How Does Your Body Make Proteins?

Proteins are essential components of cells, serving as both the workers and building materials. They are created through a universal two-step process called protein synthesis. First, DNA is transcribed into RNA, and then RNA is translated into protein. Promoters are specific DNA sequences located before genes that regulate when and how much protein is produced.

What Is A Protein?

Proteins, essential for all living organisms, play various crucial roles such as catalyzing reactions, transporting oxygen, and protecting against infections. They are vital building blocks found in wool, cartilage, and milk, and contribute to packaging DNA in chromosomes while insulating nerve cells. Simply put, proteins are incredibly important!

These molecules consist of amino acids linked together in long chains, folding into intricate three-dimensional structures, similar to origami with a lengthy, thin piece of paper. The specific shape, dictated by the arrangement of amino acids, determines the function of each protein.

Classification

Humans use only 20 out of the hundreds of amino acids found in nature. These amino acids can be classified into three groups based on whether our bodies can make them:

Non-essential amino acids: There are five amino acids (alanine, asparagine, aspartic acid, glutamic acid, serine) that our bodies can both obtain from food and produce internally.
Conditionally-essential amino acids: There are six amino acids (arginine, cysteine, glutamine, glycine, proline, tyrosine) that our bodies can normally generate, but they become essential in specific situations, such as during starvation or inborn errors of metabolism.
Essential amino acids: There are nine amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine) that cannot be produced by our bodies. We must obtain these essential amino acids from our diet to make important molecules like hormones.

Proteins Are Expressed From Genes

All living things create proteins using a similar process. It begins with a gene, which acts like an 'instruction manual' for building the protein. This whole process is known as gene expression and has two main steps: transcription and translation.

Transcription

Cell structures mark the beginning and end of a gene, scanning the DNA sequence in between (which consists of A, C, G, and T bases). This process generates a molecular message called mRNA, mirroring the gene's sequence. Essentially, mRNA resembles a single-stranded DNA fragment in most aspects.

Translation

A ribosome gets a message (mRNA) and uses it to assemble a chain of amino acids, creating a protein. The ribosome reads the mRNA in sets of three bases (codons), and each codon guides the addition of a specific amino acid in the protein-building process.

The Genetic Code Is Essentially The Same Throughout Nature

In all living things, every cell uses the same instructions for building proteins. For example, the code AGA always tells the cell to add the amino acid arginine when creating a protein, whether it's in bacteria or human cells. Simply put, all cells follow the same rules to make proteins.

Which Proteins Are Made When – The Power Of A Promoter

Inside a cell, not all proteins are made simultaneously. Essential proteins are continually produced, while others are only made when necessary. Some proteins, like those involved in ongoing processes, are needed in large quantities, while others, like hormones, are required in smaller amounts. How does a cell determine which genes to activate and how much protein to produce?

Promoters are like DNA instructions that decide when a gene is active. They're located in front of genes and act as a kind of docking station for proteins called transcription factors and RNA polymerase. Transcription factors control the gene's on-off switch, and RNA polymerase reads the DNA to create a copy called mRNA. Strong promoters make genes more active, while weak promoters result in lower gene activity.

Types Of Proteins

There are seven main types of proteins, each with specific functions:

Antibodies: Specialized proteins defending the body against foreign invaders by immobilizing them for destruction by white blood cells.
Contractile Proteins: Responsible for muscle contraction and movement, with actin and myosin playing crucial roles in cellular processes.
Enzymes: Catalysts for metabolic reactions, enabling the building, conversion, and degradation of essential chemical substances for life.
Hormonal Proteins: Messenger proteins coordinating bodily functions, such as growth factors, testosterone, and cortisol.
Structural Proteins: Maintain and protect the body's structure, with collagen being a common example found in bones, cells, and skin.
Storage Proteins: Reserve amino acids until needed, like ferritin storing iron for future use.
Transport Proteins: Carrier proteins moving molecules within the body, such as hemoglobin transporting oxygen and cytochromes in the electron transport chain.

Foods That Contain Protein

Both plant and animal foods have protein, but not all proteins are equal. High-quality proteins contain all the essential amino acids, and animal foods like meat, fish, poultry, eggs, and dairy are prime examples. These are the go-to sources for people seeking protein as they have the right amino acid balance.

On the other hand, plant foods generally have lower quality proteins because they lack some essential amino acids. While most fruits and vegetables are poor protein sources, plant foods like baked beans, split peas, lentils, peanuts, nuts, seeds, and grains contribute significantly to our protein intake. However, each type of plant protein is deficient in one or more essential amino acids.

For those not consuming animal products, it's essential to combine different types of plant foods within the same day to ensure a proper balance of essential amino acids. Combining foods like beans and rice, beans and corn, or peanut butter and bread provides a complete set of amino acids, compensating for the deficiencies in individual plant proteins.

Other Uses For Protein

Three main nutrients – protein, carbohydrate, and fat – are sources of calories. Protein and carbohydrate provide 4 calories per gram. Protein is crucial for repairing and maintaining body tissues. When people consume more protein than needed for tissue maintenance, the excess is used for energy or stored as fat. If calorie intake is insufficient, protein is used for energy instead of its primary role in maintaining the body. Ensuring adequate protein and a balanced diet with enough calories is essential. This way, protein can fulfill its intended functions in tissues, while fat and carbohydrate meet energy requirements.

Protein Requirements

Everyone needs protein for various reasons such as growth, and the amount depends on factors like body size. Children require more protein per pound than adults due to growth, while pregnant and nursing women need extra for baby development and milk production. The Dietary Reference Intake (DRI) guides us on daily protein requirements. Use the formula: 0.8 grams of protein per kilogram of body weight. To convert weight to kilograms, divide pounds by 2.2.

Example:

Person's weight = 165 pounds

165 pounds/2.2 pounds per kilogram

75 kilograms x 0.8 grams per kilogram

This person has a protein requirement of 60 grams per day.

Related Medical Conditions

Protein imbalances can cause serious health issues, including nervous system problems, metabolic disorders, organ failure, and even death. For instance, severe protein deficiency is seen in conditions like kwashiorkor and anorexia nervosa.

Malfunctioning proteins can result in various medical conditions and, in some cases, lead to death. Examples include childhood obesity, retinal breakdown causing blindness, hearing loss, and type 2 diabetes.

One specific case is the dysfunction of the protein cilia and its impact. Inadequate cilia in flagella can lead to sperm dysmotility. Defective cilia in the respiratory tract can cause chronic lung infections. Dysfunctional cilia in the fallopian tubes can result in infertility.