This document discusses the structure and function of myosin, a crucial motor protein in muscle contraction and various cellular processes. It details myosin's historical background, structure, and mechanisms of action, including its role in cellular transport, motility, and division. The summary also covers the sliding filament model and how ATP hydrolysis fuels muscle movement.

1. MYOSINSTRUCTURE
FUNCTIONAND
MODEOFACTION
RISHI SINGH
ROLL NO: 152
MSC 1- BIOTECH
1

2. INTRODUCTION
 ORGANISMS MOVES.CELLS MOVE. ORGANELLES
AND MACROMOLECULESWITHINTHE CELLS
MOVE.
MOST OFTHESE MOVEMENTS ARISE FROM
ACTIVITY OF A FASCINATING CLASS OF PROTEIN
BASED MOLECULAR MOTORS ;FUELED BY
CHEMICAL ENERGY,USUALLY DERIVED FROM ATP.
ONE SUCH PROTEIN BASED MOLECULAR MOTOR
IS MYOSIN
MYOSIN IS A MOTOR PROTEINTHAT CONVERTS
CHEMICAL ENERGY OF ATP HYDROLYSISTO
MECHANICAL ENERGY OF MOVEMENT
2

3. HISTORICAL
BACKGROUND
MOLECULARCHARACTERIZATIONOF MUSCLE DIDN’TOCCUR
OVERNIGHT:
1859WILLI KUHNE MYOSIN FROM MUSCLETISSUE
1941 ALBERT SZENT MYOSIN-A AND MYOSIN-B
 IN 1948 HUGH HUXLEY “SLIDING FILAMENT MODEL”
LATER,HUXLEYAND HANSON OBSERVED RABBIT MUSCLE
FIBRES UNDER DIFFERENT EXPERIMENTALCONDITIONSAND
CONCLUDEDTHE FOLLOWING :-
A-BANDCONSISTS OF MYOSIN
ACTINWAS PRESENTTHROUGHOUTTHE SARCOMERE
WHEN ATPWAS ADDED MUSCLE SLOWLY CONTRACTSAND I-
BAND SHORTENS,WHEN MUSCLE RELAXED I-BAND
INCREASED IN WIDTH
MYOSIN FORMS CROSS BRIDGESWITH ACTIN FIBRES

4. STUCTURE
OF
MUSCLE
MUSCLE
BUNDLEOF
MUSCLE FIBRES
INDIVIDUAL
MUSCLE FIBRE
MYOFIBRIL
SARCOMERE

5. MYOFIBRIL
 THE BANDS ARE
FORMED BY
ALTERNATING
REGIONS OF GREATER
AND LESSER
ELECTRON DENSITY
CALLED “A-BANDS”
AND “I-BANDS”
 MYOFIBRILS
REPEATING UNIT
“SARCOMERE ” IS
BOUNDED BY Z-DISKS
AT CENTRE OF EACH I-
BAND

6. MYOFIBRIL
 THE A-BAND CONTAINS
THICK FILAMENTS
 THE I-BAND CONTAINS
THIN FILAMENTS
 THESETHICK ANDTHIN
FILAMENTS ARE LINKED
TOGETHER BY CROSS
BRIDGESWHERETHEY
OVERLAP
 MUSCLE CONTRACTION
RESULTS FROM
DECREASE IN LENGTH OF
SARCOMERE CAUSED BY
REDUCTION IN LENGTH
OF I-BANDS

7. STRUCTURE
OF MYOSIN MYOSIN HAS 6 POLYPEPTIDE CHAINS/SUBUNITS
2 HEAVY CHAINS AND 2 PAIR OF DIFFERENT LIGHT CHAINS(ELC
AND RLC)
HEAVY CHAIN ACCOUNT FOR MUCH OF OVERALL STRUCTURE
N-TERMINAL GLOBULAR DOMAIN(HEAD)
C-TERMINAL LONG FIBROUS ALPHA HELICALTAIL(THE 2
TAILS ASSOCIATE TO FORM A LEFT HANDED COILED COIL)
THUS MYOSIN CONSISTS OF LONG ROD LIKE SEGMENTS WITH 2
GLOBULAR HEADS

8. THICK
FILAMENTS
 UNDER
PHYSIOLOGICAL
CONDITIONS SEVERAL
MYOSIN MOLECULES
AGGREGATETO FORM
ATHICK FILAMENT
 THE ROD LIKETAILS
PACK ENDTO END IN A
STAGGERED MANNER
;LEAVINGTHE
GLOBULAR HEADS
PROJECTINGTOTHE
SIDES ON BOTH ENDS

9. FUCTIONS
OF MYOSIN
MYOSIN IS PRIMARILY KNOWN FOR ITS ROLE IN
MUSCLE CONTRACTION BUT IT ALSOTAKES PART
INVARIOUS CELLULAR PROCESSES WHICH
INCLUDE :-
CELLULARTRANSPORT
CELL DIVISION
CELLULAR MOTILITY
MAINTENANCE OF CELL SHAPE

10. CELLULAR
TRANSPORT
MYOSIN 1, 2AND 5
TRANSPORTSVARIOUS
CARGO WITHINTHE CELLS
MYOSIN MOVE ALONG
MICRO-FILAMENTS OR
MICROTUBULES CARRYING
ORGANELLES ,VESICLES
AND OTHER CELLULAR
COMPONENTS

11. CELL
DIVISION
DURING CELL DIVISION
MYOSIN 2IS CRUCIAL
FOR CYTOKINESIS
MYOSIN FORMS A
CONTRACTILE RING
JUST BENEATH THE
CELL MEMBRANE AT
EQUATOR OF DIVIDING
CELLS
AS MYOSIN 2
CONTRACTS IT PINCHES
THE CELL MEMBRANE
LEADING TO
SEPARATION OF CELL
INTOTWO DAUGHTER
CELLS

12. CELLULAR
MOTILITY
MYOSIN IS
ESSENTIAL FOR CELL
MOTILITY
IT ALLOWS CELLSTO
MOVE, CHANGE
SHAPE AND MIGRATE
EX- AMOEBOID
MOVEMENT OF WBCs

13. MAINTENANCE
OFCELL SHAPE
MYOSIN INTERACTS WITH
CYTOSKELETON (SPECIFICALLY ACTIN
FILAMENTS)TO HELP MAINTAIN CELL
SHAPE AND INTEGRITY
IT PROVIDESTENSION AND STRUCTURAL
SUPPORT TO CELLS

14. MODEOF
ACTIONOF
MYOSIN(MUSCLE
CONTRACTION)
IN MUSCLE CONTRACTION THE
ACTUAL CONTRACTILE FORCE IS
PROVIDED BY ATP

15. MODEOF
ACTIONOF
MYOSIN(MUSCLE
CONTRACTION)
MECHANISM OF FORCE GENERATION IN
MUSCLES:-
ATP BINDSTO MYOSIN HEAD MYOSIN’SACTIN BINDING
SITE OPEN UP AND RELEASE ITS BOUNDACTIN
MYOSIN’SACTIVE SITE CLOSES AROUNDTHE ATP
HYDROLYSISOF ATP ADP+Pi ; “COCKS”THE MYOSIN
HEAD BECAUSE OF WHICH MYOSIN HEAD BECOMES
PERPENDICULARTOTHETHICK FILAMENT
MYOSIN HEAD BINDSWEAKLYTOTHE ACTIN MONOMERTHAT
IS CLOSERTOTHE Z-DISK
MYOSIN RELEASES Pi ACTIN BINDING SITE CLOSES
RESULTINGTRANSIENT STATE IS FOLLOWED BY POWER
STROKE
ADP IS RELEASEDTHEREBY COMPLETINGTHE CYCLE

16. MECHANISM
OF FORCE
GENERATION
IN MUSCLE

17. SLIDING
FILAMENT
MODEL

18. REFERENCES
Lehninger Principles of Biochemistry
by David L.Nelson,Michael M.Cox
Fundamentals of Biochemistry – LIFE AT
MOLECULAR LEVEL DonaldVoet, Judith G.
Voet , Charlotte W. Pratt
The Early History of the Biochemistry of
Muscle Contraction ;Andrew G. Szent-
Györgyi ( RESEARCH PAPER LINK-
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC223
4565/#:~:text=A%20viscous%20protein%20was%20
extracted,the%20rigor%20state%20of%20muscle )

19. THANKYOU