Hi, everybody. This screencast is going to discuss biomolecules. We're going to do
an overview as well as talk about carbohydrates and lipids. So, in one of
our last screencasts we talked about different kinds of atoms that are very
commonly combined together in biology; those are carbon, hydrogen, oxygen
nitrogen, phosphorus and sulfur. And the four building blocks are biomolecules
that we tend to see a lot of are carbohydrates, lipids, proteins and
nucleic acids. And we call these four different molecules, we call them the "big
four" or we call them "biomolecules". So over the course of the next to
screencast we're going to take a look at each of these four and we're going to
learn a few things about each one. So by the time you finish watching this
screencast and the one after it you should be able to name the building
blocks of each macromolecule, the locations that we might find each one,
and some examples. and then also what they do, so their functions. So each of
the big four, carbs, lipids, proteins and nucleic acids are what we call "organic
molecules" meaning that they contain this atom right here which is carbon. And
usually contain a lot of carbon atoms. Carbon is a really common element to
have in lots of biomolecules because it's so good at bonding. This is because,
you might remember from chemistry, it actually forms four bonds and so it has 4
valence electrons.
It also has space to form new bonds, so if we were to add a hydrogen, which has
one valence electron, to the outside like this in four different places, we would
actually form a compound that's called ch4. And that's also known as methane.
What we've just drawn here is methane gas, which is basically the gas that you
produce when you fart, so if we wanted to diagram a fart we could do this in a
couple of different ways. We could use a dot diagram like we have on the left, or
we could use a line diagram like what we have on the right. On the right we
don't actually draw in the valence electrons, they're implied. We only draw in
the atoms and the bonds. Methane is actually a pretty small molecule, so
we're going to show a slightly more complicated molecule to start our intro
into carbohydrates.
Here's a more complicated molecule, and you'll notice that it's
actually structured around a six sided ring in the center. So here's my six
sided ring right here; it's made up of five carbons and also an oxygen, and then
on the top and bottom of that ring, if you imagine this ring is kind of facing
this way, it's actually got some "decorations" that stick out from the tops
of it like this. And then it also has a couple sticking out from the bottom like this.
So, go ahead and count the number of carbons, hydrogens and oxygens that you
have in this molecule right here. If you counted correctly, you'll notice that
you have six carbons, twelve hydrogens and six oxygens, and you might recognize this
chemical formula right here. This is actually the chemical formula for
glucose, which is a really common form of sugar that you find a lot of plants.
Glucose is actually one of the carbohydrates that we're going to talk
about today, but before we get more into carbohydrates I want to show you one
more way that you can represent molecules. This here is the same
molecule on the left as we had earlier on the right;
every corner is a carbon unless otherwise specified, so 1 2 3 4 5 6
carbons. But, this corner right here is not a carbon, it's actually an oxygen; we
can tell that because it says oxygen instead of just having a blank corner.
Now onto carbohydrates. So there are four major classes of carbohydrates;
monosaccharides, disaccharides oligosaccharides and polysaccharides.
Notice that they all have the same suffix right here and whenever you see
this, this means "sugar" and the prefix "mono" "di"
"oligo" or "poly" tells you a little bit about how many sugar chunks you have all
bonded together. The two that we will spend the majority of time talking about
in this class are monosaccharides and disaccharides. Monosaccharides are going
to have one single simple sugar, whereas disaccharides will consist of two chunks
of sugar bonded together. We're going to look at those in a second, so let's talk
about monosaccharides.
These are also known as simple sugars, and one of the most common ones that
you'll hear talked about in biology is our friend glucose. Just like we saw
in the previous couple of slides, glucose is actually a hexagonal shaped sugar so
it has this hexagonal structure and then on top of it on the bottom of each
corner you have different kinds of decorations like this. The different
kinds of atoms that are added onto the outside of the molecule we call
"functional groups". The different kinds of functional groups that you add onto the
outside of a molecule can make a huge difference in terms of what the molecule
does and how it behaves. Another common monosaccharides is something called
fructose, which also has a ring structure but this is actually a pentagonal ring
structure instead of a hexagonal ring structure. Fructose also has a series of
functional groups added to the outside of its ring. I'm not going to go into
details about exactly what these functional groups are because we're
going to build these hands-on in class. One of the most important things to
remember as we move forward is that these are actually going to be the
building blocks of larger carbs, so when you assemble two monosaccharides
together you get what's called a disaccharide, and there are a couple that
you're probably already familiar with. These two disaccharides are sucrose and
lactose, and sucrose is what you have in a sugar ...(whoops) Now we're going
to talk about disaccharides that are another type of carbohydrate. So the two
that you're probably most familiar with are sucrose and lactose, and sucrose is
commonly known as "table sugar" which is the white crystals that you might find
in the kitchen and then lactose is the sugar that's found in milk. This is what
you're allergic to if you're lactose intolerant.
Now notice that both of these types of disaccharides, just like glucose and
fructose, have the suffix "ose" at the end. This is a common suffix indicating the
presence of sugar, so now we're going to take two different monosaccharides and
combine them into a new disaccharide.
On the bottom of the screen, we have a molecule of glucose and a molecule of
fructose. However when we combine the two of them,
we're going to form a new molecule which is going to be sucrose. So when we
combine the two of them like this using a bond with an oxygen in the middle,
we're going to get a new molecule and this molecule is going to be sucrose.
We will be doing this hands-on in class later on this week.
Polysaccharides have many many chunks that are strung together, and are much larger
than a disaccharide or a monosaccharide, but they're made of the same building
blocks. The polysaccharides that you may have heard of are chitin and cellulose.
Chitin is often found in the exoskeletons of organisms such as insects, you also
find in the cell walls of some fungi but this polysaccharide is what gives the
outer part of a beetle it's crunchy texture. Cellulose the polysaccharide
that's found in the cell walls of plants. While most herbivores can digest
cellulose, humans can't and this is why eating cellulose, especially beans, tends
to make you fart. When you take a Bean-O pill, it gives you the enzymes that you
need to more easily digest the cellulose and thus prevents you from becoming
really gassy.
Monosaccharides and disaccharides have a common function.
Generally speaking they're commonly used as fuel. The food that we eat contains a
different kind of energy than what our cells need to use, and so we undergo a
process called cellular respiration and this is where we take energy from sugars
and use it to recharge or rechargeable form of energy called ATP. ATP is the
energy currency that our cells need to use. Unfortunately we can't use the
energy from our foods directly, we must undergo this process, but monosaccharides
and disaccharides are both easy sources of fuel.
This is why it's really helpful to eat a small snack right before you do a lot of
exercise.
Since this course doesn't delve too much into oligosaccharides, we're going to
talk about polysaccharides. Rather than being fuel, polysaccharides are used
mostly for structure. This is a molecule of cellulose, the molecule that's found
in plant cell walls. Notice that it's made up of several of these simple
sugars all stuck together, so 1,2,3,4. You don't need to write down or memorize the
structure, but you should know that polysaccharides are made up of many
monosaccharides all strung together. Cellulose happens to be a pretty small
monosaccharide. Now let's move on to the different kinds of lipids. There are
three major classes of lipids and they're all pretty different from one
another.
The one you're probably most familiar with is fats, but there are other kinds
of lipids called phospholipids and steroids.
All of them are hydrophobic, which means that they do not dissolve in water, and
the reason that they don't dissolve in water is because they contain lots and
lots of carbon and hydrogen. The first type of lipid that we're going to talk
about are fats, the group that you're probably most familiar with, but you may
be less familiar with its molecular structure. Fats are composed of a
glycerol head attached to 3 fatty acid tails.
Let's take a closer look at glycerol. So here you'll notice that there are three
carbon atoms bonded together and that on the bottom we have 3 "O.H." groups which are
also called alcohol groups. These alcohol groups will become the attachment points
for each of the three fatty acid tails and we'll be constructing these in detail
using our model kits in class. The process of attaching the fatty acid
tails to the glycerol head is called dehydration synthesis and that involves
removing each one of these different groups down here and combining them with
another hydrogen atom from the fatty acid tails.
This produces three molecules of water and adheres the fatty acid tails of the
glycerol head.
Notice that, once again, every carbon atom is always forming four bonds. Let's
look at this fat a little bit more closely. To orient you, this top part
right here is the glycerol head, and then underneath that we have three fatty acid
tails 1 2 and 3 and you'll notice that they have a lot of carbon and a lot of
hydrogen in them which is what makes this so difficult to dissolve in water.
Notice if you look at the three fatty acid tails that the one on the left
actually has a kink in the center, so right here, this makes the leftmost fatty
acid tail different from the middle and the right-hand ones. The left fatty acid
tails is what we call an unsaturated fat. It's called unsaturated because not
every carbon is bound to the maximum number of hydrogens and because it has
a double bond in the center it causes a kink in the middle of the fatty acid
chain. Because of the kink in the unsaturated fatty acid tails, it's
difficult for them to nestle closely together thus they tend to be liquid at
room temperature, whereas the other kinds of fatty acid tails like the ones in the
middle and on the right are what we call saturated fatty acid tails, which tend to
be solid at room temp.
An unsaturated fat you're probably familiar with is something like
vegetable oil, and a saturated fat you're probably familiar with would be
something like butter. Butter tends to be solid at room temperature, whereas olive
oil or vegetable oil tends to be liquid at room temperature. Both saturated and
unsaturated fats are an excellent source of energy and fuel. Another important
class of lipids is phospholipids, and these are very important in the cell
membrane, which we're going to talk about later on in this course. They consist
of two components; a phosphorus head rather than a glycerol head and then two
fatty acid tails one of which is usually unsaturated one of which is usually
saturated. Usually in this class will represent phospholipids like this. In the
cell, you have two layers of phospholipids that form a double
membrane with a space in the center right here. The outer layer is made of
phosphate heads and the inner layer is made up of lipids which means that the
outermost layer is permeable to water whereas the inside layer is not. Because
of its components we call this the phospholipid bilayer, and it surrounds
most of the cells in our bodies as well as many of our organelles.
The most important function of the phospholipids is that they allow the
cell membrane to be selectively permeable, which means certain things can
pass through it whereas other things cannot. The last class of lipids that
we're going to talk about are steroids.
Although we're not going to talk too much about anabolic steroids, the
kind that you probably most familiar with, steroids tend to have this basic
structure; so three hexagonal rings and a pentagonal ring. Remember that each of
the corners is a carbon unless specified otherwise. Because of all these hydrogen
and carbon, it's really difficult to make steroids dissolve in water; they tend to
want to dissolve in substances like oil or fat.
I've now modified this basic steroid to become something that you may be
familiar with; this steroid is cholesterol. Now cholesterol tends to get
a bad rap because everyone associates it with heart disease, but it's actually a
very important steroid to have in one's body.
Among other things, cholesterol allows the cell membranes in your body to
respond to changes in temperature and be appropriately soft or appropriately
rigid.
You also need a certain amount of cholesterol in your body in order to
make vertebrate sex hormones like testosterone and estrogen.
Ok, that pretty much wraps up carbohydrates and lipids for now, and I
will see you all in class! Don't forget to subscribe!