Protein Structure Part 1: Where Are Proteins? What Do They Do?

[Music] Hi. In this video I’ll be talking about the basic
structure and function of proteins. I invited my friend Marcy to help me
explain what proteins are, how organisms use them to build useful structures, and how small changes in one region of one
protein can produce BIG changes in an organism. First though, what IS a protein? In everyday life, we think of protein as
the stuff that muscles are made of. As you’ll soon see though, cells and organisms have millions of different
proteins that do all kinds of jobs. So what makes up a protein? Proteins are macromolecules, which means they are large molecules made
up of repeating subunits of smaller molecules. In the case of proteins, the repeating
subunits are amino acids. Living things use 20 amino acids to make most
proteins. Amino acids are organic molecules. That means they are built mainly from carbon
atoms. Most amino acids have a central carbon atom
with four side groups. One of those side groups is an amine. A second side group is a carboxylic acid. These two side groups are found in ALL amino
acids, and are important for several reasons. For one thing, they give amino acids their
name. They also are where amino acids form covalent
bonds that join them together in long chains. The amino and carboxylic acid groups also
form hydrogen bonds within proteins. And that helps them fold into complex shapes. The third side group is usually a hydrogen. A few amino acids replace that hydrogen with
a covalent bond to the final side group. This is going to affect how some proteins
fold. The fourth side group of each amino acid
is what makes it unique. Every amino acid has a slightly different
chemical structure. The unique side group can be as small as
one hydrogen, or a big, complex ring structure. Under the conditions inside a cell,
each side group can be positively charged, negatively charged, polar but not charged,
or even non-polar. The charge, the polarity,
and the size of these side groups are what give proteins many
of their important properties. So where are proteins found? Muscles ARE mainly made of protein, but they definitely are NOT the only
place we find proteins. Every last cell contains proteins, as well
as lipids, carbohydrates, and nucleic acids. Proteins also make up larger structures in
organisms. In mammals like us,
nails and the outer layers of our skin both are made up almost entirely of
proteins called keratins. These are a large family of tough, resilient fibrous proteins that we will be
exploring more in a few minutes. Hair and horns are made of keratins too. Even the clear cornea and lens of our eye,
is made up of specialized proteins. GAAAAGGGHHH!! Marcy get off of my foot! Unh, unh, unh! Please, please, please, please move! Unh, unh, unh! Bones are made up of tough proteins called
collagens. Collagen fibers are embedded
in a matrix of other proteins and crystals of calcium and phosphate. Blood is also rich in protein. Red blood cells are basically sacs of
the protein hemoglobin, which is specialized for carrying oxygen. The liquid part of blood, called the plasma, is an aqueous solution mostly of
electrolytes and dissolved proteins. Among those dissolved proteins are clotting
factors, which he’s going to need as soon as I move
my foot. When clotting factors contact air,
they undergo a chemical reaction. Soluble blood proteins turn into a meshwork
of fibers that trap red blood cells and form a clot. [Music]

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