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Homeostasis in Prokaryotes

Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Homeostasis means maintaining a constant internal environment. Despite facing different challenges than humans, single-celled prokaryotes must maintain homeostasis in the face of constant changes in order to thrive.

Homeostasis and Prokaryotes

Homeostasis is important. If you look up the definition of life, homeostasis is one of the requirements. It means 'keeping a constant internal environment.' In humans, this means we have a more or less constant body temperature, blood pH, and blood pressure. If it starts to get too cold, we shiver and get goose bumps in an attempt to keep our body temperature constant.

Prokaryotes are small, simple cells. Your human cells, in contrast, are very big, and very complex. In addition, most prokaryotes are single-celled, meaning they live only for themselves. Bacteria are a very well-known type of prokaryotic cell. Archaea are a less well-known type. Prokaryotes can exist anywhere on Earth that there is life- even at the bottom of the ocean near hydrothermal vents.

We normally think that pH 7 and a temperature around 98.6 degrees Fahrenheit are ideal. For the many bacteria inhabiting our bodies, it is. But for other prokaryotes, different conditions are better. Archaea that live near hydrothermal vents under the oceans, or bacteria living in hot springs, prefer significantly higher temperatures. Other archaea that live in highly acidic environments like a very low pH. The point of homeostasis isn't to meet a human's criteria of comfortable- it's to help each individual organism survive where it lives.

Stresses on Prokaryotes

It's hard to think of small bacteria needing to maintain homeostasis. When you think of homeostasis, you might think of regulating entire systems. For example, when your blood sugar gets too low, your body sends hunger signals, and begins breaking down glycogen stores to make glucose. But bacteria don't have livers and pancreases. So what could they possibly do to maintain homeostasis?

Consider that prokaryotes have been surviving on Earth for 3.5 billion years. They must have some mechanism to survive, right? Bacteria have to deal with changing temperatures, food sources, pH, and more. To just die off whenever things got bad would be a horrible way to survive.

Iron Homeostasis

A specific example of bacteria maintaining homeostasis involves changing amounts of iron in the environment. Iron is an essential mineral for almost all living things. However, too much of a good thing can be toxic, causing damage to the bacterium. So, prokaryotic bacteria have to determine whether they have enough iron, too much, or just the right amount. When there are low levels of iron in the environment, bacteria will make more proteins that bring iron into the cell. If there is too much iron, they can make proteins that help detoxify iron.

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