The cytoskeleton is a network of filaments and microtubules that gives cells their shape and enables cellular movement. It is composed of three main types of protein filaments: intermediate filaments, microtubules, and actin filaments. Intermediate filaments provide strength and structure, microtubules help shape the cell and are involved in cell division and transport, and actin filaments enable cell movement and structures like microvilli. Muscle contraction occurs via the sliding of actin and myosin filaments when the myosin crossbridges attach and pull on the actin filaments.
3. INTRODUCTION
What is CYTOSKELETON ?
It is a complex network of filaments and microtubules which
forms a structural framework known as Cytoskeleton.
Skeleton and muscle of the cell.
Also responsible for segregation of chromosomes into two
daughter cell at cell division.
4.
5. The cytoskeleton is built on a framework of three
types of protein filaments.
Intermediate filaments
Microtubules
Actin filaments
6. INTERMEDIATE FILAMENTS
They have great tensile strength
Diameter is about 10 nm.
Made up of fibrous intermediate proteins.
Composed of two anti parallel dimer
9. Microtubules
Long hollow cylinders made up of tubulin.
25 nm in diameter.
Provide internal shape and support to cell.
Also involve in nucleic and cell division.
Two types of tubulin are found alpha tubulin and beta tubulin.
11. CILIA AND FLAGELLA
Cilia and flagella are hair like structure.
Made up of microtubules and covered by extension of plasma
membrane.
Cilia and flagella move liquid past the surface of the cell.
They create current for obtaining food from aquatic medium.
On epithelial cell lining of respiratory tract huge no. of cilia are found.
13. Actin Filaments
Present throughout the cytoplasm of eukaryotic cell.
Present just beneath the plasma membrane, therefore supports the outer
layer of cell.
Responsible for movement,
especially involving cell surface.
Can form structures like microvilli on
the brush bordered cells lining the intestine.
14. Actin filaments grow by addition of actin monomer but in
order to stop more of addition of actin monomer, proteins
such as thymosin and profilin binds to the monomers.
15. Movement by Actin Filament
1)Cell pushes out protrusions at its leading edge.
2)Then these protrusions adhere to the surface.
3)Rest of the cell drags itself forward on these anchorage
points.
16. Muscle Contraction
Myosin along with actin was first discovered with skeletal
muscle.
Myosin I Myosin II
1)have only one head and 1) have two ATPase heads
a tail and a tail
2)Muscle myosin belongs to
myosin II.
17.
18. 1. Each muscle fiber is a single, long, cylindrical muscle cell.
2. Sarcolemma-cell membrane
Sarcoplasm-cytoplasm with many mitochondria and
nuclei. It has myofibrils. -myofibrils are separated into
compartments called sarcomeres that contain thick
filaments and thin filaments.
a. Thick filaments of myofibrils are made up of the
protein myosin.
b. Thin filaments of myofibrils are made up of the protein
actin.
c. The organization of these filaments produces striations.
20. 3. A sarcomere extends from Z line to Z line.
a. I bands
-light bands
-made up of actin
-anchored to Z lines
b. A bands
-dark bands
-made up of overlapping thick and thin filaments.
c. In the center of A bands is an H zone, consisting of myosin filaments
only.
21. Sliding Filament Theory of Muscle Contraction
-the myosin crossbridge attaches to the binding site on the
actin filament and bends, pulling on the actin filament
-it then releases and attaches to the next binding site on the
actin,pulling again.