Fundamentals of Biological Sciences Lecture3 Dr. Açelya Yılmazer

Cells are always in motion Most of this motion occurs in the cell interior, analogous to blood flow in a human body; some cells can also “crawl” from one location to another Even cells that remain “stationary” in the body must remain in motion to stay alive; even a human body “at rest” must breathe and pump blood Most of the motion and structural stability in cells is provided by three groups of proteins, collectively called the cytoskeleton

The Cytoskeleton Is Represented by Three Functional Classes of Proteins The cytoskeleton is a complex mixture of three different types of proteins that are responsible for providing mechanical strength to cells and supporting movement of cellular contents The most visible form of cytoskeletal proteins are long filaments found in the cytosol, but these proteins also form smaller shapes that are equally important for cellular function The structural differences between the three protein types underscores their four different functions in cells

INTERMEDIATE FILAMENTS Intermediate Filaments Are Strong and Ropelike Intermediate Filaments Strengthen Cells Against Mechanical Stress The Nuclear Envelope Is Supported by a Meshwork of Intermediate Filaments (nuclear lamina)

INTERMEDIATE FILAMENTS Intermediate Filaments Are Strong and Ropelike Intermediate Filaments Strengthen Cells Against Mechanical Stress The Nuclear Envelope Is Supported by a Meshwork of Intermediate Filaments

MICROTUBULES Microtubules Are Hollow Tubes with Structurally Distinct Ends The Centrosome Is the Major Microtubule-organizing Center in Animal Cells

MICROTUBULES Growing Microtubules Display Dynamic Instability Dynamic Instability is Driven by GTP Hydrolysis Microtubule Dynamics Can be Modified by Drugs (ex: colchicine- cells stall in the middle of mitosis)

MICROTUBULES Microtubules Organize the Cell Interior Motor Proteins Drive Intracellular Transport Microtubules and Motor Proteins Position Organelles in the Cytoplasm

MICROTUBULES Microtubules Organize the Cell Interior Motor Proteins Drive Intracellular Transport Microtubules and Motor Proteins Position Organelles in the Cytoplasm Cilia and Flagella Contain Stable Microtubules Moved by Dynein

ACTIN FILAMENTS Actin Filaments Are Thin and Flexible Actin and Tubulin Polymerize by Similar Mechanisms

ACTIN FILAMENTS A Cortex Rich in Actin Filaments Underlies the Plasma Membrane of Most Eukaryotic Cells Cell Crawling Depends on Cortical Actin

ACTIN FILAMENTS Actin Associates with Myosin to Form Contractile Structures

MUSCLE CONTRACTION Muscle Contraction Depends on Interacting Filaments of Actin and Myosin Actin Filaments Slide Against Myosin Filaments During Muscle Contraction

MUSCLE CONTRACTION Muscle Contraction Depends on Interacting Filaments of Actin and Myosin Actin Filaments Slide Against Myosin Filaments During Muscle Contraction Muscle Contraction Is Triggered by a Sudden Rise in Cytosolic Ca2+