Storage lipids Lipids also have important roles as energy and carbon storage molecules. Triglycerides are particularly prominent as animal storage molecules. On a gram basis the caloric content of lipids is twice as high as carbohydrates, so motile animals get more calories per stored gram by synthesizing fats rather than accumulating starch. Plants are generally non-motile and so generally need not convert their carbohydrate reserves to fat. Interesting exceptions are oil rich seeds and some floating planktonic algae which store lipids, where weight is a concern.
Proteins have a central role in cell biology.
There are structural proteins, transport proteins, and protein catalysts called enzymes. These classes can overlap. Proteins are the expression of the genetic information carried in genes. A gene is a sequence of nucleic acids that specifies the sequence of a protein or ribonucleotide polymer. That is, the sequence of nucleotides guides the order in which protein amino acids are liked together to form the protein.