Transcript Respiration
Metabolism living things need energy – move, think, make something like saliva, hormones, etc., breaking down waste products All These processes that require energy are chemical reactions going on in all living organisms – essential for growth and repair Respiration release of energy from food – fuel for metabolic processes The Not to be confused with “breathing” Occurs in cells - cytoplasm and mitochondria. Sources of energy energy foods – carbohydrates, fats & proteins But cells don’t get their energy directly from them. ATP (adenosine triphosphate) carries the energy to power processes. ATP comes from ADP (adenosine diphosphate) that has been “charged” by food molecules. This process is called “cellular respiration” Three Adenosine P The P P last phosphate bond is where the energy is carried. Energy cycle ATP +P -P Energy Energy Energy to run the body Respiration in cytoplasm and mitochondria ADP Two important carrier molecules 1. NAD – the hydrogen carrier most energy to charge up ADP to ATP comes from the hydrogen in glucose, but it needs to be carried to the right place When carrying hydrogen the molecule is called NADH2 and when ‘empty’ it is called NAD Vitamin B (niacin) is part of NAD molecule (this is why a vit.B deficiency makes you tired – symptoms may be dermatitis, diarrhoea, mental disturbance, muscular weakness and fatigue). Two important carrier molecules 2. Co-enzyme A Coenzyme A carries acetyl groups (formed from breakdown of glucose) from one stage to the next. Called Acetyl Co-enzyme A when carrying an acetyl group. Also contains a kind of vitamin B (pantothenic acid) in its structure, but deficiency is rare as it is widespread in many foods. Aerobic cellular respiration Respiration in the presence of O2 In the body energy from glucose is released in a stepwise fashion with each step guided by an enzyme. C6H12O6 + 6O 2 6CO2 + 6H2O + energy as ATP Four stages in the process of aerobic respiration 1. Glycolysis Takes place in cytoplasm Needs 2 ATP to start the process, but get 4 ATP out of it – net gain of 2 ATP One glucose molecule (C6) is broken into two pyruvate molecules (C3) Two H2 molecules are also given out NAD picks up H2 and carries it to electron transfer chain (final stage in respiration). No oxygen needed for glycolysis. Four stages in the process of aerobic respiration 2. Formation of acetyl - coA Pyruvate (formed in glycolysis) loses a carbon to become an acetyl group Bonds with co-enzyme A to become acetyl coenzyme A (acetyl-coA) Acetyl-coA is carried to matrix in mitochondria for use in Krebs cycle Other food molecules can also be broken down into acetyl groups and carried by coenzyme A into the matrix for Krebs cycle Co-enzyme A can go back and forth to pick up more acetyl groups – it is recycled Four stages in the process of aerobic respiration 3. The Krebs cycle / Citric acid cycle Occurs in the matrix of mitochondria Acetyl group transferred to another molecule for making citrate. Several steps of chemical reactions in which citrate is broken down & in the process CO2 is released as waste More importantly, NAD get filled with H2, these are then carried to cristae for electron transfer chain. Four stages in the process of aerobic respiration 4. Electron transfer system Occurs on the membranes called cristae of mitochondria A row of cytochromes pass hydrogen electrons from one to the other generating energy This energy charges ADP to ATP In the end, the low energy hydrogen joins with oxygen and makes water Aerobic respiration i. ii. iii. iv. In the presence of oxygen Glycolysis Formation of Acetyl-coA Krebs cycle Electron transfer chain One glucose molecule can charge up 38 ATP molecules (40 – 2 used in glycolysis) Anaerobic respiration In the absence of O2 Also called fermentation Find examples of where aerobic respiration takes place If there is no oxygen, the electron transfer system blocks because there is no O2 to take the hydrogen Anaerobic respiration At the end of glycolysis we have pyruvate, some NADH2 and 2 ATP After Krebs cycle we have lots of NADH2 Without oxygen, NAD passes hydrogen to pyruvate molecules If this happens in plants you get ethyl alcohol (ethanol) and carbon dioxide as waste In animals you get lactic acid and carbon dioxide Anaerobic respiration No oxygen used No electron transfer chain Hydrogen is passed from NADH2 to pyruvate Each glucose molecule yields only 2 ATPs (38 ATPs in aerobic respiration) Waste products are ethanol (in plants), lactic acid (in animals) and carbon dioxide (from the Krebs cycle) Questions to ponder over a) b) During exercise the pH of muscles drops. i.e. it becomes more acidic. Give two reasons why this should happen. If you breathed in an isotope (a different chemical version) of oxygen, in which chemical would it come out of your body? In what chemical substance does carbon: enter the Kreb’s cycle? leave the Kreb’s cycle?