They all overlap a bit. Biochemistry does deal with chemical reactions such as in catabolism and anabolism, but its main focus tends to be the structure and function of proteins and the methods for studying these such as X ray crystallography, NMR etc Molecular biology is similar to Biochemistry in that it deals with the structure and function proteins (but less on how to study them), but it also deals with genes much more strongly. Molecular biology and biochemistry can both deal with how genes are expressed in cells, but molecular biology takes genes further by considering genetic approaches to things - e.g. genetic engineering and how to study genes. Genetics would cover most of the same genetic parts of molecular biology but also includes a non-molecular part - e.g. population genetics, evolutionary genetics etc. Cellular biology is just the biology of a cell. This takes aspects of biochemistry, molecular biology and genetics and applies it to the cell. Instead of f...