Proteins

Biology Index

Where are we going with this? The information on this page should increase understanding related to this standard:  Evaluate comparative models of various cell types with a focus on organic molecules that make up cellular structures.

Article includes ideas, images, and content from Troy Smigielski (2021-08)

Proteins

(Hmmm… This rings a bell!)

In addition to carbohydrates and lipids, there are two more types of biomolecules. One of them is proteins…

Proteins function to control what cells do. 

For instance, proteins can:

• Build muscle, tissue, and bone
• Help fight disease

Another "for instance" is…

Cells within organisms often need to communicate and work together to carry out life’s processes. Proteins play a vital part in this. Proteins on cell surfaces act as receptors to certain compounds, allowing cells to alter as needed. 

As a way of looking at it broadly, proteins regulate cell processes or transport materials into and out of cells.

Composition of Proteins

Proteins are made up of amino acids sequenced together in a chain.

(Grrrr… another chain! Why do I think this means more elements and bonds?)

Thus, the monomer of proteins are amino acids. 

This is kinesin, a motor protein, thought
to be carrying an endorphin.

An amino acid is… complicated…

Amino acids consist of a basic amino group (―NH2), an acidic carboxyl group (―COOH), and an organic R group (or side chain) that is unique to each amino acid. The term amino acid is short for α-amino [alpha-amino] carboxylic acid. Each molecule contains a central carbon (C) atom, called the α-carbon, to which both an amino and a carboxyl group are attached. The remaining two bonds of the α-carbon atom are generally satisfied by a hydrogen (H) atom and the R group (Source, 2021-09-01). 

How about trying that with less words!

Amino acids are organic compounds that combine to form proteins (Source, 2021-09-01). 

The general form of an amino acid looks like this. 

There are 20 common amino acids used by all living things. In addition to proteins, amino acids form peptides and polypeptides, but… let's hold off on that for now.

Let's recap… before we press on…

Proteins are made of amino acids. 

Amino acids have four parts arranged around  a central carbon. Carbon has 4 places stuff can bond to it.

Part 1: One bond is usually just hydrogen (H).

Part 2: One bond is usually H2N, an amino group. 

Part 3: One bond is the carboxylic acid group (usually written as -COOH or CO2H).

Part 4: The fourth bond is the "organic side chain" called the "-R Group"

How do amino acids differ from one another? Amino acids differ in their -R groups. There are 20 different -R groups, which allows for a wide variety of proteins. The -R group determines what amino acid it is. 

Hey… weren't we talking about proteins? 

So, there are 20 different amino acids, and they combine to form proteins (and peptides and poly peptides, but we're overlooking that, here). The order in which the amino acids combine determines what protein is made.

In a sense, the order of -R groups determine what protein is made. Changing the order changes the type of protein. Adding an amino acid to the chain changes the protein. Taking one away changes the protein.

Thus, each protein is identified by which amino acids are present and in what order they are arranged. Any variation of either which amino acids are present or what order they are in changes which protein is present.

So… about those peptides…and polypeptides…

When amino acids are attached, they are held together by a peptide bond. Two amino acids isn't a protein, but… we're on the way! The newly formed molecule is called a polypeptide.

When many polypeptides are joined together, a protein is made.

Also, some water is formed… 

So, connecting the amino acids (by means of the peptide bonding) creates (potentially) long chains. 

Okay…

Don’t miss this!! Proteins are made when amino acids are put together in a specific order.

A Protein Allegory…

Consider this…

… amino acids are the alphabet

… peptides are syllables

… polypeptides are words

… proteins are sentences

Just as changing which letters are arranged in what order changes the sentence, so to changing which amino acids are arranged in what order changes the protein.

Purposes of Proteins

There are many different kinds of proteins that do a very elaborate and diverse set of tasks in your body:

• Humans have thousands of different proteins. The structure of the protein determines its function.
• Typical protein = 200-300 amino acids.
• Biggest known = 34,000 The largest known protein is called titin (also known as connectin). It functions as a molecular spring which is responsible for elasticity in muscles.

Proteins have many, many functions. For example, GFP is a protein that provides a fluorescent color to an organism.

Another example: AFPs are proteins found in northern cod, and they prevent freezing. 

More example…

• Keratin is a structural protein in hair.
• Hemoglobin is a transport protein in blood.
• Albumin regulates oncotic pressure (pulls water into the blood when needed)
• Insulin is a hormonal protein that functions to regulate blood sugar.
• Actin and myosin are movement proteins in your muscles.
• Antibodies are defense proteins in your immune system.
• Enzymes are proteins that speed up chemical reactions.

Enzymes

Enzymes are mostly proteins that speed up chemical reactions.

• They do this by lowering the activation energy (energy needed to start a reaction).
• They are very selective in the reaction they choose to speed up.
• They can break molecules down or put a molecule together.
• Most enzymes end in -ase.

Cells regulate chemical reactions in order to produce things they need to grow and survive. Enzymes are most responsible for regulating chemical reactions inside cells.

Also, activation energy is the amount of energy required to start a reaction. Enzymes speed up reactions by lowering the activation energy.

Denaturation

Denaturation is the unraveling of a protein. When a protein denatures, it unravels and loses its shape.

This makes proteins biologically inactive. It can be caused by:

• Changes in pH
• High or low salt concentration
• Temperature

Examples of Proteins and Their Purposes

Keratin is a structural protein in hair.

Hemoglobin is a transport protein in blood.

Albumin regulates oncotic pressure (pulls water into the blood when needed)

Insulin is a hormonal protein that functions to regulate blood sugar.

Actin and myosin are movement proteins in your muscles.

Antibodies are defense proteins in your immune system.

Casein is a protein in milk that is beneficial for muscle repair.

Myoglobin binds oxygen in your muscles.

Thrombin helps your blood clot.

FOXP2 is required for speech, and is unique to humans.

Major Histocompatibility Complex (MHC) helps recognize foreign molecules (pathogens).

Laminin is the protein that anchors our whole body together.