Proteins

What are proteins?

Proteins are tiny particles with huge importance — they help your body do everything necessary to function and stay alive. You can’t see proteins with your eyes, but they’re inside every cell in your body, doing a range of tasks without you even realizing.

To understand what proteins are and what they do for your body, it may help to know a couple terms:

• A molecule is a particle made up of one or more elements, like oxygen, carbon or hydrogen. Proteins are molecules made up of amino acids, each of which consists of carbon and hydrogen.
• A cell is the smallest unit of life, meaning it can live on its own. All people and other living organisms are made of many different types of cells. Your body constantly creates new cells to support its functions. Proteins play a big role in that process.

Even though proteins are too small for you to see, scientists consider them large molecules compared with some other types of molecules in your body. Proteins bend and fold into complex, three-dimensional (3D) shapes suited to their specific tasks.

What is protein?

“Protein” refers to the macronutrient found in many foods and drinks. People generally say “protein” (or “dietary protein”) when talking about nutrition and “proteins” when discussing the science of how the individual molecules work within your body.

Dietary protein is a crucial nutrient that keeps your body going. How much protein you need each day depends on many factors, including your age, activity level, body weight and daily calorie needs.

When you eat beans, salmon, eggs or other foods containing protein, your digestive system takes that protein and breaks it down into its component parts — these are known as amino acids. Your body then uses those amino acids to build new proteins that perform all sorts of crucial jobs. This process is part of your metabolism.

What is the function of proteins?

Proteins keep everything in your body working and moving so you can keep moving. Proteins are so important that scientists describe them as your body’s workhorses.

Here are some things proteins do for your body:

• Help cells in your body “read” your genes and use that information to build new cells and molecules, including new proteins (yes, that’s right: Proteins indeed help create other proteins)
• Provide structure to cells and tissues throughout your body
• Attach to invaders, like bacteria and viruses, to clear them from your body
• Break down nutrients in the foods you eat — including fats, proteins and carbohydrates — into forms your body can use (this might be another surprise: Some proteins, called enzymes, break down other proteins!)
• Send chemical signals and carry information from cell to cell
• Speed up (catalyze) chemical reactions within cells, which helps create the energy your body needs to function
• Serve as channels (like little doorways) in a cell’s outer membrane that allow substances to pass in or out of the cell
• Transport small molecules throughout your body (for example, a protein in your blood called hemoglobin is like a special parcel service that carries oxygen to all your body’s tissues)

Not all proteins do all these things. And some do other functions that are too numerous to list here. There are many different types of proteins in your body, and each type of protein specializes in one or more specific tasks.

Examples of proteins

Proteins go by different names depending on what they do. They also fall into some general categories according to their function. Here are some examples:

• Defense proteins protect your body. If you’ve heard of antibodies, then you’re already familiar with one key type of defense protein. Antibodies are the hard workers that help your body ward off germs and other invaders.
• Enzymes serve as catalysts for chemical reactions, like in digestion. Enzymes make chemical reactions go at least 1 million times faster. Enzymes include lipase, which helps break down dietary fats, and carbohydrase, which breaks down carbs. Other enzyme examples include trypsin, thrombin and pepsin.
• Messenger proteins send chemical signals between different cells, tissues and organs in your body. Certain hormones are classified as messenger proteins because of the work they do to support body processes.
• Motor proteins help things move within and between your cells. For example, they support the movement of cell parts that are vital for wound healing. Motor proteins also help your muscles move, help food move through your digestive tract and support blood flow through your body. 
• Structural proteins offer support for your body’s cells. These proteins also help various cells and substances move within your body. Examples of structural proteins include collagen, tubulin and actin. Tubulins join up to form tubes that carry substances within your cells. Actin works with motor proteins to help your muscles contract. 
• Transport/channel proteins act as little doorways for molecules to move between parts of a cell or between a cell and its surrounding environment. These proteins are often embedded within a cell’s protective outer barrier (cell membrane).

Where are proteins located?

Proteins are in cells all throughout your body. In fact, any given cell holds several thousands of proteins. Each protein in a cell does a specific job to support your body’s needs.

What are proteins made of?

Proteins are made of amino acids held together by chemical bonds. One protein typically contains hundreds of individual amino acids. You can think of these amino acids like beads on a necklace. The word “polypeptide” refers to a single chain, or necklace, of amino acids. “Poly-” means many, and “-peptide” means a molecule containing at least two amino acids.

But proteins are more than simple chains of amino acids. They’re complex molecules made up of one or more chains that twist and fold together in specific ways to make the protein work as it should.

A protein’s function — what it does in your body — determines its exact structure. But all proteins share the same basic structure, which scientists break down into four levels. Let’s take a closer look.

Protein structure

There are four levels of protein structure, ranging from simple to complex:

• Primary structure of protein: This is the sequence of amino acids in a single polypeptide chain. You can compare the primary structure to the order of beads in a beaded necklace. You might choose pink first, then blue, then yellow. A polypeptide chain’s “beads” are amino acids arranged in a specific order. Chemical bonds hold them together. The order changes based on the type of protein and its function in your body.
• Secondary structure of protein: This is the shape a polypeptide chain takes due to chemical interactions between its “beads” (amino acids). The shape may be coiled (alpha helix) or folded in a zig-zag manner (beta sheet). It’s a bit like adding magnetic beads to the necklace so certain parts of the chain are drawn to one another.
• Tertiary structure of protein: This is the 3D shape that forms when the regions of secondary structure fold together into the final structure of the protein. Water attracts some amino acids and repels others. So, some amino acids stay on the outer surface of the protein, where they can bond with water molecules, while others move toward the interior. To picture this happening, imagine stringing beads onto a metal wire and then bending and shaping the wire to form a 3D shape that you can hold in your hand.
• Quaternary structure of protein: This is the fourth and most complex level. Not all proteins have this level of complexity. But some, like hemoglobin, do. It’s when a protein has more than one polypeptide chain, and those chains interact and are folded within each other. Chemical bonds hold these chains together in their unique 3D shapes.

Why do these structures matter? It’s because any changes to a protein’s expected structure can lead to health problems — ranging from sickle cell disease to Alzheimer’s disease. Your body relies on proteins adopting a certain structure to do their jobs as they should. When something goes wrong with a protein structure — even one “bead” that’s different than it should be — the effects on your body can be significant.

What are the building blocks of protein?

Amino acids are the building blocks that make up a protein. You might also hear amino acids referred to as the monomers of protein. A monomer is a single molecule that connects with other molecules to form larger structures (polymers).

What is protein synthesis?

Protein synthesis is the process of making new proteins to support your body’s needs. This process takes place inside your body’s cells constantly — it’s happening in some of your cells now as you read this article.

This is because proteins don’t last your entire life. Over time, they break down, and you need new ones to keep up with your body’s demands. That’s why you need a constant intake of protein from foods you eat so your body has new building blocks (amino acids) for protein synthesis.

You can think of cells in your body like tiny factories with equipment for building proteins. Each cell contains the same basic equipment:

• Your DNA: This acts as an instruction manual for making proteins. DNA is located in the core of the cell, called the nucleus. Each cell contains your entire DNA sequence, but factory “workers” only use the specific “chapter” of the manual they need to make a specific type of protein.
• RNA molecules: RNA stands for ribonucleic acid. It’s similar to DNA but with some structural differences. RNA molecules are the main factory workers. There are three different types of RNA, and each type does a unique job. Messenger RNA (mRNA) is the first type involved. An mRNA molecule carries a copy of the protein-making instructions out of the cell’s nucleus and to an “assembly line.”
• Ribosomes: You can think of these structures as assembly lines for building proteins. Nothing can get made without the necessary building blocks — and that’s where transfer RNA (tRNA) molecules step in. These workers deliver amino acids to the ribosomes. Ribosomal RNA (rRNA) molecules read the instructions and direct the building process of the new protein, amino acid by amino acid. 

Protein synthesis steps

Protein synthesis — all the work that takes place inside each protein-making factory (cell) — involves two major steps:

• Transcription: This is when instructions in your DNA get transcribed (copied) onto an mRNA molecule. It happens in the cell nucleus.
• Translation: This is when rRNA interprets the instructions and uses them to build the protein. Protein building involves assembling amino acids together into chains (polypeptides) and then twisting and folding those chains into the proper shape. Each protein has a unique shape that’s tailored to the job it’ll do in your body.

Like even the best of factories, your cells can make mistakes. Lots of things can go wrong in the process of building a protein. Sometimes, other workers (molecules) catch the mistakes and fix them. But some go unnoticed, and those errors in protein synthesis can lead to a wide range of health problems.

What common conditions and disorders are related to proteins?

Most of the conditions related to proteins fall into two big categories:

• Genetic disorders: This is when a gene change (mutation) alters your body’s “instruction manual.” As a result, your cells make some proteins that don’t look or act as they should, leading to conditions that range from mild to life-threatening.
• Protein folding disorders: These conditions happen when a protein doesn’t fold into its expected shape. Such misfolding can lead to all sorts of issues, like proteins that clump together or can’t do their jobs. Common protein folding disorders include Alzheimer’s disease, Parkinson’s disease and Type 2 diabetes, just to name a few.

There’s some overlap. For example, cystic fibrosis (CF) is a protein folding disorder that’s also genetic. But protein folding disorders commonly develop as we get older, and there’s often no clear gene mutation responsible. Scientists believe biological changes associated with aging and epigenetic factors play key roles.