1. Fundamentals of Biological Sciences
Lecture3
Dr. Açelya Yılmazer

2. 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

3. 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

4. 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)

5. 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

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

7. 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)

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

9. 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

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

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

12. ACTIN FILAMENTS
Actin Associates with Myosin to Form Contractile Structures

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

14. 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+