Photosynthesis And Cellular Respiration

               The structure of Chloroplast and Mitochondria

 The structure of chloroplast:

• site of photosynthesis
• thylakoid membranes
• photosynthetic pigments to absorb light
• light generated ATP production
• H+ gradient across thylakoid membrane 

The following picture show the structure of chloroplast. Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. Chloroplasts absorb sunlight and use it in conjunction with water and carbon dioxide to produce sugars. Chloroplasts capture light energy from the sun to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.

The structure of mitochondria:

• site of respiration
• ATP production by oxidation of organic molecules / fats / amino acids
• H+ gradient across inner membrane

The following picture show organelle structure of mitochondria. Mitochondria is a membrane-enclosed organelle found in most eukaryotic cells that converts glucose in to a form of energy that our bodies can use which is ATP.

The structure of a chloroplast and a mitochondria have following similarities:

• both are double membrane organelles
• both contain DNA
• both contain ribosomes
• both have an electron transport chain
• both produce ATP by chemiomosis
• both contain ATP synthase /ATPase

  ATP energy count per step

ATP- Adenosine triphosphate is a nucleotide composed of the nitrogenous base adenine,the pentose sugar ribose and three phosphate radicals. When ATP loose its energy, a phosphoric acid is very fast split away and adenosine diphosphate (ADP) is formed. The vice versa reaction takes place during ATP forming. The energy stored in ATP's phosphate bonds as a battery, permitting the cell to save and use energy in response to changing metabolic demands.

                                 Respiration: 

Respiration is the biological process that occurs in the cytoplasm of the cell. Through respiration cells convert glucose into ATP through process called glycolysis. Floppy the familiar waste products of carbon dioxide (CO2) and water.

When enzymes break the third phosphate bond, energy is released and leave the free phosphorous group and a molecular of adenosine diphosphate (ADP).

ATP is used to provide energy in several different stages of respiration:

                                     1. Glycolysis

The following graph show glycolysis

1. Glycolysis, takes place outside of the cell's mitochondria. For each molecule of glucose, Two molecules of ATP are required for each molecule of glucose, these molecules convert glucose into a different compound, called fructose 6-phosphate.












                     


The graph show 4 step of glycolysis in Cellular Respiration:

  Step 1 Energy input phase: The cell uses 2 molecules of ATP as a source of energy to do some chemical rearrangements resulting in a 6 carbon sugar called fructose 1,6 biphosphate. The ATP here serves as activation energy. Generally in cellular respiration when molecules need to be rearranged ATP needs to be used. In this case the chemical rearrangements result in a molecule which can be easily split into two three carbon molecules.

Step 2 Breaking the fructose 1,6 biphosphate into to two three carbon molecules called PGAL The PGAL is a molecule from which energy can easily be harvested.

Step 3 Energy harvesting stage 1. 2 ADP are used to make two molecules of ATP.

Step 4 Energy harvesting stage 2. Two more ADP and 2 NAD+ molecules are used to make two molecules of NADH and two more molecules of ATP. This step also yields two pyruvate molecules. The pyruvate still have most of the original energy that was found in the original glucose molecule and the point of the of aerobic cellular respiration will be to harvest as much of that energy as possible.

                             2. Transition Reaction

In Transition Reaction, the two molecules of the 3-carbon pyruvate from glycolysis are converted into two molecules of the 2-carbon molecule acetyl Coenzyme A (acetyl-CoA).
Transition Reaction takes place in the matrix of the mitochondria. Transition reaction is the beginning of aerobic respiration, what mean that this phase will continue to take place as long as there is a sufficient amount of oxygen available in the mitochondria. If there is not oxygen, then the process of fermentation will begin.

Start product is Pyruvate 3C and End products are Acetyl CoA 2C, CO2 1C, coenzyme

 

                           3. Krebs Cycle

The following diagram show Krebs Cycle.

In Krebs Cycle energy derived from the stripping of carbon atoms from a citrate molecule will form ATP inside the mitochondria. ATP will create the carbon dioxide breathed out by living organisms.In the membrane of the mitochondria there is majority of ATP production. In the membrane of mitochondria is used Electron Transport Chain which use energetic hydrogen ions to join ADP and loose phosphate groups, creating ATP.

Explanation according to this diagram is:

a) Formation of acetyl CoA

Acetyl CoA is the raw material for citric acid cycle. Acetyl CoA by b-oxidation is formed from fatty acids and from pyruvic CoA to form Acetyl CoA. B-oxidation  is accelerated by a set of enzymes called pyruvic acid dehydrogenase. B-oxidation will removed 2 hydrogen atoms and one CO₂ molecule. Removing 2 hydrogen atoms and one CO2 molecule is called oxidative decarboxylation. In oxidative decarboxylation the 2 hydrogen atoms are accepted by NAD and NAD is converted into NADH.

b)Formation of citric acid

To form citric acid oxaloacetic acid and acetyl CoA have to fuse together. In citric acid formation are 6 carbon atoms. Citirc acid rection is catalysed by  citric acid synthetase.

c) Dehydration

Dehydration happen when citric acid respire dehydration and will form cis-aconitic acid. Dehydration is catalysed by the enzyme aconitase.

d) Hydration

Hydration is when the aconitic acid is hydrated and it forms isocitric acid. Hydratation is catalysed by the enzyme aconitase.

e) Dehydrogenation I

Dehydrogenation I  happen when isocitric acid pass through dehydrogenation in the presence of isocitric acid. When isocitric acid pass through dehydrogenation it will form oxalo succinic acid. Dehydrogenation I released 2 hydrogen atoms which are accepted by NAD⁺ to form NADH.

 

 

f) Decarboxylation

To form a-ketoglutaric acid the oxalo succinic acid undergoes decarboxylation. Decarboxylation is catalysed by decarboxylase. In decarboxylation one CO₂ is eliminated. Therefore the a-ketoglutaric acid has only 5 carbon atoms.

g) Oxidative decarboxylation

A-ketoglutaric acid is converted into succinyl CoA. Oxidative decarboxylation is catalysed by a-ketoglutaric acid dehydrogenase. Then  two hydrogen atoms are released and are transferred to NAD. NAD is then converted into NADH. The next step, the succinyl CoA is decarboxylated to succinic acid, this is catalysed by succinic acid thiokinase. CoA is liberated.

h) Oxidation

During oxidation succinic acid is oxidised to fumaric acid, when 2 hydrogen atoms are removed.  Oxidation is catalysed by succinic acid dehydrogenase. Then the hydrogen atoms are accepted by FAD and it forms FADH₂.

i) Hydration

Hydration is when fumaric acid undergoes hydration to form malic acid, it is catalysed by fumarase.

j) Dehydrogenation

It is the final step in Krebs cycle. Oxalo acetic acid is regenerated from malic acid by a process of dehydrogenation. This reaction is catalysed by malic acid dehydrogenase in the presence of NAD. The 2 hydrogen atoms removed are accepted by NAD and it forms NADH.
The oxaloacetic acid formed in the above reaction condenses with the acetyl CoA to form citric acid again and thus the cycle is repeated.

                          4. Electron Transport Chain

Respiration and photosynthesis use electron transport chain to produce (ATP) through oxidative phosphorylation. It begins with an electron-carrying molecule NADH and FADH₂ in respiration and NADPH in photosynthesis. Electron transport chain transfer its electrons to an enzyme embedded in a membrane. During redox reactions, electrons move from one enzyme to another. At each stop, a small amount of energy is released that make ATP. In the first step there is first high potential energy, simply as electrons progress through the chain, free energy is incorporated into ATP as usable chemical energy. 

This diagram show Electron Transport Chain

The presence of a series of electron transport molecules is a key component for the production of energy in the form of ATP in both aerobic respiration and the light-dependent reactions of photosynthesis. These electron transport chains are embedded in the cristae of mitochondria and in the thylakoid membranes of chloroplasts.

Similar coenzymes are associated with both electron transport chains. 

Differences in Electron Transport Chain between Photosynthesis and Cellular Respiration

1. Cellular respiration involves two coenzymes: NAD⁺ and FAD. 

2. Cellular respiration the electrons were lent to the ETC by the NADH

3. Cellular respiration the primary electron acceptor is oxygen.

4. Cellular Respiration utilizes 1 electron transport chain

5. Cellular Respiration energy is provided by catabolic processes

6. Photosynthesis involves a coenzyme very similar to NAD⁺, NADP⁺, serves the same function. 

7. Photosynthesis the electrons are moving due to the energy input of light.

8. Photosynthesis the primary electron acceptor is NADPH.

9. Photosynthesis utilizes 2 electron transport chains

10.Photosynthesis energy is provided by photons 

11.Photosynthesis involves CO2 and H2O as substrates

Similarities in Electron Transport Chain between Photosynthesis and Cellular Respiration

 1. Both Photosynthesis and Cellular Respiration make ATP.

 2. Both Photosynthesis and Cellular Respiration have the process of chemiosmosis.

 3.Both Photosynthesis and Cellular Respiration electrons are moving down the concentration gradient

 4. Both Photosynthesis and Cellular Respiration utilize ATP for energy at some points.
 5. Both Photosynthesis and Cellular Respiration provide power for cellular activities.

                         Photosynthesis

Photosynthesis converts sunlight to electrical and chemical energy. This conversion create energy for a plant, glucose. To produce glucose are used carbon dioxide, water and sunlight. In photosynthesis are photosynthetic bacteria  heliobacteria that can produce carbohydrate, but no oxygen. In Photosynthesis carbon dioxide, water, and sunlight must be obtained by the leaves. Carbon dioxide and water are obtained through tiny pores in stomata.  Through the plant roots water is obtained and delivered to the leaves through vascular plant tissue systems. Sunlight is absorbed by chlorophyll. Chlorophyll is a green pigment located in plant cell structures called chloroplasts. Chloroplasts are the tract of photosynthesis.

 Photosynthesis has 4 steps: 

1. Plants absorb water and mineral nutrients from the soil.
 
2.  The leaves collect Carbon Dioxide.

3.  Chlorophyll in the plant leaves collect the Sun's Energy. In the Chloroplast of the plant cell, the Sun's Energy combines with the water, nutrients, and Carbon Dioxide to create Photosynthesis.

4. The plant then releases Oxygen and water, waste products, back into the air.

                     Function of ATP in Photosynthesis 

ATP is increase in photosynthesis. ATP is made from the thylakoid membrane of chloroplast cells of plants. Sunlight produce the photon particles which excite the chloroplast thylakoid membrane. Chloroplast thylakoid membrane converts this excitation into ATP’s chemical energy. 

Photosynthesis has two parts: -the light reaction 
                                           - the dark reaction called also Calvin Cycle):

1. Light dependent reaction produces the reducing power and ATP, the energy currency of life. Chlorophyll in photosystem II absorbs light that produce high energy and free electron. Electron than passed along a series of carriers. It cause reduction of NADP. Absorption of light in photosystem II provides electron for photosystem I. Photolysis of water produces 2 H what is called non-cyclic photophosphorylation. In cyclic photophosphorylation electron returns to chlorophyll where generates ATP by H pumped across thylakoid membrane  by chemiosmosis through ATP synthetase.

 

                              2. Calvin Cycle

 In Calvin Cycle the products of light phase are used to convert CO2 to carbohydrates. Calvin cycle take place in the stroma of chloroplasts in photosynthetic organisms whereby carbon dioxide is used to synthesize glucose. Calvin Cycle is used for carbon fixation. Part of Calvin Cycle is also carbon fixation which convert carbon dioxide into organic compounds during photosynthesis.

The following diagram show Calvin Cycle. The number in front of diagram are not readable but here is the explanation:

1. RuBisCo catalyzes the reaction of CO2 and ribulose 1.5-bisphosphate to produce 3-phosphoglycerate.

2. RuBisCo also catalyses the reaction of oxygen and ribulose 1.5-bisphosphate to produce 3-phosphoglycerate.

3. During photorespiration, 3-phosphoglycerate is converted to  3-phosphoglycerate.

4. A phosphate group is transfered from ATP to 3-phosphoglycerate producing 1.3 bisphosphoglycerate and ADP.

5. Reduced NADP transfers a proton to reduce a molecule of 1.3 bisphosphoglycerate, producing glyceraldehyde 3-phosphate and NADP.

6. Every 6 cycles, enough carbon has been fixed to produce a molecule of Fructose 6-Phosphate by combining two molecules of G3P which is an Isomer of Glucose 6-Phosphate.

7. Hexose Isomerase converts Fructose 6-Phosphate to Glucose 6-Phosphate which can then be dephosphorylated to form glucose.

8. Ribulose 5-Phosphate is regenerated through a series of enzyme catalysed reactions, and is dephosphorylated using ATP to produce Ribulose 1.5-Bisphosphate.

  Differences between Photosystesis and Respiration

1. Cellular respiration depends on oxygen as a substrate.

2. Cellular respiration utilizes 1electron transport chain.

3. Cellular respiration energy is provided by catabolic processes.

4. Cellular respiration involves the production of NADH and FDH2.

5. Photosynthesis utilizes 2 electron transport chain.

6. Photosynthesis energy is provided by photons.

7. Photosynthesis involves CO2 and H2O as substrates, splitting H2O provides the electrons for the process.

8. Photosynthesis involves the production of NADPH.

  Similarities between Photosynthesis and Respiration

1. Both involve electron transport chains.

2. Chemiosmosis allows ATP synthase to produce ATP.

3. Both take place at some point within an organelle.

4. Both utilize ATP for energy at some points.

5. Both provide power for cellular activities.

The Greenhouse Effect

Aerobic cellular respiration produces carbon dioxide, which is a greenhouse gas, and thus would contribute to the Greenhouse Effect.
Photosynthesis removes carbon dioxide from the atmosphere (to make glucose and then cellulose among other things), and thus photosynthesis would reduce the Greenhouse Effect.
Removal of rainforest would tip the dynamic balance, putting more carbon dioxide into the atmosphere and reducing photosynthesis.

 http://www.tutorvista.com/content/biology/biology-iv/respiration/krebs-cycle.php

 http://www.ehow.com/about_5121615_role-atp-respiration.html

 http://www.scribd.com/doc/14461912/MCROBAL-METABOLSM-

 http://www.ehow.com/about_5121615_role-atp-respiration.html