Cellular Respiration - SS1 Biology Lesson Note
Cellular respiration is the process by which cells convert organic molecules, such as glucose, into usable energy in the form of adenosine triphosphate (ATP). It is a fundamental metabolic process that occurs in the cells of all living organisms, and it plays a central role in generating the energy required for cellular functions.
Cellular respiration can be divided into three main stages:
1. Glycolysis: Glycolysis takes place in the cytoplasm of cells and is the initial step of cellular respiration. During glycolysis, a molecule of glucose (a six-carbon molecule) is broken down into two molecules of pyruvate (a three-carbon molecule). This process generates a small amount of ATP and NADH (nicotinamide adenine dinucleotide), which is an electron carrier.
2. Citric Acid Cycle (Krebs Cycle): The pyruvate molecules produced during glycolysis move into the mitochondria, where they undergo further breakdown in the citric acid cycle. In this cycle, each pyruvate molecule is fully oxidized, generating ATP, NADH, FADH2 (flavin adenine dinucleotide), and releasing carbon dioxide as a waste product.
3. Electron Transport Chain (ETC) and Oxidative Phosphorylation: The NADH and FADH2 produced during glycolysis and the citric acid cycle donate electrons to the electron transport chain, located on the inner mitochondrial membrane. As electrons pass through the electron transport chain, energy is released and used to pump protons (H+) across the membrane, creating an electrochemical gradient. This gradient is then used by ATP synthase to generate ATP through a process called oxidative phosphorylation.
The overall process of cellular respiration can be summarized as follows:
Figure 55 image from quora.com
Cellular respiration is an AEROBIC process, meaning it requires oxygen. It is the primary means by which cells obtain energy for various activities, including muscle contraction, active transport, and synthesis of cellular components. Without cellular respiration, cells would not have sufficient energy to perform essential functions, and life processes would be severely compromised.
It is important to note that some organisms, such as certain bacteria and yeast, can carry out ANAEROBIC respiration in the absence of oxygen. In these cases, the final electron acceptor is different from oxygen, and the overall process yields fewer ATP molecules compared to aerobic respiration. One example of anaerobic respiration is fermentation, where pyruvate is converted into different end products such as ethanol or lactic acid, with the regeneration of NAD+ for use in glycolysis.
Figure 56 image from study.com
The (aq) symbol means the reaction takes place in an aqueous solution (a solution where the solvent is water).