Diagram of human cell structure

Introducing the cell

Join us as we explore the building block of life

The cell is the smallest unit of life. Some simple organisms are unicellular, consisting of just one cell, whereas more complex beasts – like us! – are multicellular and have vast numbers of them.

Humans are among the organisms built up from eukaryotic cells, which have their DNA packaged up into a nucleus, and lots of subcellular compartments, called organelles. Prokaryotic organisms (such as bacteria) are simpler. These cells still have DNA, which exists as a non-membrane-bound plasmid instead of within a nucleus. The vast majority of these are unicellular, whereas most eukaryotic organisms are multicellular.

The intricately organised cytoplasm of the eukaryotic cells allows them to have different things happening in different compartments. Keeping a cell going depends on getting the right molecules to the right place at the right time. Having distinct spaces does half the job, but it also requires sophisticated machinery to ensure the right things get into each section. Only material the cell has finished with, for example, can be allowed into lysosomes, where powerful enzymes are poised to break down the material into smaller molecules.

Cell theory was put forward in the 1830s, soon after the cell nucleus was first identified in eukaryotes. It recognised that living things are made of cells, that cells are the basic units of life, and that new cells are created by old ones dividing into two. Viruses – simple particles of genes and protein – need to get into a cell and hijack its cytoplasmic machinery to copy themselves. We describe these as acellular, and they are not considered to be living because they can’t reproduce in the absence of a host cell.

In this issue, we’ll be focusing on animal cells and how they reproduce, grow, move, communicate and die. So join us to explore what we know, as well as what we still don’t understand, about the cells that are the basis of all of us.

Lead image:

Diagram of human cell cutaway to show content.

Miles Kelly Art Library/Wellcome Images

Further reading

About this resource

This resource was first published in ‘The Cell’ in January 2011 and reviewed and updated in September 2015.

Cell biology, Medicine, Health, infection and disease
The Cell
Education levels:
16–19, Continuing professional development