Glycolysis: Videos & Practice Problems

Glycolysis is the initial step of cellular respiration, breaking down one glucose molecule (6 carbons) into two pyruvate molecules (3 carbons 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" combines 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 six black circles, each symbolizing a carbon atom. At the end of glycolysis, the glucose molecule is split into two pyruvate molecules, each containing three carbon atoms. It is essential to note that all six carbon atoms from glucose will eventually be converted 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.

Glycolysis is unique among the stages of aerobic cellular respiration because it occurs in the cytoplasm of the cell, outside the mitochondria. Additionally, it is the only stage that does not require oxygen, allowing it to proceed in both aerobic (with oxygen) and anaerobic (without oxygen) conditions. This characteristic distinguishes glycolysis from the other stages of cellular respiration, which all take place within the mitochondria.

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 flexibility in energy production, functioning independently of oxygen and occurring in the cytoplasm.

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 it down into two pyruvate molecules, each with three carbon atoms.

The first phase, known as the energy investment phase, requires an input of energy, specifically utilizing 2 ATP molecules. This initial investment is somewhat counterintuitive, as the primary goal of aerobic cellular respiration is to generate ATP. However, this phase is essential for preparing the glucose molecule for subsequent reactions. The energy investment allows the cell to transition into the second phase of glycolysis.

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 2 NADH molecules, which serve as electron carriers, and produces a total of 4 ATP molecules. It is important to note that while 4 ATP molecules are produced, the net gain of ATP from glycolysis is only 2 ATP molecules. This is because the 2 ATP molecules used in the energy investment phase must be subtracted from the total produced.

In summary, from one glucose molecule, glycolysis yields 2 pyruvate molecules, 2 NADH molecules, and a net of 2 ATP molecules. The pyruvate molecules are then transported to the mitochondrial matrix, where they will enter the next stages of cellular respiration. Understanding these phases of glycolysis is fundamental for grasping how cells convert glucose into usable energy.

Remembering Phases of Glycolysis

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

The process begins with a glucose molecule, which consists of 6 carbon atoms. The first phase, represented by "invest," is the investment phase where the cell invests 2 ATP (adenosine triphosphate) molecules to initiate glycolysis. This investment is essential for the subsequent reactions to occur.

Next, "harvest" refers to the harvest phase, the second stage of glycolysis. During this phase, the cell can produce 4 ATP molecules, resulting in a net gain of 2 ATP after accounting for the initial investment. This phase is critical as it allows the cell to generate energy efficiently.

The "profits" in the mnemonic symbolize pyruvate, the end product of glycolysis. At the conclusion of this process, two 3-carbon pyruvate molecules are formed. These pyruvates are then transported to the mitochondria, which is represented by "travel to Mexico." This transportation is vital as it leads to the next stage of cellular respiration, where further energy extraction occurs.

In summary, glycolysis involves the breakdown of glucose into pyruvate, with an initial investment of ATP followed by a harvest of energy. The mnemonic serves as a useful tool to recall these phases and their significance in cellular metabolism.

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, which involves the consumption of 2 ATPs. This initial step is essential for the pathway to proceed.

During the energy investment phase, these 2 ATP molecules are utilized 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 consumed in the investment phase, the net gain from glycolysis is 2 ATPs.

In summary, glycolysis begins with an investment of 2 ATPs, leading to a net production of 2 ATPs after the energy harvest phase. This understanding is fundamental for grasping the overall energy dynamics of 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 and does not require oxygen, making it unique among the stages of cellular respiration. Glycolysis 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 and what happens in each phase?

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 preparing the glucose molecule for subsequent reactions. In the energy harvest phase, the cell produces 4 ATP molecules and 2 NADH molecules. Since 2 ATP were used in the investment phase, the net gain is 2 ATP. Additionally, 2 pyruvate molecules are formed, which are then transported to the mitochondria for further processing in cellular respiration.

Why is glycolysis considered unique among the stages of cellular respiration?

Glycolysis is unique among the stages of cellular respiration for several reasons. Firstly, it occurs in the cytoplasm of the cell, whereas the other stages occur inside the mitochondria. Secondly, glycolysis does not require oxygen, allowing it to occur in both aerobic and anaerobic conditions. This is in contrast to the other stages of cellular respiration, which require oxygen. Lastly, glycolysis is the only stage that involves an initial investment of ATP (2 ATP) to produce a net gain of ATP (2 ATP) and NADH (2 NADH).

What are the net products of glycolysis from one glucose molecule?

From one glucose molecule, the net products of glycolysis are 2 pyruvate molecules, 2 NADH molecules, and a net gain of 2 ATP molecules. Initially, 2 ATP molecules are consumed in the energy investment phase, but 4 ATP molecules are produced in the energy harvest phase, resulting in a net gain of 2 ATP. The 2 pyruvate molecules formed are then transported to the mitochondria for further processing in the subsequent stages of cellular respiration.

How does the energy investment phase of glycolysis differ from the energy harvest phase?

The energy investment phase and the energy harvest phase of glycolysis differ in their roles and outcomes. In the energy investment phase, the cell uses 2 ATP molecules to phosphorylate glucose, preparing it for further breakdown. This phase is essential for initiating the glycolytic pathway. In contrast, the energy harvest phase produces energy by generating 4 ATP molecules and 2 NADH molecules. Since 2 ATP were used in the investment phase, the net gain is 2 ATP. Additionally, 2 pyruvate molecules are formed, which are then transported to the mitochondria for further processing.