Biology Reviewer: Reduction-Oxidation Reactions PDF

**BIOLOGY REVIEWER** Reduction Oxidation Reactions in Biological Systems - **Metabolism** - refers to the various chemical reactions that take place in organisms to allow maintenance of normal functions and survival. Some of the most important functions of the body's metabolic proces...

**BIOLOGY REVIEWER** Reduction Oxidation Reactions in Biological Systems - **Metabolism** - refers to the various chemical reactions that take place in organisms to allow maintenance of normal functions and survival. Some of the most important functions of the body's metabolic processes include energy conversion (release of energy from food molecules or synthesis of sugar by using solar energy), removal of wastes, and the production of other different molecules necessary for survival. a. **Anabolism** - refers to the series of reactions that involve synthesizing more complex molecules from simpler ones. Organisms, for example, must be able to synthesize the materials and molecules that they need in order for their cells to continue functioning properly b. **Catabolism** - refers to the series of reactions that involve breaking down larger or more complex molecules into smaller or simpler ones. The breakdown of larger molecules involves the breaking of bonds between atoms. This process releases energy. - **Redox Reactions** - there are many chemical reactions that occur in organisms to ensure proper function and survival. These chemical reactions usually occur in a stepwise manner , which involves the loss, gain, or transfer of electrons and release or absorption of energy. If these reactions involve electron transfer, then they are known as oxidation or reduction reactions. These are also known as redox reactions , a representation of which is shown in. - The transfer of electrons is the primary method for distinguishing between reduced and oxidized components in chemical reactions. However, the gain or loss of oxygen and hydrogen, particularly in carbon-containing molecules, can also indicate the reaction\'s components a. **Transition Reaction** - This chemical reaction that involves the acetyl CoA. This involves the reduction of NAD + to NADH. At the end of the cycle, four carbon dioxide, 6 NADH, 2 FADH 2 , and 2 ATP molecules are produced for every glucose molecule that enters glycolysis - **Redox Potential** - The redox potential of a chemical reaction is a significant factor when looking at chemical reactions. Redox potential refers to the measure of how likely it is for a compound to lose its electrons. It also refers to the likelihood of a compound to gain electrons. As such, it is the quantification of the compound's tendency to be reduced or oxidized and take part in a redox reaction a. **Redox Enzymes** - Enzymes also play a very important role in redox reactions that occur in biological systems. These are particularly referred to as redox enzymes - Redox enzymes are those that catalyze redox reactions between different molecules. Many of these enzymes catalyze the transfer of electrons to or from substrates through reduction or oxidation. - some of the most significant applications of redox reactions deal with energy transfer or some other processes related to the release or storage of energy in molecules - **Redox in Organism** - Redox reactions in biological systems involve the breakdown of bonds between molecules to generate free energy, which is stored as potential energy. This energy is released when bonds are broken, allowing other processes to operate. In redox reactions, a change in free energy is observed, with spontaneous reactions releasing energy from higher states and nonspontaneous reactions requiring energy input - **Aerobic Respiration: Glycolysis and Krebs Cycle** a. **Aerobic respiration** - involves the use of oxygen molecules in order to break down organic molecules that organisms obtain from food to generate usable energy. The organisms that rely on aerobic respiration are the ones that rely on oxygen for survival. These include animals, plants, fungi, and others b. The **redox reaction in glycolysis** involves the oxidation glucose and the reduction of NAD + The pyruvates produced still have electrons remaining, and the further oxidation of these molecules will drive other processes in aerobic respiration. Glycolysis will be further discussed in a future unit (Unit 9). Glycolysis is followed by the Krebs cycle, which is also called the tricarboxylic acid cycle , as shown c. **The Krebs cycle** - involves redox reactions that utilize glycolysis products to generate ATP and feed the electron transport chain with reduced products for further ATP synthesis. This process involves oxygen and pyruvate products, generating energy and providing electrons and hydrogen for aerobic respiration - **Oxidative Phosphorylation** - Chemiosmosis and the electron transport chain are part of the process of oxidative phosphorylation (as shown in Fig. 6.2.6 ). This mechanism of ATP synthesis involves the transfer of electrons from NADH and FADH 2 , and it takes place in the mitochondrial inner membrane. This, in itself, is already indicative of the redox reactions involved - **Photosynthesis** - is the process that organisms with the pigment chlorophyll , like plants and cyanobacteria, undergo in order to convert carbon dioxide and water into oxygen and glucose with the help of solar energy. The general equation for photosynthesis can be seen in Fig. 6.2.7 , and it will be discussed in detail in a future unit - **Free radicals** - refer to uncharged atoms or molecules that are very reactive because of the presence of an unpaired electron (as shown in Fig. 6.2.8 ). Because of this unpaired electron, free radicals seek out electrons to form an electron pair. As a result, the structures where they scavenge these electrons may become damaged. The presence of free radicals in the body can pose many problems due to the damage that they can cause. Fortunately, the body can counteract the damage, and antioxidants can help by donating electrons to prevent damages to the body tissues. If there is an imbalance between the number of free radicals and antioxidants, then the body is said to be under oxidative stress Factors that Affect Enzyme Regulation and Metabolism - Enzyme Activity - The activity of enzyme is influenced by many factors. Also, regulatory mechanisms for organisms by catalyzing various chemical reactions that are necessary for maintenance, growth, development, and repair. With these into account, regulating the optimal conditions for enzymes to function properly is likewise important to the survival of the organisms. - Optimal Enzyme Activity - There are several conditions that can affect the activities of enzymes in an organism. Influencing the activity of an enzyme means that its reaction rate may either increase or decrease as a result. a. Optimal Level - refers to the most favorable conditions under which an enzyme performs at its maximum efficiency. b. Saturation Level - chemical reactions rely on the collision of molecules, wherein the reactant molecules must be physically in contact with each other for the reaction to proceed. - Concentration - refers to the amount of substrate or enzyme in a given volume. Low concentration = Few collisions High concentration = More collisions - Saturation point - wherein none of the enzymes\' active sites are free to accommodate more substrate molecules and to perform more catalysis. - Factors that Affect Enzyme Activity 1. Temperature- Affects all chemical reactions, even the ones that are not catalyzed by enzymes. Recall that frequency of collision between molecules may also increase chemical reaction rates. An increase in temperature marks the increase in kinetic energy of the molecules, which also increases their collision rates. 2. PH Level - Similar to the case in temperatures, enzymes also have an optimal pH level, wherein they can function to their fullest capacity. Recall that enzymes are globular proteins, and they are likely to have charged groups. 3. Substrate Concentration - The concentration of substrate molecules have a direct or positive relationship with the rate of enzyme- catalyzed reactions. Specifically, the highest reaction rates can be achieved when all the enzymes have available substrate for binding and catalysis. 4. Enzyme Concentration - Increasing the concentration of enzymes can also drastically increase the rate of chemical reactions. A higher enzyme concentration can ensure that there are more catalysts available to speed up a particular chemical reaction Remember: Increasing just the enzyme or substrate concentrations cannot increase the chemical reaction rates indefinitely. This is especially true if the saturation rate, which was discussed earlier, is taken into account. - Enzyme Regulation - High enzyme activity is not always ideal. There are cases wherein cells need to regulate enzyme activity for the benefit of the organism. 1. Inhibitors - one important way to regulate enzyme activity is through the use of inhibitors. - Inhibitors - are substances that are capable of slowing down or terminating catalytic reactions. - Inhibitors may be considered competitive inhibitors or noncompetitive inhibitors depending on their mechanism of action. a. Competitive inhibitors - have a structure that closely resembles the substrate molecules of enzymes. As such, these inhibitors are capable of binding to the enzyme\'s active sites. If binding occurs, then the active site becomes blocked, and the enzyme will not be able to accommodate substrate molecules as long as the inhibitor remains. These inhibitors compete with the substrates for binding to the enzyme\'s active site b. Noncompetitive inhibitors - can bind to enzymes outside of the active site. When these bindings occur, the enzyme\'s structure may become modified and can reduce the active site\'s capacity to bind to substrates - Chemical Modifications - There are several substances that are chemically linked to enzymes, and this chemical linkage can either increase or decrease that rate of enzymatic activity. The formation or the removal of these chemical linkages can drastically alter the activity of the enzyme in question. - An example of enzyme modification is the addition of phosphate groups. Protein kinases add these phosphate groups through phosphorylation, which can either speed up or slow down the enzyme\'s activity. Protein phosphatases can remove the phosphate groups through dephosphorylation, returning the enzyme to its original form. Key Points: - The factors that can affect enzyme activities are temperature, PH. and concentration of enzymes and substrate. - Increased temperatures can increase the activity of enzymes by increasing the collision rate with the substrate molecules. - Enzymes have varying optimal ranges for pH. Some enzymes optimally function at an acidic pH, while others at a basic pH level. - A higher enzyme concentration can ensure that there are catalysts available to speed up the chemical reaction in question. - Increasing substrate concentration may only increase the reaction rate up to the point where enzymes are already saturated.