How Cells Acquire Energy

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• Chapter 7
• How Cells Acquire Energy

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Autotrophs

• Self nourishing
• Obtain carbon from carbon dioxide
• Photosynthetic autotrophs (plants, protistians,
  and bacterial membranes) harness light energy
• Chemosynthetic autotrophs (few bacteria) extract
  energy from chemical reactions involving
  inorganic substances (e.g.Sulfur compounds)

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Heterotrophs

• Obtain carbon and energy from the autotrophs
• Include protistans, bacteria, animals, and fungi
• Carbon and energy enter the web of life by
  photosynthesis and in turn are released by
  glycolysis and aerobic respiration

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Overview of Photosynthesis

• A. Photosynthesis Transforms Solar EnergyB.
  Organic molecules built by photosynthesis provide
  both the building blocks and energy for cells.C.
  Plants use the raw materials carbon dioxide and
  waterD. Chloroplasts carry out photosynthesis
• 2 stages of photosynthesis takes place in the
  chloroplast
• Which has two layers (membranes) stroma and
  thylakoids
• E. Chlorophylls and other pigments involved in
  absorption of solar energy reside within
  thylakoid membranes of chloroplasts

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Plants as Solar Energy Converters

• A. Solar Radiation - Only 42 of solar radiation
  that hits the earths atmosphere reaches surface
  most is visible light.

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• B. Photosynthetic Pigments - Pigments found in
  chlorophyll absorb various portions of visible
  light absorption spectrum.
• 1. Two major photosynthetic pigments are
  chlorophyll a and chlorophyll b.2. Both
  chlorophylls absorb violet, blue, and red
  wavelengths best.3. Very little green light is
  absorbed most is reflected back this is why
  leaves appear green.4. Carotenoids are
  yellow-orange pigments which absorb light in
  violet, blue, and green regions.5. When
  chlorophyll breaks down in fall, the
  yellow-orange pigments in leaves show through.

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Secondary Pigments

• Carontenoid absorbs blue-green wavelengths but
  reflect yellow, orange, and red
• Anthocyanins Pigments found in flowers
• Phycobilins are the blue and red pigments of red
  algae and cyanobacteria

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Properties of Light

• Electromagnetic Spectrum light energy travels in
  waves through space from gamma rays to radio
  waves
• The shorter the wavelength the more energy
  Example Suns radiation

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• Photoautotrophs use a small range (400-750 nm) of
  wavelength for photosynthesis -- which is the
  range for visible light
• Light energy is packaged as photons, which vary
  in energy as a function of wavelength
• Blue violet light most energetic
• Red light least energetic

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Where are photosynthetic pigments located?

• Photosynthetic bacteria pigment is found at the
  plasma membrane
• In thylakoid membrane systems of cholorplast the
  pigments are organized in clusters called
  photosystems consisting of 200 to 300 pigment
  molecules

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Things that Dont need Glucose

• Light-dependent reactions convert light energy to
  chemical energy (which is then stored into ATP)
• Liberated electrons are picked up by NADPH
• Light-independent reaction assemble sugars and
  other organic molecules using ATP, NADPH, and CO2
• 12 H20 6CO2 ? 602 C6H12O6 6H20

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Light Dependent Reactions

• Light Dependent Reactions occur in the thylakoid
• Thylakoid are folded into grana (stacks of disks)
  and channels
• The interior spaces of the thylakoid disks and
  channels are coninuous and are filled with H
  needed for ATP synthesis
• Carbohydrates formation occurs in the stroma
  (semifluid) area that surrounds the grana

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Light Dependent Reactions

• First reaction of photosynthesis
• Three events occur
• 1- Pigment absorb sunlight energy and give up
  excited electrons
• 2- Electron and hydrogen transfer lead to ATP and
  NADPH formation
• 3- Pigments that gave up the electrons in the
  first place get electron replacements

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What Happens to the Absorbed Energy?

• The pigments harvest photon energy from
  sunlight
• Absorbed photons of energy boost electrons to a
  higher level.
• Electrons return to lower level
• Released energy is trapped by cholorphylls
  located in the photsystems reaction center
• The trapped energy is then used to transfer a
  chlorophyll electron to an acceptor molecule

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Electron Transfer Chain

• Is an organized array of enzymes, coenzymes, and
  other proteins embedded in or anchored to a cell
  membrane
• Accept electrons which are then processed through
  a step-by-step array to produce ATP and NADPH

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Cyclic Pathway

• Oldest mean of ATP production being used by early
  bacteria
• Excited electrons leave the P700 reaction center,
  pass through an electron transport system, and
  then return to the original photosystem I
• Energy associated with the electron flow drives
  the formation of ATP from ADP
• Figure 7.12

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Noncyclic Pathway SPLITS WATER, PRODUCES NADPH
ATP

• ATP Formation transfer through two photosystems
  and two electron transport systems (ETS) in the
  thylakoid membrane
• Boosted electrons moves through a transport
  system that releases energy for
• ADP Pi?ATP
• Electrons fills hole left by electron boost in
  P700 of photosystem I

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• Electron from photolysis of water fills electron
  hole left in p689 and produces oxygen byproduct
• Pathway continues when chlorophyll P700 of
  photosystemI is absorbs energy
• Energy hole is filled by elctron from P680
• Boosted electron from P700 passes to acceptor,
  then ETS is finally joins NADP to form NADPH
  (which along with the ATP can be used in
  synthesis of organic compounds
• Turn to page 123 (Figure 7.13)
• Hyperlink\Light reactions.mht

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• Watch movie here
• You can watch this movie going to my
  portaportal.com website
• Guest Name Mssweikle
• Go to the AP Biology Folder
• Find Photosynthesis movie

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The New Atmosphere

• Oxygen is a by-product of the noncyclic pathway
• Beginning about 1.5 billion years ago, large
  amounts of oxygen began accumulating in the
  atmosphere, which at the time was oxygen-free

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Light-Independent Reactions

• These reactions (Calvin-Benson Cycle) are the
  synthesis of phytosynthesis
• Handout Slide 27
• The participants and their roles in the synthesis
  of carbohydrates are
• ATP, which provides energy
• NADPH provides the hydrogen atoms and electrons
• Atmosphere provides the Carbon dioxide
• The reactions are dependent on sunlight

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Fixation of Carbon Dioxide

• CO2 fixation is the attachment of CO2 to an
  organic compound called RuBP.
• RuBP (ribulose bisphosphate) is a five-carbon
  molecule that combines with carbon dioxide.
• The enzyme RuBP carboxylase (rubisco) speeds this
  reaction this enzyme comprises 2050 of
  theprotein content of chloroplasts, probably
  since it is a slow enzyme.

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Reduction of Carbon dioxide

• With reduction of carbon dioxide, a PGA
  (3-phosphoglycerateC3) molecule forms.
• Each of two PGA molecules undergoes reduction to
  PGAL in two steps.
• Light-dependent reactions provide NADPH
  (electrons) and ATP (energy) to reduce PGA to
  PGAL.

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Regeneration of RuBP

• 1. Every three turns of Calvin cycle, five
  molecules of PGAL are used to re-form three
  molecules of RuBP.
• 2. Every three turns of Calvin cycle, there is
  net gain of one PGAL molecule five PGAL
  regenerate threemolecules of RuBP.

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Importance of the Calvin Cycle

1. PGAL, the product of the Calvin Cycle can be
   converted into all sorts of other molecules.
2. Glucose phosphate is one result of PGAL
   metabolism it is a common energy molecule
3. Glucose phosphate is combined with fructose to
   form sucrose used by plants.
4. Glucose phosphate is the starting pint for
   synthesis of starch and cellulose.
5. The hydrocarbon skeleton of PGAL is used to form
   fatty acids and glycerol the addition of
   nitrogen forms various amino acids.

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Calvin Cycle
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How Do Plants Build Glucose?

• Each PGA then receives a phosphate group from ATP
  plus H and electrons from NADPH to form PGAL
• Most PGAL molecules will continue in the cycle to
  fix more carbon dioxide, but two PGAL join to
  form a sugar phosphate, which will be modified to
  sucrose, starch, and cellulose.
• Final Tally

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• Sugar phosphate are used as cellular fuel and as
  building blocks in synthesis of sucrose or
  starch.
• Sucrose is the most easily transportable
• Starch is the main storage form, but will be
  converted by to sucrose for distribution to
  leaves, stems, and roots
• Photosynthesis yields intermediates and products
  that can be used in lipid and amino acid synthesis

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Factors that affect photosynthesis

• Light Quality (color)
• Light intensity
• Light Period
• Carbon Dioxide Availability
• Water Availability

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How gases enter and leave plants?
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C3 Plants

• 1. The Calvin Cycle is the MOST Common Pathway
  for Carbon Fixation. Plant Species that fix
  Carbon EXCLUSIVELY through the Calvin Cycle are
  known as C3 PLANTS.
• 2. Other Plant Species Fix Carbon through
  alternative Pathways and then Release it to enter
  the Calvin Cycle.

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• 3. When a plant's Stomata are partly CLOSED, the
  level of CO2 FALLS (Used in Calvin Cycle), and
  the Level of O2 RISES (as Light reactions Split
  Water Molecules).
• 4. A LOW CO2 and HIGH O2 Level inhibits Carbon
  Fixing by the Calvin Cycle. Plants with
  alternative pathways of Carbon fixing have
  Evolved ways to deal with this problem.

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C4 Plants

• C4 PLANTS - Allows certain plants to fix CO2 into
  FOUR-Carbon Compounds. During the Hottest part of
  the day, C4 plants have their Stomata Partially
  Closed. C4 plants include corn, sugar cane and
  crabgrass. Such plants Lose only about Half as
  much Water as C3 plants when producing the same
  amount of Carbohydrate.

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CAM Plants

• Cactus, pineapples, and other succlents have
  different adaptations to Hot, Dry Climates. They
  Fix Carbon through a pathway called CAM.
• Plants that use the CAM Pathway Open their
  Stomata at NIGHT and Close during the DAY, the
  opposite of what other plants do. At NIGHT, CAM
  Plants take in CO2 and fix into Organic
  Compounds.
• During the DAY, CO2 is released from these
  Compounds and enters the Calvin Cycle.
• Because CAM Plants have their Stomata open at
  night, they grow very Slowly, But they lose LESS
  Water than C3 or C4 Plants.

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Ocean Photoautotrophs

• The ocean host a vast number of photoautotrophic
  prokaryotic cells and protistans
• They shape the global climate