The Need for Energy…Living Organisms need a constant supply of energy to drive the metabolic reactions that take place inside their cells.This includes:• Movement (muscular contractions)• Maintaining constant Body Temperature• Making new compounds (biosynthesis - as forming new chemical bonds requires energy)• Getting things in and out of cells (active transport)
Summary of Energy Uses: All organisms get their energy from Respiration, this involves the Molecular breakdown of glucose (whichMechanical transport comes from our food) and it usually(Muscles) (Across involved oxygen from the air. Membranes) Can you remember the equation for Respiration? The chemical bond energy in your food could be release by burning (combustion) but this reaction isBiosynthesis Heat (Temp uncontrolled and would be fatal (making control) inside our cells!molecules in the cell) Respiration involves the gradual release of energy in controlled small steps which release small amounts of energy to make a molecule called ATP…
Types of respiration During aerobic respiration, a respiratory substrate, e.g.glucose, is split in the presence of oxygen to release carbon dioxide and water. A large number of ATP molecules are produced, releasing the energy from the glucose. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 36 ATP In anaerobic respiration, glucose is converted (in the absence of oxygen) to either lactate or ethanol. A small number of ATP molecules are produced. C6H12O6 → 2 C2H5OH + 2 CO2 + 2 ATP ethanol C6H12O6 → 2 C3H6O3 + 2 ATP lactate
Where does respiration occur? Respiration occurs in all living cells. In eukaryotes the earlystages of respiration occur in the cytoplasm. The later stages of respiration are restricted to the mitochondria. Mitochondria contain highly folded inner membranes that hold key respiratory proteins (including the enzyme that makes ATP) over a large surface area. Mitochondria provide an isolated environment to maintain optimum conditions for respiration. Mitochondria have their own DNA and ribosomes, so can manufacture their own respiratory enzymes.
Stages in Aerobic RespirationThere are four main stages in the breakdown of glucose duringaerobic respiration:• glycolysis (in the cytosol – cytoplasm of cell)• the link reaction (in mitochondrial matrix)• Krebs Cycle (in matrix)• electron transport chain (on cristae, inner membrane of mitochondria)You need to know about all 4 of these stages but not in as much detail asyour text suggests!
Glycolysis – the 1st stageThis is the splitting (–lysis) of glucose. It takes place in a number of enzyme-controlled reactions and oxygen is not required. The process yields little energy but takes little time.1. Glucose molecule is phosphorylated to make hexose phosphate* (6C) [caused by the addition of a 2 phosphates from 2 ATP molecules]2. The 6-carbon hexose phosphate is split into two molecules of triose phosphate** (3C sugars)3. Each 3-carbon sugar is converted into pyruvate [takes places in a series or reactions where Hydrogen is removed reducing a molecule of NAD+ -> NADH and producing 2 ATP molecules!]Overall Glycolysis produces 4 molecules of ATP (but 2 are used), 2 molecules of pyruvate and 2 molecules of NADH…see flowchart on handout *sometimes referred to as fructose-6-phosphate **sometimes referred to as glyceraldehyde 3-phosphate
The Link Reaction – 2nd stage If oxygen is present this next stage of aerobic respiration can take place:• Occurs in the matrix of mitochondria (Pyruvate from the end of theglycolysis stage enters through the double membrane from the cytoplasm)• Pyruvate (3C) combines with coenzyme A to form acetylcoenzyme A [Acetyl-CoA] (2C molecule)• In the process a molecule of CO2 and Hydrogen (2H) are removed• Acetyl-CoA then enters the next stage of Respiration…The Krebs Cycle … where it combines with a 4C compoundOxaloacetate to form Citrate (6C) Coenzyme A 2H Pyruvate Acetyl-CoA [3C] CO2 [1C] [2C]
The Krebs CycleThis series of reaction was discovered by Sir Hans Kreb in 1937, it is also known as the Citric Acid Cycle.• The Krebs cycle occurs in matrix of mitochondria• Remember: Acetyl coenzyme A (2C) combines with Oxaloacetate (4C) to form Citrate (6C)• A series of other reactions take place in which Citrate (6C) is both decarboxylated [CO2 removed] and dehydrogenated [Hydrogens removed]• Carbon dioxide is removed as a waste product & Hydrogen atoms are picked up by H acceptors (like NAD).The most important part of the Krebs Cycle is the release of hydrogenions to be used in the Electron Transport System for generation of ATP
Keeping track of the products For each molecule of glucose, glycolysis produces: 2× 2× 2×For each molecule of glucose, the link reaction produces: 2× 2 × 2 ×
Keeping track of the products For each molecule of glucose, Krebs cycle generates: 4× produced by decarboxylation 6× produced by redox reactions 2× produced by redox reactions 2× produced by substrate-level phosphorylationThe NADH and FADH2 contain the potential energy originally locked in glucose. This energy is now transferred to ATP byoxidative phosphorylation in the electron transport chain.
The Electron Transport Chain – 4th & final stageThe ETC allows the energy from Hydrogen atoms (removed from compounds in the previous stages) to be used to make large amounts of ATP. Oxygen is required and the reactions take place on the inner membrane (cristae) of the mitochondria.• NADH & FADH2 deliver H+ (protons) and e-(electrons) to cristae.• e-’s "transported" along cristae through electron acceptors, providingenergy to pump H+ from matrix into the intermembrane space.• Concentration of H+ is now higher in intermembrane space. H+ passthrough ATP synthases in the cristae back out to matrix.• Last step involves H+ & e- added to oxygen. This frees NAD+ toreturn to glycolysis & Krebs Cycle to pick up more H+ & e-.• The overall process of forming ATP in this way is called oxidativephosphorylation. 28 ATP are made in total.•The movement of H+ ions across a membrane to generate ATP iscalled chemiosmosis.
Outline of the Electron TC ATP ATP[Reduced Carrier 1] [Oxidised Carrier 2] ATP [Reduced Carrier 3] [Oxidised Carrier 4] NADH + H+ FAD Water 2H 2e- 2e- 2e- Oxygen[Oxidised Carrier 1] [Reduced Carrier 2] [Oxidised Carrier 3] NAD + FADH2 [Reduced Carrier 4] 2H+ Electrons being transported have come from these two H atoms
How much ATP is produced? Process ATP in ATP produced Net ATP out glycolysis 2 4 2link reaction 0 0 0Krebs cycle 0 2 (per glucose) 2 (per glucose) Via the electron transport chain and chemiosmosis, each NADH can yield 2.5 ATP and each FADH2 1.5 ATP.From one molecule of glucose, glycolysis yields 2 NADH, the link reaction yields 2 NADH and the Krebs cycle yields 6 NADH and 2 FADH2.10 × 2.5 = 25 ATP from NADH 2 × 1.5 = 3 ATP from FADH2 total = 2 + 2 + 25 + 3 = 32 ATP overall
Anaerobic RespirationAnaerobic respiration takes place in the absence of oxygen, and occurs via Glycolysis. Some organisms carry put aerobic respiration if O2 is available but are able to respire anaerobically in its absence.Most anaerobes fall into this category, some bacteria however can thrive in the absence of O2 – such as C. welccii which causes gangrene!The two main types of Anaerobic Respiration are:• Alcoholic Fermentation – carried out by yeast and plants• Lactic Acid (Lactate) Fermentation – takes place in animals
Comparison of aerobic and anaerobic respiration Aerobic Anaerobic Respiration respiration in animals in plants and yeastOxygen required? yes no noGlycolysis occurs yes yes yesATP yield 32ATP 2ATP 2ATPGlucose completely yes no no broke down?End products Carbon Lactic acid Ethanol and dioxide and carbon dioxide water
Respiratory rate The respiratory rate is the rate at which an organismconverts glucose to CO2 andwater. It can be calculated bymeasuring an organism’s rate of oxygen consumption. Studies on simple animals often use a respirometer. Respirometers measure the change in gas volume in aclosed system. Any change is due to the respiratory activityof the study organisms. Potassium hydroxide or soda lime is used to absorb the carbon dioxide produced, meaning any changes in volume are due to oxygen consumption.