topic 6: phototrophic metabolism Flashcards
label regions of the chloroplast involved in photosynthesis
The chloroplast is an organelle found in plant cells and eukaryotic algae that conducts photosynthesis. It has several distinct regions that are involved in the photosynthesis process:
Outer Membrane: This is a permeable membrane that surrounds the entire chloroplast and serves as a boundary between the chloroplast and the cytosol.
Inner Membrane: The inner membrane is less permeable and encloses the stroma. It contains transport proteins that regulate the passage of materials into and out of the chloroplast.
Stroma: The stroma is a fluid-filled inner space where the Calvin cycle (also known as the light-independent reactions or the dark reactions) occurs. This is where CO2 is fixed into sugars.
Thylakoid Membrane: Within the stroma is a system of interconnected membranous sacs called thylakoids. The thylakoid membrane contains the chlorophyll and is the site of the light-dependent reactions of photosynthesis.
Thylakoid Space (Lumen): This is the interior of the thylakoid sacs. The space inside plays an essential role in the light-dependent reactions, particularly in the generation of a proton gradient for ATP synthesis.
Grana (singular: Granum): These are stacks of thylakoids. The grana are connected by stroma thylakoids, sometimes referred to as lamellae. Light-dependent reactions also occur on the membranes of the grana.
Photosystems I and II: These are protein complexes in the thylakoid membrane that contain light-absorbing pigments including chlorophyll. They are vital for the light-dependent reactions, capturing solar energy and converting it into chemical energy.
ATP Synthase: Located in the thylakoid membrane, this enzyme helps synthesize ATP from ADP and inorganic phosphate during the light-dependent reactions.
NADP+ Reductase: Also located in the thylakoid membrane, this enzyme is involved in the final step of the light reactions, producing NADPH from NADP+ and H+.
Here’s how the photosynthetic process uses these components:
Light-dependent reactions: These occur in the thylakoid membranes and involve the absorption of light by photosystems II and I, water splitting (photolysis), oxygen release, proton gradient formation across the thylakoid membrane, and ATP and NADPH production.
Calvin cycle: This takes place in the stroma and uses the ATP and NADPH generated by the light-dependent reactions to fix carbon dioxide into glucose.
These regions and processes work together to convert light energy into chemical energy in the form of ATP and NADPH, which are then used to convert carbon dioxide into glucose in the Calvin cycle.
Describe how solar energy is captured by antenna pigment molecules and transferred to reaction centre pigments with short but precise
Solar energy is captured in the chloroplasts of plant cells through a series of pigment molecules known as antenna pigments, which are primarily chlorophylls and accessory pigments like carotenoids. Here’s a concise description of the process:
Photon Absorption: Antenna pigments absorb photons of light. Each pigment molecule is tuned to absorb light at specific wavelengths. This absorption raises the energy level of electrons within the pigment molecules to a higher energy state, known as an excited state.
Energy Transfer: Once excited, the energy (not the electron itself) is transferred from one pigment molecule to another within the antenna complex. This transfer is a resonance energy transfer, also known as Förster resonance energy transfer (FRET). It occurs rapidly and efficiently through dipole-dipole coupling without any significant loss of energy.
Migration to Reaction Center: The energy migrates through the antenna complex until it reaches a specialized pair of chlorophyll a molecules in the reaction center. These chlorophyll a molecules are finely tuned to have a slightly lower energy state than the surrounding antenna pigments, which facilitates the energy transfer towards them.
Charge Separation: Once the reaction center chlorophyll a molecules (P680 in Photosystem II and P700 in Photosystem I) receive the energy, an electron is excited to a higher energy level with sufficient potential to be transferred to a nearby primary electron acceptor, creating a charge separation. This marks the beginning of the electron transport chain in the light-dependent reactions of photosynthesis.
This highly coordinated process allows plants to efficiently capture solar energy and initiate the conversion of that energy into a chemical form, which is utilized in the synthesis of glucose.
descirbe the major steps in the flow of energy though the photosynthetic electron transport chain
The photosynthetic electron transport chain (ETC) is a sequence of biochemical reactions that convert light energy into chemical energy in the form of ATP and NADPH, which are then used to fix carbon dioxide during the Calvin cycle. The major steps in the flow of energy through the photosynthetic electron transport chain are as follows:
Photon Absorption: Photosystem II (PSII) absorbs light energy, which excites electrons in the chlorophyll pigment. This is the initial step where solar energy enters the ETC.
Water Splitting and Oxygen Evolution: The excited electrons leave PSII, creating an electron deficit. To fill this deficit, an enzyme associated with PSII splits water molecules into electrons, protons (H+), and oxygen (O2). The oxygen is released as a byproduct.
Plastoquinone Reduction: The excited electrons are transferred to a small lipid-soluble carrier molecule in the thylakoid membrane called plastoquinone (PQ), reducing it to plastoquinol (PQH2).
Proton Gradient Formation: As plastoquinol carries the electrons through the thylakoid membrane, it also transports protons into the thylakoid space (lumen), contributing to a proton gradient.
Cytochrome b6f Complex: Plastoquinol delivers the electrons to the cytochrome b6f complex. The energy released from this transfer is used to pump more protons into the thylakoid space, further increasing the proton gradient.
Photosystem I Excitation: Electrons move from the cytochrome b6f complex to Photosystem I (PSI) via a protein called plastocyanin. Light energy is again absorbed by PSI, which further excites the electrons to an even higher energy level.
NADP+ Reduction: The high-energy electrons from PSI are eventually transferred to the enzyme NADP+ reductase, which uses them to convert NADP+ and H+ into NADPH.
ATP Synthesis: The proton gradient across the thylakoid membrane has a higher concentration of protons in the thylakoid space than in the stroma. This gradient powers the enzyme ATP synthase to synthesize ATP from ADP and inorganic phosphate.
Through these steps, the photosynthetic ETC produces ATP and NADPH, which are essential for driving the synthesis of carbohydrates from carbon dioxide and water in the Calvin cycle, ultimately storing the energy from sunlight in the form of chemical bonds.
describe/ draw how electron flow through photosynthetic ETC results in the formation of an electrochemical gradient, ATP and NADPH short answer
1.Electron Excitation and Water Splitting: Light energy excites electrons in Photosystem II (PSII), and these high-energy electrons are passed to the plastoquinone (PQ) pool. To replace the lost electrons, PSII oxidizes water, releasing oxygen and protons into the thylakoid lumen, contributing to the proton gradient.
2.Electron Transport and Proton Pumping: The electrons are transferred from PQ to the cytochrome b6f complex. As electrons move through this complex, additional protons are pumped from the stroma into the thylakoid lumen, enhancing the proton gradient.
3.Electron Transfer to Photosystem I: Electrons move to Photosystem I (PSI) through plastocyanin (PC). PSI re-excites the electrons with another photon capture.
4.NADPH Formation: These re-energized electrons are transferred to NADP+ via the enzyme ferredoxin-NADP+ reductase, reducing it to NADPH.
5.ATP Synthesis: The proton gradient across the thylakoid membrane, now high inside the lumen and low in the stroma, drives protons back into the stroma through ATP synthase. This flow of protons powers ATP synthase to catalyze the conversion of ADP and inorganic phosphate into ATP.
Outline the interdependence of light-dependent and light-independent reactions
The light-dependent and light-independent reactions of photosynthesis are intrinsically interconnected, each set of processes relying on the other to sustain the cycle of energy conversion that powers plant growth and metabolism. Here is how they are interdependent:
1.Products of Light-Dependent Reactions Drive Light-Independent Reactions:
The light-dependent reactions occur in the thylakoid membranes and produce ATP and NADPH.
These molecules are then used as the energy and reducing power, respectively, for the light-independent reactions, also known as the Calvin cycle.
2.The Calvin Cycle Consumes ATP and NADPH:
The ATP and NADPH generated by the light-dependent reactions are consumed in the Calvin cycle to convert carbon dioxide into glucose.
Without the continuous supply of ATP and NADPH from the light-dependent reactions, the Calvin cycle would stall, and the synthesis of sugars would cease.
3.The Calvin Cycle Regenerates ADP and NADP+:
The Calvin cycle uses the energy and electrons from ATP and NADPH, converting them back into ADP and NADP+.
The ADP and NADP+ are then recycled back into the light-dependent reactions to be re-energized and reduced again, maintaining the flow of the cycle.
4.Stomatal Gas Exchange:
The light-independent reactions rely on the diffusion of CO2 into the leaves through the stomata.
The oxygen produced as a byproduct of the light-dependent reactions is expelled through these same stomata.
- Diurnal Cycle Regulation:
Light-dependent reactions, as the name suggests, require light and typically occur during the day.
The light-independent reactions, while not directly driven by light, often coincide with the light-dependent reactions because the necessary substrates (ATP and NADPH) are readily available during daylight hours.
- Feedback Regulation:
High concentrations of the products of the Calvin cycle can regulate the light-dependent reactions, providing a feedback mechanism that balances the rates of both processes.
In summary, the light-dependent reactions capture solar energy and convert it into chemical energy, which is then used by the light-independent reactions to fix carbon dioxide into organic compounds. The Calvin cycle, in turn, uses the products of the light-dependent reactions and regenerates their substrates, creating a cycle that is continuous as long as light is available.
Draw the three major stages of the carbon fixation (calvin cyle) reactions, and the important inputs and outputs of each
The Calvin cycle, also known as the carbon fixation cycle, can be broadly divided into three major stages: carbon fixation, reduction, and regeneration of the acceptor molecule. Here’s a brief overview of each stage with their important inputs and outputs:
1.Carbon Fixation:
Inputs: CO2, Ribulose bisphosphate (RuBP), and the enzyme Rubisco.
Outputs: 3-phosphoglycerate (3-PGA).
Process: CO2 is attached to RuBP by the enzyme Rubisco, resulting in an unstable 6-carbon intermediate that immediately splits into two molecules of 3-PGA.
2.Reduction:
Inputs: ATP, NADPH, and 3-PGA from the first stage.
Outputs: Glyceraldehyde-3-phosphate (G3P), ADP, NADP+, and Pi (inorganic phosphate).
Process: ATP and NADPH are used to convert the 3-PGA molecules into G3P. This is a two-step process where ATP first phosphorylates 3-PGA, and then NADPH transfers electrons to it, creating G3P.
3.Regeneration of RuBP (the CO2 acceptor):
Inputs: G3P, ATP.
Outputs: RuBP, ADP, and Pi.
Process: Some G3P molecules exit the cycle to be used in the synthesis of glucose and other carbohydrates, while the rest are used in a series of reactions that consume ATP and regenerate RuBP, allowing the cycle to continue.
The Calvin cycle turns three times to fix three molecules of CO2 and to form one molecule of G3P that can exit the cycle to contribute to the formation of glucose and other sugars. Six turns are required to generate one molecule of glucose (C6H12O6).
Compare and contrast ATP production in respiration and in photosynthesis (how is oxidative phosphorylation like/different from photophosphorylation?)
ATP production is a fundamental process in both respiration (specifically in oxidative phosphorylation) and photosynthesis (specifically in photophosphorylation). Despite their shared goal of synthesizing ATP, the processes have distinct characteristics and mechanisms:
Similarities between Oxidative Phosphorylation and Photophosphorylation:
1.Chemiosmosis: Both processes use a chemiosmotic mechanism to produce ATP, which involves the generation of a proton gradient across a membrane and the subsequent flow of protons back across the membrane through ATP synthase, driving the production of ATP from ADP and inorganic phosphate.
2.Electron Transport Chain (ETC): Both involve an electron transport chain where electrons move through a series of membrane-bound carriers, releasing energy that is used to pump protons across a membrane and generate the proton gradient.
3.Membrane-bound ATP Synthase: The enzyme ATP synthase is utilized in both processes to produce ATP, exploiting the potential energy of the proton gradient.
Differences between Oxidative Phosphorylation and Photophosphorylation:
1.Energy Source:
Oxidative phosphorylation uses the energy released from the oxidation of nutrients, such as glucose, to pump protons and create an electrochemical gradient.
Photophosphorylation uses light energy to excite electrons, which are then used to create the proton gradient.
2.Location:
Oxidative phosphorylation occurs in the mitochondria in both eukaryotic and prokaryotic cells (in the latter, across the plasma membrane since they lack mitochondria).
Photophosphorylation occurs in the chloroplasts of photosynthetic organisms (e.g., plants, algae).
3.Electron Donors and Acceptors:
In oxidative phosphorylation, the primary electron donor is NADH (or FADH2), and the final electron acceptor is molecular oxygen, producing water.
In photophosphorylation, the initial electron donors are water molecules in Photosystem II (PSII), and the final electron acceptor varies between NADP+ in non-cyclic photophosphorylation (producing NADPH) and the initial electron donor itself in cyclic photophosphorylation.
- End Products:
Oxidative phosphorylation’s primary end products are ATP and water (from the reduction of oxygen).
Non-cyclic photophosphorylation results in the production of ATP and NADPH (and O2 as a byproduct of water splitting), while cyclic photophosphorylation mainly produces ATP.
5.Oxygen Role:
In oxidative phosphorylation, oxygen is essential as the final electron acceptor.
In photophosphorylation, oxygen is a byproduct (in non-cyclic electron flow), produced when water is split to provide electrons to the ETC.
Flow of Electrons:
In oxidative phosphorylation, electrons flow unidirectionally from donors to oxygen.
In photophosphorylation, electrons can flow in a cyclic manner (only in cyclic photophosphorylation) where they return to the photosystem after passing through the ETC.
Understanding these similarities and differences helps to illustrate how life has evolved to harness energy in various forms — chemical bonds in nutrients or direct energy from sunlight — to drive the synthesis of ATP, the universal energy currency of the cell.
Differentiate between cyclic and non-cyclic (linear) electron flow and its importance in photosynthesis
Alright, imagine you’re playing with two different types of toy car tracks. One is a loop that goes round and round, and the other starts at one end and finishes at the other.
In photosynthesis, plants use sunlight to make energy, just like your toy cars need a push to start moving. The plants have two tracks to use the sunlight: the cyclic track and the non-cyclic (linear) track.
Cyclic Electron Flow:
This is like the loop track for your toy car. In cyclic electron flow, the electron starts in a chlorophyll molecule in the plant, gets a push from the sunlight, and goes around the track. It ends up back where it started, ready to go around again.
This track doesn’t make oxygen; it’s just for making a little bit of ATP, which is like the energy or “battery power” that the plant needs to do other stuff.
Non-Cyclic (Linear) Electron Flow:
Now, the non-cyclic flow is like the track that starts at one end and stops at the other. The electron starts in one place, gets a push from the sunlight, and moves down the track, passing through different molecules and making energy (ATP) and a special energy carrier called NADPH.
At the end of this track, the electron doesn’t go back to the start; instead, it gets attached to a new molecule, and oxygen gas is made as a byproduct. This is important because we need oxygen to breathe!
Importance in Photosynthesis:
Plants need to make ATP for energy and NADPH for building stuff, like sugars.
The non-cyclic track is really important because it makes both ATP and NADPH, and it also makes oxygen, which is pretty important for us and for animals.
The cyclic track is like a backup. It makes extra ATP if the plant needs more energy.
So, the plant can choose between two tracks depending on what it needs: more energy (ATP) or making stuff to grow and oxygen for the environment. It’s like having two different playsets; you choose the one that’s the most fun for what you want to do!
