Hi, this is Mr. W from ScienceMusicVideos.com, and this video is about functional groups. There are eight functional groups, groups of atoms that are worth getting to know because they explain how molecules work. Let's look at glucose, the fuel of life.
See these OHs that are attached to the carbon atoms? This is a functional group that's called hydroxyl. Hydroxyl consists of an oxygen and a hydrogen.
That R represents the rest of the molecule that the functional group is attached to. Think of hydroxyl as a water molecule that's lost its second hydrogen. The oxygen will have a partial negative charge. The hydrogen will have a partial positive charge. That polarity will make any molecular region where hydroxyl is attached hydrophilic.
And that's why molecules with hydroxyl groups are water soluble. Coffee contains caffeine. Caffeine has several functional groups, but we're going to focus on this one. This carbonyl group is a carbon double bonded to an oxygen.
Like hydroxyl, it's polar and hydrophilic. This is carboxyl. It's a carbonyl group with a carbon attached to a hydroxyl. When dissolved in water, this hydrogen tends to break off, making a carboxyl group a weak acid and leaving this ionized form of carboxyl behind. That's what you'd find in a cell.
You should be able to identify both the non-ionized and the ionized forms. Amino groups consist of a nitrogen attached to two hydrogens. When you connect an amino group to a molecule, that makes it a base because the amino group in water will pick up a proton from the solution, increasing the pH. That makes the amino group look like this.
It'll have three hydrogens and a positive charge. Just remember that amino sounds like ammonia. Ammonia's formulas. NH3 and it's a base just like the amino group.
Sulfhydryl groups consist of a sulfur bonded to a hydrogen. Sulfhydryl groups are important in determining the shape of proteins because when two sulfhydryl groups become close to one another they can form a disulfide bridge. That creates turns and bends in a protein chain and that determines the protein's overall shape. A phosphate group is a negatively charged ion that consists of one phosphorus atom surrounded by four oxygen atoms.
Phosphate groups make molecules acidic. You should be able to identify this ionized form of a phosphate group, which is what's found in cells, this non-ionized form, which you might find in a textbook or on a test, and phosphate's chemical formula, PO4. Phosphate groups are incredibly important. Here are phosphate groups making up the backbone of DNA.
Here are phosphate groups in the head of a phospholipid, the key molecule in cell membranes, and here are three phosphate groups in life's key energy molecule, ATP. A methyl group is a carbon connected to three hydrogens. If you know the natural gas methane, then a methyl group is very easy to identify. You'll also see methyl represented by its empirical formula in one of these two forms.
Adding methyl groups to a molecule is called methylation. and it creates a nonpolar region where the methyl was added. Cells use methylation to modify DNA. Methylated DNA won't be transcribed, essentially turning the DNA off.
Finally, here's an acetyl group. It consists of a methyl group bonded to a carbonyl. Take a look at this molecule.
This piece over here is the acetyl group. This molecule is known as acetaminophen, better known as Tylenol. Adding an acetyl group to a molecule is called acetylation.
Later in the course, when we learn about control of gene expression, we'll see that cells will add acetyl group to certain regions of DNA in order to make it easier for the genes in those regions to be transcribed. That's it. We've done it.
Those are the eight functional groups. Right now, head on over to ScienceMusicVideos.com, where you can do the tutorial that I've written for you about functional groups. It'll really help you learn this material.
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