5 Chapter 5: Metabolism, Cellular Respiration and Photosynthesis (5/16) -- Human Biology

5 Chapter 5: Metabolism, Cellular Respiration and Photosynthesis Chapter Outline - Energy and Metabolism - ATP: Adenosine Triphosphate - Enzymes - Energy in Living System - Glycolysis - Oxidation of Pyruvate and the Citric Acid Cycle - Oxidative Phosphorylation - Metabolism Without Oxygen - Connections of Carbohydrates, Proteins, and Lipid Metabolic Pathways - Regulation of Cellular Respiration - Overview of Photosynthesis - The Light-Dependent Reactions of Photosynthesis - Using Light Energy to Make Organic Molecules Figure 5.1 A hummingbird needs energy to maintain prolonged periods of flight. The bird obtains its energy from taking in food and transforming the nutrients into energy through a series of biochemical reactions. The flight muscles in birds are extremely efficient in energy production.(credit: modification of work by Cory Zanker) Introduction Virtually every task performed by living organisms requires energy. Energy is needed to perform heavy labor and exercise, but humans also use a great deal of energy while thinking, and even during sleep. In fact, the living cells of every organism constantly use energy. Nutrients and other molecules are imported, metabolized (broken down) and possibly synthesized into new molecules, modified if needed, transported around the cell, and may be distributed to the entire organism. For example, the large proteins that make up muscles are actively built from smaller molecules. Complex carbohydrates are broken down into simple sugars that the cell uses for energy. Just as energy is required to both build and demolish a building, energy is required for both the synthesis and breakdown of molecules. Additionally, signaling molecules such as hormones and neurotransmitters are transported between cells. Pathogenic bacteria and viruses are ingested and broken down by cells. Cells must also export waste and toxins to stay healthy, and many cells must swim or move surrounding materials via the beating motion of cellular appendages like cilia and flagella. The cellular processes listed above require a steady supply of energy. From where, and in what form, does this energy come? How do living cells obtain energy, and how do they use it? This chapter will discuss different forms of energy and the physical laws that govern energy transfer. This chapter will also describe how cells use energy and replenish it, and how chemical reactions in the cell are performed with great efficiency. Learning Objectives You will be able to describe these basic functions of metabolism: - define metabolism - describe the role of enzymes in metabolism - recognize that enzymes are proteins - describe the role of ATP in cellular processes - understand energy production in a cell from sources like glucose - understand ATP production from light in photosynthesis 5.1 | Energy and Metabolism Scientists use the term bioenergetics to discuss the concept of energy flow (Figure 5.2) through living systems, such as cells. Cellular processes s