What Is Cellular Respiration - How Do Cells Obtain Energy - Energy Production In The Body
In this video we discuss what is cellular respiration, and how the body converts food into energy.
Transcript/Notes
What is cellular respiration? Well cellular respiration is basically the breakdown of organic molecules such as carbohydrates, fats and amino acids, which make up proteins, to produce energy. Glucose, which is a simple carbohydrate, is the preferred source for the cellular respiratory pathway.
In this video we are going to go through the basics of this process, we are not going to go through every single step in detail, rather a summary of the steps.
There are four main stages that take place during the cellular respiratory pathway, glycolysis, an intermediate stage, the citric acid cycle and the electron transport system. An important thing to know is that glycolysis does not require oxygen making it anaerobic, and the other 3 stages do require oxygen, making them aerobic.
So, lets say you eat a banana, which contains glucose. And your body wants to take some of that glucose and convert it to cellular energy. Inside the cytosol of a cell is where the first step, glycolysis, takes place.
During glycolysis a molecule of glucose, which has 6 carbons, goes through a series of steps which lead to the glucose molecule being converted to 2 pyruvate molecules. These pyruvate molecules have 3 carbons each, so 6 carbon glucose to 2 3 carbon pyruvates. During glycolysis 2 ATP molecules are invested and 4 ATP molecules are produced, so a net gain of 2 ATP’s.
ATP is the energy currency in cells, so you can think of it like a gas can that provides the fuel to do cellular work.
Another key thing is that during glycolysis 2 molecules of NADH are produced and these molecules will be used in a later process.
The pyruvates that are produced have 2 pathways, if sufficient oxygen is available they will enter into the citric acid cycle, and if oxygen is not available pyruvate is converted to lactate, we will cover this pathway in depth in a later video.
Next is the intermediate stage. With oxygen available, the pyruvates will enter a mitochondria, which is an organelle in the cell. Here, pyruvate is converted into acetyl coa and 2 more molecules of NADH are produced, and a carbon dioxide molecule is released.
Next is the third stage, the citric acid cycle. In the citric acid cycle, acetyl coa goes through several steps leading to the production of one ATP molecule, three NADH molecules and one FADH2 molecule as well as the release of 2 co2 molecules.
But remember, we started with 2 acetyl coa molecules, so the citric acid cycle must occur twice, which gives a total of 2 ATP’s, 6 NADH’s, and 2 FADH2’s, and 4 co2 molecules released.
Now for the fouth stage, the electron transport chain. This is where the most ATP production occurs. Here, NADH and FADH2 release electrons, which after a series of steps leads to the production of 32 to 34 ATP molecules.
So, in theory we have 2 atp’s from glycolysis, 2 atp’s from the citric acid cycle and 34 from the electron transport chain, for a total of 38 atp’s produced. However, the actual number is estimated to be between 28 and 30, because some of the processes along the pathway need to use atp to complete their functions. And so now the path of cellular respiration is complete.
Well, how about other food molecules?
Glucose is a simple carbohydrate, and we have seen how it fits into the cellular respiratory pathway, but, other simple carbohydrates such as fructose, and galactose can enter the pathway during the glycolysis stage as well.
Proteins are made up of amino acids and most of the time they are not used to produce energy via cellular respiration. However, if the body needs to use amino acids for energy, it can. First they must have their amino NH2 group removed. Once this is done, different amino acids enter the cellular respiratory pathway at different stages.
Lipids or fats can also enter the pathway. Triglycerides, the main form of fat in the body consist of 4 parts, a glycerol unit and 3 fatty acids. The glycerol unit can be modified and enter the pathway in the glycolysis stage, and the fatty acids can be broken down further and enter at the citric acid cycle stage.
Timestamps
0:00 Overview of cellular respiration
0:28 The 4 steps of cellular respiration
0:50 Glycolysis
1:52 The intermediate stage
2:20 The citric acid cycle
2:54 The electron transport chain
3:54 Protein/Amino acids entering the pathway
4:14 Lipids/Fats entering the pathway
