Only molecules with a phosphate group have phosphorus
- The idea
- Predict
- See it
- Why
- Check
The idea
“Phospholipids and DNA have phosphorus, so fats, steroids and big proteins must too.”
Fats and phospholipids are both lipids built on glycerol, and DNA and proteins are both big polymers. It's easy to assume relatives share elements.
The short version
The mistake: Phospholipids and DNA have phosphorus, so fats, steroids and big proteins must too.
What's actually true: Phosphorus sits in phosphate groups. Nucleic acids, ATP and phospholipids have them. Fats, steroids, sugars and amino acids don't.
- In cells, phosphorus comes in phosphate groups, one phosphorus atom bonded to four oxygens.
- Each nucleotide in DNA or RNA has a phosphate. ATP has three. A phospholipid has one in its polar head.
- Sugars, fats and steroids are made of carbon, hydrogen and oxygen. Amino acids add nitrogen, and a few add sulfur. None has phosphorus.
On the exam: Look for a phosphate group. Nucleic acids, ATP and phospholipids have one. Fats, steroids and sugars don't.