Captions are on! Click CC at bottom right to turn off. ATP. We love it. You’ll find ATP in so much of our science
art…whether it’s a GIF of a mitochondrion or cell transport…or a comic about cellular
respiration or fermentation, you’ll see ATP mentioned. So why the big deal? Why is it all over the place? Many times students will get in their mind
that it is an energy currency of some kind. When I first started studying biology, I noticed
that in textbooks it’s often represented as like this starburst thing or thunderbolt,
and you know, I guess in my mind I imagined it was like some big blast of energy that
helped the cells do things. And by do things, I mean that we need ATP
to do many cellular processes. Examples include active transport such as
when a cell is trying to move something against its concentration gradients. Or its role in muscle contraction with the
actin and myosin cross bridge…we need another video for that. ATP is critical for many types of cell signaling;
you need your cells to be able to communicate. Those are all just some examples. But what is ATP? How do we get it? And…how does it work? Those are the basics of what we’re going
to focus on in this short video. So what is ATP? If you remember the four major biomolecules,
ATP would fit in with the nucleic acids. Yes, like DNA and RNA. ATP is a nucleotide derivative so it has those
three parts you’d see in DNA or RNA nucleotides: phosphate, sugar, base, but it actually has
3 phosphates. ATP is short for its full name, adenosine
triphosphate. This fancy name is helpful as it tells you
that it contains the nitrogenous base known as adenine, and three phosphates---hence the
“tri” in adenosine triphosphate. Its sugar is ribose. How do you get ATP? All cells need ATP and so they need processes
that can be used to generate it. But the process can differ. It might involve oxygen such as aerobic cellular
respiration. It might not involve oxygen such as anaerobic
respiration or fermentation. During cellular respiration, plants break
down the glucose they MADE from photosynthesis to make ATP. During cellular respiration, animals break
down the glucose they CONSUMED to make ATP . And it's not just plants and animals; bacteria,
fungi, protists, and archaea---they all need to make ATP. We have a video on cellular respiration and
another one on fermentation that can be helpful to understand the process, but one thing that
we do want to mention about making ATP is that it is important to understand it is part
of a cycle. With the ATP cycle you have ATP, which can
be hydrolyzed, releasing energy and losing one of its phosphates in this process. A process like cellular respiration can provide
the energy needed to add a phosphate to ADP in order to regenerate ATP again, which is
important as ATP can be used quickly. This brings us to how ATP is able to work. So how does ATP work? It’s not just about ATP being hydrolyzed
and releasing energy. It’s more than that. Ok, honestly, it’s more than our short video
can go into, which is why we provide some further reading links, but let’s look at
some basics. So when ATP is hydrolyzed, meaning here it
involves the addition of water, it’s not really that the bond between this second and
third phosphate itself is a super strong bond. It’s actually more that the bond between
the second and third phosphate contributes to this ATP being unstable. These phosphates with their negative charges
don’t like being arranged like this. The change from ATP losing its third phosphate
to become the more stable ADP is an exergonic reaction and releases free energy. A popular example for understanding ATP is
to use the spring illustration. Like a wire spring. Consider how you might compress the spring---ATP
would be modeled by that compressed spring---and then you would let it go until it just goes
into this relaxed state, which would be represented by ADP. When ATP is hydrolyzed, if the energy was
just released, it will likely not be useful for a cell if it’s not actually coupled
to something that needs it. Thankfully, the energy release can be coupled
to endergonic processes that the cell needs to do. This can occur when the phosphate from the
ATP is transferred to a molecule that is going to be acted upon. For example, this cell transport protein here
is supposed to move some kind of molecule against its concentration gradient. Recall if it was passive transport, these
molecules would be moving from high to low concentration, but in active transport thanks
to ATP, this protein can move them against the gradient. When the phosphate is transferred to this
protein, we say the protein has been phosphorylated. Sounds powerful. We can say, in our example, that this protein
is more reactive and less stable in this form, this phosphorylated intermediate state. When it reverts into its original, more stable
shape, it can assist in moving them the other direction. So from marveling at the beating of a single
cilia hair, or chromosomes being separated in cell division, or binding the correct amino
acid on a tRNA, I could go on---we hope that little ATP symbol will mean something every
time you see it. Well, that’s it for the Amoeba Sisters,
and we remind you to stay curious.