P h y s i c s o f b i o l o g i c a l s y s t - - PowerPoint PPT Presentation

P h y s i c s

• f

b i

• l
• g

i c a l s y s t e ms – P H 5 4 9

L E C T U R E 1 7 :

Mo l e c u l a r mo t

• r

s

mithun@phy.iitb.ac.in Office: Physics 303

T h e c h e mo me c h a n i c a l c y c l e C H E MI C A L E N E R G Y ME C H A N I C A L E N E R G Y

ATP hydrolysis Directed non-random motion

R N A p

• l

y me r a s e mo t

• r

T R A N S L A T I O N A L MO T O R S

T H E MY O S I N S U P E R F A MI L Y

F O R C E

• V

E L O C I T Y C U R V E S

Different motors have different mechanisms

C h a r a c t e r i z a t i

• n
• f

MO T O R S

➢ DIRECTION OF MOTION ➢ SPEED OF THE MOTOR ➢ PROCESSIVITY ➢ FORCE EXERTED DURING A SINGLE STEP

Kinesin – Plus-end-directed Dynein – Minus-end-directed Kinesin step size – 8 nm Kinesin speed – 6 µm/s Fmax Kinesin 10 pN ( ) ~ RNA polymerase – 1000s of bases Muscle myosin – 2-3 steps

B I D I R E C T I O N A L MO T I O N O F C A R G O

Lu et. al. J. Vis. Exp. 81, 50838 (2013)

F O R C E G E N E R A T I O N

MU S C L E C O N T R A C T I O N

MU S C L E C O N T R A C T I O N

F O R C E S D U R I N G C E L L D I VI S I O N

F O R C E S D U R I N G C E L L D I VI S I O N

G L I D I N G A S S A Y S

G L I D I N G A S S A Y S

G L I D I N G A S S A Y S

DeCamp et. al. Nature Materials 2015

B E A D

• B

A S E D S I N G L E MO T O R A S S A Y S

ME C H A N I S MS O F MO T O R MO T I O N

MO D E L S O F MO T O R MO T I O N

MO D E L S O F MO T O R MO T I O N

➢ What is the mean velocity of a motor? ➢ How does the mean velocity depend on the

applied force?

➢ What is the stall force of the motor? ➢ How does the velocity depend upon the

concentration of ATP?

➢ How stochastic are motor trajectories? ➢ How do binding and unbind rates depend on

applied force?

Soppina et. al. PNAS 2009 Rai et. al. Cell 2013

B I D I R E C T I O N A L T U G

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WA R

Ally et. al. J. Cell Biol. 2009 Martin et. al. Mol. Biol. Cell 1999

Leidel et. al. Biophys J. 2012 Rai et. al. Cell 2013

K i n e s i n D y n e i n

Kunwar et. al. PNAS 2011

T h e d i s c r e t e P

• s

t a t e mo d e l

pm(n ,t) = ?

T h e d i s c r e t e O n e

• s

t a t e mo d e l

T h e d i s c r e t e O n e

• s

t a t e mo d e l

T h e d i s c r e t e O n e

• s

t a t e mo d e l

p(n ,t+Δ t) = k+Δ t p(n−1,t)+k-Δ t p(n+1,t) +(1−k+Δ t−k-Δ t) p(n ,t) ∂ p ∂t = −V ∂ p ∂ x +D ∂

2 p

∂ x

2

V =a[k+(F)−k-(F)] D= a

2

2 [k+(F)+k-(F)]

T h e d i s c r e t e O n e

• s

t a t e mo d e l

p(x ,t) = 1

√4 π Dt

e

−(x−Vt)

2/4 Dt