Metabolism Metabolism is essentially how the cell is able to use glucose and turn it into energy to carry on life processes. Note: Do Not spend any time on photosynthesis. We will not be covering that cycle in this class. • The definition of metabolism is the sum of all chemical reactions that occur in a living cell. This includes things like, protein synthesis, DNA replication, cell growth and division, etc. • These chemical reactions are divided into two categories. – Catabolism, which are the decomposition reactions in a living organism. In other words, they are the reactions responsible for the breakdown of complex organic compounds into simpler ones. An example is the breakdown of glucose. – Anabolism, which are the synthesis reactions in a living organism. In other words, they are the reactions that complex organic molecules from simpler ones. So DNA made from nucleotides. • Catabolism and Anabolism coupled reactions. That means that you can’t have one without the other. For example, glucose is broken down so that ATP can be made. 4 stages of metabolism • There are 4 basic stages of metabolism that we’ll discuss. They are: • 1. Digestion; • 2. Movement of nutrients across the cell membrane; • 3. Glycolysis; • 4. Kreb Cycle and electron transport chain. Digestion • Digestion is the process in which nutrients are broken down into small molecules that can be utilized by the cell. • Enzymes (specialized proteins) are needed to speed up these chemical reactions. • Each enzyme has a specific job in the process of digestion. – For example, amylase is an enzyme found in saliva. It’s job is to break down starch. • In addition, each enzyme has a unique physical shape. It is like a lock and key. Only the right shape of key will open the lock. With enzymes, only the right enzyme can work an a particular substance. – For example, amylase can recognize, bind to, and break down starch but it can’t synthesize ATP. • Most enzymes are named by using their function as the first half of the name and adding the suffix –ase on the end. So when you see a word with –ase on the end you’ll know that it is some kind of enzyme. – Examples: • Dehydrogenase: removes water • Transferase: transfers a chemical group from one compound to another • ATP synthase: synthesizes ATP • Bacterial cells make exoenzymes to help break down nutrients for their use. An exoenzyme is an enzyme that is made by the cell and excreted outside of the cell. The exoenzym is then used to break down large molecules outside of cell into molecules small enough to be transported across the cell membrane. Transport See pages 193-196 for a figures and more detailed explanations. • Transport refers to the movement of nutrients from outside the cell to the inside of the cell. There are 4 types of transport utilized by cells. • 1. Passive Diffusion: the nutrient moves down the concentration gradient. In other words, it moves from an area of high concentration to an area of low concentration. This type of transport requires No Energy. • 2. Facilitated Diffusion: uses a carrier molecule to bring the nutrient into the cell. The carrier molecule is one of those proteins that it found in the cell membrane. Like enzymes, it is specific for the nutrient that it can bind to and bring into the cell. This type of transport requires No Energy. • 3. Active Transport: movement of nutrients against the concentration gradient. Active transport requires the help of proteins in the cell membrane and ATP. Again, this type of transport requires Energy. • 4. Endocytosis: substance engulfed by cell membrane. This type of transport is utilized by some eukaryotic cells, such as some white blood cells that work to clean up bacterial infections. • In the next lecture we will focus on glycolysis, Kreb Cycle, and the electron transport chain. • Then we will look at how they function in aerobic respiration, anaerobic respiration and fermentation. Make sure you review the location in the cell in which cellular respiration occurs for both prokaryotic and eukaryotic cells.