Higher Biology Assignment Flashcards
(6 cards)
Assignment Title?
The Effect of Different Substrates on the Rate of Respiration
Aim?
To investigate the effect of different substrates on the rate of respiration.
Underlying Biology Point 1 - intro to respiration and the stages.
Cellular respiration is a series of metabolic pathways which are present in cells from all three domains in life. These pathways yield energy and are connected to many other pathways. There are three main stages in cellular respiration: Glycolysis, The Citric Acid Cycle and the Electron Transport Chain.
Underlying Biology Point 2 - Glycolysis
The first stage of respiration is called Glycolysis and takes place in the cytoplasm with a series of enzyme-controlled reactions. During this stage glucose is broken down to form pyruvate. During the first half of the reaction 2 ATP is used per molecule of glucose. This is known as the energy investment stage. In the second half of the reactions in glycolysis a direct regeneration of 4 ATP is released. This is known as the energy pay-off phase as a net gain of 2 ATP is collected. During this phase dehydrogenase enzymes remove hydrogen ions and these are passed to a coenzyme molecule called NAD, forming NADH. The process of Glycolysis does not require oxygen, but if present the NADH will transport the hydrogen to the electron transport chain.
Underlying Biology Point 3 - The Citric Acid Cycle
The next stage of respiration is the Citric Acid Cycle which takes place in the central matrix of the mitochondria. Pyruvate is broken down into carbon dioxide and an acetyl group. The acetyl group then combines with coenzyme A to form acetyl coenzyme A. While this process is happening more hydrogen ions are released and bind with NAD forming NADH. Next the acetyl group of acetyl coenzyme A combines with oxaloacetate to form citrate. The citrate then goes through a series of enzyme-mediated steps, resulting in the generation of 1 ATP as well as the release of carbon dioxide and the regeneration of oxaloacetate. At the 3 steps of the cycle, dehydrogenase enzymes remove hydrogen ions and high energy electrons. These are passed to the coenzyme NAD to form NADH.
Underlying Biology Point 4 - The Electron Transport Chain
The Electron Transport Chain is the final stage in aerobic respiration and takes place on the inner membrane of the mitochondria. An electron transport chain consists of a group of protein molecules and there are many of these chains in a cell. NADH released the high energy electrons to the electron transport chain. These electrons start in a high energy state and as they flow along a chain of electron acceptors, they release energy. The energy is used to pump hydrogen ions from the matrix side to the intermembrane space, where a high concentration of hydrogen ions is maintained. The return flow of the hydrogen ions back into the matrix drives the enzyme ATP synthase to synthesise ATP from ADP and Pi. This stage produces most of the ATP generated by cellular respiration. When electrons come to the end of the electron transport chain, they combine with oxygen - the final electron acceptor. While this happens, oxygen combines with a pair of hydrogen ions to form water.
