Role of Oxygen in Cellular Respiration

Role of Oxygen in Cellular Respiration
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  • 0:00 Defining Cellular Respiration
  • 1:20 Steps of Cellular Respiration
  • 4:06 Production of ATP
  • 5:00 Lesson Summary
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Lesson Transcript
Instructor: Amanda Robb
This lesson focuses on oxygen in cellular respiration. In this lesson, we'll define cellular respiration and discuss why it's important for our bodies. We'll also look at the essential role of oxygen in the cellular respiration process.

Defining Cellular Respiration

Take a deep breath in and gently exhale. Every day, all day and all night, our lungs inhale and exhale air. Although calming, the goal of this process is to bring oxygen into the body. But ,why do we really need oxygen? Most students say to breathe, but this isn't quite accurate. We breathe to get oxygen, not the other way around. As it turns out, oxygen is the essential ingredient for making energy in a process called cellular respiration.

Cellular respiration is the process cells use to make energy. Our body cells need oxygen to do this process, although other organisms, like yeast or bacteria, don't always need it. They have other ways of making energy. But since the focus of this particular lesson is on the role of oxygen, we'll stick with animal cells, like the ones in our body.

All body cells engage in cellular respiration. They use oxygen and glucose, a sugar found in the foods we eat and convert them to ATP (adenosine triphosphate), or cellular energy, and carbon dioxide. Although this process can be represented by a single equation, there are actually many small steps that take place before we actually use oxygen to get ATP. Let's examine each of the three main steps in detail next.

Steps of Cellular Respiration

Cellular respiration has three main steps: glycolysis, the citric acid cycle, and oxidative phosphorylation, where oxygen is used.

Step 1: Glycolysis

Glycolysis is the first step in cellular respiration, and it occurs in the main compartment of the cell: the cytoplasm. Cells let glucose in from the blood--the glucose comes from the food we eat. Next, cells convert glucose through several different compounds to make two ATP molecules and a molecule called pyruvate. A compound called NADH (nicotinamide adenine dinucleotide + hydrogen) is also created. This molecule stores electrons harvested from the glucose, which will be used later to create a larger amount of ATP.

Step 2: Citric Acid Cycle

Next, the cell takes the pyruvate made in glycolysis and converts it to a molecule called acetyl Co-A. This happens in the powerhouse of the cell, the mitochondria. Acetyl Co-A is also converted to several different compounds but, ultimately, acetyl Co-A is regenerated, hence the 'cycle' part of the citric acid cycle. The citric acid cycle also creates another molecule of ATP, additional NADH, and the molecule FADH (flavin adenine dinucleotide + hydrogen), which also transports electrons.

Step 3: Oxidative Phosphorylation

The entire point of cellular respiration up until now has been to get a few ATP, but now it focuses on the electrons housed in the NADH. The NADH is taken to the mitochondrial membrane, or barrier of the mitochondria. There are actually two membranes--an inner and an outer membrane--and a small space in between called the intermembrane space. Here, electrons are transferred between proteins in the membrane in the electron transport chain. The proteins act like factory workers, passing down the electrons in a chain. As the electrons pass through, four proteins use the energy stored in the electrons to move hydrogen ions into the intermembrane space.

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