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MCAT Content / Cytoskeleton / Microfilaments Composition And Role In Cleavage And Contractility

Microfilaments: composition and role in cleavage and contractility

Topic: Cytoskeleton

Microfilaments, which are the thinnest among the cytoskeletal elements, support the cellular shape and all of its internal parts via absorbing tension.

They function in cellular movement, have a diameter of about 7 nm, and are made of two intertwined strands of a globular protein called actin. For this reason, microfilaments are also known as actin filaments.

Microfilaments are made of two intertwined strands of actin. Their ends are structurally different.

Actin is powered by ATP to assemble its filamentous form, which serves as a track for the movement of a motor protein called myosin. This enables actin to engage in cellular events requiring motion such as cell division in animal cells and cytoplasmic streaming, which is the circular movement of the cell cytoplasm in plant cells. Actin and myosin are plentiful in muscle cells – when they slide past each other, your muscles contract. In animal cell division, a ring made of actin and myosin pinches the cell apart to generate two new daughter cells.

Microfilaments also provide some rigidity and shape to the cell. They can disassemble and reform quickly, thus enabling a cell to change its shape and move. This is named as amoeboid movement, taken from the name of unicellular eukaryote Amoeba that extensively relies on it. White blood cells (your body’s infection-fighting cells) also make good use of this ability. They can move to the site of an infection and engulf the pathogen.


Practice Questions


Khan Academy   


MCAT Official Prep (AAMC)

Biology Question Pack, Vol 2. Passage 1 Question 1

Section Bank B/B Section Passage 1 Question 5

Sample Test B/B Section Passage 6 Question 33

Key Points

• Microfilaments assist with cell movement and structure and are made of a protein called actin. Their main role is to absorb tension.

• Actin works with another protein called myosin to produce muscle movements and cell division, and cytoplasmic streaming in plants.

Key Terms

Cytoskeleton: network of protein fibers that help with cellular movement and maintaining its structure/shape

Actin: a globular structural protein that polymerizes in a helical fashion to form an actin filament (or microfilament)

Myosin: a large family of motor proteins found in eukaryotic tissues, allowing mobility in muscles

Microfilaments: thin protein fibers made up of actin proteins; their fundamental role is to absorb tension.

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