This humble group of atoms (phosphorus surrounded by oxygen) can carry energy, shape your cell membranes, and help form the backbone of your DNA. Learn what a phosphate group is and how it does these important jobs.
What is a Phosphate Group?
Surround a phosphorus atom with four oxygen atoms, and you get a phosphate. Attach that cluster to one of the many carbon-containing molecules in our bodies (or, really, in any living thing), and we call that group of one phosphorus and four oxygen atoms a phosphate group. Phosphate groups turn up in all kinds of important places.
Their electrons, shared among all those oxygen molecules, can store lots of energy, and this is key for some of their roles in the cell.
Phosphate Groups in Nucleic Acids
Nucleic acids, like DNA, are made of nucleotides. Where do phosphates come in? Well, nucleotides include a base, a sugar, and one or more phosphates.
When the nucleotide is off by itself, it may have three phosphates. When it gets joined to the growing strand of DNA (or RNA), two of its phosphates are lost, and the remaining one attaches to another nucleotide’s sugar. This makes a sugar-phosphate backbone with those important bases (like adenine, thymine, and so on) hanging off.
Phosphate Groups Can Carry Energy
Where would ATP be without its phosphates? Perhaps you’ve heard of this energy-carrying molecule. It’s not an accident that ATP, or adenosine triphosphate, has three phosphate groups; the energy is carried in the phosphates’ chemical bonds. The electrons in these bonds are high energy, meaning that when the bond is broken, plenty of energy can be released to do work. That’s why ATP is used as an energy carrier all over the cell.
When you contract your muscles, for example, your muscle proteins use ATP to do it.Removing a phosphate group to release the energy is called ATP hydrolysis. The result is a free-floating phosphate plus ADP, or adenosine diphosphate (meaning it only has two phosphate groups). An enzyme called ATP synthase can use energy from the food we eat to attach the phosphate again.
Phosphate Groups Can Activate Proteins
When a phosphate group is attached to a protein, we say that protein has been phosphorylated.
That means its function has changed; usually, phosphorylation activates that protein so it can do a particular job, such as carrying a message to another protein in the cell. Proteins that add phosphates to other proteins have a special name: kinases. Sometimes a kinase’s job is to phosphorylate another kinase!
Phosphate Groups & Cell Membranes
Let’s talk about one last important job of phosphate groups.
Attached to fatty acids, phosphates can make phospholipids.What’s so important about that? Well, phosphates are hydrophilic, which means that they love water, while fatty acids are hydrophobic, which means they do not like water. So, this means that phospholipids can usually be found near other oily and watery molecules.
If the phospholipids line up with their fatty-acid tails together and their hydrophilic phosphate heads toward the water, they can make a sheet called a phospholipid bilayer. This sheet is so stable that it’s what our cells are made of! This bilayer makes up our cell membranes – think of it as a cell’s skin.
A phosphate group is just a phosphorus atom bound to four oxygen atoms, but it has many important roles. Along with sugars and bases, it makes up nucleic acids, like DNA and RNA. As part of energy carriers, like ATP, it provides energy for moving our muscles.
When it’s added to a protein, it can activate enzymes and cellular messages. With fatty acids, it makes the phospholipid bilayer that holds our cells together. Hooray for phosphate groups – we just wouldn’t be the same without them.
Vocabulary & Definitions
|Phosphate group||a phosphorus atom bound to four oxygen atoms|
|Nucleotides||contain a base, a sugar, and one or more phosphates|
|Sugar-phosphate backbone||nucleotide gets joined to the growing strand of DNA (or RNA), two of its phosphates are lost, and the remaining one attaches to another nucleotide’s sugar|
|Adenosine triphosphate||a molecule that has three phosphate groups|
|ATP hydrolysis||removing a phosphate group to release the energy|
|ATP synthase||an enzyme that can use energy from the food to attach the phosphate again|
|Phosphorylated||a phosphate group is attached to a protein|
|Kinases||proteins that add phosphates to other proteins|
|Phospholipids||phosphates attached to fatty acids|
|Hydrophilic||phosphates that love water|
|Hydrophobic||fatty acids do not like water|
|Phospholipid bilayer||creates a sheet with phosphates and fatty acids that holds cells together|
Working your way through this lesson should help you complete the following:
- Define a phosphate group
- Describe what phosphate groups do
- Identify what phosphates may attach to and for what purpose