Glycolysis: Videos & Practice Problems

Glycolysis is the initial step of cellular respiration, breaking down one glucose molecule (6 carbon atoms) into two pyruvate molecules (3 carbon atoms each). This process occurs in two phases: the energy investment phase, which consumes 2 ATP, and the energy harvest phase, producing 4 ATP and 2 NADH, resulting in a net gain of 2 ATP. Glycolysis takes place in the cytoplasm and does not require oxygen, making it unique among cellular respiration stages. The pyruvates produced are then transported to the mitochondria for further processing.

Glycolysis

Glycolysis is the initial step of cellular respiration, where a single glucose molecule is broken down into two pyruvate molecules. The term "glycolysis" is derived from two roots: "glyco," meaning sugar, and "lysis," meaning to break down. Thus, glycolysis literally translates to the breakdown of sugar, specifically glucose.

Glucose, which consists of six carbon atoms, is represented in glycolysis as a molecule with six carbon atoms. At the end of this process, glucose is converted into two pyruvate molecules, each containing three carbon atoms. It is essential to note that all six carbon atoms from glucose will eventually be transformed into carbon dioxide (CO₂) during the later stages of cellular respiration, specifically in the second and third steps. This CO₂ is ultimately exhaled into the environment.

One of the unique aspects of glycolysis is that it occurs in the cytoplasm of the cell, outside of the mitochondria, making it the only stage of aerobic cellular respiration that does not require oxygen. This means glycolysis can take place whether oxygen is present or not, unlike the subsequent stages of cellular respiration, which all occur within the mitochondria and require oxygen.

In summary, glycolysis is a crucial metabolic pathway that initiates the process of cellular respiration by converting glucose into pyruvate, while also serving as a key point of energy production that can function in both aerobic and anaerobic conditions.

Where does the first stage of aerobic cellular respiration take place within a cell?

• A. Mitochondrial matrix.
• B. Inner mitochondrial membrane.
• C. Intermembrane space.
• D. Cytoplasm.

Answer: (D)

Phases of Glycolysis

Glycolysis is a crucial metabolic pathway that consists of 10 chemical reactions, which can be divided into two distinct phases: the energy investment phase and the energy harvest phase. This process begins with a single glucose molecule, which contains six carbon atoms, and ultimately breaks down into two pyruvate molecules, each with three carbon atoms.

The first phase, known as the energy investment phase, requires an input of energy in the form of two ATP molecules. This phase is somewhat paradoxical because, while the overall goal of cellular respiration is to produce ATP, glycolysis initially consumes ATP to facilitate the breakdown of glucose. The investment of these two ATP molecules is essential for the cell to transition into the second phase.

The second phase, the energy harvest phase, is where the cell begins to reap the benefits of its initial investment. During this phase, the process generates energy by producing two NADH molecules, which serve as electron carriers, and a total of four ATP molecules. However, it is important to note that the net gain of ATP from glycolysis is only two ATP molecules. This is because the two ATPs used in the energy investment phase must be subtracted from the four ATPs produced, resulting in a net yield of two ATPs.

In summary, from one glucose molecule, glycolysis yields two pyruvate molecules, two NADH molecules, and a net of two ATP molecules. The pyruvate produced is then transported to the mitochondrial matrix, where it will enter the next stages of cellular respiration. Understanding these phases of glycolysis is fundamental as it sets the stage for the subsequent energy-producing processes within the cell.

Remembering Phases of Glycolysis

Glycolysis is a crucial metabolic pathway that breaks down glucose to extract energy. A helpful mnemonic to remember the phases of glycolysis is "Gary invests to harvest his profits and travel to Mexico." This phrase corresponds to the key steps in the glycolytic process.

The first letter, G in "Gary," signifies the starting molecule, glucose, which consists of six carbon atoms. This is represented by six black circles in diagrams. The next part, I in "invest," refers to the initial investment phase of glycolysis. During this phase, the cell invests two ATP (adenosine triphosphate) molecules to initiate the breakdown of glucose.

Moving on, the H in "harvest" represents the harvest phase, the second stage of glycolysis. Here, the cell can double its energy investment, producing four ATP molecules. After accounting for the initial two ATPs spent, the net gain is two ATPs.

The P in "profits" stands for pyruvate, the end product of glycolysis. The process results in the formation of two three-carbon pyruvate molecules, which are essential for the next stages of cellular respiration.

Finally, "travel to Mexico" symbolizes the movement of these pyruvates to the mitochondria, where the next stage of cellular respiration occurs. This imagery of the mitochondria relaxing on a beach in Mexico serves as a fun reminder of the pyruvates' journey.

In summary, using the mnemonic "Gary invests to harvest his profits and travel to Mexico" can effectively aid in recalling the phases of glycolysis: starting with glucose, investing ATP, harvesting energy, producing pyruvate, and the subsequent travel to the mitochondria for further energy production.

Glycolysis Example 1

Glycolysis is a crucial metabolic pathway that consists of two distinct phases: the energy investment phase and the energy harvest phase. To initiate glycolysis, an energy investment is required, specifically the use of 2 ATPs. This initial investment is essential for the pathway to proceed.

During the energy investment phase, these 2 ATP molecules are consumed to prepare glucose for subsequent breakdown. Following this phase, the process transitions into the energy harvest phase, where the cell generates a total of 4 ATPs and 2 NADH. However, since 2 ATPs were used in the investment phase, the net gain from glycolysis is only 2 ATPs.

In summary, the energy investment step of glycolysis requires the use of 2 ATPs, making it a critical component of the overall process. Understanding this investment is key to grasping how glycolysis functions and its role in cellular respiration.

Starting with one molecule of glucose, glycolysis results in the net production of which of the following sets of energy-containing products?

• A. 2 NAD⁺, 2 pyruvate, and 2 ATP.
• B. 2 NADH, 2 pyruvate, and 2 ATP.
• C. 4 NADH, 2 pyruvate, and 4 ATP.
• D. 6 CO₂, 2 pyruvate, and 2 ATP.

Answer: (B)

Which of the following is a result of glycolysis?

• A. A net gain of four ATP per one glucose molecule.
• B. Conversion of FAD to FADH₂.
• C. Conversion of one glucose molecule to two pyruvate molecules.
• D. Conversion of NADH to NAD⁺.

Answer: (C)

Here’s what students ask on this topic:

What is glycolysis and where does it occur in the cell?

Glycolysis is the first step of cellular respiration, involving the breakdown of one glucose molecule (6 carbon atoms) into two pyruvate molecules (3 carbon atoms each). This process occurs in the cytoplasm of the cell. Unlike other stages of cellular respiration, glycolysis does not require oxygen, making it unique. The process consists of two phases: the energy investment phase, which consumes 2 ATP, and the energy harvest phase, which produces 4 ATP and 2 NADH, resulting in a net gain of 2 ATP. The pyruvates produced are then transported to the mitochondria for further processing.

What are the two phases of glycolysis?

Glycolysis consists of two phases: the energy investment phase and the energy harvest phase. In the energy investment phase, the cell uses 2 ATP molecules to initiate the breakdown of glucose. This phase is crucial for setting up the subsequent reactions. The energy harvest phase follows, where the cell produces 4 ATP molecules and 2 NADH molecules. However, since 2 ATP were used in the investment phase, the net gain is 2 ATP. These phases ensure that the cell efficiently breaks down glucose into pyruvate while generating a small amount of energy.

What are the net products of glycolysis?

The net products of glycolysis from one glucose molecule are 2 pyruvate molecules, 2 NADH molecules, and a net gain of 2 ATP molecules. Initially, 4 ATP are produced, but 2 ATP are consumed during the energy investment phase, resulting in a net gain of 2 ATP. The pyruvate molecules are then transported to the mitochondria for further stages of cellular respiration, while NADH carries electrons to the electron transport chain.

Why is glycolysis considered an anaerobic process?

Glycolysis is considered an anaerobic process because it does not require oxygen to occur. This is in contrast to other stages of cellular respiration, such as the Krebs cycle and the electron transport chain, which require oxygen. Glycolysis takes place in the cytoplasm and can proceed in both the presence and absence of oxygen, making it a versatile and essential pathway for energy production in cells, especially under anaerobic conditions.

How does the energy investment phase of glycolysis work?

The energy investment phase of glycolysis involves the consumption of 2 ATP molecules to phosphorylate glucose and its intermediates. This phase prepares the glucose molecule for subsequent breakdown and energy extraction. The ATP molecules provide the necessary energy to add phosphate groups to the glucose, converting it into a more reactive form. This investment is crucial for driving the reactions that follow in the energy harvest phase, where the cell ultimately gains more ATP than it initially invested.