Cytoskeleton

Cell Biology

1. CYTOSKELETON By  Mrs Sanchita Choubey (M.Sc., PGDCR, Pursuing Ph. D) Assistant Professor  of Microbiology Dr. D Y Patil Arts Commerce and Science College Pimpri , Pune

2. 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.

3. The cytoskeleton is built on a framework of three types of protein filaments. Intermediate filaments Microtubules Actin filaments

4. INTERMEDI A TE FIL A MENTS They have great tensile strength Diameter is about 10 nm. Made up of fibrous intermediate proteins. Composed of two anti parallel dimer

5. TYPES OF INTERMEDIATE FILAMENTS Keratin filaments Vimentin filaments Neurofilaments Nuclear lamins DISORDERS OF INTERMEDIATE FILAMENTS Epidermolysis bullosa simplex (EBS) Amyotrophic lateral sclerosis (ALS) Progeria

6. Mic r otubules 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 .

7. STRUCTU R E OF MICROTUBULES

8. 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.

9. 9 + 2 arrangement Drugs that affect microtubules Taxol Colchicine V i n b l asti n e

10. 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.

11. 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.

12. 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.

13. Muscle Contraction Myosin along with actin was first discovered with skeletal muscle. Myosin I 1)have only one head and a tail Myosin II h a ve two A TPase he a ds and a tail Muscle myosin belongs to myosin II.

14. Each muscle fiber is a single, long, cylindrical muscle cell. 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. Thick filaments of myofibrils are made up of the protein myosin . Thin filaments of myofibrils are made up of the protein actin . The organization of these filaments produces striations.

15. Thin filament Thick filament

16. A sarcomere extends from Z line to Z line. I bands -light bands -made up of actin -anchored to Z lines A b a nds -dark bands -made up of overlapping thick and thin filaments. In the center of A bands is an H zone , consisting of myosin filaments only.

17. 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.

18. Thank you