Fundamentals of Biological Sciences

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Fundamentals of Biological Sciences

Lecture3

Dr. Açelya Yılmazer

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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

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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

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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)

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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

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MICROTUBULES

• Microtubules Are Hollow Tubes with Structurally Distinct Ends

• The Centrosome Is the Major Microtubule-

organizing Center in Animal Cells

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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)

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MICROTUBULES

• Microtubules Organize the Cell Interior

• Motor Proteins Drive Intracellular Transport

• Microtubules and Motor Proteins Position

Organelles in the Cytoplasm

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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

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ACTIN FILAMENTS

• Actin Filaments Are Thin and Flexible

• Actin and Tubulin Polymerize by Similar

Mechanisms

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ACTIN FILAMENTS

• A Cortex Rich in Actin Filaments Underlies the Plasma Membrane of Most Eukaryotic Cells

• Cell Crawling Depends on Cortical Actin

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ACTIN FILAMENTS

• Actin Associates with Myosin to Form

Contractile Structures

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MUSCLE CONTRACTION

• Muscle Contraction Depends on Interacting Filaments of Actin and Myosin

• Actin Filaments Slide Against Myosin Filaments

During Muscle Contraction

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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 Ca

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