Photosynthesis contrasts with cellular respiration

• Endergonic-
  • Redives CoQ to sugar
• cellular respiration is exergonic
  • oxidizes sugar to cAy

photosynthesis

• uses sunlight to power the synthesis of organic molecules
• Energy for all life comes from photosynthesis
• Global photosynthesis captures only 1% of the huge supply of radiant energy

Forms of Photosynthesis

• Anoxygenic photosynthesis does not produce oxygen
  • found in four different bacterial groups
• oxygenic photosynthesis does produce oxygen
  • Carried out by Cyanobacteria, 7 groups of algae and land plants
  • primarily in leaves - in chloroplasts
  • combines 102 and 120 to produce sugar and 02

chloroplasts

• have own DNA
• symbiotic

Stages of Photosynthesis

• 2 sets of chemical reactions
  • reactions that use the energy in sunlight to make ATP and reduce the compound NADP+, an electron carrier to NAPH.
  • Reactions that use the ATP and NADPH to power the synthesis of organic molecules using CO2 from the air

photosynthesis reactions

• light-dependent reactions - Daytime
  • Light
  • energy from sun-captures
  • makes ATP and Reduces NADP+ to NADPH
• Carbon fixation reactions or light-independent reactions
  • no light required
  • uses ATP and NAPPh to synthesize organic molecules from COQ

chloroplast is a photosynthetic machine

• internal and external membranes contributes to its function Thylakoid membrane- Internal phospholipid bilayer
  • contains chlorophyll and other photosynthetic pigments for capturing light energy
• Pigments Clustered into photosystems
  • Grana - Stacks of flattened sacs of Thylavioid membrane
  • Stroma - semiliquid substances surrounding thylakoid membranes
• houses the enzymes needed to assemble organic molecules from CO2

Research on Photosynthesis

• photosynthesis is a chemical process
• originally thought plants obtain food through soil
• experimentation shows the role of carbon dioxide, water, and sunlight

Jan Bapista van Helmont (1580-1644)

• showed substance of the plant was not produced from soil alone
• incorrectly concluded that water was the reason for plant growth

Joseph Priestly (1733-1804)

• plants restore air
• Air restored by vegetation is not inconvenient to a morse

Jan Inger/hous 2 11730-1799)

• extended priestly's results
• Air is restored by leaves and the pressure of sunlight, not roots
• sunlight splits carbon dioxide carbon and oxygen
• oxygen released as O2 gas into the air.
• carbon forms with water to produce carbohydrates

F.F. Blackman (1866-1947)

• photosynthesis is a multistage process.
• light v. Darn reactions
• evolved enzymes

C.B. Van Neil (1897-1958)

• purple sulfur bacteria as not release O2
  • accumulate Sulfur
• Photosynthesis Formula - 7O2 + 2H2A+ light energy→( CH2O) +H2O + 2A
  • plants -> A = oxygen, H2O = water, water is split; providing electrons and releasing oxygen
• Bacteria -) A = sulfur

Robin Hill (1899-1991)

• light energy can be harvested and generate reduced power
• chloroplasts isolated from leaves reduce a dye and release oxygen
• electrons from water become NADP+
• Illuminated Chproplasts deprived of CO2 Accumulate ATP
• CO2 is assimilated into organic molecules

Light is a form of energy

• light exhibits properties of both waves and particles
• wave nature produces an electromagnetic spectrum that differentials light.
  • visible light is small: separated into colors via prism
• Photon - a particle of light
  • Discrete energy
  • helps us understand energy transfers during photosynthesis

Energy in Protons

• energy content is inversely proportional to wavelength
  • short wavelength-higher energy
  • long wavelength-lower energy
• photoelectric effect - Photons transfering energy to an electron
• chloroplasts are photoelectric devices base of light depenset reactions
  • Pigments absorb light and excited elections are transfered to a carrier

Pigments in Photosynthesis

• 2 types used in green plant photosynthesis
  • Chlorophyll - several
  • Carotenoids - orange

Absorption spectrum

• when a proton strikes a molecule, energy is
  • lost as neat
  • absorbed by the elections of the moleule -
    • boosts energy
• To be absorbed, energy in Photon must match energy needed to rais the electron
• each molecule has a characteristic absorption spectrum-range and efferiency of photon absorption
  • Carotenoids absorb blue and greenlight and transmit yellow, orange, or red light
    • has a broader spectrum

Chlorophylls

• reflect photons with wavelengths between 500 and 600 nm
• chlorophyll A
  • main pisment in plants and cyanobacteria
  • only pigment that can act directly to convert light into chemical energy
• Chlorophyll b
  • Absorbs what chlorophyll A doesn't.

Structure of chlorophyll

• chlorophyll porphyrin Ring
• Alternating double and single bonds
• magnesium ion at the center of the ring
• The tail keeps Molecules embedded in the thylakoid membrane
  • photons excite electrons in the ring
  • elections are shuttled away from the ring

Action spectrum

• corresponds to the absorption spectrum
• for chlorophylls

Carotenoids

• can absorb photons with a wide range of energies
• scavenge free radicals acting as antioxidants to lessen the damage

photosystem organization

• Antenna complex
  • hundreds of accessory pigment molecules
  • Gather photons and feed the captured light energy to reaction center
• reaction center where photons gather
  • 1 or more chlorophyll A molecules
  • passes excited electrons out of the photosystem
    • Pigment = something excited by the proton

saturation of photosynthesis

• Robert Emerson And William Arnold
  • Tested hypothesis - output of photosynthesis plateaued because all the chlorophyll molecules had absorbed a photon
  • saturation was achieved with one molecule of 02 per 2500 chlorophyll molecules
  • light is absorbed by clusters of chlorophylls - photosystems
  • light absorbed by pigment in photosystem results in transfer of the excitation energy - reaction center

Photosystems

• 2 closely linked components
  • Antena complex of hundreds of pigments gather photons and feed captured light to the reaction center
  • reaction center consisting of one or move chlorophyll A molecules in Protein matrix. passes excited elections to photosystem

Antena complex

• light-harvesting complex
• captures photons from sunlight and Channels them to reaction center chlorophylls
• Chloroplasts, consists of a web of chlorophyll molecules linked together and held tightly in the thylakoid membrane by a matrix of proteins
• varying amounts of carotenoids
• Excitation energy from absorption passes from one pigment to another on the way to a reaction center
  • Reduces in the reaction center

Reaction Center-Gathers Photon energy

• Transmembrane protein-pisment complex
• chlorophyll in the reaction center absorbs photon- electron is excited
• Light energized electrons can be transferred to the primary election acceptor-reduces
• oxidized chlorophyll then replaces lost electron by oxidizing another molecule

Light-dependent reactions

• Primary photoevent
  • Photon is captured by a pigment molecule
• Charge separation
  • the excited electron is transferred to an acceptor
• Electron Transport
  • electrons more through carriers to reduce NADP+
• Chemiosmosis
  • movement of protons up
  • like aerobic respiration
  • produces ATP

Purple and Green Bacteria

• generate ATP through election transport
• does not generate sufficient oxidizing power to oxidize water to form oxygen gas
• chloroplasts utilize two connected Photosystems

Oxygenic Photosynthesis

• photosystem 1 (700)
  • Absorption peak at 700 NM
  • functions live sulfur bacteria
• Photostem 2 (P680)
  • Absorption Peak at 680 nm
  • can generate an oxidation potential high enough to oxidize water
  • happens before 1
• Makes ATP
• Both carry-out non-cyclic Transfer of
• electrons-Generate ATP and NADPH

Photosystems 1 and 2

• named in order of discovery
• photosystem 1 transfers electrons NADP+ becomes NADPH
• Electrons lost in 1 are replaced in two
• photosystem I oxidized water to replace electrons transferred to photosystem 2
• connected by Cytochrome

NonCylic Photophosphoralation

• plants use photosystems 2 and 1 to produce ATP and NADPH
• photosystems replenished with electrons from splitting water
• Z-diagram demonstratse

Photosystem 2

• essential for the oxidation of water
• Protons pumped into the thylakoid space

Photosystem 1

• unique to plants
• accepts an electron from plastocyanin into the hole created by the exit of light energy
• NADP+ to NADPH
  • Except electrons from photosystem 2

Chemiosmosis uses a proton gradient

• proton concentration is higher in thylakoid Space
  • b6f complex in photosystem 2 pumps protons from the stroma into the thylakoid compartment
• splitting of water adds protons to the thylakoid compartment
• electromechanical gradient synthesizes ATP
  • electrons replenish chlorophyll

ATP synthase

• chloroplast has atp synthase enzymes in the thylakoid membrane
  • form a channel, allowing protons back to Stroma
• As protons pass out of the thylakoid, ADP is phosphorylated to ATP and released from the stroma
  • uses energy from the proton stream

Production of Additional ATP

• passage of an electron pair from water to NADPH in noncyclic photophosphorylation generates…
  • one molecule of NADPH
  • A little more than one ATP molecule
• Building organic molecules takes 1.5 times more ATP than NADPH
• cyclic photophosphorylation is used to produce additional ATP
  • Addition of proton gradient instead of electron

Carbon Fixation - Calvin Cycle

• To build carbohydrates cells use…
  • Energy
    • ATP
    • provided by cyclic and noncyclic photophosphorylation
    • Drives endergonic reaction
  • Reduction
    • NADPH
    • provided by Photosystem 1
    • source of protons and energetic electrons

Calvin Cycle Builds organic molecules

• Melvin Calvin 1911-1997 )
• C3 photosynthesis
  • The first intermediate in the cycle is a 3-carbon acid
• Attachment of CO2 to ribose 1, 5 biphosphate forms 3 phosphateslycerate
  • the reaction is catalyzed by the enzyme ribulose biphosphate carboxylase

Phases of Calvin Cycle

• Carbon fixation
  • RUBP+ CO2 → 2 3PG
• Reduction
  • 3PG becomes G3P using ATP and NADPH
• Regeneration
  • G3P converted to RUBP by ATP
• 3 turns move new G3P
• 6 turns man I glucose molecule

Output of Calvin Cycle

• G3P-3 carbon sugar
  • Used to form sucrose
    • major transport of sugar in plants
    • Disaccharride mac 28 Fruose and Glucose
  • used to more starch
    • Insolvable glucose polymer
    • stored for later

energy cycle

• photosynthesis is used products of respiration is starting substrates
• Respiration uses products of photosynthesis as starting substrates
• production of glucose glycolytic Pathway in reverse
• Principle proteins in ATP and election transport related to mitochondria

Photorespiration

• Carbon-fixation
  • Addition of CO2 to RuBP to make 3PG

Stomata

• specialized openings in the leaf
• closed to conserve water
• closing cutts of supply of CO2 entering the leaf, O2 cannot exit

conditions favoring phosphoralation photorespiration

• under not, aria conditions, casing Somata to conserve water favors photorespiration

Types of carbon Fixation

• C3 combines with RuBP using the Calvin cycle to form 3PG
• C4 Plants fix carbon by combing it with photophoeolpyrovate using PEP Carboxylase to form oxciocate
• 2 advanagesof PEP
  • Grater affinity for CO2
  • no oxidase activity

4-carbon advantage

• decarboxylated, releases CO2
• CO2 is used in Calvin Cycle
• CO2 stored in organic form and released in different cell or time

Plants that use PEP

• C4 plants
  • use spatial solution to avoid photorespiration
  • capture of CO2 happens in one cell
  • decarboxylation occurs in adjacent cell
• CAM Plants
  • both reactions in same cell, Avoid photorespiration
  • capturers coz at night
  • decarboxylate during the day

C4 plants

• corn, suger cane, sorghum
• fix carbon using PEP in mesophyll cells
• produces oxaloacetate, converted to malate, transferred to bundle sheath cans
• decarboxylate to produce pyruvate and CO2
• carbon fixation then calvin cycle
• Pyruvate is transported back to mesophyll cells to be converted back to PEP

Cost of C4 pathway

• requires 12 Additional ATP
• Advantages in not dry chimalcs

CAM Pathway

• somata opens at night, close during the day
• Fix CO2 using pep At night a store organic compounds in vacuole
• during the day, high levels of CO2

CAM and C4

• both use C3 and C4 pathways
• C4-paths in different cells
• CAM-night pathway (L),