Two general types are recognised in nature. They are prokaryotic and eukaryotic cells.
Prokaryotes were the first cells to arise in biological evolution. They are very small and simple having only a single membrane. The cell membrane, is usually surrounded by a rigid cell wall.
They are devoid of nucleus and membranous organelles such as mitochondria and endoplasmic reticulum etc. (Fig. 1.1).
Eukaryotic cells are presumably derived from prokaryotes. They are much larger and much more complex than prokaryotic cells (Fig. 1.2).
They have nucleus and membrane bound subcellular organelles. Many of their metabolic reactions are segregated within structural compartments. The significant differences between prokaryotic and enkaryotic cells are:
The eukaryotic cell structure is composed of (i) cell membrane, (ii) nucleus (iii) mitochondria (iv) endoplasmic reticulum (v) golgi apparatus (vi) ribosomes (vii) lysosomes and others. These specialised structural units are called as subcellular organnelles. Biochemistry today is increasingly concerned with the structure of cells and their organelles.