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

Learning Intentions By the end of this section you should be able to: Identify ATP as the high energy compound which transfers energy, and is produced when ADP combines with phosphate in phosphorylation, building up energy, and releases energy when broken down into ADP and phosphate once more. State that cells use high energy electrons to pump hydrogen ions across a membrane, which activates the enzyme ATP synthase, and helps to produce ATP. Describe the process of glycolysis including the energy investment stage and the energy pay off phase, and the use of phosphofructokinase in progressing the glycolysis pathway. Describe the sequence of events that occur after pyruvate production, and onto the citric acid cycle, in the presence of oxygen including the production of acetyl coenzyme A, citric acid and oxaloacetate. State the number of carbon atoms present in each of the main carbon compounds in respiration, and the use of dehydrogenase enzymes to remove hydrogen ions which are then passed to the coenzyme molecules FAD and NAD. Describe NAD and FAD as carrier molecules, which carry the high energy electrons to the electron transport 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).

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

ATP Adenosine Triphosphate This terminal bond breaks by enzyme action to release energy Adenosine diphosphate (ADP) and an inorganic phosphate is produced adenosinePi

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

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

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

ATP transfer diagram CO 2 + water Glucose + Oxygen ATP ADP + Pi Amino acids Protein respirationenergy transferwork

Some bacterial cells require 2 million molecules of ATP per second In fact, about 400g is produced and used / hour but only 50g 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

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

Use/Role of ATP 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

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

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 – GLYCOLYSIS – KREBS CYCLE – ELECTRON TRANSFER SYSTEM

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

The reactions in the first half of the chain make up the energy investment phase where 2ATP are used up. The reactions in the second half of the chain make up an energy payoff phase where 4ATP 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 2ATP

Glycolysis 2 +

Mitochondria Krebs Cycle takes place in the matrix of the mitochondria. Electron Transfer System takes place on the cristae.

Krebs Cycle Takes place in the matrix of the mitochondria. Requires oxygen. 3-C Pyruvic acid/Pyruvate converted to CO 2 and Acetyl CoA (2-C). H+ ions reduce the NAD to NADH Acetyl CoA 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.

Krebs Cycle cont… 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.

Electron Transfer System Also known as cytochrome system or hydrogen transfer system. Takes place on the cristae of the mitochondria on groups of protein molecules. The reduced co-enzymes (NADH and FADH 2 ) from the glycolytic 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.

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.

Electron Transfer cont… 36 molecules of ATP are produced from the electron transfer system. The hydrogen combines with oxygen to form water.

Overview 38 molecules of ATP produced in total 2 from glycolysis and 36 from electron transfer system.

Anaerobic Respiration The process where a little amounts of energy are derived from the partial breakdown of sugar. It takes place in the absence of oxygen. Only glycolysis occurs. 2ATP molecules are produced.

Anaerobic Respiration Due to the oxygen debt, pyruvic acid is converted to lactic acid. When the oxygen debt is repaid, the lactic acid is converted back to pyruvic acid which then enters the aerobic pathway.

Anaerobic Respiration Glucose (6C) Pyruvic Acid (2 X 3C) Lactic Acid (2 X 3C) Oxygen debt builds up Oxygen debt repaid

Aerobic V Anaerobic Aerobic Respiration Anaerobic Respiration Number of ATP molecules per glucose molecule 382 Products of reaction (other than ATP) Carbon dioxide and water Lactic acid Location in cell mitochondrioncytoplasm

Substrates for Respiration Carbohydrates Starch and glycogen are made up of chains of glucose. This means that they can act as respiratory substrates since they can be broken down into glucose. Sucrose and maltose – these can be converted to glucose or intermediates Fats These are broken down into glycerol and fatty acids Glycerol – converted to a glycolytic intermediate Fatty Acids – these are metabolised into metabolic fragments that enter the pathways as acetyl coenzyme A. Proteins These are broken down into amino acids by enzymes. These undergo deamination forming urea and respiratory intermediates.

Regulation of the Respiratory Pathway The third step in this process is catalysed by phosphofructokinase. This is an irreversible step so is therefore a key regulatory point. When the cell has too much ATP the high concentration inhibits phosphofructokinase and slows down glycolysis. When the concentration of ATP decreases the enzyme is no longer inhibited so glycolysis speeds up. Phosphofructokinase is also inhibited by high concentrations of citrate.

Feedback Inhibition This regulates and synchronises glycolysis and the Krebs Cycle pathways. This is important because: Build up on unnecessary intermediate is prevented ATP is only produced when it is needed Resources are conserved

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