proteins, unlike actin and microtubules!
“
Drive Early After Midnight (DEAM: Cyclins D, E, A, B with CDKs 4, 2, 2, 1)
Picture This (Mental Hook): Think of a racing championship: You Drive Early After Midnight (Cyclins D, E, A, B)! Under their engines roar CDKs 4, 2, 2, 1! Cyclin D hits the pedal in G1, Cyclin E crosses the restriction gate into S, Cyclin A drives DNA replication, and Cyclin B launches Mitosis!
📊 Visual Diagram & Mental Flow:
G1 Phase ──────────────► Restriction Point ──► S Phase ──► G2 Phase ──► M Phase (Mitosis) │ │ │ │ │ [Cyclin D] [Cyclin E] [Cyclin A] [Cyclin A] [Cyclin B] + + + + + [CDK 4/6] [CDK 2] [CDK 2] [CDK 1] [CDK 1] (MPF!) * Cyclin D-CDK4 phosphorylates Rb protein ──► releases E2F transcription factor! * Cyclin B-CDK1 (Maturation Promoting Factor - MPF) triggers nuclear envelope breakdown
🔍 The Decoded Sequence:
D-4
Drive (G1)
Cyclin D + CDK4/6 regulates progression through mid-G1
E-2
Early (G1/S)
Cyclin E + CDK2 triggers G1/S transition and centrosome duplication
A-2
After (S)
Cyclin A + CDK2 coordinates DNA replication firing
B-1
Midnight (M)
Cyclin B + CDK1 forms MPF driving entry into Mitosis
Examiner Trap / Never Forget: p53 acts as the 'Guardian of the Genome' by activating p21 (CDK inhibitor) when DNA is damaged, halting the cell cycle at the G1 checkpoint!
