How do carbohydrates differ from fats?
Differences between carbohydrates and Fats:
Chemical composition and structure: Carbohydrates are polymers of monosaccharides, which are polyols (many OH groups) with an aldehyde or ketone functional group. Fats are esters of fatty acids and glycerol.
Most carbohydrates are hydrophilic, smaller ones are soluble in water. Fats are hydrophobic.
Carbohydrates are the first choice energy source in biological systems, since they can be broken down to glucose. This is used to generate ATP through Glycolysis, Kreb's cycle and the electron transport chain. Fats are a less desirable choice as a source of energy because of lower ATP yield, and are metabolized by beta oxidation. The body is also capable of converting fats to glucose (gluconeogenesis) and vice versa (formation of triglycerides from AcetylCoA)
Complex carbohydrates like cellulose form plant and bacterial cell walls. Fats are important components of the cell membrane
Both carbohydrates and Fats are modified extensively and sometimes combine to perform specialized biological functions. There are phospholipids, glycolipids, glycerophospholipids, sphingolipids, etc which yield different properties to areas of the cell membrane known as lipid rafts.
Many proteins are modified by events such as glycosylation (combination with carbohydrates) to help with protein folding and cell-cell adhesion. In a similar way, proteins also combine with fats to form lipoproteins, important for transport of hydrophobic fats through a largely aqueous cell.
I might be missing many salient points. Please do additional reading from the following sources:
Intermediate level: Biochemistry by Stryer
More advanced, lots of mind boggling end-of-chapter questions: Biochemistry by Lehninger.