Chapter 14 Photosynthesis, calvin benson cycle)

Electron transport chain

A series of membrane-embedded electron carrier molecules that facilitate the movement of electrons from a higher to a lower energy level, as in oxidative phosphorylation and photosynthesis.

Chemiosmotic coupling

Mechanism that uses the energy stored in a transmembrane proton gradient to drive an energy-requiring process, such as the synthesis of ATP by ATP synthase or the transport of a molecule across a membrane.

Mitochondria role in ATP production

Oxidative phosphorylation in mitochondria produces most of the ATP used in eukaryotic cells

Mitochondria role in NAD+ regeneration

NAD+ is required for glycolysis to take place and NAD+ is regenerated when NADH donates electrons to the ETC

Mitochondrial matrix

Large internal compartment within a mitochondrion. Only lets small molecules pass through due to inner mitochondria membrane impermeability. Where the citric acid cycle takes place

Cristae

Folds within the inner mitochondrial matrix that increases its surface area

Inner mitochondrial membrane

Folded into numerous cristae, contains most of the proteins that carry out oxidative phosphorylation and transport molecules that move selected molecules in and out of matrix. Where the electron transport chain takes place

Outer mitochondrial membrane

Contains large channel forming proteins called porins and is located on the outside of the mitochondria

Intermembrane space

Space between the inner and outer mitochondrial membranes where enzymes use ATP to move nucleotides and proteins

Respiratory enzyme complexes

Set of 3 proteins in the inner mitochondrial membrane that facilitates the transfer of electrons from NADH to oxygen while pumping protons into the intermembrane space in the electron transport chain

NADH dehydrogenase

First complex in the ETC which accepts electrons from NADH to convert into a proton and 2 high energy electrons for mobile electron carriers to move onto he next complex

Ubiquinone (Q)

Hydrophobic, lipid soluble molecules embedded within the inter mitochondrial membrane that can accept or donate electrons from complexes in the electron transport chain

Cytochrome C

A small water-soluble hemoprotein that can carry one electron at a time

pH gradient in electron transport chain

Pumping of electrons into the matrix increases its pH than the intermembrane space

Voltage gradient in electron transport chain

Pumping protons makes the matrix more negative while the intermembrane space becomes more positive

ATP synthase

Abundant membrane associated enzyme complex that catalyzes the formation of ATP from ADP and inorganic phosphate during oxidative phosphorylation and photosynthesis through H+ movement from matrix to intermembrane space by moving through pump and pushing carrying motor

Rotary motor (c-ring)

Protons move through this structure causing a conformation change where each proton that goes through rotates it 1/12th round. Releases all protons when it has moved all the way around. Rotation causes conformation changes in parts of the ATP synthases complex allowing 3ATP to be synthesized from 3ADP and 3Pi

ADP/ATP translocase

A protein that acts as an antiporter, pumping one molecule of ATP out of the matrix while importing one molecule of ADP in to transport the ATP formed by ATP synthase.

Photosynthesis

The process by which plants, algae, and some bacteria use the energy of sunlight to drive the synthesis of organic molecules from carbon dioxide and water

Stroma

In a chloroplast, the large interior space that contains the enzymes needed to incorporate CO2 into sugars during the carbon-fixation stage of photosynthesis, equivalent to the matrix of a mitochondrion. Location of the Calvin-Benson cycle and carbon fixation.

Thylakoid

In a chloroplast, the flattened, disc like sac whose membranes contain the proteins and pigments that convert light energy into chemical bond energy during photosynthesis C

Thylakoid lumen

The fluid-filled interior enclosed by the thylakoid membrane in a chloroplast where protons are pumped into during the light dependent photosynthesis reactions

Thylakoid membrane

The site of light reactions which encloses a space known as the thylakoid lumen. This is where all the light dependent reactions occur.

Chlorophyll

Light-absorbing green pigment that plays a central part in photosynthesis

Light reactions

In photosynthesis, the set off reactions that converts the energy of sunlight into chemical energy in the form of ATP and NADPH (stage 1 of photosynthesis)

Photosystem

Large multiprotein complex containing chlorophyll that captures light energy and converts it into chemical bond energy; consists of a set of antenna complexes and a reaction center

Antenna complex

In chloroplasts and photosynthetic bacteria, the part of the membrane bound photosystem that captures energy from sunlight; contains an array of proteins that bind hundreds of chlorophyll molecule and other photosensitive pigments

Reaction center

In photosynthetic membranes, a protein complex that contains a special pair of chlorophyll molecules; it performs the photochemical reactions that convert the energy of photons (light) into high-energy electrons for transport down the photosynthetic electron transport chain

Carbon fixation

Process by which green plants and other photosynthetic organisms incorporate carbon atoms from atmospheric carbon dioxide into sugars. The second stage of photosynthesis

Photosystem II

First photosystem center in light dependent reactions found in the thylakoid membrane. Uses light energy to oxidize water molecules to release O2, H+ ions into thylakoid lumen and electrons. Energizes electrons with a special chlorophyll pair at reaction center after jumping from other chlorophylls. and passes it to electron carrier plastoquinone.

Photosystem I

Second photosystem in light dependent reactions found in the thylakoid membrane. Oxidizes plastocyanin using light energy which brings electrons to reaction center to be reenergized which then leaves to primary electron acceptor. Electron then goes from acceptor to short ETC and NADP+ reduces it into NADPH which gets accumulated in the stroma

ATP synthase in thylakoid

Located in the thylakoid membrane, it uses the H+ from the transfer of electrons with plastoquinone in PS1 and uses the gradient to create ATP from ADP which accumulates in the stroma.

Carbon fixation formula

CO2 + NADPH + ADP → CH2O + NADP+ + ADP + Pi

RuBisCo

Super slow enzyme that catalyzes reaction 3 times a second only and is therefore extremely abundant in the cell to fix CO2 into a 6 carbon intermediate to be able to split into two 3 carbons to regenerate RuBP

Carbon fixation reaction with RuBisCo enzyme

Ribulose 1,5 bisphosphate (RuBP, C5) + CO2 → C6 intermediate

C6 is split → 2 molecules 3-phosphoglycerate (C3)

What occurs in the stroma?

• ADP + Pi → ATP (Via ATP synthase) (at outer face of thylakoid membrane

• CO2 fixed into carbohydrate (via rubisco)

• NADPH → NADP+

• Synthesis of glucose (and cytoplasm)

What occurs within the thykaloid membrane?

• Photons absorbed and funneled

• Electrons are excited and transported

What occurs at the thylakoid lumen

• Oxygen generated and H+ accumulates

• Water is split into oxygen, 2H+ and 2 electrons (at inner face of thylakoid membrane)

What occurs across the thylakoid membrane

• H+ is pumped (from stroma into lumen)

• H+ flows through ATP synthase (from lumen to stroma)

Inputs and outputs of light dependent interactions

Inputs: 2 H2O, 2NADP⁺ , (3ADP + Pi)

Outputs: 1 O2, 2NADPH, 3ATP

Inputs and outputs of light independent reaction

Inputs: 1 CO2, 3 ATP, 2 NADPH

Outputs: 2 molecules of 3-PGA (phosphoglycerate), (3 ADP + P_i), 2NADP⁺

Chloroplast

Double-membrane organelle in plant cells where photosynthesis occurs; converts light energy into chemical energy stored in carbohydrates.

Chloroplast envelope

Two membranes surrounding the chloroplast: a permeable outer membrane containing porins and an impermeable inner membrane containing specific transporters.

Thylakoid

Flattened membranous sac inside chloroplasts containing the machinery for light-dependent reactions.

Thylakoid membrane

Membrane containing photosystems, electron transport proteins, and ATP synthase; site of light absorption, electron transport, and proton pumping.

Thylakoid lumen

Innermost compartment enclosed by the thylakoid membrane where oxygen is produced and protons accumulate during light-dependent reactions.

Grana

Stacks of thylakoid sacs inside chloroplasts; their lumens are connected to form one continuous thylakoid compartment.

Chloroplast endosymbiotic theory

Theory that chloroplasts evolved from photosynthetic bacteria engulfed by an early eukaryotic cell.

Light-dependent reactions

Reactions occurring in the thylakoid membrane that use light energy to split water, generate oxygen, create a proton gradient, and produce ATP and NADPH.

Photosystem

Functional unit of pigment molecules and proteins in the thylakoid membrane that absorbs light energy and uses it to excite electrons

Antenna complex

Collection of pigment molecules, including chlorophylls and carotenoids, that absorb photons and transfer the energy to a photosystem's reaction center.

Reaction center

Region of a photosystem where absorbed light energy drives electron excitation and transfer.

Carotenoids

Accessory photosynthetic pigments that absorb light and transfer energy to reaction centers.

Photolysis of water

Light-driven splitting of water into electrons, protons (H+), and oxygen; supplies electrons to photosystem II and contributes protons to the thylakoid lumen.

NADP+

Oxidized electron carrier that accepts high-energy electrons and H+ at the end of the light-dependent reactions to become NADPH.

NADPH

Reduced electron carrier produced during light-dependent reactions that provides high-energy electrons for CO2 reduction during the Calvin-Benson cycle.

Light-dependent proton gradient

Difference in H+ concentration across the thylakoid membrane; created by water splitting and proton pumping from the stroma into the lumen, driving ATP synthesis.

Light-independent reactions

Reactions occurring in the chloroplast stroma that use ATP and NADPH from light-dependent reactions to fix CO2 into carbohydrates.

Calvin-Benson cycle (Calvin cycle)

Cyclic series of reactions in the stroma that uses ATP and NADPH to convert CO2 into carbohydrate while regenerating RuBP.

Carbon fixation

Process of incorporating inorganic CO2 into an organic carbon molecule, beginning carbohydrate synthesis during the Calvin-Benson cycle.

RuBP (ribulose-1,5-bisphosphate)

Five-carbon molecule that combines with CO2 during the Calvin-Benson cycle to form an unstable six-carbon intermediate.

3-PGA (3-phosphoglycerate)

Three-carbon molecule produced when the unstable six-carbon product of carbon fixation splits; converted into carbohydrate using ATP and NADPH.

Glyceraldehyde-3-phosphate (G3P)

Three-carbon sugar produced during the Calvin-Benson cycle; one of the 6 formed leaves the cycle and is used to synthesize larger carbohydrates such as fructose and sucrose.

RuBP regeneration

Process in the Calvin-Benson cycle that uses ATP to regenerate RuBP so the cycle can continue fixing CO2.

Photosynthesis vs. cellular respiration

Cellular respiration breaks down glucose using oxygen to release energy, producing CO2 and H2O; photosynthesis uses light energy to convert CO2 and H2O into carbohydrates and oxygen.

Mitochondria vs. Chloroplast

Similarities: Contains inner and outer membranes, both has DNA and ribosomes

Differences: Inside of mitochondria is matrix, inside of chloroplast is stroma. Chloroplasts have thylakoids which have membrane. Chloroplasts are much larger than mitochondria.

Calvin-Benson cycle step 1

Rubisco attaches 3 inorganic CO2 molecule to ribulose 1,5- biphosphate (RuBP) which creates unstable 6 carbon intermediate which is split into 2 molecules of 3-phosphoglycerate (3-PGA). This makes 6 molecules of 3-PGA.

Calvin-Benson cycle step 2

ATP is used to convert the 6 molecules of 3-phosphoglycerate (3-PGA) into 1,3 biphosphoglycerate. This turns 6 ATP into 6 ADP.

Calvin-Benson cycle step 3

6 NADPH donates electrons for reducing power to 6 1,3 biphosphoglycerate which forms 6 glyceraldehyde 3- phosphate (G3P) One of these G3P leaves to form other macromolecules. The NADPH turns into NADP+

Calvin-Benson cycle step 4

The 5 glycerladehyde 3-phosphate (G3P) are phosphorylated to form 3 molecules of ribulose 1,5 bisphosphate (RuBP) which uses 3 ATP that turns into ADP.