Welcome to My AP Biology Thoughts podcast, my name Morgan and I am your host for episode #72 called Unit 3 Cellular Energetics: Glycolysis. Today we will be discussing the first step in the process of cellular respiration
Segment 1: Introduction to Glycolysis
Glycolysis is the first of roughly three, kind of three and a half, steps in the process of cellular respiration. It occurs in the cytoplasm of the cell, and is an anaerobic process. This means that it does not require oxygen to occur, although the overall process of cellular respiration does require oxygen. The purpose of glycolysis in cellular respiration is to start the breakdown of glucose in order to extract energy needed for cell work and metabolism, made in the form of ATP. In organisms that do not use aerobic respiration and cannot perform cellular respiration, the goal of glycolysis is to produce a little bit of ATP, as well as generating NADH to restart the process and continue making small amounts of ATP. The process is started with a molecule of glucose, and at the end we are left with 2 molecules of ATP, 2 of NADH and 2 of a molecule known as pyruvate. So, let's take a deeper look into the steps and energy transfers in glycolysis
Segment 2: More About Steps of Glycolysis and Energy Transfers
The starting molecule of glucose enters the cytoplasm of the cell, and is rearranged into 2 3-carbon sugars with phosphate groups attached. These phosphate groups come from two molecules of ATP splitting into ADP and P. From there, both of these 3-carbon sugars are oxidized, meaning they lose their electrons. These electrons go to molecules of NAD+, and reduce them to NADH. This is an oxidation-reduction reaction, since the molecules of glucose leave and go to NAD+, so glucose is oxidized and once again NAD+ is reduced to NADH. What's left of the oxidized glucose is now our key 3-carbon molecule of pyruvate. Through the reactions oxidizing the 3-carbon sugars of glucose into pyruvate, we have made 2 molecules of ATP and 1 of NADH. However, we must remember that there are 2 molecules of pyruvate that were made, meaning we have a total yield of 4 ATP and 2 NADH. And since we used up two molecules of ATP to get our phosphate groups in the beginning, we have a net yield of only 2 ATP.
Throughout the process of glycolysis, and really all of cellular respiration we are focused on oxidizing and breaking down glucose. This means we are breaking chemical bonds, which we know releases energy. Therefore, glycolysis is an exergonic process.
Segment 3: Connection to the Course
Glycolysis has many important connections to our unit of cellular energetics and our ap biology course overall. First, we remembered OILRIG and oxidation-reduction reactions when dealing with glucose and NAD+/NADH. We also talked about how glycolysis is an exergonic process, since the breaking of bonds releases energy. This means that the delta G of the process is negative.
Additionally, glycolysis occurs in all organisms, whether they are in anaerobic or aerobic conditions. Glycolysis is part of anaerobic respiration for organisms to produce a small amount of ATP as energy and keep regenerating NADH, but for more information on anaerobic respiration listen to episode #76.
Lastly, we can connect topics of enzymes to the process of glycolysis. Each step in the process of glycolysis has a specific enzyme to catalyze it, the most important one being phosphofructokinase. We can apply our knowledge of enzyme activity here, to know that increasing or decreasing factors like pH and temperature can speed up or slow down the rate of the reaction, since they affect the enzyme's ability to lower activation energy.
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"Ice Flow" Kevin MacLeod (incompetech.com)
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