Microfilaments

Question 1

What are microfilaments?

Answer 1

Polymer of actin, with a diameter of about 7 nm, that is an integral part of the cytoskeleton, contributing to the support, shape, and mobility of eukaryotic cells

Question 2

Microfilaments (MFs) are the _______ of the cytoskeletal filaments and are best known for their role in contractile fibrils of muscle cells

Answer 2

Smallest

Question 3

What are the roles of microfilaments?

Answer 3

They play a role in cell migration, amoeboid movement, cytoplasmic streaming, development and maintenance of cell shape and serve as structural core of microvilli.

Question 4

What makes up microfilaments?

Answer 4

Actin

Question 5

What is Actin?

Answer 5

Principal protein of the microfilaments found in the cytoskeleton of non-muscle cells and in the thin filaments of skeletal muscle; synthesized as a globular monomer (G-actin) that polymerizes into long, linear filaments (F-actin)

Question 6

How can G-actin monomers polymerize into F-Actin microfilaments?

Answer 6

G-actin monomers can polymerize reversibly into filaments with a lag phase corresponding to filament nucleation, which begins with formation of dimers or trimers, called nucleation seeds, followed by a rapid polymer elongation phase. All the actin monomers are oriented in the same direction so that an MF has an inherent polarity, demonstrated by incubating MFs with myosin subfragment 1 (S1), a proteolytic fragment of myosin

Question 7

What do S1 fragments do?

Answer 7

Bind to, or “decorate” the actin MFs in a distinctive arrowhead pattern

Question 8

What is the term for plus end?

Answer 8

Barbed end

Question 9

What is the term for minus end?

Answer 9

Pointed end

Question 10

What are some specific drugs that affect polymerization of microtubules?

Answer 10

They include Cytochalasins, Latrunuculin A, and Phalloidin

Question 11

What does Cytochalasins do?

Answer 11

They are fungal metabolites that prevent the addition of new monomers to existing MFs

Question 12

What does Latrunculin A do?

Answer 12

Is a toxin that sequesters actin monomers and prevents their addition to MFs

Question 13

What does Phalloidin do?

Answer 13

Stabilizes MFs and prevents their depolymerization

Question 14

What do Actin-Binding Proteins do?

Answer 14

Proteins that bind to actin microfilaments, thereby regulating the length or assembly of microfilaments or mediating their association with each other or with other cellular structures, such as the plasma membrane