Biological molecules
Biological molecules
- Living things are built from a few kinds of molecule.
- The main ones are carbohydrates, fats and proteins.
- Big molecules are built from small units, like beads on a string.
Elements and building blocks
- carbohydrates and fats contain C, H and O.
- proteins also contain N (nitrogen).
| Large molecule | Built from |
|---|---|
| starch, glycogen, cellulose | glucose units |
| proteins | amino acids |
| fats and oils | fatty acids + glycerol |
- One fat = 3 fatty acids + 1 glycerol; proteins use about 20 kinds of amino acid.
Practice
Which element is found in proteins but NOT in carbohydrates or fats?
All three contain C, H and O; proteins also contain nitrogen (and some contain sulfur).
Practice
Proteins are built from:
Proteins are chains of amino acids; carbohydrates are built from glucose; fats from fatty acids + glycerol.
Practice
One fat molecule is made from:
A fat is three fatty acids joined to one glycerol.
DNA
- DNA carries the genetic instructions.
- It is a double helix (two strands coiled like a twisted ladder).
- The bases always pair: A with T, and C with G.
Practice
In DNA, the bases pair as:
Complementary base pairing in the double helix: A–T and C–G.
You've got it
Key idea
- carbohydrates & fats = C, H, O; proteins also contain N
- built from units: glucose (starch/glycogen/cellulose), amino acids (proteins), fatty acids + glycerol (fats)
- DNA = double helix; bases pair A–T and C–G