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Cell Biology

Learn the toughest concepts covered in Cell Biology with step-by-step video tutorials and practice problems by world-class tutors

2. Chemical Components of Cells

Small Molecules


Water and Carbon

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Hi in this video, we're gonna be talking about small molecules. So the first molecule that we're going to talk about is water, which of course is extremely important in biology. So we're gonna I'm gonna list a few properties of waters that are important in cell biology specifically. So first is that water is a universal solvent, which means that it can dissolve Many types of molecules. And so this is extremely important as uh as and you can tell this by looking at how much water is actually composed of the cell weight. So actually 70% of the cell weight is made up of water. Now with water we talk about some classifications and there's these terms that continually prop up bio and intro bio again and cell biology and that's hydra filic and hydrophobic. Um so I know you've probably been beat over the head with this, but it's really important that you understand these terms. Um and so in water hydro filic molecules dissolve and in hydrophobic or in water hydrophobic molecules do not dissolve. Now, water is also polar, which means that there is an uneven distribution of charge within the water molecule. So how this works is you have a water molecule and oxygen draws electrons towards it, giving it a negative charge. Where as the hydrogen that water is attached to gains a slight positive charge. Water molecules are cohesive meaning that because of their polar nature they can stick together and that cohesion actually gives water unique properties and makes it really this temperature stabilizing molecules. So one of the ways that we measure this is through specific heat um which you don't need to know necessarily how to catch that in cell biology. But what you do need to know is just that it exists and that it's really this value that is the amount of absorbed heat program to raise the temperature by one degree. So this is really high. So it takes a lot of temperature, a lot of heat to raise the temperature of water by one degrees. So here is an example of one water molecule here interacting through its cohesive properties with other water molecules. So you'll notice um here that you can measure the polarity because the oxygen's have the slight nega charge, whereas the hydrogen is have the slight positive charge. Um and this is what allows the cohesion between water molecules because the slight negative charge of this, this oxygen can interact with a slight positive charge of the nearby hydrogen. So water is extremely important in cell biology. So now let's talk about another important small molecule and that is carbon. Um carbon is extremely important and combined up to four molecules at once. Now in cell biology, this is typically oxygen, hydrogen, nitrogen, sulfur and a few other ones. Now, carbon bonds form through covalin bonds and these are extremely stable. And so one way to measure the stability of a bond is through bond energy and that measures the amount of energy necessary to break it. So more stable bonds are more um have a higher bond energy. Now in chemistry, you'll see bond energy demonstrated in jewels formal but in cell biology usually typically see it as calories per mole. Um and you won't be doing any kind of like calculations of this in cell biology but just in case your professor text mentions it, I just wanted to throw that out there. It's a measure of bond strength and covalin bonds are strong and stable now because carbon molecules can bind to four other molecules. They can have these multiple configurations. So um these configurations can be called stereo I Summers and um these are formed when there is a carbon molecule bind to different things and therefore they have the same chemical nature but can be mirrored structure. So you can see this down here in this image best. So you have this carbon molecule, it's buying to four different things. But then the position of these four things actually create stereo I Summers because obviously this one here is a mirror image of this one here. So the same chemical nature. But they're mirror images. And so um to stereo SmR conservations are possible. So this one here and the second one here for what we term an asymmetric carbon atom. Now in chemistry, you'll see Cairo center a lot more but in cell biology and in your textbook you'll be reading a lot about the asymmetric carbon atom which is just this carbon atom. And by asymmetric it means that on each side it's it's bound to different things. So it's it's not symmetrical. Um and so stereo customers are really important and found in a lot of biological molecules. And we're going to talk about them a lot moving forward. Now there are these groups additionally called functional groups and they are found um on carbon molecules. And they are unique in the fact that they give particular characteristics to the molecule that contain them. So functional groups are attached to carbons but they have specific characteristics that will be important to got to give the carbon molecules various functions in cell biology. So these are the really two important small molecules in cell biology, water and carbon. So now let's move on.

Which of the following is not a property of water?


Which type of molecule dissolves in water?


A carbon atom can bind how many independent molecules at once?