Intro to Coenzymes: Study with Video Lessons, Practice Problems & Examples

Redox reactions, often catalyzed by dehydrogenases, require coenzymes for activation. Key coenzymes include Adenosine triphosphate (ATP), which consists of adenine, ribose, and three phosphates; NAD⁺, which features adenosine diphosphate (ADP) and nicotinamide; and FAD, containing ADP and flavin. Coenzyme A, important in metabolic pathways, includes pantothenic acid. These coenzymes play crucial roles in the Citric Acid Cycle, facilitating energy production through oxidation-reduction processes, essential for cellular metabolism and energy transfer.

Intro to Coenzymes Concept 1

Many reactions we will see involve redox reactions catalyzed by dehydrogenases. Now, these are just a subclass of oxidoreductases. And when it comes to dehydrogenases, they require coenzymes to become active. Now, here we're going to talk about different types of coenzymes, and we're going to say the most common coenzymes we will need to know are the following. So the first one we know is ATP. ATP here is composed of 3 things. It's composed of our adenine nitrogenous base, our ribose sugar, and then our 3 phosphates. Next, we have NAD⁺, and think of the next 3 as different variations of the ADP molecule. So all of them have this ADP portion which is adenosine diphosphate and connected to it is this new portion to make it something different. Here for NAD⁺, after the adenosine diphosphate, we have our CH₂ group connected to a ribosugar again. And then we have this nitrogen portion which is nicotinamide. Next, we have FAD. FAD, we have our Adenosine Diphosphate portion. We have our Ribotol, which is an alcohol portion. And then flavin. Now, remember that these two things must be involved in some way within the Citric Acid Cycle. When we talked about food catabolism, we talked about the 3rd step involving these 2 in the production of NADH and FADH₂. And then finally, we have Coenzyme A which has the ADP portion again, the pantothenic acid, and then we have aminoethanethiol portion. You may also notice that these are in some type of mustard color because those are the sites of some of the redox reactions we're going to see. Because remember, we said that these are involved in redox reactions, those are the sites where it will occur. Now, there are other coenzymes that are important but their structures are too complex and beyond the scope of the course. So, it's less important to know what they look like. It's more important to know that they are also common types of coenzymes. And those would be the coenzymes of B₁₂ and Q. Right? So these would represent our most common types of coenzymes.

Intro to Coenzymes Example 1

In this example, we have to identify the substrate, coenzyme, and product for the following reaction which involves the enzyme Succinate dehydrogenase. Alright. So, we're going to say here, Succinate would have to be our substrate because we said earlier that one of our common coenzymes is FAD. The question doesn't ask this, but we know that this ends with ACE, which represents our enzyme. The enzyme and this coenzyme put together, make it active in order to change our substrate succinate into fumarate. Fumarate here would have to be our product. In this process, we've created FADH₂. So FAD has been transformed into FADH₂. Here, this is just another product but not the main product that we're concerned with. So, here again, Succinate will be our substrate. FAD is one of our common coenzymes. We have our enzyme that works in conjunction with it to create fumarate, which is our product.

Here’s what students ask on this topic:

What are the main types of coenzymes involved in redox reactions?

The main types of coenzymes involved in redox reactions include ATP (Adenosine Triphosphate), NAD+ (Nicotinamide Adenine Dinucleotide), FAD (Flavin Adenine Dinucleotide), and Coenzyme A. ATP consists of adenine, ribose, and three phosphates. NAD+ features adenosine diphosphate (ADP) and nicotinamide. FAD contains ADP and flavin. Coenzyme A includes pantothenic acid and an aminoethanethiol portion. These coenzymes are crucial in the Citric Acid Cycle, facilitating energy production through oxidation-reduction processes essential for cellular metabolism and energy transfer.

How does ATP function as a coenzyme in metabolic reactions?

ATP (Adenosine Triphosphate) functions as a coenzyme by providing energy for various biochemical reactions. It consists of adenine, ribose, and three phosphate groups. When ATP is hydrolyzed to ADP (Adenosine Diphosphate) and an inorganic phosphate, energy is released. This energy is used to drive endergonic reactions, such as muscle contraction, protein synthesis, and cell division. ATP acts as an energy currency, transferring energy from catabolic processes to anabolic processes within the cell.

What is the role of NAD+ in cellular metabolism?

NAD+ (Nicotinamide Adenine Dinucleotide) plays a crucial role in cellular metabolism by acting as an electron carrier in redox reactions. It consists of adenosine diphosphate (ADP) and nicotinamide. During metabolic processes like glycolysis and the Citric Acid Cycle, NAD+ accepts electrons and becomes reduced to NADH. NADH then carries these electrons to the electron transport chain, where they are used to produce ATP through oxidative phosphorylation. This process is essential for energy production in cells.

How do FAD and NAD+ differ in their roles in the Citric Acid Cycle?

FAD (Flavin Adenine Dinucleotide) and NAD+ (Nicotinamide Adenine Dinucleotide) both act as electron carriers in the Citric Acid Cycle, but they differ in their specific roles and the reactions they participate in. NAD+ is reduced to NADH in three steps of the Citric Acid Cycle, while FAD is reduced to FADH2 in one step. NADH and FADH2 then transfer electrons to the electron transport chain, but FADH2 donates electrons at a later stage than NADH, resulting in the production of fewer ATP molecules per FADH2 compared to NADH.

What is the structure and function of Coenzyme A in metabolic pathways?

Coenzyme A (CoA) is a vital coenzyme in metabolic pathways, consisting of an ADP portion, pantothenic acid, and an aminoethanethiol group. Its primary function is to carry acyl groups in various biochemical reactions. In the Citric Acid Cycle, CoA forms acetyl-CoA by combining with an acetyl group. Acetyl-CoA then enters the cycle, where it is oxidized to produce energy. CoA is also involved in the synthesis and oxidation of fatty acids, making it essential for energy metabolism and biosynthetic processes.