molecular motors · 2018-12-10 · thermodynamic cycle we apply thermodynamics to molecular motors....

Molecular Motors

Neil Thomas,University of Birmingham,UK.

ニール　トーマス

バーミンガム大学

イギリス

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Acknowledgements

My thanks to:• The British Council (Tsuji-san & Shimura-san)• Monbukagakusho, JSPS & JST• Dr Yasuhiro Imafuku (Kyushu University)• Dr Shinji Kamimura (Tokyo University)

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Birmingham University

The University was established in 1905.It now has over 15000 students.

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Birmingham and the UK

Birmingham is England’s second city.It is in the Midlands, about 200 km north-west of London.

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Canals and RailwaysBirmingham is at thecentreof England's canal system.Canals were once veryimportant for carryingmaterials for industry.Nowadays, 'narrow boats'can be hired for leisure.

Railways were built fromabout 1830.The trains were pulled bysteam locomotives.

The 'Age of Steam' madeBritain very wealthy.

Photo: Brian Townsley

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James WattJames Watt (1736-1819), pioneer ofthe steam engine, worked withMatthew Boulton in Birmingham.He invented the condenser and thegovernor.

Steam engines led to the science of Thermodynamics.

Animation: Matt Keveney

Watt’s Beam Engine

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Molecular Motors & MovementI’m a physics lecturer.

My main research interest is themolecular motors that producemovement in living systems, fromsingle cells to whole animals.

This seminar will show youwhy molecular motors arean exciting and importanttopic.

A single-celled amoeba

A galloping horse

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Outline of Seminar

How Muscles Work

How Cells Move How Cells Generate Energy

How Cells Make DNA

Videos from Essential Cell Biology CD-ROM

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Muscles & Movement

Cheetah

Humming-bird

Bumble-beeSharkVideos from How Animals Move CD-ROM

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Muscles

Structure of muscleHuman arm muscles

Diagrams from The Ultimate Human Body CD-ROM

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Bundle of Muscle Fibres(viewed with an optical microscope)

• Fibres show a periodic striation pattern• Black ‘blobs’ are cell nuclei

Photo from How Animals Move CD-ROM

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Single fibre of striated muscle

• Muscle fibres are single biological cells• Fibre diameter is typically about 100 microns (0.1 mm)• Fibres consist of bundles of smaller myofibrils

Photo from How Animals Move CD-ROM

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Single myofibril(viewed with an electron microscope)

• Each myofibril is about 1 micron in diameter• Myofibrils also show the periodic striation pattern• The repeating unit is called a sarcomere

Photo from How Animals Move CD-ROM

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Muscle Contraction(Sliding-filament model)

A nervous impulse (guided by T-tubules) causes therelease of calcium inside a muscle cell.Calcium switches on the molecular motors that causesliding of the actin and myosin filaments.

Video from Essential Cell Biology CD-ROM

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Actomyosin: the molecular motorthat powers our muscles

• The actomyosin motor works in a cycle.

• Myosin binds to actin, its lever arm tilts over, and thenit detaches.

• Each cycle uses up one molecule of ATP.

• ATP is the ‘fuel’ that allows the motor to performwork.

• The chemical reaction is ATP → ADP + Pi

Video from Essential CellBiology CD-ROM

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Heat Engines Work in aThermodynamic Cycle

We apply Thermodynamics to molecular motors.

Car Engine (Otto Cycle)

Steam Engine (RankineCycle)

Actomyosin also works in a cycle.Its power stroke is only 5 – 10 nm.(1 million nanometres = 1 millimetre)

Animations: Matt Keveney

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Cilia and Flagella

Cilia (Stentor)

Beating cilia(Simulation)

Flagellum (Sperm)

Beating flagellum(Simulation)

Videos from How Animals Move CD-ROM

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Molecular Motors in Cilia

Dynein motors causesliding of microtubules.Sliding produces bending:

Cross-section of a ciliumshowing microtubulesand dynein arms.(Diameter = 250 nm)

Cilia and flagella beat spontaneously!

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How Do Cells Move?

A keratocyte (from a fishscale) crawls rapidly .

Neurites grow slowly fromnerve cells by means ofgrowth cones.

An amoeba moves rapidlyby extending pseudopodia.

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Cells move by using theircytoskeleton.

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The Cytoskeleton

Actin filaments (red) allow the cell to crawl.Microtubules (blue) transport chemical signals thatcontrol the movement.Intermediate filaments (green) add strength to the cell.

Photo from Video Tour of Cell Motility by Vic Small

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Crawling Cancer Cell

Formation of actin filaments inside the lamellipodiumpushes the front of the cell forwards.The rear of the cell is pulled along by actomyosin.

From Video Tour of Cell Motility by Vic Small

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Crawling of white blood cells

A neutrophil chases abacterium.

Lymphocytes migrate to awound.

In both cases, the movement is in response to achemical signal (‘chemotaxis’).

From Video Tour of Cell Motility by Vic Small

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Propulsion by Actin

An actin filament moves by‘treadmilling’.The motion consumes ATP.

Listeria bacteriamove by ‘hijacking’a cell’s actin.

From Video Tour of Cell Motility by Vic Small Video from Essential Cell Biology CD-ROM

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Movement inside Cells

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Organelle Movement

Molecular motors transport material along the cytoskeleton.The video shows organelle transport along a microtubule.Kinesin motors transport material to the ‘plus’ end (awayfrom the nucleus).Dynein motors transport material in the opposite direction.

Video from Essential Cell Biology CD-ROM

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The Kinesin Molecular Motor

The video shows how two-headed kinesin may stepalong a microtubule.The model is based on many different experiments.We have used a similar picture to develop amathematical model of the kinesin motor foranalysing the results of laser-tweezer experiments.

Video from Essential CellBiology CD-ROM

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Laser Tweezers

Laser tweezers are used to trap tiny beads in a focussedlaser beam.They exert a force comparable to that due to a singlemolecular motor (typically a few piconewtons).

1 gram weighs about 10 thousand million piconewtonsVideo from Essential Cell Biology CD-ROM

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Laser Tweezers

Laser tweezers are used to study kinesin stepping alonga microtubule.The kinesin molecule is attached to a bead that istrapped in the focussed laser beam.The tweezers exert a force that slows down the kinesinmotor.

Visscher et al. (1999)

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Molecular Motors and DNA

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DNA carries the Genetic Code

• A DNA molecule is a double helix (like a spiral staircase)• The two strands of the helix are joined by base pairs• Base C always pairs with base G• Base A always pairs with base T• The sequence of bases CAA… stores the genetic information

Videos from Essential Cell Biology CD-ROM

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DNA Motors 1:Transcription(Reading a single gene)

The RNA polymerase motor copies (transcribes) agene from DNA to RNA inside the cell nucleus.

Video from Essential Cell Biology CD-ROM

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DNA Motors 2: Translation(Making a protein from a gene)

A ribosome translates the genetic code in theRNA to make a protein from the correct sequenceof amino acids.Our bone marrow makes 100 million millionmolecules of haemoglobin per second.

Video from Essential Cell Biology CD-ROM

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DNA motors 3: Replication(Making an exact copy of DNA)

A DNA helicasemotor separates theDNA double helixinto two strands.

Videos from Essential Cell Biology CD-ROM

DNA polymerasemotors copy eachstrand.

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DNA Motors 4: Mitosis(Cell division)

Microtubules form aspindle (green).Pairs of chromosomescontaining DNA (blue)attach to the spindle bykinetochores (pink) alongthe equator.

Cells in a frog embryodivide rapidly.Molecular motors pullchromosomes to oppositepoles of the spindle.Each cell gets the sameDNA.

Videos from Essential Cell Biology CD-ROM

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How Do Cells Generate Energy?

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Mitochondria: the Cell’s Power-Stations

A heart muscle cell containsmyofibrils (orange). It requiresmany mitochondria (red),which supply ATP for theactomyosin molecular motors.

Glucose oxidationproduces protons in theinter-membrane space.Proton flow back acrossthe inner membranegenerates ATP.

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ATP Synthase: A MolecularTurbine

ATP synthase is a molecularturbine that converts energyfrom a proton gradient intothe chemical energy in theform of ATP that powers thecell.

The molecular structureillustrates how ATP maybe synthesized.

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Rotation of ATP Synthase

Kinoshita and colleaguesobserved rotation of ATPsynthase by attaching afluorescent actin filamentto the shaft.

Kinoshita et al. 1998

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Electricity Generation

#1 Turbine from ChibaThermal Power Station(TEPCO Museum)

A steam turbine rotates agenerator to produce electricity.The Chiba #1 turbine generatorproduced 125 MW (125 millionwatts).

A marine turbine from a ship

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Turbines Compared

The Chiba steam turbine is over10 m long.It can generate about 100million watts (108 W = 100 MW).

Both machines are governedby the laws ofThermodynamics.

Chiba #1 TurbineTEPCO Museum (Kawasaki).

ATP synthase is about 20 nm long.It generates 1/(million million million)watts (10-18 W =1 aW).

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Summary

• Molecular motors are the fundamentalagents of movement in living systems

• They are cyclic machines like steamengines

• They generally consume one molecule ofATP per cycle

• They typically produce force ∼1 pN andpower ~ 1 aW

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But molecular motors workingtogether in muscle can produce

large forces…

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終