Proteins

• Proteins differ from carbohydrates and lipids in that they contain nitrogen and usually sulfur in addition to carbon, hydrogen, and oxygen
• Proteins make up about two-thirds of the total dry mass of a cell
• Amino acids are the building blocks of proteins
• Polypeptide and proteins are terms that can be used interchangeably, but when a polypeptide is about 20 amino acids long, it is generally agreed to have become a protein
• Proteins are incredibly diverse in their structure and function due to having 20 different building block units for their synthesis
• The order of the amino acids in a protein determines its shape and therefore its function
• Amino acids have a carboxyl group (-COOH) at one end and an amino group (-NH2) at the other end
• There are 20 different amino acids which are universal to all living organisms
• Each type of amino acid differs in the composition of their variable side chain (denoted ‘R’)
• A dipeptide is a molecule consisting of two amino acids linked by a peptide bond
• A polypeptide is a molecule consisting of many amino acids linked by peptide bonds
• Two amino acids form a dipeptide. The carboxyl group of one amino acid reacts with the amine group of another amino acid
• A water molecule is eliminated in a condensation reaction
• A peptide bond is formed between N and C, which is a covalent bond
• Each type of protein has a unique sequence of amino acids and there are many thousands of proteins in cells
• The proteome is the entire set of proteins found in an individual organism
• The 20 amino acids used to make proteins are coded in the genetic code
• A gene is a sequence of DNA that encodes a polypeptide sequence or protein molecule
• Peptide chains can have any number of amino acids, from a few to thousands, and the amino acids can be in any order
• The function of a protein is very dependent on its structure
• Some proteins are shaped like fibers while others are folded to form globular proteins
• Proteins have a very precise three-dimensional shape resulting from intramolecular bonds between amino acids, for example hydrogen bonds
• Denaturation occurs when the ionic interactions, ionic bonds, and other weak intermolecular forces within the globular protein break, changing the shape of the protein including the active site of the enzyme
• Small changes to pH of the medium similarly alter the shape of the proteins
• Some nutrients are essential components of our diets while others are non-essential
• A nutrient is a chemical substance found in foods that is used in the human body
• A non-essential nutrient can be made in the body or has a replacement nutrient that can fulfill the same dietary purpose
• An essential nutrient cannot be synthesized by the body and therefore has to be included in the diet