Actin remodeling is a biochemical

Biochemistry

Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

 process in cells

Cell (biology)

The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

. In actin

Actin

Actin is a globular, roughly 42-kDa moonlighting protein found in all eukaryotic cells where it may be present at concentrations of over 100 μM. It is also one of the most highly-conserved proteins, differing by no more than 20% in species as diverse as algae and humans...

 remodeling, there is a cycle of actin monomer

Monomer

A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...

s being polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

ized, affecting the cell membrane

Cell membrane

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

, and being broken down into monomers again. Actin filament remodeling occurs on cell surfaces, and the variety of actin filament lengths and shapes caused by actin-binding protein

Actin-binding protein

Actin-binding proteins are proteins that bind to actin. This may mean ability to bind actin monomers, or polymers, or both....

s (ABPs) accounts for the diverse structure and changes in shape of eukaryotic

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

 cells.

Actin remodeling cycle

Cell surface (cortical) actin remodeling has a nine-step cyclic process, and each step is responsive to cell signaling

Cell signaling

Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. The ability of cells to perceive and correctly respond to their microenvironment is the basis of development, tissue repair, and immunity as well as normal tissue...

, making this a dynamic

System dynamics

System dynamics is an approach to understanding the behaviour of complex systems over time. It deals with internal feedback loops and time delays that affect the behaviour of the entire system. What makes using system dynamics different from other approaches to studying complex systems is the use...

process. Actin starts out as a monomer, is transformed into a polymer with attached ABPs, and is disassembled back into a monomer so the process can start over again.

• 1. Initiation and barbed-end uncapping

• 2. Elongation and barbed-end capping

• 3. Termination

Barbed-end capping

Polymerization promoters, barbed-end capping inhibitors

Lateral stabilization

• 4. Branching amplification

• 5. Actin filament crosslinking

• 6. Actin filament contraction and cargo motoring

• 7. Membrane attachment

• 8. Actin filament disassembly

Strong filament severing and barbed-end capping

Weak severing

Accelerated pointed-end depolymerization

• 9. Monomer sequestration that prevents spontaneous nucleation