Energy And Respiration A2 Notes 2d1a4r

Energy and respiration

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Content • The need energy for living organisms • Respiration as an energy transfer process • Aerobic respiration • Anaerobic respiration • The use of respirometer

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1)outline the need for energy in living organisms, as illustrated by anabolic reactions, active transport, movement and the maintenance of body temperature; The need for energy in living organisms: 1) The synthesis of complex substance from simpler ones (anabolic reaction)

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Active transport sodium potassium pump Mechanical work such as muscle contraction Electrical discharge in few organisms, mammals and birds for thermal energy Maintaining constant body temperature

2)describe the structure of ATP as a phosphorylated nucleotide; The structure of ATP: It consists of adenine (an organic base) and ribose (pentose sugar), which together make adenosine (a nucleoside). Adenosine is then combined with three phosphate groups to make ATP (adenosine triphosphate).

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3)describe the universal role of ATP as the energy currency in all living organisms; ATP as energy currency:  It acts as immediate donor of energy to the cell’s requiring reactions.  ATP is the universal intermediary molecule between energy-yielding reaction and energy requiring reactions used in a cell.  The cells ‘trades’ in ATP rather than making use of number of different intermediates.

Properties of ATP as an energy currency :  ATP is small, water-soluble molecule. This allows it to be easily transported around the cell.  When a phosphate group is removed from the ATP, adenosine diphosphate (ADP) is formed and 30.5 KJ mol-1 of energy is released.  Removal of a second phosphate produces adenosine monophosphate (AMP) and 30.5 KJ mol-1 of energy released.  Removal of the last phosphate, leaving adenosine, releases only 14.2 KJ mol-

1.  These reactions are all reversible:

Energy transfers are inefficient because : 1) Some energy is converted to thermal energy.

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2) Many energy-requiring reactions in cells use less energy than that released which will change to thermal.

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4) explain that the synthesis of ATP is associated with the electron transport chain on the membranes of the mitochondria; Synthesis of ATP: Energy for ATP synthesis can be become available in two ways: 1) In respiration, energy released by reorganizing chemical bond during glycolysis and Krebs cycle (chemical potential energy) is used to make ATP. 2) Most ATP in cells in generated using electrical potential energy.

Chemiosmosis (electrical potential energy):  It is the process in which ATP is generated using electrical potential energy.

 The energy is from the transfer of electrons by electron carriers in my mitochondria.  Phospholipids membranes in mitochondria are impermeable to hydrogen ions.  Hydrogen ions are then allowed to flow down their concentration gradient through protein .part of this protein acts as an enzyme which synthesis ATP called ATP synthesis.  The flow of three hydrogen allows the production one ATP molecules provided that ADP and inorganic phosphate group (Pi) are available inside the organelles 

ATP synthesis has three binding sites and a part of the molecules (Y) that rotates as hydrogen ions , this produce structural changes

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and allow them to sequentially through three phase:1) binding ATP and (Pi), 2) forming tightly bound ATP, 3) releasing ATP. 5) outline glycolysis as phosphorylation of glucose and the subsequent splitting of hexosephosphate (6C) into two triose phosphate molecules, which are then further oxidised with a small yield of ATP and reduced NAD; Glycolysis:  It is the splitting, or lysis of glucose.  Glucose does not react easily as it is actually quit stable, because of the activation energy.  So energy must first be used to make the reaction easier this by adding ATP (phosphorylation).  Two ATP molecules are used for each molecule of glucose to make hexose

biphosphate (6C) which breaks down to produce two molecules of triose phosphate (3C).  Hydrogen is then removed from triose phosphate by NAD (hydrogen carrier), two molecules of reduced NAD are produced, 2 ATP will be given off and intermediates will form.  Another two ATP molecules will be given off from the intermediates forming two pyruvate.  When free oxygen is available ,some of the energy in pyruvate can be released

via krebs cycle and oxidative phosphorylation.  However, the pyruvate first enters the link reaction in mitochondria.

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6) explain that, when oxygen is available, pyruvate is converted into acetyl (2C) coenzyme A, which then combines with oxaloacetate (4C) to form citrate (6C); Link reaction:  Pyruvate es by active transport from the cytoplasm, through the outer and inner membranes of a mitochondrion and into the mitochondrial matrix.  Here it is decarboxylated (that’s when CO2 is removed), dehydrogenated and combined with coenzyme A (COA) to give acetyl coenzyme A.  Coenzyme A act as carrier of acetyl groups in the Krebs cycle. 7) outline the Krebs cycle, explaining that citrate is reconverted to oxaloacetate

in a series of small steps in the matrix of the mitochondrion (no further details are required); explain that these processes involve decarboxylation and dehydrogenation and describe the role of NAD; Krebs cycle: The Krebs cycle is a closed pathway of enzyme-controlled reactions.  Acetyl coenzyme A combines with four-carbon compound to form a six carbon compound (citrate).  The citrate is decarboxylated and dehydrogenated in a series to yield carbon dioxide, and hydrogen are accepted by hydrogen carries NAD and FAD.  Oxaloacetate is regenerated to combine with another acetyl coenzyme A. For each turns of the cycle, two carbon dioxide molecules are produced , one FAD and three NAD molecules are reduced, and one ATP is generated. No use of molecular oxygen. However, oxygen is necessary for the final stage which is called oxidative phosphorylation. 10

The most important contribution of the Krebs cycle to the cell’s energetics is the release of the hydrogens, which can be used in oxidative phosphorylation to provide energy to make ATP.

outline the process of oxidative phosphorylation, including the role of oxygen (no details of thecarriers are required); Oxidative phosphorylation and the electron transport chain. In the final stage of aerobic respiration, the energy for the phosphorylation of ADP to ATP comes from the activity of the electron transport chain. This takes place in the mitochondrial membranes. Reduced NAD and reduced FAD are ed to electron transport chain. Hydrogens are removed from the two hydrogen carriers and each is split into its constituent hydrogen ion (H+) and electron. The electron is transferred to the first of a series of electron carriers whilst the hydrogen ion remains in solution in the mitochondrial matrix. Once the electron is transferred to oxygen a hydrogen ion will be drawn from solution to reduce the oxygen to water. The transfer of electrons along the series of electron carriers makes energy available which is used to convert ADP + Pi to ATP. About 25% of the total energy yield of electrons transfer is used to transport ADP into the mitochondrion and ATP into the cytoplasm. Each reduced NAD molecule entering the chain produces on average two and half molecules of ATP and each reduced FAD produces one and half molecules of ATP.

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Electron carrier molecules: are all proteins and mostly cytochromoes .these proteins have a haem prosthetic group in which the iron atom oscillates between the fe2+ and fe3+ states as it accepts electrons. The energy released by the electron transport chain is used to pump hydrogen ions from the mitochondrial matrix into spaces between the two membranes. The concentration of hydrogen ions in the intermembrane space therefore becomes higher than that in the matrix. Hydrogen ions back into the mitochondrial matrix through protein channels in the inner membrane. Associated with each channel is the enzyme ATP synthase. As the ions through the channel, their electrical potential energy is used to synthesise ATP.

explain the production of a small yield of ATP from anaerobic respiration and the formation ofethanol in yeast and lactate in mammals, including the concept of oxygen debt; Anaerobic respiration: When free oxygen is not present, hydrogen cannot be disposed of by combination with oxygen. The electron transfer chain therefore stops working and no further ATP is formed by oxidative phosphorylation. There are two different anaerobic pathway in cytoplasm of the cell: 1) Alcoholic fermentation:(ethanol pathway)  In various microorganisms such as yeast and in some plant tissues, the hydrogen

from reduced NAD is ed to ethanol.  This releases the NAD and allows glycolysis to continue.  First,pyruvate is decorbxylated to ethanol; then the ethanol is reduced ethanol by the enzyme alcohol dehydrogenase 12

 The conversion of glucose to ethanol is referred to as alcoholic fermentation.

2) The lactate pathway: 

 In other microorganisms and in mammalian muscles when deprived of oxygen, pyruvate acts as the hydrogen acceptor and is converted to lactate by the enzyme lactate dehyrogenase.  Again the NAD is released and allows glycolysis to continue in anaerobic conditions.  Ethanol and lactate ,are toxic, the reactions cannot continue indefinitely  The pathway leading to ethanol cannot be reversed and the remaining chemical energy energy of ethanol is wasted. The liver oxidizes some (20%) of the incoming lactate to carbon dioxide and water via aerobic respiration when oxygen is available again. The reminder of the lactate is converted by the liver to glycogen called oxygen debt. 

explain the relative energy values of carbohydrate, lipid and protein as respiratory substrates; Respiratory substrates: glucose is the essential respiratory for some cells , such as neurons in the brain, red blood cell and lymphocytes, other cells can oxidize lipids and amino acids. When lipids are respired, carbon atoms are removed in pairs, as acetyl coA. 13

Energy values of respiratory substrates: Most of the energy liberated in aerobic respiration comes from the oxidation of hydrogen to water when reduced NAD and reduced FAD are ed the electron transport chain. Hence, the greater the number of hydrogens in the structure of the substrate molecule, the greater the energy value Fatty acids have more hydrogens per molecules than carbohydrate and so lipids have a greater energy value per unit mass, or energy density, than carbohydrates or proteins. The energy value of substrate is determined using calorimeter The energy liberated by oxidizing the substrate can be determinant from the rise in temperature of a known mass of water in the calorimeter. For the aerobic respiration of glucose: RQ =Co2/O =6/6 =1.0 2 For the aerobic respiration of fatty acid: C18H34O2 + 25.5O2 --> 18Co2 + 17H2o + energy RQ=Co2/O2 =18/25.5=0.7 and for protein RQ=0.9 In the yeast cell some respiration will be aerobic and so a small volume of oxygen will be taken up and the RQ will be <2. 14

High values of RQ indicate that anaerobic respiration is occurring Note that no RQ can be calculated for muscle cells using the lactate pathway since no carbon dioxide is provide: Glucose (C6 H 12 O6) --) 2 lactate acid (C3 H6 O3) + energy

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