Steph has a PhD in Entomology and teaches college biology and ecology.
Anchorage Dependence Defined
You probably feel better about your life when you feel grounded. When you are connected to your friends, family and community and to your body through physical activity, you are better able to face the challenges in your life. What if I told you that your cells need to be grounded, too? And it's a good thing they do!
Anchorage dependent cells need to be 'grounded' to divide. That is, if they aren't anchored to a surface - such as a tissue in your body or a jar in a laboratory - they won't reproduce. Cells that aren't anchored may even undergo apoptosis, which is basically programmed cell death.
In this lesson, we are going to learn what happens when cells aren't grounded, and how cells 'know' whether or not they're grounded. Then, we'll talk about what happens when cells break the rules and divide even when they shouldn't.
Why would cells be programmed to kill themselves? Apoptosis is actually a very important feature that allows your cells to work together as a team. In single-celled organisms, every cell is out for itself. But in multicellular organisms, cells have to work together for the good of the body.
Sometimes, what's good for your body is getting rid of unnecessary cells. For instance, a cell that is damaged or has been infected by a virus may undergo apoptosis so that the damage won't spread, or cells may be needed in an earlier stage of development but no longer be necessary as you get older. For instance, when you were a developing fetus, you grew a whole bunch of neurons you didn't need. Most of these neurons died off as you were forming the neural pathways you now use to think. Another classic example of apoptosis in development is the tail of a tadpole. Tadpoles need tails, but adult frogs are better off without them. So apoptosis is used during the transition from tadpole to frog so that adult frogs do not have tails.
How Cells Know What to Do
So, how do cells know what to do? Integrins are proteins that can help regulate whether our cell undergoes apoptosis, will grow and divide, or will simply survive intact. Not coincidentally, integrins are also the proteins that cells use to stick to a surface.
How do cells 'know' if they are stuck to a surface or not? Well, free-floating cells often have a very large, folded, wrinkled cell surface. Think of a raisin, but with even deeper wrinkles. Attached to this surface are growth factor receptors. Growth factors are signals that your body produces to let cells know that it is a good time to divide. Growth factor receptors are like little antennae that stick on the surface of the cell and pick up growth factors when they are present.
When a cell is free-floating, all those raisin-like folds seem to cover up the growth factor receptors, so even if growth factor is present, the receptors may not detect it. On the other hand, when a cell is attached to a surface, it becomes stretched out. More growth factor receptors are exposed to the surrounding environment, and so, the cell is better able to tune into signals that tell it to divide.
What happens if a cell becomes anchorage independent; that is, if a cell starts dividing regardless of whether it is stuck to a surface or not? Then the cell goes rogue; it keeps dividing even when it shouldn't. Does that sound like something you have heard before?
Oncogenic cells, or cancer cells, are known for their ability to divide even when they shouldn't, causing tumors. Indeed, anchorage independence is one of the hallmarks of oncogenic cells. A link has been found between cancer and certain mistakes in your integrins - remember, those are the proteins that help cells to stick to things and help them 'decide' whether to divide or undergo apoptosis.
Anchorage dependent cells will not grow unless they are attached to a surface, such as a tissue in your body or the wall of a jar in your laboratory. Sometimes anchorage dependent cells will undergo apoptosis, or programmed cell death, if they are not attached to a surface.
Apoptosis is very important to multicellular organisms because cells need to work as a team, and sometimes the best way for a cell to aid the body is to die off . Proteins called integrins can aid in signaling cells to undergo apoptosis. Integrins also help cells stick to surfaces; these two functions are tightly intertwined.
Free-floating cells often have a wrinkly shape, and their wrinkles may hide growth factor receptors that respond to growth factors telling cells to divide. This may in part help explain how cells 'know' whether they are attached to a surface.
Cancer cells often have something wrong with the system that tells them not to divide unless they are attached to a surface. This can lead to unregulated growth, a hallmark of tumors.
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