Like other types of fuel we take in, proteins are metabolized as part of the digestive process. They are broken down from large molecules into amino acids in the diet. The amino acids are small enough to be absorbed by the body and, through different cellular processes, are used to put together new and different proteins, including those used for structural parts of the cells and those used for the making of enzymes, which are mostly made from protein and play an active role in new protein synthesis.
Proteins are initially broken down by stomach acid and enzymes into smaller and smaller fragments until the building blocks of proteins, amino acids are made.
From there, this process happens:
• Large protein molecules are broken down into 22 different amino acids. This is a process called “proteolysis.”
• The amino acids are broken down into alpha-keto acids in the liver where they can be transported into cells to make different things.
• Alpha-keto acids are recycled so that they can make different amino acids, proteins, and enzymes.
• Some of the alpha-keto acids are made into glucose or fat, depending on the body’s needs and on how much protein the body takes in.
• Nitrogen is removed from certain proteins, which makes ammonia, which, in turn, creates urea. The urea is excreted by the kidneys if not needed to make more proteins or enzymes.
• Other amino acids are made from alpha-keto acids by a process called “transamination.”
• Glucose is made from protein by a process called “gluconeogenesis.”
• New enzymes and proteins are made using messenger and transcription RNA in the ribosomes of the cells.
• Proteins take on a unique shape and are further metabolized to make the correct protein shape and function.
Some amino acids cannot be created through bodily processes and are called essential amino acids. You get these amino acids through your diet alone.
Amino acids can be positively charged, neutral, or negatively charged. This is how, during the metabolic process in which proteins are made, that proteins can maintain their unique shape.
Besides protein bonding, the amino acids on a chain of amino acids are attracted or repelled from one another so that the protein takes a specific shape.
Some amino acids are completely hydrophobic, so they must be in the inner milieu of a large protein or protected from the water in the cellular cytoplasm by molecules that are both water loving and water-phobic.
Proteins rely on several basic nutrients for growth. These include:
• Carbon atoms
• Hydrogen atoms
• Oxygen atoms
• Nitrogen atoms
• Sulfur atoms
Nitrogen is specifically important for protein metabolism because it makes up about 20 percent of the total mass of any given protein. Sulfur is also important in the diet to create certain proteins. When the nitrogen is lost from the amino acid (in a process known as “deamination”) the carbon skeleton of the amino acid is left. This is what can turn into glucose or fat if enough protein is available in the body.
Protein Turning Into Fat
The amount of protein that is eventually turned into glucose or fat is not very significant under normal circumstances. Intense exercises or in extremely carbohydrate limited diets, there isn’t enough glucose to use to make cellular fuel so that gluconeogenesis must occur in order to have enough cellular fuel. It also means that there is an excess of nitrogen that isn’t needed to make amino acids and there will be more urea excreted by the kidneys.
Some of the proteins made by RNA are made into enzymes. Enzymes have specific jobs to do within the cells and are called “working proteins” as opposed to structural proteins that have the job of creating cellular components.