Question

The total ATP production during EMP pathway is (a) 24 ATP molecules (b) 8 ATP molecules (c) 38 ATP molecules (d) 6 ATP molecules

Short answer

(b) 8 ATP molecules

Step-by-step solution

Identify the EMP pathway

The Embden-Meyerhof-Parnas (EMP) pathway, also known as the glycolytic pathway, is a 10-step process where glucose is converted into pyruvate, while also generating ATP and NADH. In biochemistry, this pathway is ubiquitously used for energy production.

Breakdown the pathway into phases

The EMP pathway is divided into two main phases. In the first phase (energy-investment), two ATPs are consumed per molecule of glucose. In the second phase (energy-yielding), four ATPs are produced per molecule of glucose, hence a net gain of two ATPs. Also, two NADH molecules, which are later used in the electron transport chain to produce additional ATPs, are generated.

Calculate total ATP production

In the electron transport chain, each NADH molecule can generate about 2.5 ATPs (theoretically 3, but it is closer to 2.5 in many organisms due to losses across the mitochondrial membrane). Therefore, 2 NADH x 2.5 ATP/NADH gives a total of 5 ATPs. When added to the net 2 ATPs from glycolysis itself, we get a total of 7 ATPs. However, this is a conservative estimate and can be up to 8 ATPs in certain organisms due to variations in mitochondrial efficiency.

Key concepts

Glycolytic Pathway

Imagine glucose as the starting line of a race. The Glycolytic Pathway, also known as the Embden-Meyerhof-Parnas (EMP) pathway, guides glucose through a series of 10 steps. During this process, glucose is transformed into pyruvate. It's akin to passing a baton in a relay race, where each step is crucial for passing energy to the next. This pathway is essential for both creating energy and providing critical intermediates for other pathways.
This occurs in the cell's cytoplasm and is a universal process, present in almost every living cell. The Glycolytic Pathway can be divided into two general phases: the energy investment phase and the energy generation phase.
Here's a quick breakdown of what happens:

• Energy Investment Phase: 2 ATP molecules are used to phosphorylate glucose and its derivatives. This is a kind of setup phase where glucose is primed for energy release.
• Energy Payoff Phase: 4 ATP and 2 NADH molecules are produced. This phase involves the breaking down of molecules and harvesting the energy stored within them.

Remember, while it seems a little counterintuitive to use energy to make energy, this setup is crucial for kickstarting the process of glycolysis.

ATP Production

In the Glycolytic Pathway, ATP production is a critical outcome. ATP, or Adenosine Triphosphate, is like the energy currency of the cell. Cells "spend" ATP to fuel various tasks, from muscle contractions to cellular communication and beyond.
Here’s what you need to know about ATP production in glycolysis:

• The process starts with an initial investment of 2 ATP molecules to break down glucose into different intermediate forms. It's like spending some money to make more money later.
• In the subsequent phases, the breakdown of glucose eventually leads to the production of 4 ATPs. However, since 2 ATPs have already been "spent," the net gain is actually 2 ATPs.

Think of ATP as rechargeable batteries. The Glycolytic Pathway helps recharge these batteries, ensuring the cell can keep its activities running smoothly.

NADH

As glucose journeys down the Glycolytic Pathway, we also generate another molecule: NADH. Consider NADH as a kind of "energy check" that denotes stored potential energy. It plays a pivotal role in the cell's energy economy.
During glycolysis, each molecule of glucose processed results in the production of 2 NADH molecules. Here's why they are special:

• Energy Carrier: NADH carries electrons. This makes them similar to energy vouchers that can be redeemed later for ATP.
• Role in Electron Transport Chain: NADH contributes by donating the electrons it holds.

Now, imagine these "energy checks" being sent to a "power plant" inside the cell—the electron transport chain—where they are "cashed in" for actual energy. The complete oxidation of one NADH results in about 2.5 ATPs, but actual yield can vary.

Electron Transport Chain

The Electron Transport Chain, much like a factory assembly line, takes in specific inputs and churns out valuable outputs. This process occurs in the mitochondria or "powerhouses" of the cell.
Let's delve into the specifics:

• The electrons carried by NADH pass through a series of proteins known as complexes. These complexes are embedded in the mitochondrial membrane.
• As electrons move from one complex to another, they release energy that helps pump protons across the membrane, creating a gradient—imagine it like water held behind a dam.
• Finally, as protons flow back across the membrane, through a structure called ATP synthase, this stored energy is harnessed to produce ATP.

So when NADH, which arrives from the glycolytic pathway, engages in this process, it helps generate more ATP for the cell. If each NADH can produce approximately 2.5 ATPs, and the glycolytic pathway yields 2 NADH per glucose molecule, understanding and mastering this concept can illuminate how energy is efficiently harvested in organisms.