Higher Human Biology Unit 1 Human Cells Section

Higher Human Biology Unit 1 – Human Cells Section 7 – Cellular Respiration

What can you remember? Glucose + oxygen water and carbon dioxide • What is the equation for respiration? • What two forms of respiration are there? Aerobic and anaerobic • What is the energy currency molecule? ATP • Describe the process of glycolysis 2 • How many molecules of ATP are created overall from glycolysis? • What organelle is involved in aerobic respiration mitochondria • What is produced from anaerobic respiration in plants and animals? Animals – lactic acid Plants – ethanol and carbon dioxide

a – Cellular Respiration We will be learning to… • State that glycolysis is the breakdown of glucose to pyruvate • Describe the phosphorylation of glucose and intermediates during the energy investment phase of glycolysis • State that this leads to the generation of more ATP during the energy pay-off stage which results in a net gain of ATP. • State that under aerobic conditions pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A • Describe how in the citric acid cycle the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate. • State that the citric acid cycle if a series of enzyme-controlled steps. • State that citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide. • State that the location of the citric acid cycle occurs in the matrix of the mitochondria. • Describe the role of dehydrogenase enzymes in both glycolysis and the citric acid cycle. • State the location of the electron transport chain • Describe how electrons and hydrogen ions from NADH are passed to the electron transfer chain.

What is a Cellular Respiration? • This is a series of metabolic pathways that bring about the release of energy from a foodstuff and the regeneration of the high-energy compound adenosine triphosphate (ATP). • Respiration is the process by which chemical energy is released from glucose by oxidation. • It takes place in every living cell, and involves the regeneration of ATP from ADP + Pi by a complex series of biochemical reactions.

Adenosine Triphosphate (ATP) • Adenosine Triphosphate • This is made up of three inorganic phosphate (Pi) and an adenosine molecule. • Molecule able to provide energy immediately. adenosine Pi Pi Pi

ATP and Energy Transfer ATP molecules are the energy currency of the cell adenosine Pi Pi Adenosine diphosphate The bond between the end phosphate must be broken by enzymes in order to release the energy. Adenosine triphosphate Pi

adenosine Pi Pi The enzyme breaking the bond results in adenosine diphosphate (ADP) and inorganic phosphate (Pi) Pi Energy released However, this reaction is reversible – where energy is required to regenerate ATP. This is called Phosphorylation. ATP breakdown releasing energy building up requiring energy Pi ADP + Pi

Phosphorylation This is the process, controlled by enzymes in which phosphate groups are added to a molecule e. g. ADP + Pi ATP Phosphorylation can also occur when a phosphate and energy are transferred from ATP to the molecules in a metabolic pathway, making them more reactive Often this stage has to occur for the next reaction to take place. The reactant is now phosphorylated and energised which allows the pathway to proceed. In respiration, some reactants must undergo phosphorylation in what is called the investment phase

The first step in the glycolysis pathway involves such a phosphorylation. The enzyme hexokinase transfers the phosphate group from ATP to the 6′ carbon of the glucose molecule. The effect of this is twofold. Firstly, it prepares the glucose for the next step in the chain of reactions. Secondly, it reduces the concentration of glucose in the cell and, at the same time, prevents its loss from the cell as glucose 6 -phosphate is much less able to cross the cell membrane.

ATP acts as a link between catabolic, energy-releasing reactions, and anabolic, energy-consuming, reactions.

ATP Transfer Diagram CO 2 + water respiration Glucose + Oxygen ATP energy transfer ADP + Pi Amino acids work Protein

ATP Production and Consumption Some bacterial cells require 2 million molecules of ATP per second In fact, about 400 g is produced and used per hour but only 50 g is ever present within the body This is possible due to the rapid turnover of ATP molecules – where ATP is breaking down and being regenerated

Cellular Respiration • Process by which energy is released from foods by oxidation. • It involves the regeneration of ATP which is a high energy compound. • Consists of 3 stages 1. Glycolysis 2. Citric Acid Cycle 3. Electron Transport Chain

1. Glycolysis Takes place in the cytoplasm of the cell. It consists of a series of enzyme controlled reactions Does not require oxygen (anaerobic). Glucose (6 -C) is broken down into two molecules of Pyruvate (3 -C). • Net gain of 2 ATP. • Hydrogen released binds to a co-enzyme, NAD by reduction to form NADH (Nicotinamide Adenine Dinucleotide) • •

Energy Investment vs Energy Payoff • The reactions in the first half of the chain make up the energy investment phase where 2 ATP are used up. • The reactions in the second half of the chain make up an energy payoff phase where 4 ATP molecules are produced per molecule of glucose. H+ ions are also released from the substrate by the dehydrogenase enzyme. These are passed to NAD. • This gives a net gain of 2 ATP

Glycolysis (in cytoplasm) Glucose is the starting point of respiration and DOES NOT REQUIRE OXYGEN (anaerobic). It is broken down into two pyruvate molecules via a series of enzyme controlled steps. GLUCOSE 2 ATP 2 NAD 2 ADP+Pi 4 ADP+Pi 2 NADH 4 ATP (net gain of 2 ATP!!!) Used in stage 3 Glycolysis literally means: “Glucose splitting” PYRUVATE NAD is a molecule which is known as a hydrogen acceptor

GLUCOSE 2 ATP 2 NAD 2 ADP+Pi These two ATP make up the energy investment phase 4 ADP+Pi 2 NADH 4 ATP (net gain of 2 ATP!!!) Used in stage 3 These two additional ATP make up the energy payoff phase PYRUATE The hydrogen ions are released in the payoff stage by the enzyme dehydrogenase

Glycolysis in More Detail During this stage, two phosphorylation's take place. A molecule of ATP is converted to ADP; the phosphate group which is released is added to the substrate molecule. The first occurs when glucose is converted to glucose 6 phosphate. This step is irreversible, but the glucose 6 -phosphate can be used in a variety of metabolic pathways: • it can enter the pentose phosphate pathway, generating the reducing agent NADPH, which supplies the hydrogen necessary for several reactions, such as fatty acid synthesis, and the precursor of nucleotides for DNA synthesis in the form of ribose phosphate; • it can be converted to glycogen for storage.

Structure of the Mitochondria The mitochondrion is bounded by a double layer of membranes, each of which is itself composed of a phospholipid bilayer. The outer membrane surrounds the mitochondrion and acts as a boundary; although it is highly permeable to small molecules, the entry of larger molecules is strictly regulated. The inner membrane is folded, forming structures called cristae. • Citric Acid Cycle takes place in the matrix of the mitochondria. • Electron Transport Chain takes place on the cristae.

Mitochondria When O 2 is present, aerobic respiration occurs in the cell’s mitochondria. The sausage shaped organelles are within the cytoplasm. The inner membrane is folded into many extensions (CRISTAE) which increases the surface area for ATP production.

2. Citric Acid Cycle (Central Matrix) • Takes place in the matrix of the mitochondria and is a series of enzyme controlled steps. • Requires oxygen (aerobic). • 3 -C Pyruvate converted to CO 2 and Acetyl Co. A (2 -C). H+ ions reduce the NAD to NADH for transfer to the electron transport chain • Acetyl Co. A enters Krebs and combines with a 4 -C (oxaloacetate) compound to form a 6 -C compound (citrate). • The Coenzyme A returns to combine with more acetyl.

2. Citric Acid Cycle (Central Matrix) • This Citrate (6 -C) compound is converted back to a oxaloacetate (4 -C) compound by a series of enzyme controlled reactions. This will again combine with acetyl coenzyme A to begin the cycle again. • During the cycle, carbon is released in the form of carbon dioxide and hydrogen H+ ions are released and become bound to NAD, forming NADH.

2. Citric Acid Cycle (Central Matrix) Pyruvate anaerobic 2 NADH 2 CO 2 Used in stage 3 Acetyl Coenzyme A Pyruvate crosses the double membrane and enters the inner space of the mitochondrion, which is called the matrix. Here it is oxidised. Coenzyme A under aerobic conditions pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A

Acetyl Coenzyme A 2 C the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate. Citrate 6 C 3 NADH Oxaloacetate 4 C citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide. 3 NAD Citric Acid cycle 2 CO 2 Used in stage 3 Many enzyme controlled reactions FADH 2 FAD ADP + Pi ATP

Dehydrogenase Enzymes Each step in the cycle is catalysed by a different enzyme which is specific to the substrate involved. the enzymes involved all belong to a class of enzyme called dehydrogenases. These enzymes transfer hydrogen ions and electrons to carrier molecules which then convey them to the electron transport system on the cristae. A similar reaction occurs later but to the coenzyme is FAD (flavine adenine dinucelotide) Also ATP is produced and carbon dioxide is released

3. Electron Transport Chain (Cristae) • Also known as cytochrome system, electron transfer system or hydrogen transfer system. • It is aerobic • Takes place on the cristae of the mitochondria on groups of protein molecules. • The reduced co-enzymes (NADH and FADH 2) from glycolysis and citric acid pathways transfer the hydrogen to a chain of carriers. • High energy electrons are also released and pass to the electron transport chains. • Produces the most ATP

3. Electron Transport Chain (Cristae) • There are two parts to the system which are said to be coupled, meaning that one cannot occur without the other: • the electron transport chain, which comprises a series of enzyme -controlled electron donors and electron acceptors - each transfer of an electron provides the energy to pass a hydrogen ion (or proton) across the inner membrane into the space between the inner and outer membranes of the mitochondrion; • the ATP synthesis stage, which involves the enzyme ATP synthase - the protons are passed back from the intermembrane space into the matrix of the mitochondrion, releasing energy which is used to form ATP.

Electron Transport Chain • The reduced coenzyme NADH brings the positive hydrogen ions and electrons to the inner membrane of the mitochondrion. Here the hydrogen ions are released and the electrons are passed to a series of protein acceptors and donors which are arranged in three closely linked complexes. • When the electrons are passed from donor to acceptor, energy is released. This energy is used to pump the hydrogen ions across the inner membrane into the intermembrane space, building up a concentration there that can be up to ten times that of the matrix. • As the electrons pass along the chain, their energy level declines until eventually they reach their lowest energy level. At that point they are released to combine first with oxygen, and then with two hydrogen ions to from a water molecule (H 2 O). • The following illustration shows the stages in the electron transport chain. The electrons are shown passing from their coenzymes to carriers in the transport chain. The changing height of the carriers across the diagram indicates the relative energy level of the electrons.

Electron Transport Chain • As the electrons pass along the chain, their energy level declines until eventually they reach their lowest energy level. At that point they are released to combine first with oxygen, and then with two hydrogen ions to from a water molecule (H 2 O).

Electron Transport Chain • The electrons begin in a high energy state and as they release their energy it is used to pump hydrogen ions across the membrane from the inner cavity (matrix) to the intermembrane space. This helps maintain a high H+ ion concentration. • The return journey of the H+ ions from the intermembrane to the matrix is via ATP synthase. This drives the synthesis of ATP from ADP and Pi. • This transfer releases 3 ATP molecules.

• When the electrons come to the end of the chain, they combine with oxygen , the final acceptor. • Oxygen also combines with two hydrogen ions to form water. • 36 molecules of ATP are produced from the electron transfer system.

Overview • In aerobic respiration 38 molecules of ATP are produced in total • 2 from glycolysis and 36 from the electron transport chain

b – ATP Synthesis We will be learning to… • Describe the process of ATP synthesis • State this energy allows hydrogen ions to be pumped across the inner mitochondrial membrane • Describe how the flow of ions results in the production of ATP • State that oxygen is the final acceptor when hydrogen ions and electrons combine with oxygen.

Synthesis of ATP When glucose is broken down it releases energy to synthesise ATP from ADP + Pi How? A flow of high energy electrons, from the respiratory pathway, transfer their energy to proteins in the membrane. This provides the energy used to pump hydrogen ions across the inner mitochondrial membrane, by active transport. It helps maintain a higher concentration of hydrogen ions on one side of the membrane

ATPsynthase Molecules of the enzyme ATPsynthase are embedded in the mitochondrial membrane The return flow of hydrogen ions from a region of higher concentration to a region of lower concentration makes the ATPsynthase molecules rotate and catalyse the synthesis of ATP from ADP and Pi

The return flow of hydrogen ions makes the ATPsynthase molecules rotate and catalyse the synthesis of ATP from ADP and Pi

c – Role of ATP in the Transfer of Energy We will be learning to… • State the role of ATP in the transfer of energy

Use/Role of ATP is important because it acts as a link by which chemical energy is transferred from one type of reaction to another ATP breakdown promotes the transfer of energy to new chemical bonds e. g. peptide bonds joining amino acids together ATP is necessary for muscle contraction, protein synthesis, and active transport

• • • Oxidation is the removal of electrons (hydrogen) from a substance. Reduction is the addition of electrons (hydrogen) to a substance. OIL RIG!!!!!!

Now I can…. . a – cellular Respiration • State that glycolysis is the breakdown of glucose to pyruvate • Describe the phosphorylation of glucose and intermediates during the energy investment phase of glycolysis • State that this leads to the generation of more ATP during the energy pay-off stage which results in a net gain of ATP. • State that under aerobic conditions pyruvate is broken down to an acetyl group that combines with coenzyme A forming acetyl coenzyme A • Describe how in the citric acid cycle the acetyl group from acetyl coenzyme A combines with oxaloacetate to form citrate. • State that the citric acid cycle if a series of enzyme-controlled steps. • State that citrate is gradually converted back into oxaloacetate which results in the generation of ATP and release of carbon dioxide. • State that the location of the citric acid cycle occurs in the matrix of the mitochondria. • Describe the role of dehydrogenase enzymes in both glycolysis and the citric acid cycle. • State the location of the electron transport chain • Describe how electrons and hydrogen ions from NADH are passed to the electron transfer chain.

Now I can…. . b – ATP Synthesis • Describe the process of ATP synthesis • State this energy allows hydrogen ions to be pumped across the inner mitochondrial membrane • Describe how the flow of ions results in the production of ATP • State that oxygen is the final acceptor when hydrogen ions and electrons combine with oxygen. c – Role of ATP State the role of ATP in the transfer of energy

Higher Human 2017 – A Q 5 A

Higher Human 2017 – A Q 6 B

Higher Human 2016 – A Q 5 D

Higher Human 2016 – A Q 6 C

Higher Human 2016 – A Q 7 B

Word Definition Acetyl group produced by breakdown of pyruvate; joins with oxaloacetate in the citric acid cycle ADP adenosine diphosphate; molecule that is phosphorylated to produce ATP Alternative respiratory substrates for respiration other than glucose ATP adenosine triphoshate; molecule used for energy transfer in cells ATP synthase membrane-bound enzyme that synthesises ATP Cellular respiration release of energy from respiratory substrates Citrate citric acid; first substance produced in the citric acid cycle Citric Acid Cycle second stage of aerobic respiration occurring in the matrix of mitochondria Coenzyme A substance that carries acetyl groups into the citric acid cycle Dehydrogenase enzymes that remove hydrogen from their substrates; important in the citric acid cycle Electron Transport Chain group of proteins embedded in membranes of mitochondria and chloroplasts FAD hydrogen carrier important in the citric acid cycle

Word Definition Glucose sugar that is the main respiratory substrate in cells Glycolysis first stage in cellular respiration – anaerobic, yields 2 ATP overall, occurs in the cytoplasm High-energy electrons that can yield energy as they pass through an electron transport chain Intermediate substance in a metabolic pathway between the original substrate and the end product Matrix central cavity of mitochondrion in which the citric acid cycle occurs Mitochondrion cell organelle in which the areobic stages of respiration occur (plural: mitochondria) NAD hydrogen carrier important in the citric acid cycle Oxaloacetate substance that combines with the acetyl groups in the citric acid cycle to form citrate Phosphate inorganic phosphate used to phosphorylate ADP Phosphorylation addition of a phosphate to a substance Pyruvate the end product of glycolysis Oxidation is the removal of electrons (hydrogen) from a substance. Reduction is the addition of electrons (hydrogen) to a substance.

ATP and Energy 1. What is ATP? 1 2. What is ATP broken down to? 1 3. What is the first stage of respiration called? 4. Where does this take place in the cell? 1 5. What is glucose broken down into? 1 6. How many carbon atoms has this substance? 1 1

7. How many ATP molecules are needed to start the process of respiration? 1 8. How many carbon atoms does Acetyl Co. A have? 1 9. What is the second stage of respiration called? 1 10. Where does this stage take place? 1 11. How many carbons does citric acid have? 1 12. Apart from carbon dioxide what else is produced in the second stage of respiration? 1

13. What picks up the hydrogen that is produced? 1 14. Where is the hydrogen transported to? 1 15. Where does this stage take place? 1 16. What useful substance is formed? 1 17. What is the final hydrogen acceptor? 1 18. What other substrates could be used in respiration if carbohydrates were not available? 1

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