HESI A2 Exam: Cellular Respiration
• What is the principal source of energy for cellular respiration?
• Glucose molecules are broken down into two smaller pyruvate molecules due to the process of _________
• The burning sensation of the muscles when undergoing anaerobic respiration is due to the __________
• The process by which electrons are released and gathered by acceptor molecules is the __________
Intro
Cell respiration is overall an oxidative reaction, meaning it loses electrons and loses hydrogen.
Respiration is the biochemical process in which the cells of an organism obtain energy by combining oxygen and glucose, resulting in the release of carbon dioxide, water, and ATP (the currency of energy in cells).
Cell respiration includes both aerobic and anaerobic phases.
Nutrients that are commonly used by animal and plant cells in respiration include sugar, amino acids and fatty acids, but the most common oxidizing agent providing most of the chemical energy is molecular oxygen (O2).
The main organelle involved in respiration is the mitochondria. The enzymatic reactions of cellular respiration begin in the cytoplasm, but most of the reactions occur in the mitochondria.
Glycolysis
Glycolysis is the anaerobic phase of cellular respiration which breaks down glucose into two molecules of pyruvate. Glycolysis is the metabolic pathway that converts glucose into pyruvate and a hydrogen ion. The free energy released in this process is used to form ATP and NADH. Glycolysis is a sequence of ten enzyme-catalyzed reactions. Most monosaccharides, such as fructose and galactose, can be converted to one of these intermediates.
Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or to fatty acids through a reaction with acetyl-CoA.
Krebs Cycle
The citric acid cycle (CAC) – also known as the Krebs cycle – is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions.
Electron Transport Chain
The electron transport chain pumps electrons across the membrane to create a proton gradient. Electrons also move from one carrier molecule to the next.
Oxidative phosphorylation is the production of ATP using energy from the electron transport chain. This produces the most ATP during cellular respiration. About 32 ATP are produced during oxidative phosphorylation, compared to 2 ATP during glycolysis and 2 ATP during the citric acid cycle.
NAD+ carries electrons to the electron transport chain from the Krebs Cycle.
NAD carries electrons to the ETC from glycolysis and Krebs cycle.
Fermentation
Fermentation only generates ATP if there is an adequate supply of NAD+. The NAD+ has to be present in order to accept the electrons.
Lactic acid fermentation happens when one is undergoing exercise. Lactic acid builds up during fermentation, causing muscles to cramp up.
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