Antenna pigments Photoprotection

PHOTOSYNTHESIS PART 1 Flashcards by Mia Daniella Cayas

In photosynthesis, _____ assimilated to form
carbohydrate and oxygen

CO2

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Chemical energy used to utilized in enzymatic reactions that convert
CO2 into organic molecule

NADPH and ATP

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Formula of Oxidation of water

2H2O → 4 electrons + 4 protons + O2

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How does Reduction of CO2 forms organic compounds

through the transfer of e- from donor to acceptor molecule

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What is the equation of photosynthesis?

6 CO2 + 6 H2O ———–> C6H12O6 + 6 O2

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What is the equation of respiration?

C6H12O6 + 6 O2 ———–> 6 CO2 + 6 H2O

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Turning Chemical Energy into Fuel for Growth,
Development and Reproduction

Respiration

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Since growth requires a net gain of energy – in
plants, photosynthetic energy gain must exceed
______________

respiratory energy loss

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What is the photosynthetic tissue?

Messophyl

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Drought-Stressed Plants Give off more
_________ Wavelengths

Infrared

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Under carotenoids

Carotene ±
Xanthophyll ±

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the pigment that initiates the
light dependent reactions of PS; bright green

Chlorophyll a

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accessory pigment; yellow green
difference: methyl group (-CH3); carbonyl (-CHO)

Chlorophyll b

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yellow and orange
expands the spectrum of light that provides
energy

Carotenoids

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electrons in pigment molecules
absorb photons of light energy, which results to what?

boosting electrons to a higher energy level

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Carotenoid functions

Antenna pigments
Photoprotection *

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the condition in which all its
electrons are in their normal, lowest-energy
levels (dissipates as heat or as an emission of
light of a longer wavelength than the absorbed
light, fluorescence)

Ground state

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Reactions where
* Light energy is transferred to ATP and NADPH
* Water molecules are split, releasing O2

Light-dependent reactions

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Reactions where
Energy in ATP and NADPH drives synthesis of
glucose and other carbohydrates from CO2 and
water

Light-independent reactions

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include chlorophyll, accessory pigments
organized with pigment-binding proteins into
antenna complexes

Photosystems

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special pair of chlorophyll a molecules
release energized electrons to acceptor

Reaction center

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reaction center for photosystem I

P700

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reaction center for photosystem II

P680

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Electrons lost from photosystem II are
replaced by what?

photolysis of water molecules,
which dissociate into hydrogen ions and
oxygen

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* Process by which light energy breaks down a molecule such as water

* Photolysis

* A light-driven reaction that attaches a phosphate group to a molecule

Photophosphorylation

* Electrons cycle within photosystem I

Cyclic photophosphorylation

* Electrons move from water to photosystem II, to photosystem I, to NADPH

Noncyclic photophosphorylation

It is an example of how organisms harvest energy from their environment

Energy Flow in Photosynthesis

first step in light- dependent reactions

* Entry of electrons from a photosystem into the electron transfer chain

* ATP forms in the _______ * Electron energy is used to build up a ___________ across the membrane * H+ flows through __________, which attaches a phosphate group to _____

-stroma -H+ gradient -ATP synthase -ADP

Electrons lost from a photosystem enter an _____________________ in the thylakoid membrane

electron transfer chain

Organized arrays of enzymes, coenzymes, and other proteins that accept and donate electrons in a series

Electron transfer chains

Outputs of Non-cyclic Electron Flow

* ATP (non-cyclic photophosphorylation) * O2 * NADPH

It is synonymous to Photolysis of Water

(Hill reaction)

PS I and II are _____segregated

spatially

PS I and ATP synthase located exclusively in the ______thylakoids and _________ of thylakoids (regions where the membranes are not paired to form grana)

-stroma -non-appressed regions

PS II is present only in _______ regions of grana thylakoids

appressed

uniformly distributed throughout both regions

Cytochrome b6/f complex

* ETC 1 (P680) * Primary electron acceptor: _____________ * via carriers : p_______________ -- __________ → ______________→ ____________ (PC)

-pheophytin (pheo) -plastoquinone (PQ) -H carrier -cyt b/f complex -plastocyanin

ETC 2 (P700) * Primary electron acceptor:____ *_______________→ NADPH

-A0 - Ferredoxin (Fd)

The coenzyme NADPH forms in a pathway that also releases _______

oxygen

Enzyme-mediated reactions that build sugars in the stroma of chloroplasts

Calvin-Benson cycle

* Extraction of carbon atoms from inorganic sources (atmosphere) and incorporating them into an organic molecule * Builds glucose from ____ * Uses bond energy of molecules formed in light-dependent reactions (ATP, NADPH)

-Carbon fixation -CO2

3 phases of carbon fixation

* CO2 uptake phase * Carbon reduction phase * RuBP regeneration phase

* Enzyme rubisco * (ribulose bisphosphate carboxylase/ oxygenase) * combines CO2 with ribulose bisphosphate (RuBP), a five-carbon sugar * forms 3-carbon phosphoglycerate (PGA)

CO2 Uptake Phase

what does For each 6 CO2 fixed

* 12 G3P are produced * 2 G3P leave cycle to produce 1 glucose

* Remaining G3P molecules are modified to regenerate RuBP

RuBP Regeneration Phase

dissipate excess ATP and reducing power under conditions of high light intensity, thus preventing damage to chloroplast

Photorespiration

Cells under photorespiration

Chloroplasts, Peroxisome, Mitochondrion

* Rubisco acting as an oxygenase, catalyzes the reaction of RuBP and O2 forming phosphoglycolate (2-C compound) in addition to PGA in the chloroplast * Phosphoglycolate is rapidly converted to _________ * PR is a light-induced respiration occurring in green tissues as a response to ______________________

-glycolate -low CO2/O2 ratio

_____________: RuBP is oxygenated to form phosphoglycolate → glycolate

Chloroplast

_____________:glycolate is oxidized /converted to glycine

Peroxisome:

_________: glycine (2 molecules) metabolized into serine (releasing ammonia and CO2)

Mitochondria

* occurs more at high temperature and high irradiance due to: * the substrate specificity of rubisco shifts in favor of O2 as temperature increases; * leaf of CO2 concentration becomes very low at high irradiance largely due to rapid photosynthesis; the low [CO2] favors oxygenation

Photorespiration

* Internal cellular recycling of 3 gases: CO2, O2 and NH3 * Glycolate synthesis in the leaf can decrease toxic levels of oxygen * Physiological defense against high irradiance and thermal load (dissipation of excess photochemical energy) * Contribution to cell amino acid pool (Gly; Ser) * Response to niche diversificaiton scheme

Importance of Photorespiration

Examples of C3:

rice, tobacco, soybean

C3 is about Each turn of the cycle: fix one molecule of CO2; input: ____________- and ______________; product: G3P/Triose phosphate (TP) * 1 TP = _____________ : 6 CO2 = _____________

-3 ATP and 2 NADPH -3 turns (3 CO2) -hexose

C4 or __________________ examples:______________________ * Substrate: __________ instead of CO2 * First Stable Product: ___________________

-Hatch-Slack Pathway -corn; sugarcane -HCO3 -4-C oxaloacetate

* It reduces photorespiration and water loss

C4 or Hatch-Slack Pathway

____________________ (CAM) * similar to C4 pathway * PEP carboxylase fixes carbon at night * in _______________ cells * Calvin cycle occurs during the day * Examples: ________________________

-Crassulacean acid metabolism -mesophyll -succulents, cactus, pineapple

* main form of translocatable carbohydrates in plants * synthesized outside the chloroplast ---cytosol

* Sucrose

* synthesized in chloroplast stroma where it is built up during the day and used as energy source at night * produced and stored in amyloplast

* Starch

Factors Affecting Photosynthesis

Light CO2 availability Temperature Water Nutrients Leaf Age Carbohydrate translocation