Photosynthesis

Front 1

Photosynthesis: How plants make their food!

Back 1

-inorganic compounds ----> organic compounds
-"primary production"
-focus on carbon

Front 2

Chloroplast

Back 2

-plastid
-green from chlorophyll
-once were free living bacteria (endosymbiotic theory)
-has multiple (3) membranes
-own DNA, enzymes, and ribosomes (maternally inherited)
-reproduce by binary fission

Front 3

Chemical Equation for Photosynthesis in Plants

Back 3

light
6H2O + 6CO2 ---------> C6H12O6 + 6O2
glucose

typically sucrose is the plants byproduct (C12-disaccharide)

Front 4

General Equation for Photosynthesis that includes bacteria

Back 4

light
6H2A + 6CO2 ------> C6H12O6 + 6A2

Front 5

There are 2 stages in Photosynthesis

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1) Light dependent reactions (light reactions)

2) Light independent reactions
-dark reactions
-carbon fixation reactions
-Calvin-Benson Cycle

Front 6

Stage 1) Light Dependent Reactions

Back 6

Plants use light to make ATP and NADPH-"photophosphorylation".
In the process, water is split and oxygen is released-Hill Reaction/hydrolysis
-happens within thylakoid membrane

Front 7

Stage 2) Light Independent Reactions

Back 7

Plant fixes CO2 and makes it into sugar using ATP and NADPH from stage 1

The Calvin-benson cycle makes the sugar and regenerates the starting materials

Front 8

biological cycle

Back 8

series of chemical reactions that end with that they started with

Front 9

what is a pigment?

Back 9

chemicals that capture and selectively absorb or reflect certain wavelengths or colors of light.

Chlorophyll A+B are most important
Accessory pigments:
-carotene (orange)
-xanthophyll (yellow)
anthocyanin (purple, sometimes red)

Front 10

why are plants green?

Back 10

the major pigment of photosynthesis is chlorophyll, which absorbs red and blue light, and reflects green light (550 nm)!

green leaves= a lot of chlorophyll
dormant leaves= low chlorophyll so other pigments show

Front 11

Chlorophyll A+B

Back 11

large carbon compounds
-magnesium plays a large role in their strucures
-A is more important in energy transfer
-only difference between the two is a methyl group in A and a carboxylic acid in B
-hydrocarbon chain anchors chlorophyll

Front 12

Electron Excitation

Back 12

photons: packets of light that move like a wave but act like energy

photons excite electrons!

Front 13

When exicted, electrons:

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1) Give off light
2) Give off heat
3) Vibrate
4) Transfer to another molecule
5) Cause chemical reactions to occur

Front 14

Antenna complex

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Large proten complexes
2 kinds: Photosystem 1 (p680) and Photosystem 2 (p700)
-accessory pigments!
-electron is passed from chemical to chemical until it reaches the reaction center

Front 15

How do plants capture light?

Back 15

-mesophyll cells containing chloroplasts
-light passing through single cell layer

Front 16

Light

Back 16

behaves as a wave and a particle

Front 17

Wave characteristics

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wavelength: distance from peak to peak
frequency: number of waves that pass through observer
speed=(wavelength)(frequency)

visible light moves at a speed of 3.0x10^8 m/s

Front 18

Particle

Back 18

a particle if a photon (sack of energy)
-amount of energy in each sack depends on the frequency
-Planck's Law= E=hv
-h is Planck's constant (6.626x10^-34 J/s)
higher energy=shorter wavelength, higher frequency
lower energy=larger wavelength, lower frequency

Front 19

Chlorophyll

Back 19

There are four known chlorophyll molecules:
1) Chlorophyll A A+B are in higher plants
2) Chlorophyll B
3) Chlorophyll C
4) Chlorophyll D C+D are in protist/ bacteria

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When excited, pigments can:

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1) capture and release photons (Fluorescence)

2) Return back to ground state and release heat

3) Return back to ground state and transfer energy to another molecule (accessory pigments)

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Major Accessory Pigments are Carotenoids

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long linear chain of fatty acids with ring on either side
-multiple db's
-absorb between 400-500 nm
-all photosynthetic organisms have
-protect organisms from UV damage

Front 22

Chlorophyll molecules transmit energy from excited electrons in the antenna complex to a reaction center

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antenna systems all vary, but have a general motif with low energy being passed down to higher energy

-what pigments the system has varies species to species
-95-99% efficient at energy transfer

Front 23

Accessory pigments are associated but not covalently bound to the photosystems

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in Photosystyem 1 pigments are found on edges of grana lamella, where they are exposed to the stroma

in photosystem 2 pigments are imbedded in grana lamella

Front 24

Order of Electron Transfer

Back 24

1)Photosystem 2
2) Plastoquinone
3)Cytochrome b6/f complex
4) Plastocyanin
5) Photosystem 1
6) Proton transport
7) ATP synthesis

Front 25

Photosystem 2

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-where electrons first form
-large protein comlex with multiple proteins

-Hill Reaction-water oxidation: two water molecules split inside the lumenon
-D1 and D2 protein are where the splitting complex is
-only protein complex inthe world that can oxidize water

Front 26

Photosystem 2 continued

Back 26

Chlorophyll is hit by light and excited electrons are passed to the Pheo (pheophitin-pigment), that then passes the electrons to two major carriers, Plastoquinones A+B

Pheo --> Plastoquinone A --> Plastoquinone B

Front 27

Plastoquinone

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Once electrons are passed from Pheo to plastoquinone A and then to plastoquinone B, plastoquinone B (large folded protein with B-pleated sheets, prosthetic group) can leave and find the cytochrome b6/f complex

Front 28

Cytochrome b6/f complex

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-open pore down center
-oxidation of plastoquinone is coupled with the transport of hydrogen ions ino the lumen
-heme groups (prosthetic)-aid in protein function
-gives electrons to plastocyanin

Front 29

Plastocyanin

Back 29

-copper containing protein, blue in color
-carries electrons to photosystem 1

Front 30

Photosystem 1

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sends electrons to NADP, which becomes NADPH
with help from Feredoxin (Fd) and feredoxin NADP reductase enzyme (FNR)

Front 31

NADP

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terminal electron acceptor
-end of the transport chain

Front 32

Proton Transport

Back 32

through the transport of protons along the thylakoid membrane, an electrochemical gradient is created, with H+ ions from photosystem 2 and the cyctochrome b6/f complex, flowing into the lumen. H+ ions want to balance out the chemical gradient and move upwards and into the ATP synthase molecule

Front 33

ATP synthesis

Back 33

ATP synthase is a huge molecular complex (> embedded in the inner membrane of mitochondria. Its function is to convert the energy of protons (H+) moving down their concentration gradient into the synthesis of ATP. 3 H+ moving through this machine is enough to convert a molecule of ADP and Pi (inorganic phosphate) into a molecule of ATP.

Front 34

The Carbon Reactions:
Calvin Cycle, carbon fixation reactions, dark reactions, light independent reactions

Back 34

CO2 --> triose sugar using ATP and NADPH from the light dependent reactions

Front 35

Calvin Cyle

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There are 3 steps:
1) Carbon Fixation
2) Reduction
3) Regeneration

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1) Carbon Fixation

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carbon dioxide binds to ribulose-1,5-bisphosphate (RuBP) (catalyzed by enzyme rubisco)

the binding makes a 6c compound that is unstable and immediately slits into two 3-phosphoglycerates (3PG)

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2) Reduction

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3-phosphoglycerate reduced into glyceraldehyde-3-phosphate (G3P-main product of Calvin Cycle) by kinase that work on phosphate groups (add phosphotases)

Front 38

3) Regeneration

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to regenerate RuBP, the calvin cycle must cycle six times resulting in twelve (G3P's). Ten of the twelve G3P's are used to regenerate another six cycles of RuBP, and the other two G3P's are used to make sugar

-multi-step, multi-enzyme rearrangement of cabrons, to regenerate RuBP

Front 39

Regulation of the Calvin Cyle

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-highly regulated, no waste, no loss of byproducts
-turned off or on like a light switch (mostly off at night)
-transcriptional and post-transcriptional regulation
-nuclear genomes (80s ribosomes) and chloroplast genomes (70s ribosomes-like bacteria) control and regulate the calvin cyle at a transcriptional level

Front 40

Anterograde Regulation

Back 40

-most of Calvin Cyle udnergoes
-transcriptional regulation (geneticl level)
-nuclear genes turn on by environmental signal (light or enzymes) and act as transcriptional factors to signal to the chloroplast genes to turn on

Front 41

Light Regulated Calvin Cycle

-most important and most common regulator of the Calvin Cyle is LIGHT

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post-transcriptional regulation; "enzyme kinetics"

-rate starting/stopping enzymes, modifying non-covalent interactions

Front 42

The Calvin cycle is regulated by light-dependent activation of at least 5 enzymes:

Back 42

1) Rubisco
2) NADP-glyceraldehyde-3-phosphate dehydrogenase
3) Fructose-1,6-bisphosphate phosphatase
4) Sedheptulose-1,7-bisphosphate phosphatase
5) ribulose-5-phosphate kinase (phosphoribulokinase)

Front 43

Light-dependent ion movements:

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Rubisco and other enzymes are activated by light-induced increase in stromal pH. All enzymes have an optimal pH range in which they function most effectively. Rubisco works best at a pH close to 8 but is relatively inactive at pH 7. As light-driven electron transport leads to the generation of a pH gradient across the thylakoid membrane, the stromal pH increases from around pH 7 to pH 8.

Front 44

pH Change

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As a result of the pH change, other ions move across the thylakoid membrane to compensate for charge differences. In particular, Mg++ moves out as H+ moves in. Rubisco requires Mg++ to function and the combination of increase in pH and Mg++ leads to a significant increase in rubisco activity.

Front 45

C2 Oxidative Photosynthetic Carbon Cycle- Photorespiration

Back 45

-oxygen binds to RuBP, creating one 3-carbon and one 2-carbon compounds
-the two carbon compund cannot be ued and through the long process of photorespiration is conveted into 3PG
-75% efficient (lots of time/energy, waste)

Front 46

C4 Carbon Cycle

warm environment plants (grasses, corn, sugar cane)

Back 46

modify photosynthetic pathway to avoid photorespiration
-CO2 and O2 are brought into the mesophyll cell
- phosphophenol pyruvate enzyme (PEP) binds with CO2 resulting in malate (PEP (C3) +CO2 --> 4C Malate) (O2 cannot bind)
-only malate can be shuttled into the bundle sheath cell, where it then drops CO2 off to enter into the Calvin Cycle

Front 47

CAM (Crassulacean Acid Metabolism)

arrid environment (dry)
-pineapple
-agavi
-orchid
-cacti

Back 47

open up stomata in the dark and allow CO2 to enter, and then carry out the same reaction as C4 carbon cycle, BUT malate waits until the day to be shuttled and undergo the calvin cycle

-stomata closed during the day to conserve water