Describe the similarities and differences in the production of ATP in the mitoch

ID: 82625 • Letter: D

Question

Describe the similarities and differences in the production of ATP in the mitochondrion (oxidative phosphorylation) and chloroplast (photophosphorylation). Where is high [H+] stored (a form of potential energy) in each organelle? What protein complex releases this potential energy in mitochondria? in chloroplasts? What is created as a result? What is the electron donor (reducing agent) that starts electron transport in each? What is the final electron acceptor for each? what compound forms when the e- are accepted? What is the immediate (proximal) source of energy for the "light independent" (dark) reactions? What is the ultimate source of energy for these reactions? What waste product of the light reactions is key to many forms of life on Earth? How/why is this waste product formed in the light reactions? What similarities can you describe between the inner mitochondrial membrane and the thylakoid membrane? What differences can you describe?

Explanation / Answer

Que-4:

Chemiosmosis in photosynthesis

Chemiosmosis in cellular respiration

The hydrogen ions are pumped against their concentration gradients (from lower to higher concentration).

Enzymes diffuse from higher to lower concentration gradients, the energy released is utilized to generate ATP.

Redox reactions occur during electron transport systems, the energy released is utilized to generate ATP

Chemiosmosis in cellular respiration occurs in the mitochondria.

No organic compound is needed for energy transfer in photosynthesis, this is actually mediated by chloroplasts that transform light energy into ATP

Hydrogen ions are transported from the mitochondrial membrane to the intermembrane space.

ATP synthase is located in inner mitochondrial membrane

The thylakoid lumen pH is to be lower during the day time relative to the night because day time "light reactions including photosynthesis" in the presence of water predominates compared to nights result in higher photooxidation and water splitting to generate more "proton gradient" across the thylakoid lumen compared to the stroma finally low pH. The photosynthesis rate and light reaction & photooxiation rate of water molecules is lesser during night time and majority of stomata is closed compared to day time, where light depedent reactions are higher result day-night difference in pH. These are resulting in changes in rate of hydrogen ions are transported from the stroma to the thylakoid space

During the light reactions of photosynthesis, the NADP+ is reduced to NADPH which is an essential step in creating proton gradient across the chloroplast membrane, in this reaction ATP and NADPH (electron transport molecule) are produced. This NADPH is essential for light-independent reactions, which act as electron carrier and its reducing activity is essential for the conversion of carbon dioxide and H2O into organic compounds (such as sugars and proteins).

Where is high (H+) stored (a form of potential energy) in each organelles?

The H+ stored in inner mitochondrial membrane and mitochondrial space in mitochondria where as H+ ions are stored in stroma in case of chloroplasts to mediate ATP synthesis

What protein complex releases this potential energy in mitochondria? in complexes in chloroplast?

The cytochrome c-oxidase-c, cytochorme –c reductase in mitochondria are going to release potential energy as explained below, whereas P700, P680 photosystems with cytochrome b6- complexes have involved in mediating energy synthesis apart from F0-F1- aATP synthase complexes

The state of oxidation in abundant NADH in the absence of O2 is reduced because NADH is a strong electron donor whereas oxygen is electron acceptor. In the absence of electron acceptor, the chances of electron transfer is lower from coenzyme Q to cytochrome C result in no generation of ATP during oxidative phosphorylation in electron transport.

Part-:b

In the higher abundance of O2 even NADH is exhausted, there is an electron donor i.e. FADH2 (quinone) to send electrons to electron acceptor O2 through coenzyme Q to cytochrome C finally generation of ATP during oxidative phosphorylation. The state of oxidation still occurs during electron transport

The energy derived from the movement of H+ ions down an electrochemical gradient from the intermembrane space into the matrix is used to derive the synthesis of ATP. There are total "three" (3) catalytic sites at Fernadez-Moran (F0-F1) particles therefore total 3 H+ ions must be moved into the matrix to generate 1 mole of ATP ---> H+/ATP = (total no of c-subunits at F0/F1 of mitochondria) / 3

What is created as a result?

In mitochondria, ATP is generated whereas in chloroplasts, both NADH, ATP are generated

What is the final electron acceptor for each? what compound forms when the e- are accepted?

The final electron acceptor in photophosrylation & oxidative phosphorylation is oxygen

Differences between photorespiration and cellular respiration:

1. There is variety of disparities between oxidative phosphorylation associated cellular respiration in mitochondria compared to the photophosphorylation that is taking place in chloroplasts.

2. Oxidized organic molecules enable in delivering high energy electrons into the electron transport chain but in chloroplasts water is the crucial and predominant source of protons to synthesize energy in the form of ATP through photosystyem I (from FADH2 and QH2) and photosystem II using ATP synthase. If there is a high ratio of NADPH/NADP+ photophosphorylation increases due to high proton supply by the splitting of water molecules in presence of light.

2. Chloroplasts do not utilize sugar sources to produce energy in the form of ATP instead they use photons from light energy through light dependent and light independent reactions. These photons enable in getting electrons from water molecule splitting and further to transport them to the photosystem II and ATP synthase pump. During splitting of water molecule, molecular oxygen will be evolved.

Light-dependent reactions of photosynthesis: These are going to takes place in thylakoid membrane and lumen when light catalyses splitting of water molecules into protons (through proton gradient) and finally releases oxygen. These protons pumped according to concentration gradient across the lumen to generate ATP in the presence of ATP synthase.

Stroma:

Light independent reactions occur in a fluid filled cavity outside the thylakoid called as "stroma". In these reactions the product is glucose by the reaction happened between CO2 and other compounds.

3. Mitochondrial chemiosmosis –cellular respiration (through Fernadez Moran inner mitochondrial oxysomes particles) during cellular respiration obtain energy from chemical enzymatic breakdown of the organic food molecules (glucose, pyruvate, acetylcoA) to produce ATP in the presence of O2 consumption. During electron transport, the final electron acceptor is oxygen for oxidative phosphorylation. Therefore, it is going to "oxygen" that accepting electrons at the end of the electron transport chain to generate ATP via mitochondrial respiratory complex-I to V. Every 3 protons used to produce one ATP molecule. Inner membrane possess small protein channels known as porins in mitochondria & these channels promote the movement of any small molecules such as ATP through them

Similarities between photorespiration and cellular respiration:

Both mitochondrial cellular respiration and photorespiration, movement of electors occur through carriers on high electronegative side in the form of protons further this electron transport

In both mitochondrial cellular respiration and photorespiration, ATP synthase enzymatic complex with Fernandez-Moran (F1-F0) complex enables to produce ATP by the phosphorylation of adenosine diphosphate, which is by the addition of protons according to electrochemical gradient.

Proton reservoirs: The pumping protons are from mitochondrial matrix to inner mitochondrial membrane. In the same manner thylakoid membrane is proton reservoir by sending protons from stoma to thylakoid membrane.

Directions of electron transfer chain (ETC) in mitochondria is from NADH---> Complex I --> coenzyme Q --> complex III ---> cytochrome c ---> Complex IV finally oxygen acceptor.

Proton pump in electron transport chain takes place from Complex I which pumps considerably 4 protons (H+), whereas Complex III pumps nearly 4 protons (H+) finally Complex IV that pumps out two protons.

Net input in oxidative phosphorylation ----> NADH, ADP, O2, and net output in oxidative phosphorylation ----------> ATP, NAD+ and Water

Similarities:

The F0-F1 complexes involved in ATP synthesis

The different reduction potential of cytochorne" during electron transport is going to favor unidirectional electron flow across the energy -synthesizing organelle (mitochondria or chloroplast) from "electron carriers" such as NADH and FADH2 to O2. Therefore, ATP synthesis is prominent without defects due to these differences for the electron (H+) transport

These reduction potential differences across the cytochrome c reductase & cytochrome c oxidase will promote efficient “proton motive force generation to drive proton movement across the mitochondrial membrane to synthesize ATP in respiratory chain