Download Progress in 20th century Simplified block-diagram

Progress in 20th century
Sci 190 E
Lecture 14
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Discovery of DNA
Discovery of proteins
Application of X-ray diffraction to reveal protein structures
Site-specific mutagenesis allows to modify natural systems
Quantum physics can explain and predict energy transfer and
conversion processes
• Modern spectroscopic techniques allow real-time monitoring
of the energy transfer and conversion processes
Simplified block-diagram of photosynthetic
machinery
Simplified chemical reaction:
hν
CO2 + H2O
Antenna
light
energy
Antenna captures
light and passes its
energy to RC
Biosynthesis
(CH2O) + O2
Reaction current
center (RC)
Reaction center
generates
electrical current
Chemical
battery
The electrical
current drives
chemical reactions
creating molecules
that store energy in
their chemical bonds
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Photosynthetic apparatus of plants
Photosynthetic powerplant is located in thylakoid membranes
Photosynthetic apparatus: PS II
Photosystem II (PS II) complex uses energy of light to split
water and generate electron and proton current.
Oxygen molecules are byproduct of this processes
The PS II is extremely strong oxidant - it can oxidize water!
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Photosynthetic apparatus: cytochrome b6f
Cytochrome b6f complex transfers electrons (current) from PS
II to photosystem I (PS I) complex.
In addition, the fraction of this electron current is used to
transports protons across the thylakoid membrane.
Plastoquinones (Q, QH2) and plastocyanins (PC) serve as
intermediate electron carriers
Photosynthetic apparatus: PS I
Photosystem I gets electrons from PS II via cytochrome b6f and
uses light to boost the energy of these electrons and transfer
them to mobile ferredoxin (Fd) complex
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Photosynthetic apparatus: FAD
Ferredoxin (Fd) uses the energy of the electron to reduce
NADP+ molecule to NADPH and store the energy in chemical
bond of NADPH. This reaction is mediated by ferredoxinNADP+ reductase (FAD)
Photosynthetic apparatus: proton pumps
PS II and cytochrome b6f also pump protons creating
elecrtochemical potential across the membrane (like charging a
capacitor). That creates strong electric field across the
membrane.
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Photosynthetic apparatus: ATP synthase
This strong electric field drives protons through a molecular
size ‘turbine’ motor called ATP synthase. The axle of that
molecule spins and mechanical force drives chemical reaction
transforming ADP molecule to ATP - the energy is stored in
extra chemical bond
ATP synthase
ADP + Pi
ATP
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ADP→ATP coupled to mechanical motor
Motion coupled to proton current
Proton current coupled to electron current
Electron current coupled to absorption of light
http://www.biologie.uni-osnabrueck.de/Biophysik/Junge/overheads.html
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ATP synthase: visualizing
A. Aksimentiev
Yoshida et al. Nature Reviews Molecular Cell Biology 2 669-677 2001
http://www.ks.uiuc.edu/~alek/
Photosynthetic apparatus: charging chemical battery
Absorption of light causes the synthesis of NADPH and ATP.
The chemical energy stored in these molecules is used by other
protein ‘machines’ in the cell to synthesize necessary
components and fuel life.
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To understand the molecular processes of photosynthesis we
need to know:
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What is light?
How can light energy be absorbed by a molecule (chlorophyll)?
How can this energy initiate charge flow (current)?
How can an electron drive a chemical reaction
How can a proton spin a large molecule (protein)
How can a protein spin and drive chemical reaction
….
Nature of Light
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Light: wave or particles?
• 1621: W. Snell - refraction
• 1664: R. Hooke - interference: color in thin films
• 1665: F. Grimaldi - diffraction
• 1677: C. Huygens - wave theory.
Light is a wave moving in ‘ether’
analagy: water waves
• 1704: I. Newton - light is particles!
• 1801-1814: T. Young, Fresnel - it must be a wave!
How can light wave interact with matter?
Electrical and magnetic forces
Between charged objects
Between moving charged objects
Electromagnetic forces
Light is an electromagnetic wave moving in space
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Electric charges
• Two types: positive (+) and negative (-)
• Notation: q, Q
• Likely charges: repel.
Opposite charges: attract
Magnitude of charge is measured in
Coulombs (C)
• Net charge of a system:
algebraic sum of all the charges
Law:
Conservation of charge:
The net charge of a closed system never changes
The origin of charge
charge
mass
electron
-e
me
proton
+e
1836.me
neutron
0
1839.me
undivisible!
Elementary charge:
e = 1.602 × 10-19 C
C=Coulomb, SI unit of charge
me = 9.11 × 10-31 kg
Net charge is always a multiple of e: Qnet=Ne
Charge is quantized
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Coulomb’s law
Point charge:
a point-like object with nonzero charge
• The force exerted by one point charge on another acts along the line
joining the charges.
• The force varies inversely as the square of the distances separating
the charges, and is proportional to the product of the charges.
• The force is repulsive if the charges have the same sign an attractive
if the charges have opposite signs
F =k
q1 q 2
r2
k = 8.99 × 109
Nm 2
C2
F - force on each charge (N)
q - charges measured in C
r - distance between charges (m)
Electric field
Suppose we are inside a black box holding charge q and sense
that electric force acts upon it as shown:
Can we tell where the other
charges outside the box?
- No! We can have negative
charge on the left side, or
F
positive on the right side…
There is a property at that spot to induce electric force on any
charge. This property is called electric field E:
E=
vector!
Fe
q
Electric field at some point is force per unit
‘probe’ charge placed at that point in space
Fe = qE if we know E - can find F on any charge
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Electric field: analogy with gravity
Gravity (Cavendish, 1798)
m
Fg = G
M
g=
mM
r2
Fg
m
g – gravitational field
Fg = mg
Gravitational force is always
parallel to gravitational field
(m>0)
Electric force (Coulomb, 1795)
qQ
r2
Fe = k
E=
Fe
q
q
Q
E – electric field, N/C
Fe = qE
Electric force can be either parallel
(q>0) or antiparallel (q<0) to
electric field
Electric force versus gravity
Gravity (Cavendish, 1798)
mm
Fg = G 1 2 2
r
G = 6.67×10-11 m3/(kg.s2)
3m
What is the attraction force?
70 ⋅ 70
Fg = 6.67 × 10
N
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Fg = 0.000000036 N
−11
Electric force (Coulomb, 1795)
q q
Fe = k 1 2 2
r
k = 8.99×109 Nm2/C2
3m
q1 = q2 ≈ 1028 ⋅ e = 1.6 × 109 C
1.6 × 109 ⋅ 1.6 × 109
N
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Fe = 2.6 × 1027 N
Fe = 8.99 × 109
Electric forces are much stronger than gravitational forces
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Magnetic field
Permanent magnets and moving charges can produce another
kind of field called magnetic field.
It is a field concept similar to electric or gravitational fields,
but it acts only on moving charges or magnets
Magnetic force is perpendicular to both magnetic field B and
velocity of the charge on which it acts:
Magnetic force on a moving point charge
v
FB = qv × B
vector cross-product
v×B
Magnitude:
q
B
right-hand rule
FB = q v⊥ B = q vB sin θ
Note: for negative charge FB
will point in the direction
opposite to the cross product v × B
Electric and magnetic field
In the first half of the 19th century it was shown that changing
electric field can produce electric field, and changing magnetic
field can produce magnetic field.
Can one create changing electromagnetic
field that will exist without charges?
1831-1879
James Clerk Maxwell
IDEA:
Changing E will generate
changing magnetic field B
Changing B will generate
changing electric field E
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Electromagnetic wave
~1864:
Maxwell introduced four
equations that described all known
electro-magnetic phenomena and
showed theoretically that
electromagnetic pulse or wave
moving in space could exist.
Maxwell’s equations
q
∆Φ E =
E⊥ A =
∆Φ B =
B⊥ A = 0
E =
E||l = −
ε0
∆Φ B
∆t
B||∆l = µ0 I + ε 0
∆Φ E
∆t
Surprisingly, he found that this
EM-wave must move at a speed of
300,000 km/s - i.e. speed of light!
Maxwell suggested that
light is electromagnetic wave
EM wave characteristics
E - electric field
λ-w
avele
ngth
B - magnetic field
c - speed
of light
Frequency: at which frequency E-field oscillates at certain point
in space
Note: λ = c/ν
speed of light
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EM wave characteristics
E - electric field
B - magnetic field
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