Previously you’ve learned about atomic structure
and how atoms come together to form molecules and all of that is based on electrons in the valence shell.
Now we’re going to venture into exploring how these smaller molecules come together
to form the four major classes of macromolecules or biological molecules.
So in this lecture, you’ll learn to identify what the monomers and polymers
are of the four classes of macromolecules as well as explain the process of dehydration synthesis -
that is how these molecules come together;
and you’ll also be able to identify carbohydrate molecule structure
and discuss why we can’t eat grass.
So let’s begin by taking a look at how macromolecules come together.
All organic macromolecules are composed of hydrocarbon chains with additional functional groups.
By hydrocarbon we mean simply hydrogens and carbons covalently bonded to each other.
In this example you can see the hydrogen carbons in black and white
and then a functional group on the far end of that molecule.
This one's myristic acid but that doesn’t really matter at the moment.
The point here is you can see that there are single covalent bonds
between each of the carbon molecules in that chain and they are fully saturated, they are covered in hydrogens.
In this case the chain is straight, on occasion you’ll see that these chains has kinks in it
and that might be because of double bonds between the carbons,
but either way, it’s a carbon hydrogen chain with functional group on the end.
We’ll discuss those functional group shortly.
Here’s a comparison of those three molecules
again, each of them the point here being that they have a hydrocarbon chain
with functional groups added to the basic structure of the hydrocarbon chain.
Now, we’re going to be looking at a variety of different functional groups.
Here are some of the main ones that we’ll see in biology.
First of all, we have the hydroxyl group that I previously introduced.
It’s simply an OH, we’ll see that in a lot of carbohydrates, proteins, nucleic acids and lipids,
so when all four classes of macromolecules we also will see the carbonyl group
which we’ll see in carbohydrates and nucleic acids.
We can also see the carboxyl group and proteins and lipids.
We will see amino group again in proteins and we will see sulfhydryl
on occasion in proteins where we create disulfide bridges and protein folding
and phosphate groups in nucleic acids; methyl groups we’ll see in proteins and in DNA.
Before we begin our discussion of the various macromolecules,
we need to understand two major terms, the first of which is monomer and the other is polymer.
Mono means single mer means units so monomers are single units that are strong together
to form polymers, multiple units. Here we have a bunch of monomers,
for example, glucose molecules.
Glucose molecules are polymerized or brought together through a process
called dehydration synthesis that we’ll investigate shortly
and they will form a polymer strand so many units of glucose
in this case it could be glycogen for example.
So let’s look briefly at each of the four classes of macromolecules
so that I can introduce them to you and later we’ll explore them with much more depth.
First of all, we look at carbohydrates. Carbohydrates are long chain sugars
often they could be single sugars or they could be disaccharides or polysaccharides.
The monomer is a monosaccharide in this case, glucose.
Multiple glucoses are strong together to form a starch or many different forms of polysaccharides.
Then let's look at the basics of polypeptides or proteins.
Polypeptides are strings of amino acids.
The monomer, being the amino acid, the polymer being the whole polypeptide,
the string of amino acids.
Now the polypeptide will fold and form eventually it's protein but we’ll cover
that in much more detail in the following lecture.
A brief look at nucleic acids, we see that the polymer is the DNA strand or the RNA strand
and that polymer is composed of multiple repeating sub units of a monomer
which in this case is the nucleotide.
The nucleotide is composed of three sub units itself but we’ll deal with them
in much more detail, again, in a following lecture.
Lipids are a little bit different because they are nonpolymer macromolecules
which means they don’t have repeating sub units of exactly the same type of thing
for example amino acids or glucose molecules or monosaccharides.
In this case we have three fatty acids tails tied together by one glycerol molecule
so it’s not a repeating thing so lipids are a class of nonpolymer macromolecules,
the other three classes are polymer macromolecules,
we have monosaccharides linking together to form polysaccharides,
amino acids to form polypeptides, nucleic acids are formed by monomers of nucleotides.