Growing cells – known as Cell Culture – is a fundamental process carried out in most biochemistry research labs. Having a never-ending supply of cells available is a valuable resource for researchers. It allows us to manipulate cells and investigate the effects of new drugs in a way that would be impossible, expensive and unethical to do in animal models or in people. They also provide a consistent and plentiful source of material to perform lots of experiments in a relatively short period of time.
There are hundreds of different types of cells, referred to as ‘cell lines’, which come from different parts of the body, different species, and are created in different ways.
Some neuronal cells growing in a dish
Broadly, there are 2 categories of cell line:
These cells are taken directly from a piece of tissue, and have a finite lifespan. They will not continue to grow and divide, so are used in short-term experiments.
Continuous cells have originated from a piece of tissue, but they have been transformed in the lab so that they continue to grow and divide indefinitely. These are often referred to as ‘immortalised’ cells. The most famous and most common cell line is known as HeLa, which originated from a biopsy of an extremely aggressive case of cervical cancer. HeLa cells are a particular oddity as they appear to have transformed themselves without any manipulation in the lab. HeLa cells have a complicated and controversial history relating to medical and research ethics – to find out more about them, I would highly recommend reading ‘The Immortal Life of Henrietta Lacks’ by Rebecca Skloot (don’t worry, it’s not too sciencey!).
So what do you need to grow cells?
All cell lines are different and may have specific needs, but the basics are the same. Cells are grown in a nutrient-rich liquid referred to as ‘media.’ Media helps stabilise cells and provides the essential nutrients required for cells to grow.
In loose terms, growing cells isn’t too dissimilar to growing a human baby – it’s a case of food in and waste out, and some care in between to make sure they don’t get sick. It’s also beneficial to avoid dropping them on the floor. Media therefore commonly contains the following:
Growing cells just like growing babies….kinda
Glucose: Provides energy to the cells,
Glutamine: An amino acid that acts as an extra energy source
Phenol Red: A pH indicator, which changes colour if the acidity of a solution changes. Cell culture media is commonly a reddish-pink colour because of the phenol red, but if the culture becomes too acidic, perhaps by cell overgrowth, infection or an accumulation of waste, then the media will turn a gross yellowish colour so it is easy to see when something is wrong. Media needs to be removed and replaced regularly, as the cells will use up energy and consequently produce waste, which is toxic to the cells if it builds up.
Antibiotics: To help prevent any unwanted infections.
Serum: The remaining component of blood after clotting and the removal of any remaining blood cells. The most common serum used in cell culture is fetal bovine serum (from cow fetuses), referred to as ‘FBS,’ and is a by-product of slaughterhouses for the meat industry. Serum is essential in cell culture because it provides all of the components normally present in the body that helps cells to grow and survive, such as proteins, carbohydrates, hormones and vitamins.
Sadly, there is no additive to correct researcher clumsiness.
Cell culture in action using media containing phenol red
But it’s still not quite as straightforward as feeding and cleaning!
Cells have to be cultured in special sterile conditions – because the cells are no longer growing in a complicated system made up of hundreds of different cell types and a functional immune system, they have no protection against infection. The addition of antibiotics to the media helps protect against bacterial infection, but they are no substitute for proper sterile technique!
Sterile technique involves using a special cabinet (or hood) that has a particular flow of air. Air is sucked into the cabinet and passed through a filter to get rid of any nasties before reaching the area containing the cells. Used air is extracted from the cabinet and disposed of elsewhere. Everything that enters the hood is sprayed with ethanol, and all of the equipment, such as pipettes and tubes, are always certified as sterile by the manufacturer and are only ever used once to prevent any potential contamination.
Cells must also be grown in special incubators that carefully regulate their environment – the majority of cells will grow best at 37˚C (body temperature – what a coincidence!), with some humidity and 5% carbon dioxide in the air, which helps maintain the correct pH.
What happens once you have a batch of cells happily growing?
They grow some more!
Happy cells are growing & dividing cells
Continuous cells will carry on dividing and growing – they will run out of space and nutrients, so will eventually poison themselves and starve if left to their own devices. This means that cells need to be regularly ‘split’ (officially called ‘passaging’) – this simply means that the cells in one flask or dish will be split up into several other flasks or dishes to continue to grow with more space and more nutrients. This method means that cells can quickly be bulked up into huge numbers and can then be prepared and used for various experiments.
I’ve spent the majority of my fledgling research career doing cell culture, so I’m bound to be biased, but I think it’s pretty awesome.
If you have any questions about cell culture, feel free to ask in the comments section below, and let me know if you have any other biochemistry or neuroscience questions you’d like answered! You can also follow me on Twitter @TheBiocheminist