BIOL 2P03 Lecture Notes - Lecture 18: Endocytosis, Cell Membrane, Formins

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Cell Organization and Movement: Microlaments I
Cellular contents are organized in a specic fashion
Organelles in specic locations
Cell takes on a dened shape
Proteins located in appropriate regions based on their assigned functions
Cell organization is achieved by the cytoskeleton
The cytoskeleton is a lamentous network of proteins consisting of:
Microlaments
Microtubules
Intermediate laments
The cytoskeleton is a dynamic system that can reorganize itself to meet the changing
needs of the cell
Reorganization is achieved by assembly and disassembly
Regulated by signal transduction pathways
Microlaments
Structure:
Microlaments are made up of the protein actin
Monomers of actin are globular and are known as G-actin
G-actin monomers can be polymerized into lamentous structures known as F-actin
G-actin monomers non-covalently bind to each other to form F-actin
The G-actin monomers that make up F-actin each contain an ATP/ADP binding site
They also possess an intrinsic ATPase
The orientation of these binding sites di)ers at each end of F-actin
F-actin is therefore said to be
polarized
It possesses positive and negative ends
Microlament Dynamics
in Vitro
The polymerization of G-actin to form F-actin can be studied
in vitro
Puried ATP-G-actin is present in solution at a dened concentration
If this concentration is high enough, ATP-G-actin will spontaneously polymerize
to form F-actin
The process of actin polymerization can be broken down into three stages:
Nucleation
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