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Proteins are a very important nutrient needed for a healthy diet, they make up twenty percent of the body mass. They are known as the building blocks of muscle, bones, skin, cartilage and blood. They are not used for energy by the body unless there is not enough fats and carbohydrates in the body. We will be looking how the protein in the body is dissembled and then reassembled to form proteins. The protein goes through many processes, this process first starts from the mouth all the way through to the Intestine or the Anus. Protein can be found in milk products, poultry and eggs and these are all very good sources of protein.
Each of the cells in the body contains protein, the protein is repeatedly broken down and reassembled to meet the bodies maintenance and growth needs. It is therefore important to consume enough levels of protein daily to ensure there is enough raw materials to nourish these proteins. When digesting protein, the body breaks it down in to amino acids, and this is used to support or maintain muscle, hormone Synthesis, immune function, tissue repair and formation of red blood cells. Proteins are large compounds formed of Hydrogen, Oxygen, Nitrogen and Sulfur atoms. They are made from small units of amino acids, which are attached tightly together to form three dimensional structured long chains, these unique chains are called a polypeptide.

This diagram shows how proteins are formed of compounds formed of Hydrogen, Carbon, Oxygen, Sulfur and nitrogen.
The digestion of Protein starts in the stomach. The digestion enzyme called pepsin is found here, and pepsin will help the protein to break down. The pepsin will try to break down the bonds that hold protein molecules known as peptide bonds. When the bonds are broken down, there will be long chains of amino acids connected together known as polypeptides. Then these polypeptides will move down in to the small intestine. Here there will be pancreatic enzymes known as Trypsin, carboxypeptidase and Chymotrypsin. These will carry on helping further break down the polypeptide. These enzymes will go down through to the duodenum, the brush border enzymes which help the pancreatic enzymes, they are found on the microvilli of the small intestine that will help to complete the digestion. The peptide bonds that hold the polypeptides together continue to break down and become smaller units known as peptides. These peptides are defined as two or more amino acids attached together. The enzymes will continue to break the polypeptides and peptides in to amino acids, amino acids are small therefore they are absorbed very easily through the small intestine in to the bloodstream. The end results of the protein digestion consist of free amino acids. If the protein food is chewed properly most of the ingested protein will be broken down in to amino acids and absorbed by the body and the rest will be expelled with the faeces.

An anatomy of the digestive system, showing the different organs
The amino acids and the peptides are transported through cells of the gut Epithelium. This is done through transporter proteins found in the luminal plasma membrane. The amino acids will be transported by a mechanism that use the gradient for sodium ions for the source of energy to carry out this process, and this is known as secondary active transport. This sodium gradient is carried out by sodium/potassium pumps found in the basal membrane. The peptides are transported via facilitated diffusion, where it uses hydrogen ions gradient as the source of energy. When it is in the cell the peptides are converted to amino acids. The concentration is high in the absorptive cells than the blood and therefore the amino acid transporter proteins found on the basal membrane then transfer the amino acids in to the blood stream.
Amino acid contains a hydrogen group, Amine group and a variable R group. This R group differs between twenty types of amino acids, which are all chemically different. Amino acids can be categorised as non-essential, which can be synthesised from components in the body. The second is Essential amino acids which are unable to be synthesised, therefore it needs to be obtained from food.
Small proteins can consist of short chains of amino acids. But larger proteins are made of more than one polypeptide chain attached together. Each of the different amino acid’s sequences can develop a different protein, which has a different function in the body
There are different types of proteins depending on their function. The enzyme lipase performs as catalysts to increase chemical reactions in the body. The protein keratin which is found in the nails and hair gives a structure and support. Contractile proteins called And Myosin help to contract and relax muscle fibres to give movement. Immunologist proteins called antibodies are to protect the body against infections from foreign substances. And regulatory proteins known as the hormone Insulin which are the chemical messengers which help to regulate the homeostasis of the body.
We can see that proteins are an important macronutrient that is vital for the body and it is used by the body for many different purposes. Proteins can be mostly found in animal products but is also found in foods such as beans, eggs, peas, soy products, and seeds. We have seen that protein is composed of amino acids, and they are made of Carbon, Hydrogen, oxygen, Nitrogen and Sulfur.

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