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4.1 Importance of ATP – Page 2 S. Preston 1
A2 Unit 4: Metabolism, Microbiology and Homeostasis Name: Date: Topic 4.1 The Importance of ATP – Page 2 l. ATP Production Completed 1. Go through the PowerPoint in Class 2. Read through the notes page 2-4 and complete the questions 3. Read through the BioFactsheet on Chemiosmosis and complete the
questions
4. Have a look at some past paper questions on the wikispace.
4.1 Importance of ATP – Page 2 S. Preston 2
The addition of phosphate is known as phosphorylation. ATP acts as an energy carrier in all cells and all cells use it so it is referred to as universal. ATP can be produced within cells by two methods:
• Substrate-Level Phosphorylation
And
• Chemiosmosis (used in both oxidative and photophosphorylation)
Substrate-Level Phosphorylation (SLP) Involves the transfer of phosphate from a high-energy intermediate molecule to ADP, with the aid of an enzyme. The process of forming ATP by the physical addition of a phosphate group to ADP is known as phosphorylation. ADP + Pi ATP This takes place in the cytoplasm during the first stage of aerobic respiration known as glycolysis and also within the mitochondrion in another stage of aerobic respiration known as the Krebs cycle.
Why is the synthesis of ATP described as a phosphorylation reaction? The phosphorylation of ADP to form ATP requires 30.6 kJ mol-1 of energy. The energy to power this reaction must come from somewhere within the cell. Any chemical reaction that occurs within the cell and releases 30.6 kJ mol-1 of energy and can donate a phosphate group could be used to convert ADP and Pi into ATP. What does Pi stand for? Why do you think that the letter P is not used? Using the energy from chemical reactions to produce ATP is known as substrate level phosphorylation. i.e. using the energy from substrate molecules to power phosphorylation.
4.1 Importance of ATP – Page 2 S. Preston 3
Substrate level phosphorylation takes place during glycolysis, the first stage of respiration (in the cytoplasm) and also the Krebs cycle, which takes place in the matrix of the mitochondria.
Glycolysis Krebs Cycle Looking at ATP generation in glycolysis. Using the diagram of glycolysis to outline two reactions that must produce at least 30.6 kJ mol-1 of energy and produce ATP and are hence are examples of substrate level phosphorylation reactions.
1. 2. How many substrate level phosphorylation reactions occur per turn of the Krebs cycle?
4.1 Importance of ATP – Page 2 S. Preston 4
Chemiosmosis Look at the diagram of a hydroelectric power station.
In a hydroelectric power station there is a difference in the level of water on either side of the dam wall and this is a store of potential energy. A gate is opened in a dam wall and the water flows through, turning turbines that turn generators to create electricity. In chemiosmosis ATP is generated in a similar manner. In a cell what structure do you think could act as a dam wall? In cells the difference is not with water but is created using protons (H+), so more protons are on one side of the membrane compared to the other side. This creates a gradient (a difference) in protons on one side of the membrane compared to the other. What do you think could act as a gate in the membrane? This allows the controlled flow of protons through the membrane. Attached to this membrane protein is an enzyme ATP synthetase. As the H+ ions flow through the protein pore energy is released. This energy and the enzyme ATP synthetase are used to attach a Pi group to the molecule ADP to produce ATP.
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Chemiosmosis is used in both aerobic respiration and photosynthesis. In order to create a proton gradient the energy to drive this comes from high-energy electrons. In respiration these high-energy electrons are produced from oxidation reactions and the production of ATP in this manner is known as oxidative phosphorylation. In photosynthesis these high-energy electrons are produced by the absorption of light energy and the production of ATP in this manner is known as photophosphorylation.
Protons have to be pumped into a space for chemiosmosis. In mitochondria this space is known as the intermembrane space and is found between the inner and outer membranes.
• Label this on the diagram on the left
In chloroplasts this space is found inside the thylakoid.
• Label this on the diagram
Summary Chemiosmosis requires a phospholipid bilayer, a proton pump, a proton gradient and the enzyme ATP synthetase. Energy from high-energy electrons is used to pump protons into a space either an inter membrane of a mitochondria or a thylakoid space of a chloroplast. The proton gradient is used to rotate the enzyme ATP synthetase and power the addition of a phosphate group onto ADP.
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Revision Summary for 4.1 4.1 THE IMPORTANCE OF ATP 1. Chemical energy is contained within food substances. 2. Energy may be converted from one form to another. 3. Green plants are able to convert light into chemical energy. All living organisms are able o convert chemical energy to other energy forms. 4. Candidates should be able to label the general structure of adenosine triphosphate ATP): sugar, nitrogenous base and three phosphate groups joined together.
5. Energy is required to combine ADP and phosphate to form ATP and this is an endergonic reaction. Energy is needed to make ATP. This is an ENDERGONIC reaction. ATP Synthetase catalyses the reaction. The reaction requires 30kJ.mol-‐1 6. Energy is released when ATP is broken down to ADP and phosphate and this is an exergonic reaction; this is linked to energy-‐requiring reactions e.g. active transport muscle contraction, synthesis of organic chemicals. Energy is released when ATP is broken down. This is an EXERGONIC reaction. ATPase catalyses the reaction. The breakdown of ATP occurs when energy is needed. Eg. Active Transport, Muscle Contraction, Synthesis of Organic Molecules, Nerve impulses 7. Candidates should appreciate the importance of ATP as an energy carrier in cells and the reason why it may be called the ‘universal energy currency in living organisms’. ATP is known as being Universal as it is present in all organisms. It is the common source of energy. ATP is advantageous due to it needing only 1 enzyme for energy to be released, energy can be released in small amounts when needed, and can be used in many different reactions, increasing efficiency and control by the cell. 8. Candidates should be able to define the terms ‘proton’ and ‘electron’. Proton – Positively charged particle found in the nucleus of an atom Electron -‐ Negatively charged particle that surrounds the nucleus of an atom. 9. ATP is produced across the internal membranes of mitochondria and chloroplasts. Oxidative Phosphorylation – Occurs in the membranes of Mitochondria in Respiration Photo Phosphorylation – Occurs in the membranes of the Thylakoids of Chloroplasts in Photosynthesis 10. In mitochondria the internal membrane separates the intermembrane space from the matrix. In chloroplasts the corresponding membrane separates the thylakoid component from the stroma. ATP Synthetase is found on the inner membrane of the Mitochondria, and on the thylakoid membrane of the Chloroplast. 11. The synthesis of ATP takes place by means of a flow of protons across these membranes down a concentration gradient through the enzyme ATP synthetase (chemiosmosis). High concentration of Protons in the intermembrane space (Resp) causes them to diffuse back down their concentration gradient to the matrix of the Mitochondria, via STALKED ATP SYNTHETASE PARTICLES. This causes the production of ATP
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12. To maintain the concentration of protons in the inter membrane space, proton pumps are needed which are fuelled by electron energy. Hydrogen atoms are split into Protons and Electrons. The Electrons are passed from one complex to another by ELECTRON CARRIERS. Each time this occurs, small amounts of ENERGY are RELEASED. This energy is used to fuel PROTON PUMPS which pump protons from the Hydrogen into the intermembrane space. This creates an ELECTROCHEMICAL GRADIENT across the membrane. 13. Candidates should be able to draw a diagram to explain the synthesis of ATP as described above.
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