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Proteins I: Structure and Function

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  • 0:06 Proteins
  • 0:53 Structure
  • 2:00 Enzymes
  • 3:25 Other Functions
  • 5:34 Summary
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Lesson Transcript
Instructor: Meg Desko

Meg has taught college-level science. She holds a Ph.D. in biochemistry.

We need our proteins, not just as a major food group but for the many useful roles that they play in our bodies. In our introductory lesson to proteins, you'll learn about the many functions we rely on them to perform.

Proteins and Peptide Bonds

Diagram of a peptide bond
Peptide Bond Definition

Proteins are something that we've heard about because they're an important part of our diet. If we look at this nutrition label for macaroni-and-cheese, we can see that, in addition to containing several grams of carbohydrates and fats, there also contain proteins. Proteins are large biological molecules that are made of amino acids that are joined together by peptide bonds.

To form proteins, many amino acids come together by dehydration to form peptide bonds, which is a bond between the carbonyl group of amino acid and the amino group nitrogen of another amino acid. Peptide bonds are incredibly strong and help proteins stay together to perform their jobs.

Proteins as Structure

Proteins can be used to provide structure. One example is a protein called keratin. Keratin is a protein that's found in our hair, skin and nails.

Keratin proteins come together and form filaments, which are long strands intertwined. If you think of a thick rope, which consists of many different smaller pieces of rope, it's made stronger by the fact that all of these different pieces are twined together, and that's exactly the case with keratin. Keratin is hydrophobic and insoluble in water; this fear of water is part of why keratin is so strong. The different strands of keratin proteins are very attracted to one another and less so to the outside environment, which helps them stay together. Another important structural protein is collagen. It's an important component of connective tissue, which is found in tendons and ligaments. Again, it's very important for the structure that we find in our bodies.

Magnified image of the protein keratin
Keratin

Enzymes

Another important role that proteins can play is they act as enzymes, which can make chemical reactions happen in our bodies.

The way that they make chemical reactions happen is that they decrease the activation barrier to make a reaction happen. So, to see what I mean by an activation barrier, let's say your alarm goes off, but you really don't want to get out of your bed. It's really cold outside of your bed and that increases the activation barrier to your getting out of bed, or the amount of 'oomph' to get yourself out of bed.

In the case of chemical reactions, we're talking about the amount of energy required to make that chemical reaction happen. By decreasing the activation barrier, enzymes make a chemical reaction more likely to occur. That would be akin to someone brewing you a nice hot cup of coffee or maybe putting down a nice warm rug for when you get out of bed. Maybe that would decrease your resistance to getting out of bed.

Now, enzymes can make chemical reaction happens, which are really important for many areas of our body. One example outside of our body that you may have heard of is called lactaid. This pill contains enzymes that can help people digest lactose sugars. This is really important for some people who can't digest lactose, since it saves them from indigestion. By breaking down these lactose sugars, these enzymes help peoples' stomachs feel better.

Hemoglobin is a protein that transports oxygen
Hemoglobin Definition

Other Protein Functions

Another important function of proteins is that they allow for movement. Two of the most important proteins that are involved in movement are actin and myosin. Actin is highly involved in cell motility and mobility. It's also important for our muscles contract so that we can move or walk. Myosins - I say myosins because there are many different versions of this protein - are a motor protein and are also really important for making our muscles contract.

Proteins can also transport things throughout our body. An example of this is hemoglobin, which is a protein that carries oxygen from our lungs to tissues throughout our bodies.

Lipoproteins are proteins that can transport multiple fat molecules throughout our blood.

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