Krebs Cycle Mnemonic - Allfit Well

Memorizing the Krebs cycle can be hard. A good Krebs cycle mnemonic can make it easier.

Here you’ll find mnemonics and tips to help you remember each step.

Table of Contents

What is the Krebs Cycle?

The citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle, is a critical step in cellular respiration.

It’s where our body turns the energy from carbohydrates, fats, and proteins into ATP (adenosine triphosphate), our primary source of energy.

The citric acid cycle goes by a few names, including the Krebs cycle, after Hans Krebs who first described it in the 1930s.

It begins with the breakdown of glucose into a 2-carbon molecule called acetyl-CoA in the mitochondrial matrix of eukaryotes and the cytoplasm of prokaryotes.

The Krebs cycle is imperative for our survival. Let’s break down the steps to make it easier to memorize!

The Krebs Cycle is a Circular Process

What’s unique about this cycle is the self-sustaining mechanism. Oxaloacetate produced at the end of each turn is recycled back into new cycles as long as substrates are available.

It’s essential for aerobic metabolism and allows various molecules converted to acetyl-CoA (carbs, fats, proteins) to be used through pyruvate dehydrogenase complex catalyzing pyruvate into acetyl-CoA during energy production stages.

Acetyl-CoA is multi-faceted because it feeds into this cycle through several pathways:

Aerobic glycolysis breaks down glucose to limited ATP and NADH before full blown Krebs cycle where full oxidation of fatty acids and amino acids turns into carbon dioxide and creates concentrated pools of energy molecules NADH and FADH2.

At its heart is the fundamental function of cellular respiration: producing energy while providing intermediates for synthesis elsewhere in the living system, making it not just necessary but multi-functional across both breakdown (catabolic) and synthesis (anabolic) pathways.

Krebs Cycle Mnemonic : Step by Step

One of the most difficult parts about studying the Krebs cycle is memorizing the steps.

Here’s a great mnemonic to help you remember the intermediates:

“Can I Keep Selling Substances For Money, Officer?”

Each word corresponds to the intermediates of the Krebs Cycle:

Can – Citrate
I – Isocitrate
Keep – α-Ketoglutarate
Selling – Succinyl-CoA
Substances – Succinate
For – Fumarate
Money – Malate
Officer – Oxaloacetate

In addition to a great mnemonic, I recommend studying a diagram or flowchart of the Krebs cycle. This will help you remember the enzymes and products at each step.

Combine your visual with your verbal learners by creating a cheat sheet with your diagram or flowchart.

Using mnemonics and visual aids will help you to remember the steps of the Krebs cycle, but it will also help you understand the process better.

Instead of just memorizing a list of steps, you’ll know how each segment flows into the next as CoA is transformed into acetyl groups and then regenerate into oxaloacetate.

Here’s another mnemonic for the Krebs cycle.

Mnemonic

“Our City Is Kept Safe and Secure From Monsters.”

Each word represents an intermediate in the Krebs cycle:

O – Oxaloacetate
C – Citrate
I – Isocitrate
K – α-Ketoglutarate
S – Succinyl-CoA
S – Succinate
F – Fumarate
M – Malate

Krebs Cycle Enzymes

Each step of the Krebs cycle is catalyzed by a key enzyme. The first enzyme, citrate synthase, combines acetyl-CoA with oxaloacetate to form citrate. Aconitase removes a hydroxyl group from citrate, turning it into isocitrate.

The next enzyme, isocitrate dehydrogenase, converts isocitric acid into α-ketoglutarate, producing NADH and releasing carbon dioxide.

This is an important regulatory step in the Krebs cycle because it senses the energy needs of the cell.

The next enzyme, α-ketoglutarate dehydrogenase, is a complex that turns α-ketoglutarate into succinyl-CoA, producing even more NADH and carbon dioxide.

This is another critical regulatory step because it’s sensitive to the cell’s energy needs. Both of these regulatory points are important because they help the cell decide whether to use glucose for energy or excrete it.

Krebs Cycle is a Biochemical Wheel

The last step is succinate thiokinase, which changes succinyl-CoA back into succinate, producing ATP (or GTP) during substrate-level phosphorylation.

FAD is reduced to FADH2 in the process. The next enzyme, malate dehydrogenase, converts malate back into oxaloacetate, regenerating the starting molecule of the Krebs cycle.

This is where FAD is restored to FADH2. It’s important to cycle back to oxaloacetate because this is where the Krebs cycle starts over.

The citric acid cycle is a wheel that’s connected to the outside world through citrate synthase.

Clinical Significance of Krebs Cycle

The Krebs cycle is important for our survival, and defects in the cycle can cause a variety of metabolic disorders.

A deficiency in the Pyruvate Dehydrogenase Complex affects the conversion of pyruvate into acetyl-CoA, leading to metabolic acidosis.

This complex is sensitive to lifestyle factors like carbohydrate intake and is linked to decreased cognitive function and brain white matter disease.

Mutations in the pyruvate dehydrogenase complex are associated with Leigh syndrome, a fatal central nervous system degradation disease.

The Krebs Cycle is Essential, Not Duplicable

Fumarase Deficiency is another great example of the Krebs cycle’s importance.

This rare genetic disorder causes severe neurological problems because fumarase, the enzyme that changes fumarate into malate, is either absent or defective.

Isocitrate dehydrogenase mutations have also been linked to certain types of cancer, affecting key metabolic pathways that fuel tumor growth.

SDH: The Krebs Cycle’s Gateway to the Electron Transport Chain

Succinate dehydrogenase is a critical enzyme because it feeds into the Krebs cycle and out to the electron transport chain.

It changes succinate into fumarate, preparing it for the next metabolic cycle.

At the same time, SDH complexes within the mitochondrial inner membrane are a part of the electron transport chain, generating ATP during oxidative phosphorylation.

The Krebs cycle is a critical step in preparing products to enter the electron transport chain, making succinate dehydrogenase a crucial enzyme in cellular respiration.

Pyruvate Dehydrogenase Complex

The pyruvate dehydrogenase complex (PDC) is a key regulatory step in metabolism because it converts pyruve into acetyl-CoA, the substrate for the Krebs cycle.

This complex, along with the Krebs cycle, is a rate-limiting step in glucose metabolism because it’s regulated by multiple factors. Lipoic acid is a cofactor for PDC, and it’s necessary for converting pyruvate into acetyl-CoA and carbon dioxide.

Oxidation reactions involve the lipoic acid moieties, making it a essential component of the pyruvate dehydrogenase complex.

The activity of PDC is regulated by substrate presence (or lack thereof), product accumulation, and the levels of important cofactors like lipoic acid and thiamine.

The redox state of the system can also influence PDC activity due to reactive oxygen species.

Sirtuin 4 Regulates the Pyruvate Dehydrogenance Complex

Sirtuin 4 is a regulator of PDC, interacting with lipoamidase to remove excessive lipid moieties from the complex.

This enzyme system is highly regulated due to its impact on energy production and metabolism.

PDC is also regulated by glutathionylation, which is a reversible modification that can recur multiple times, allowing the enzyme to “remember” to go back online when glutathione is replenished.

Energy Production and Carbon Dioxide Release

The Krebs cycle is an important step in generating energy for the cell.

Each complete turn of the wheel produces 3 NADH molecules, 1 FADH2 molecule, and either 1 ATP or 1 GTP molecule.

These molecules are critical for generating energy in the electron transport chain during oxidative phosphorylation.

Carbon dioxide is also produced and released as a byproduct through the Krebs cycle.

In addition to generating energy, the Krebs cycle is important for releasing carbon dioxide as a waste product of aerobic metabolism.

When acetyl-CoA is completely oxidized during the Krebs cycle, carbon dioxide is produced.

This is in contrast to incomplete oxidation, which occurs during fatty acid metabolism when carbon atoms are reduced to acetyl-CoA.

The Krebs cycle is important for yielding NADH and FADH2, but it’s also critical for removing carbon atoms from the cell by excreting them as carbon dioxide.

Other Metabolic Pathways

The Krebs cycle is connected to other metabolic pathways, including amino acid metabolism and gluconeogenesis. It’s also important for producing and cleaving citrate, which is necessary for fatty acid synthesis.

The Krebs cycle is a central hub that interconnects various biochemical pathways, making it an essential step in many different metabolic processes.

How to Memorize the Krebs Cycle

Memorizing the Krebs cycle may seem daunting but there are ways to simplify it.

For example, using mnemonics like “A Cool Cycle Is Krebs’ Super Surprise For Medical Offers” helps to remember the main intermediates of the cycle while “Cool Aunts In Kansas Sell Special Fudge Monthly” helps to remember the enzymes involved.

Using visual aids is another way to help consolidate memory. Associating each step of the cycle with an image or chart helps to remember.

Review and self-test consistently. Repetition and active recall helps to retain long term.

Using different study methods , including mnemonics, illustrations and active recall helps to break down the complex Krebs cycle into smaller and more memorable chunks.

Using an integrative learning approach helps to commit details to memory and understand how these biochemical processes work in this pathway.

Wrap Up

I hope this post helped you to understand the Krebs cycle a little better, including its enzymes and clinical relevance. If you’re studying biochemistry or medicine, the Krebs cycle is an important process to understand.

Use mnemonics, visual aids, and regular review to help you study the Krebs cycle.