Microbial Photosynthesis

1. Microbial Photosynthesis
Shivaveerakumar S.

2. THE SUN:
MAIN SOURCE OF ENERGY
FOR LIFE ON EARTH

3. Our Star, the Sun

4. The Sun is the Largest Object in
the Solar System
• The Sun contains more than 99.85%
of the total mass of the solar system
• If you put all the planets in the solar
system, they would not fill up the
volume of the Sun
• 110 Earths or 10 Jupiter's fit across
the diameter of the Sun

5. The Sun goes through periods of
relative activity and inactivity

6. The Sun’s
interior has
three layers:
(1) Core
(2) Radiative zone
(3) Convective zone
Energy generated in the core of the sun
propagates outward through these different layers,
and finally, through the atmosphere of the Sun. This
process takes tens of thousands of years or more.

7. • Like most stars, the sun is made up mostly of hydrogen and
helium atoms in a plasma state.
• The sun generates energy from a process called nuclear fusion.
• During nuclear fusion, the high pressure and temperature in
the sun's core cause nuclei to separate from their electrons.
• Solar energy is any type of energy generated by the sun.
• Solar energy is created by nuclear fusion that takes place in
the sun.
• Fusion occurs when protons of hydrogen atoms violently
collide in the sun's core and fuse to create a helium atom.
• Like the Earth, the sun has layers. But unlike the Earth, the
sun is entirely gaseous; there is no solid surface.
• Sun provides two types of energy: Heat and Light.

8. • Also known as light energy or electromagnetic
energy, radiant energy is a type of kinetic energy that travels
in waves.
• Examples include the energy from the sun, x-rays, and radio
waves.
• The energy from the sun that reaches the earth arrives
as solar radiation, part of a large collection of energy called
the electromagnetic radiation spectrum.
• Solar radiation includes visible light, ultraviolet light,
infrared, radio waves, X-rays, and gamma rays.
• 4 types of sun's radiation include:
• Infrared rays,
• Visible rays.
• Ultraviolet light.
• Radio waves.

9. • The Sun's diameter is about 1.39 million kilometers
(864,000 miles), or 110 times that of Earth.
• Its mass is about 3,30,000 times that of Earth, comprising
about 99.86% of the total mass of the Solar System.
• Roughly three-quarters of the Sun's mass consists
of hydrogen (~73%); the rest is mostly helium (~25%), with
much smaller quantities of heavier elements,
including oxygen, carbon, neon, and iron.
• The sun has extremely important influences on our
planet.
• It drives weather, ocean currents, seasons, and climate,
and makes plant life possible through photosynthesis.
• Without the sun's heat and light, life on Earth would not
exist.

10. Sunlight or Energy of Sun:
• Improves your sleep. Your body creates a
hormone called melatonin that is critical
to helping you sleep.
• Reduces stress.
• Maintains strong bones.
• Helps keep the weight off.
• Strengthens your immune system.
• Fights off depression.
• Can give you a longer life.
• Deficiencies could increase the risk for
osteoporosis, heart disease, some cancers,
infectious diseases and even the flu.

11. • Sunlight also helps our skin make vitamin D,
which is needed for normal bone function and
health. Yet sunlight can also cause damage.
Sunlight travels to Earth as a mixture of both
visible and invisible rays, or waves. Long
waves, like radio waves, are harmless to
people.
• Regular sun exposure is the most natural way
to get enough vitamin D. To maintain healthy
blood levels, aim to get 10–30 minutes of
midday sunlight, several times per week.
People with darker skin may need a little
more than this. Your exposure time should
depend on how sensitive your skin is to
sunlight.

12. • Deficient of sunlight, all plants would die and,
eventually, all animals that rely on plants for
food — including humans — would die, too.
• While some inventive humans might be able to
survive on a Sun-less Earth for several days,
months, or even years, life without the Sun
would eventually prove to be impossible to
maintain on Earth.
• About 5 billion years, the sun will run out of
hydrogen. Our star is currently in the most
stable phase of its life cycle and has been
since the formation of our solar system, about
4.5 billion years ago. Once all the hydrogen
gets used up, the sun will grow out of this
stable phase.

13. • Almost all plants are photosynthetic autotrophs,
as are some bacteria and protists
– Autotrophs generate their own organic matter through
photosynthesis
– Sunlight energy is transformed to energy stored in the
form of chemical bonds
(a) Mosses, ferns,
(b) and flowering plants
(b) Kelp
(c) Euglena (d) Cyanobacteria
THE BASICS OF PHOTOSYNTHESIS

14. Light Energy Harvested by Plants &
Other Photosynthetic Autotrophs
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

15. • Photosynthesis is the process by which
autotrophic organisms use light energy to
make sugar and oxygen gas from carbon
dioxide and water
AN OVERVIEW OF PHOTOSYNTHESIS
Carbon
dioxide
Water Glucose Oxygen
gas
PHOTOSYNTHESIS

16. • The Calvin cycle makes
sugar from carbon
dioxide
– ATP generated by the light
reactions provides the
energy for sugar synthesis
– The NADPH produced by the
light reactions provides the
electrons for the reduction
of carbon dioxide to glucose
Light Chloroplast
Light
reactions
Calvin
cycle
NADP
ADP
+ P
• The light reactions
convert solar
energy to chemical
energy
– Produce ATP & NADPH
AN OVERVIEW OF PHOTOSYNTHESIS

17. Chloroplasts: Sites of Photosynthesis
• Photosynthesis
– Occurs in chloroplasts, organelles in
certain plants
– All green plant parts have chloroplasts
and carry out photosynthesis
• The leaves have the most chloroplasts
• The green color comes from chlorophyll in
the chloroplasts
• The pigments absorb light energy

18. • In most plants, photosynthesis
occurs primarily in the leaves,
in the chloroplasts
• A chloroplast contains:
– Stroma, a fluid
– Grana, stacks of thylakoids
• The thylakoids contain
chlorophyll
– Chlorophyll is the green pigment
that captures light for
photosynthesis
Photosynthesis occurs in chloroplasts

19. General Mechanism of Bacterial
Photosynthesis
• Light-harvesting pigments (LHPs) embedded in
membranes capture light energy and transfer it to
a protein-complex called a reaction center
• The energy is converted into excited, low
potential electrons
• Electrons are fed into an electron transport chain,
where they "fall" through a series of electron
carriers, generating a proton motive force (PMF)
• Membrane-bound ATPases then use the proton
motive force to make ATP.

20. Classification of Photosynthetic
Bacteria
• Five photosynthetic groups within domain
Bacteria (based on 16S rRNA)
• Oxygenic Photosynthesis
– Cyanobacteria and Prochlorophytes
• Anoxygenic Photosynthesis
– Purple bacteria
– Green sulfur bacteria
– Heliobacteria
– Green gliding bacteria

21. Oxygenic Photosynthesis
• Occurs in Cyanobacteria and Prochlorophytes
• Synthesis of carbohydrates results in release of
molecular O2 and removal of CO2 from atmoshphere
• Occurs in lamallae which house thylakoids
containing chlorophyll a/b and phycobilisomes
pigments which gather light energy
• Uses two photosystems (PS):
- PS II- generates a proton-motive force for making ATP
- PS I- generates low potential electrons for reducing power.

22. Oxygenic Photosynthesis

23. Anoxygenic Photosynthesis
• Uses light energy to create organic compounds,
and sulfur or fumarate compounds instead of O2
• Occurs in purple bacteria, green sulfur bacteria,
green gliding bacteria and heliobacteria
• Uses bacteriochlorophyll pigments instead of
chlorophyll
• Uses one photosystem (PS I) to generate ATP in
“cyclic” manner

24. Anoxygenic Photosynthesis
Reduction potential: A tendency of a
chemical species to be reduced by gaining
an electron

25. • Chloroplasts contain several pigments
Chloroplast Pigments
– Chlorophyll a
– Chlorophyll b
– Carotenoids
Figure 7.7

26. Chlorophyll a & b
•Chl a has a methyl
group
•Chl b has a carbonyl
group
Porphyrin ring
delocalized e-
Phytol tail
Phytol tail of chlorophyll is a long hydrocarbon
chain that is hydrophobic in nature. It anchors
the pigment to membranes of thylakoids. The
hydrophobicity of the tail allows it to anchor
the pigment to the membranes of thylakoids.
Mg ion is present in the Porphyrin head.

27. Different pigments absorb light differently

28. Excited
state
e
Heat
Light
Photon
Light
(fluorescence)
Chlorophyll
molecule
Ground
state
2
(a) Absorption of a photon
Excitation of chlorophyll in a
chloroplast
e Photolysis of water:
When the electrons leave
the chlorophyll molecules,
it leaves behind a 'hole.'
This electron hole is filled
in by a water molecule that
is oxidized, or loses
electrons, as it essentially
splits into two hydrogen
atoms, or protons, and an
oxygen atom.

29. Cyclic Photophosphorylation
• Process for ATP generation associated with some
Photosynthetic Bacteria
• Reaction Center => 700 nm

30. Water-splitting
photosystem
NADPH-producing
photosystem
ATP
mill
• Two types of
photosystems
cooperate in the light
reactions

31. Primary
electron acceptor
Primary
electron acceptor
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy for
synthesis of
by chemiosmosis
Noncyclic Photophosphorylation
• Photosystem II regains electrons by splitting water,
leaving O2 gas as a by-product

32. • The O2 liberated by photosynthesis is made from
the oxygen in water (H+ and e-)
Plants produce O2 gas by splitting H2O

33. 2 H + 1/2
Water-splitting
photosystem
Reaction-
center
chlorophyll
Light
Primary
electron
acceptor
Energy
to make
Primary
electron
acceptor
Primary
electron
acceptor
NADPH-producing
photosystem
Light
NADP
1
2
3
How the Light Reactions Generate ATP and NADPH

34. • Two connected photosystems collect
photons of light and transfer the
energy to chlorophyll electrons
• The excited electrons are passed from
the primary electron acceptor to
electron transport chains
– Their energy ends up in ATP and NADPH
In the light reactions, electron
transport chains generate ATP,
NADPH, & O2

35. • The electron transport chains are
arranged with the photosystems in the
thylakoid membranes and pump H+
through that membrane
– The flow of H+ back through the membrane
is controlled by ATP synthase to make ATP
– In the stroma, the H+ ions combine with
NADP+ to form NADPH
Chemiosmosis powers ATP
synthesis in the light reactions

36. The production of ATP by
chemiosmosis in photosynthesis
Thylakoid
compartmen
t
(high H+)
Thylakoid
membrane
Stroma
(low H+)
Light
Antenna
molecules
Light
ELECTRON TRANSPORT
CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE

37. Review: Photosynthesis uses light
energy to make food molecules
Light
Chloroplast
Photosystem
II
Electron
transport
chains
Photosystem I
CALVIN
CYCLE Stroma
LIGHT REACTIONS CALVIN CYCLE
Cellular
respiration
Cellulose
Starch
Other
organic
compounds
• A summary
of the
chemical
processes of
photosynthe
sis

38. “Dark” reaction (Light-independent Reaction)
6CO2 + 12H2O + light energy C6H12O6 + 6O2 + 6H2O
• “Dark” reaction:
Calvin cycle
• regenerative
• anabolic
• CO2 in, sugar out
• during daylight
CO2
NADP+
ADP
Pi
+
RuBP 3-Phosphoglycerate
Calvin
Cycle
G3P
ATP
NADPH
Starch
(storage)
Sucrose
(export)
Chloroplast
Light
H2O
O2

39. Carbon fixation
• 3 stages of Calvin-
cycle:
• #1 – carbon fixation
• CO2 link to 5-C
• 5-C: ribulose bisphosphate (RuBP) - enzyme: Rubisco
abundant
• 6-C unstable – split  2(3-C)

40. Reduction
• #2 – reduction
• reduced 3-C: G3P
• 3-C reduced
• e- from NADPH
• 3 stages of Calvin-
cycle:

41. Regeneration of C-acceptor
• multiple steps
• uses ATP
• every 3 cycles:
1 G3P made
3 RuBP regenerated
• #3 – regenerate C-
acceptor
• still 5 G3P  3 RuBP
• C3 plants – CO2 fixed into 3-C
• 3 stages of Calvin-
cycle: