本期内容是 实验五：细胞呼吸：测量运动时的能量消耗 的实验手册，实验模拟的部分请看下一期。本部分内容来自 University of California, Berkeley - UC Berkeley Extension, 虚拟实验的内容来自 Labster. 本部分内容均不会标记为为原创，但由于是UP主购买的课程，因此不接受非授权的转载，谢谢您的理解。

每一个生物基础实验均会分为三部分：第一部分为实验的生物理论；第二部分为实验的指导手册；第三部分为 Labster 的虚拟实验模拟。第一部分的基本信息由 Ying Liu, Ph.D. 提供，第二部分的实验手册来自 Labster, 第三部分的实验模拟过程由UP主操作。

Virtual Lab Manual 5

Cellular Respiration: Measuring energy consumption during exercise

Synopsis

A simpler version of this simulation intended for principles or high school courses can be found at “Cellular Respiration (Principles): Measure energy consumption during exercise”.

What does it mean to work up an appetite? In this simulation, you will learn about how we metabolize glucose through aerobic and anaerobic respiration. You will be taken through the three stages of cellular respiration: glycolysis, the Krebs cycle and the electron transport chain.

Evaluate cellular respiration through exercise

Beginning by outlining the structural changes that take place during phosphorylation and glycolysis, you will identify the important products of the Krebs cycle and follow their electrons through the electron transport chain. Then, you will apply what you have learned about cellular respiration to experiments on exercise intensity and oxygen consumption using a mouse model.

Respirometry and blood sample analysis

You will measure cellular respiration by analyzing the blood glucose and lactic acid concentrations of basketball players throughout their game. This data will be compared to experimental exercise data collected using a mouse model and respirometry. The experimental portion of this simulation is supported with strong theoretical explanations of the central steps of glycolysis, phosphorylation and the Krebs cycle using 3D molecules and interactive feedback. The simulation includes an immersive experience of jumping inside mitochondria that demonstrates how protein complexes in the inner membrane of the mitochondria contribute to the electrochemical gradient used by ATP synthase to generate ATP.

Help athletes perform during exercise

Experiment using a mouse model to understand the role of glucose, lactic acid and oxygen during exercise. Apply your knowledge from mouse experiments and of glycolysis, the Krebs cycle and the electron transport chain to help basketball players perform their best during their game.

Learning Objectives

At the end of this simulation, you will be able to…

● Explain the structural changes of glucose and ATP during glycolysis

● analyze blood glucose and lactic acid concentrations of athletes before and after exercise

● Determine electron carrier products of the Krebs cycle

● Understand the role of the electron transport chain in generating ATP

● Experiment on oxygen consumption in mice at various exercise intensities

Techniques in Lab

● Respirometry

● Measure and analyze blood glucose and lactic acid concentrations

Theory

Metabolism

The word metabolism comes from the Greek word “metabolë” meaning “change”. It refers to the chemical transformations that take place in cells. These reactions sustain all life, i.e. allow the organism to maintain their structures, grow, reproduce and respond to their environment.

Metabolic reactions can be divided into catabolic reactions or anabolic reactions that are interconnected and form metabolic pathways.

Cellular respiration

Cellular respiration is the process by which animals convert food into a type of energy usable by their cells, known as ATP. The first step of cellular respiration is called glycolysis and results in the formation of pyruvate.

Aerobic cellular respiration occurs when oxygen is present, and pyruvate will enter the Krebs cycle allowing the electron transport chain to proceed. Anaerobic cellular respiration does not require the presence of oxygen and pyruvate will undergo lactic acid fermentation. Comparing the result of aerobic and anaerobic respiration highlights why oxygen is so important for cellular respiration.

Cellular respiration is the process that converts the energy from chemical bonds in food to a form of energy that the cell can use, ATP.

ATP

Adenosine triphosphate, or ATP, is a molecule which acts as a universal energy currency for living cells. Its structure consists of the nucleoside adenosine and a tail of three phosphate groups.

During ATP synthesis via reactions or by ATP synthase energy is safely stored as chemical energy in the structure of ATP, specifically in the high energy phosphate bonds. The negative charges in the phosphate groups repel each other and need high amounts of energy to bond them together. When these high-energy bonds are broken, this energy is released through ATP hydrolysis.

Glycolysis

Glycolysis is the first step in cellular respiration and occurs in the cytoplasm of the cell. The word glycolysis literally means “breaking down sugars”. During this process, the 6-carbon glucose molecule is split into two 3-carbon pyruvate molecules, producing only a small amount of energy (see detailed steps). Nearly all living organisms carry out glycolysis as part of their metabolism. The process does not use oxygen and is therefore anaerobic.

Krebs cycle

The Krebs cycle is also called the tricarboxylic acid (TCA) cycle or citric acid cycle. It is the continuation of aerobic cellular respiration after glycolysis, and it takes place in the mitochondrial matrix. During the Krebs cycle preparation step, pyruvate is transformed to acetyl-CoA. After this, several Krebs cycle reactions couple the oxidation of pyruvate to CO2, reduce the electron carriers NAD+ and FAD , and produce ATP via substrate-level phosphorylation. The reduced electron carriers (NADH and FADH2) are used in the electron transport chain to produce more ATP by oxidative phosphorylation.

Electron transport chain

The electron transport chain takes place in the inner mitochondrial membrane and is the final step of aerobic cellular respiration. The proteins involved in the electron transport chain are outlined in Figure 1 below.

The electron transport chain consists of a series of redox reactions that transfer electrons from NADH and FADH2 through various intermediates to the final electron acceptor, oxygen (see detailed ETC steps). This process generates an electrochemical gradient that couples the oxidative reactions with the phosphorylation of ADP producing ATP in a process called oxidative phosphorylation.

Chemiosmosis

Chemiosmosis is the movement of ions across a selectively permeable membrane down an electrochemical gradients. In the context of cellular respiration, it refers to the diffusion of protons through ATP synthase. This process is coupled to the generation of ATP via oxidative phosphorylation. If the electrochemical gradient is disrupted for any reason, the electron transport chain is stopped.

Different electron carriers yield different amounts of ATP. On average, each NADH molecule results in the production of 3 ATP molecules, and each FADH2 molecule produces 2 ATP molecules.

Respirometry

Respirometry refers to a group of techniques where a quantitative measurement of respiration is performed. It is based on an indirect measurement of metabolic changes by recording variations in oxygen levels in a respirometer due to energy consumption of a experimental animal model.

Energy use

Our bodies require energy produced through ATP synthesis. Our cells can produce ATP through the oxidation of glucose via aerobic cellular respiration or lactic acid fermentation, depending on oxygen availability. When we exercise, energy requirements increase and glucose is consumed more quickly. Also, oxygen consumption of the electron transport chain increases resulting in heavy breathing. We can measure oxygen consumption using respirometry.

In situations with low oxygen for prolonged periods of time, lactic acid can accumulate leading to lactic acidosis.

The importance of aerobic respiration is reflected in the consequences of blocking it: cells are not able to produce the energy our bodies need to maintain vital functions. This can even lead to the death of the organism. On the other hand, boosting aerobic respiration, for example by increasing oxygen availability through blood doping, leads to an increase in energy production used to improve the performance of athletes.

本期内容到此结束，感谢阅读！下一期将进行 Labster 实验！