Gathering, Storing, and Using Energy from the Sun

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Chapter 6 Gathering, Storing, and Using Energy
from the Sun

• Autotrophs and heterotrophs
• The energy in sunlight
• Capturing light energy in chemical bonds
• An overview of photosynthesis
• The light-dependent reactions Synthesizing ATP
  and NADPH
• The light independent reactions Making
  carbohydrates

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The Role of Photosynthesis

• Sunlight is the ultimate source of energy for
  almost all life1.5 x 1022 kJ falls on the earth
  each day
• 1 is absorbed by photosynthetic organisms and
  transformed into chemical energy
• Autotrophs???? producers or self-feeder
• Plants, algae, and certain protists and bacteria
  are the members of the living world that are able
  to carry out photosynthesis or use chemical
  energy in a similar way, make glucose from H2O
  and CO2
• Glucose is used as a source of energy to make
  ATP and as building blocks to construct larger
  molecules
• Autotrophs also use inorganic nutrients such as
  phosphate and nitrates to build large molecule
  from glucose
• Some autotrophs (ex. diatoms) use unusual
  nutrients such as silicates
• Heterotrophs???? consumers or other-feeder
• Organisms that cannot produce their own food.
• Instead, they obtain organic energy by ingesting
  autotrophs or other heterotrophs.
• Most species (95, all animals, all fungi, and
  most protists and bacteria) of organisms on Earth
  are heterotrophs.

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The Role of Photosynthesis

• Photosynthesis is the major biosynthetic pathway
  to convert CO2 and H2O into polysaccharides and
  major source of oxygen in the earths atmosphere
• 6CO2 6H2O ?C6H12O6 6O2 G0
  2870 kJ/mol
• Plant, algae, and some microorganisms catalyze
  the CO2 fixation
• 1011 tons of CO2 are fixed globally per year
• Oxygen (O2) derived from H2O is released as
  by-product of photosynthesis
• Part of energy obtained from photosynthesis or
  oxidation is trapped in ATP
• Basic principle for biofuel cell design

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Major Metabolic Pathways of Autotrophs and
Heterotrophs
-Aerobic cellular respiration The process that
organisms unlock the energy in food -The energy
released is captured as ATP, O2 serves as the
terminal electron acceptor
Some organisms do not breath oxygen, make ATP
by either anaerobic cellular respiration or
fermentation by using nitrate or sulfate as the
terminal electron acceptor.
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The Metabolic Machine
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The Energy in Sunlight

• Sunlight waves of electromagnetic radiation or
  particles (photons)
• photons have discrete amounts of energy
• Wavelength inversely proportional to energy
  level
• (short wavelength high energy)
• Visible light wavelengths 380-750 nm

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The Energy in Sunlight
Light has two aspects wavelike and particle-like
Plancks law E hn hc/l
The wave aspect of light
C 2.99 x 108 m/s Red light from neon laser l
632.8 nm or 6.328 x 10-7 m Then, n 4.73 x 1014
s-1
Photons a stream of light particles Quantum
energy unit of photon One einstein a mole of
photons
The particulate aspect of light
Plancks constant 6.626 x 10-34 J s E 6.626 x
10-34 x 4.73 x 1014 3.14 x 10-19 J 189
kJ/mol
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The Energy of Photons

• Photosynthesis depends primarily on light in the
  visible and near-IR region, cause transitions in
  the electronic states of organic molecules that
  drives chemical reactions
• Photons of far-UV have energies capable of
  breaking covalent bonds
• UV can penetrate only a very short distance into
  water, and is thus unavailable to photosynthetic
  organisms living in the sea
• Photons of IR radiation can do little except
  stimulate molecular vibration, perceived as heat

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Capturing Light Energy in Chemical Bonds

• Photons are too energetic for the cellular
  processes. Thus, it must be converted to organic
  molecules of lower energy before it can be used
  by living organisms.
• Pigments are molecules which absorb some
  wavelengths and reflect others
• Electrons within pigments are temporarily boosted
  to higher energy levels
• There are two types of photosynthetic pigments
• Chlorophylls primary pigments
• Absorb photons of violet-blue and red
• Antenna pigments (carotenoids)
• Absorb photons of green, blue, violet Increase
  range of energy absorption

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Absorption Spectra and Light Energy

• Chlorophylls are located in the thylakoid
  membranes of the chloroplast.

• Chlorophylls a and b absorb deep blue and red
  light strongly. The reflected light (the light
  not absorbed) is (green) and is what we see when
  we look at most plants.
• The other colors of plants arise from the colors
  of accessory pigments. Loss of chlorophylls in
  the autumn allows both the accessory and
  nonphotosynthetic pigments of leaves to become
  apparent.

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An Overview of Photosynthesis

• Photosynthesis is a process to convert light
  energy, carbon dioxide, and water into
  carbohydrates.
• Carbohydrate is a common energy storage form
• Main product of this process should be
  glyceraldehyde-3-phosphate while oxygen (O2) is
  the by-product.
• Photosynthesis can be carried out by
  cyanobacteria, algae, and all plants.

Photosynthesis occurs in chloroplast, an
organelle usually seen in photosynthetic
eukaryotes.
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Photosynthesis light reactions dark reactions

• Light reactions capture light energy and convert
  it to chemical energy to carry out the
  photochemical oxidation of H2O, results in the
  reduction of NADP to from NADPH, and
  phosphorylating ADP to produce ATP with evolution
  of O2, within or on the thylakoid membrane
• Dark reactions (occur both in the dark and
  light) use NADPH and ATP to drive the endergonic
  process of hexose sugar formation from CO2 in a
  series of reactions, in the stroma

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How Photosystems Capture Light?

• Electrons of pigments absorb energy of photons
  and are boosted to a higher energy level.
• These high energy electrons travel along a series
  of membrane carriers to a particular chlorophyll
  a called P700 or P680.
• These energy is used to produce ATP and NADPH

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The Photosynthetic Unit

• Many chlorophylls but only a single reaction
  center
• Photosystem light-harvesting pigments
  associated proteins (PSI, PSII, LHC)
• The "unit" consists of several hundred
  light-capturing chlorophylls (antenna) plus a
  pair of special chlorophylls in the "reaction
  center"
• Light is captured by one of the "antenna
  chlorophylls" and routed from one to the other
  until it reaches the reaction center

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Synthesizing ATP and NADPH

• There are two types of photosystems photosystem
  I (P700 chlorophyll a) and photosystem II (P680
  chlorophyll a)
• Electrons of chlorophyll a return to same (cyclic
  flow) or to different (non-cyclic flow)
  chlorophyll molecule.
• Excited electrons are replenished in the
  non-cyclic process by breakdown of water.

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Noncyclic Electron Flow
1) Four photons are absorbed by pigments in
photosystem II. 2) Energized electrons are
funneled to p680 3) Electron ejected from p680 4)
The electron acceptor within thylakoid membrane
take the electrons 5) p680 pulls 4 electrons from
nearby water 6) Water is forced to split into two
hydrogen ions and oxygen atom. Two oxygen atoms
join quickly and form a molecule of oxygen
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The Two-Photosystem Light Reactions

• In each of the two photosystems, the primary step
  is transfer of a light-excited electron from a
  reaction center (P680 or P700) into an electron
  transport chain.
• The ultimate source of the electrons is water
  molecules. In this part of the process, the
  destination of the electrons is NADP, to form
  NADPH.

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Noncyclic Electron Flow
7) The energized electrons are past through a
series of electron carriers and fall to lower
energy levels. 8) Electron transport chain pumps
the protons from stroma into inner thylakoid
space 9) 10) ATP synthase on the membrane
utilize H gradient to generate ATP 11)Electrons
further transfer to p700 12)13) Electrons are
past thru electron transport chain to NADP and
generate NADPH
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Cyclic Electronic Flow
When NADPH is not needed or NADP level is low
for eukaryotic organisms, the excited electrons
in photosystem I will go through cyclic electron
flow to make more ATP.
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The Dark Reaction The Calvin Cycle

• Photosynthetic organisms use ATP and NADPH to
  fix three CO2 into three RuBP to form six 3-PG,
  called carbon fixation or the Calvin cycle.
• Two molecules of glyceraldehyde-3-phosphate (G3P)
  are used to generate one glucose (and other
  carbohydrates).
• The ribulose-1,5-bisphosphate (RuBP) is reformed
  to begin the cycle again.

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Chapter 6 Gathering, Storing, and Using Energy
from the Sun

• An overview of cellular respiration
• Preparing nutrients for aerobic respiration in
  the human body
• Glycolysis
• The Krebs cycle
• The electron transport chain

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An Overview of Cellular Respiration

• Cellular respiration is to extract energy in
  carbohydrates through oxidative, exergonic
  processes and store the energy in ATP molecules
  (for later use in cell reactions).
• C6H6O6 6O2 6CO2 6H2O 36 ATP
• Cellular respiration can be divided into three
  parts Glycolysis, Krebs cycle, and the electron
  transport chain.

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Overview of Cellular Respiration
Glycolysis occurs in cytosol Krebs Cycle occurs
in mitochondrial matrix Electron Transport Chain
carriers occur in cristae of inner mitochondrial
membrane
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Preparing Nutrients for Aerobic Respiration

• Large, complex food molecules digested to smaller
  building blocks
• proteins --gt amino acids
• starch --gt glucose
• fats --gt fatty acids and glycerol
• Small molecules enter pathway at several points.

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• Glycolysis can be divided into four stages
• Glucose mobilization priming the pump
• Glucose cleavage 6C --gt two 3C
• Oxidation begin energy gain NADH produced
• ATP generation during formation of PEP and
  pyruvate

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Transition from Glycolysis to Krebs Cycle

• Pyruvate becomes Acetyl CoA
• loses CO2 and NADH
• Acetyl CoA enters mitochondrial matrix for Krebs
  cycle

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Krebs Cycle

• Preparation Acetyl coA combined with starting
  molecule yields citric acid
• Energy extraction Citric acid oxidized and
  rearranged to yield ATP, NADH, FADH2, and CO2
• NADH, FADH2 are electron carriers that transfer
  high energy electrons to the electron transport
  chain for further energy extraction.

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The Electron Transport Chain

• Electron transport system, composed of five huge
  complexes, is embedded within the inner membrane
  of mitochondria
• The energy carried by electrons of NADH and FADH2
  is released by raveling along the electron
  transport chain and is used to pump H across the
  inner mitochondrial membrane.
• H return by facilitated diffusion through ATP
  synthase in membrane for the generation of ATP
  molecules.
• Chemiosmosis ATP synthase couples energy (from
  proton gradient in membrane) to ATP formation
• Oxygen molecule is the final electron acceptor of
  electron transport chain.
• water is produced from H and O2

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Fermentation

• Certain organisms (anaerobic organisms bacteria
  and yeast) or muscle cells can release energy
  from carbohydrates under condition with
  insufficient oxygen called fermentation.
• In this process organisms regenerate NAD by
  producing a hydrogen accepting compound from
  pyruvate for electron transport chain.
• NADH is oxidized to NAD as pyruvate is reduced
  to ethanol (yeast), lactic acid (muscle cell) or
  other compounds (bacteria)