Introduction to carbohydrates | Biology foundations | High school biology | Khan Academy
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Introduction to carbohydrates | Biology foundations | High school biology | Khan Academy


– [Instructor] What we’re
going to do in this video is give ourselves a quick
introduction to carbohydrates, and you might already be
familiar with the notion. If you look at some packaged food, there’s usually a nutritional label and will say carbohydrates. It will tell you a certain
number of grams per serving. And not all carbohydrates are edible, but many of the things that we eat or many carbohydrates are edible and many of the foods we eat have some carbohydrate component to it. But what is it actually? Well, we can look at the
word and we see carbo, so maybe it has something
to do with carbons. And it says hydrates, so maybe it has something
to do with water. And if you said that,
you’d be pretty close because carbohydrates do involve carbons. In fact, this is a very
typical carbohydrate, a very simple one right over here. This is a glucose molecule. And in gray, you see
that it has six carbons. And the hydrate part refers to, that carbohydrates typically
have oxygen to hydrogens in the same ratio as you
would expect in water. So, for every one oxygen, two hydrogens, and you see that right over here, where in glucose, you have one, two, three, four, five, six oxygens and you have 12 hydrogens, and so that’s where this word comes from. Now, another word that is often used interchangeably with carbohydrates
is the term saccharide. Saccharide, and saccharide
comes from Greek for sweet, and that makes sense because
if you were to taste glucose, it would taste sweet to you. Now, what’s interesting
about something like glucose is glucose can be a standalone molecule, a very simple sugar in this case or you can build up larger molecules with really glucose as a building block. So for example, right over here, we have a part of a glycogen molecule. And as you can see, it’s just a repeating
sequence of glucose molecules. And so, something like this, we would call glucose a monosaccharide. It’s one simple sugar right over here. Monosaccharide. And we would call this
glycogen a polysaccharide. Polysaccharide. Or another way to think about it is glucose is the building
block for the glycogen. Another term you might see
is monomer and polymer. Those are the general terms or if I’m building a large molecule out of a chain of smaller ones, the building blocks, we
consider to be monomers, and then the thing that we
build out of those monomers could be our polymer. And as we’ll see, this
monomer polymer phenomenon is not limited to
carbohydrates or saccharides. We’re gonna see that same
relationship, for example, between amino acids and proteins. Now, what role do carbohydrates play inside of biological systems? Well, saccharides or carbohydrates are often associated
with the source energy. Glucose can be converted very quickly to energy
in biological cells. Glycogen is also a store of energy in your liver and your muscles. And once again, it can be broken down into the glucose molecules,
which once again, is a very readily
available source of energy. Now, in plants especially,
some of these polysaccharides could also play a structural role if we’re talking about
things like cellulose, which is another polysaccharide. So, there’s also a structural role. Now, I will leave you there. We have focused only on one type of monosaccharide in glucose, and only on one type of
polysaccharide in glycogen. As we will see, glucose does show up a lot but there are many other
types of monosaccharides and there are many other
types of polysaccharides. And polysaccharides in particular are part of a broader group of molecules
known as macromolecules. And as you can imagine,
from the macro prefix, it’s referring to large molecules, oftentimes that have
thousands of atoms in them. But don’t get the wrong idea. They’re very large at an atomic level but each of these circles are still atoms, so you would still need a very, very, very, very powerful microscope
to even to take a look at even some of the
largest macromolecules, including polysaccharides.

12 thoughts on “Introduction to carbohydrates | Biology foundations | High school biology | Khan Academy

  1. Monosaccharides- Glucose, Fructose, Galactose.
    There are Disaccharides- Sucrose. Which is sugar.
    Polysaccharides- Glycogen.
    This is how it works
    Glucose breaks down by the Oxidation that is breathing into Carbon dioxide + Water + Energy(1gm of glucose give 673kcal).
    Equation
    C6H12O6 + 6O2 -> 6CO2 + 6H20 + 673 K cal.

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