Energy Production In Biochemical Pathways: Study with Video Lessons, Practice Problems & Examples

Biochemical systems generate energy primarily through oxidation reactions and hydrolysis. Oxidation reactions involve electron carriers like NADH and FADH₂, as seen in the citric acid cycle where malate converts to oxaloacetate and succinate to fumarate. Hydrolysis, such as ATP cleavage, releases energy by breaking high-energy phosphate bonds. Understanding these processes is crucial for grasping metabolic pathways and energy production in cells, highlighting the significance of enzymes and substrates in biochemical reactions.

Energy Production In Biochemical Pathways Concept 1

Hey everyone. So here we can say that biochemical systems most commonly employ 2 methods to produce energy. Now in the first one, we have oxidation reactions. And they produce energy in the form of electron carriers, so we're talking about the production of NADH and FADH₂. If we take a look here, we have step 8 of our citric acid cycle where we have malate being changed into oxaloacetate. Here, we have NAD⁺. It's going to gain electrons to become NADH, and through the use of our substrate, malate, and our enzyme, Malate dehydrogenase, we create Oxaloacetate. Remember, when we talk about dehydrogenases as enzymes, we're talking about oxidation reactions. Over here, this represents step 6 of our Citric Acid Cycle where we have Succinate being changed into Fumarate. Again, we're using a dehydrogenase, so this is an oxidation that's occurring. In this case though, we have FAD becoming FADH₂. Remember, FAD to FADH₂ will be utilized in order to create a pi bond. In this case, we created a Pi bond between these two carbons which transforms our succinate into fumarate. Now, next, we're going to say we have what's called cleavage reactions or just simply hydrolysis. We're going to have the cleavage or hydrolysis of high energy bonds to release energy stored in them. A great way to look at this is the cleaving of our phosphate bonds in ATP to release energy. So here we have ATP, we include our water, here it's going to help break one of these bonds, releasing an inorganic phosphate, and in the process, because we're breaking that high energy bond, we're gonna release ATP. So here's the ATP that's released. So just remember, when it comes to these biochemical systems, biochemical reactions, there's mainly 2 major ways to produce energy, either through oxidation reactions or through cleavage/hydrolysis.

Energy Production In Biochemical Pathways Example 1

Here it says, identify the following biochemical reaction would use energy or produce energy. In this reaction, we have isocitrate plus NAD⁺. We're using the enzyme isocitrate dehydrogenase. This creates alpha-ketoglutarate, carbon dioxide, NADH plus H⁺. Now, here, we're going to say that we're using a dehydrogenase. Remember, this is the enzyme of choice for an oxidation reaction. And we're going to say this is an oxidation reaction because we've produced NADH. Remember these NADH, FADH₂ productions for these oxidation reactions will make energy, so this is going to produce energy. This particular reaction itself represents reaction 3 or step 3 in the Krebs cycle or citric acid cycle. Okay? So here, because we're using a dehydrogenase, this is an oxidation reaction. We're making NADH which is an electron carrier. This is indicative of a biochemical reaction that's going to produce energy.

Which of the following biochemical reactions would not produce energy?

• A. ATP + H₂O → ADP + HOPO₃²⁻ + H⁺
• B. 6-phosphogluconate + NADP⁺  → ribulose-5-phosphate + CO₂ + NADPH
• C. Pyruvate + NAD⁺ + HS–CoA → Acetyl CoA + CO₂ + NADH
• D. Glucose + ATP → glucose-6-phosphate + ADP + H⁺

Here’s what students ask on this topic:

What are the main methods of energy production in biochemical pathways?

Biochemical pathways primarily produce energy through two main methods: oxidation reactions and hydrolysis. Oxidation reactions involve the transfer of electrons to electron carriers like NAD⁺ and FAD, forming NADH and FADH₂. For example, in the citric acid cycle, malate is oxidized to oxaloacetate, producing NADH. Similarly, succinate is oxidized to fumarate, producing FADH₂. Hydrolysis involves the cleavage of high-energy bonds, such as the phosphate bonds in ATP. When ATP is hydrolyzed, it releases energy by breaking these bonds, forming ADP and an inorganic phosphate. These processes are crucial for cellular energy production and metabolic pathways.

How does the citric acid cycle contribute to energy production?

The citric acid cycle, also known as the Krebs cycle, is a key metabolic pathway that contributes to energy production by oxidizing acetyl-CoA to CO₂ and transferring electrons to NAD⁺ and FAD. This results in the formation of NADH and FADH₂, which are electron carriers. For instance, in step 8, malate is converted to oxaloacetate, producing NADH. In step 6, succinate is converted to fumarate, producing FADH₂. These electron carriers then donate electrons to the electron transport chain, leading to the production of ATP, the primary energy currency of the cell.

What role do dehydrogenases play in biochemical energy production?

Dehydrogenases are enzymes that play a crucial role in biochemical energy production by catalyzing oxidation reactions. They facilitate the transfer of electrons from substrates to electron carriers like NAD⁺ and FAD. For example, in the citric acid cycle, malate dehydrogenase catalyzes the conversion of malate to oxaloacetate, producing NADH. Similarly, succinate dehydrogenase catalyzes the conversion of succinate to fumarate, producing FADH₂. These reactions are essential for generating the electron carriers that drive ATP production in the electron transport chain.

How does ATP hydrolysis release energy?

ATP hydrolysis releases energy by breaking the high-energy phosphate bonds within the ATP molecule. When ATP is hydrolyzed, it reacts with water (H₂O) to form ADP (adenosine diphosphate) and an inorganic phosphate (P_i). The reaction can be represented as:

${\mathrm{ATP}}_{}+H_2{O}_{}\to {\mathrm{ADP}}_{}+P_i+\mathrm{energy}$

This reaction releases energy because the bonds between the phosphate groups in ATP are high-energy bonds. The energy released is then used to power various cellular processes, making ATP the primary energy currency of the cell.

What is the significance of NADH and FADH₂ in cellular respiration?

NADH and FADH₂ are crucial electron carriers in cellular respiration. They are produced during metabolic pathways like the citric acid cycle. NADH is formed when NAD⁺ gains electrons, and FADH₂ is formed when FAD gains electrons. These carriers transport electrons to the electron transport chain in the mitochondria. Here, the electrons are passed through a series of protein complexes, ultimately leading to the production of ATP through oxidative phosphorylation. The energy from the electrons is used to pump protons across the mitochondrial membrane, creating a proton gradient that drives ATP synthesis. Thus, NADH and FADH₂ are essential for efficient energy production in cells.