Acetyl Coenzyme A (Acetyl-CoA): Formation, Structure & Synthesis

Instructor: Darla Reed

Darla has taught undergraduate Enzyme Kinetics and has a doctorate in Basic Medical Science

In this lesson, you'll learn what acetyl coenzyme A is by discovering its structure and how it's synthesized or formed by the cell. You will further uncover a bit about the function of coenzyme A.

What Makes Up Acetyl Coenzyme A?

Understanding the structure of acetyl coenzyme A (Acetyl CoA) is a bit like understanding the structure of Frankenstein's monster. Part of acetyl CoA -- coenzyme A (CoA) -- is quite the monster itself, which is why scientists often use its abbreviation (CoA) when writing out structures that involve CoA (and there are many).

Like Frankenstein's monster, which was composed of different corpse parts, CoA is composed of different pieces of various molecules and chemical groups. Once CoA is conquered, the acetyl part of acetyl CoA is relatively simple. So first we will conquer the parts of CoA.

Structure of CoA

The monster CoA consists of three parts:

  • The body: Vitamin B5
  • The head: A form of ADP
  • The tail: beta-mercaptoethylamine

The main body of the beast is composed from Vitamin B5- pantothenate (you eat vitamins so you may be able to remember the name by thinking Panto then ate), or pantothenic acid (Panto then ick! acid).

Structure of Pantothenate.
Vitamin B5 structure- body of the beast

The head of the beast is a form of ADP (adenosine diphosphate), a nucleotide, and like your head has different parts that make it up (eyes, nose, mouth) a nucleotide has different groups that make it up: a base- adenine (yes, like what you find in DNA), a sugar (ribose) and phosphate (PO4) groups.

Structure of ADP form in CoA.
CoA ADP form structure- head of the beast

Now that you know the head and body, it's time to talk about the tail of the beast.

The tail of the beast is called beta-mercaptoethylamine.

Structure of beta-mercaptoethylamine.
Sulfhydryl tail of the beast structure

It's quite the mouthful, but the important thing to remember about the tail is the sulfhydryl group (SH-). The sulfhydryl group is how other groups and molecules attach themselves to the beast that is CoA.

Sulfhydryl Group.
Sulfhydryl group

Coenzyme A is exactly what the name implies, a co-enzyme. It assists enzymes to function, but it also acts as a sort of a hanger for other molecules. You can hang all kinds of molecules onto the tail of CoA as well as add groups to make fatty acids.

CoA acts as a CoAt hanger.
CoA acts like a CoA t hanger.

Structure of Acetyl CoA

The head (nucleotide), the body (Vitamin B5) and the tail (beta-merceptoehtylamine) make up the whole of the beast CoA- now for the acetyl part. An acetyl group is simply a carbon with three hydrogens bonded to another carbon that is bonded to another group and double bonded to an oxygen (CH3-CO-). It sounds more complicated than it looks.

Acetyl Group.
acetyl group

When an acetyl group is added to the tail of CoA, the whole molecule becomes known as Acetyl-Coenzyme A (Acetyl-CoA). Therefore, Acetyl CoA's structure is simply CoA with an acetyl group attached to the tail (the sulfhydryl group).

Structure of Acetyl-CoA.
Acetyl-CoA structure

Synthesis of Acetyl-CoA

One important molecule used by the cell is pyruvate which is formed when sugar (glucose) is broken down. Pyruvate looks like an acetyl group combined with carbon dioxide (CO2).

Structure of Pyruvate.
pyruvate structure

Pyruvate can be cannibalized by the cell to make up Frankenstein's monster, or rather the cellular beast acetyl-CoA. The cell uses a scalpel -- or, ahem, the enzyme pyruvate dehydrogenase -- to cleave off CO2 and add the acetyl group to a carrier molecule. The acetyl group is then transferred from the carrier molecule onto a CoA that's hanging around the cell after being made by a different process we won't get into here.

Pyruvate can be used to synthesize acetyl-CoA.
Pyruvate can be used to synthesize acetyl-CoA.

Some amino acids can be used to synthesize acetyl-CoA as well. Alanine, serine, glycine, cystine and threonine all form acetyl-CoA through the pyruvate pathway. Leucine, phenylalanine, tyrosine, lysine and tryptophane use a separate pathway to form acetyl-CoA.

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