Structure and function of proteins

• The end of the amino acid chain that has the unbonded amine group is called the N-Terminal.
• The other end of the amino acid chain has the unbonded carboxyl group is called the C-Terminal.
• The R/Side Chain varies between the different amino acids.
• The primary structure of a protein is the specific linear sequence of amino acid that make up a polypeptide chain. Amino acids are connected by peptide bonds.
• The secondary structure of a protein is regular, repeated patterns of folding of the protein backbone (the amino acid chain).
• Alpha helix is an example of a secondary structure. It is a single stranded structure that is formed by hydrogen bonds between the amino acids. The backbone coils around an imaginary helix axis in a clockwise direction.
• Beta sheets are another example of secondary structure. The protein backbone is nearly fully extended (more linear). The R-groups (side chains) are alternately pointed above and then below the extended backbone. Sheets are held together by hydrogen bonds.
• Tertiary protein structure is the overall folding of the entire polypeptide chain into a specific 3D shape.
• Quaternary protein structure occurs when a protein is made up of two or more polypeptides. It describes the way in which the different polypeptide subunits are arranged together to form the overall structure of the protein.
• Protein structure is directly related to the function that the protein has to undertake. Proteins are essential to all biological processes. The structure of the protein is always essential to its function.
• Transform proteins are involved in either the active or passive movement of substances across cellular membranes or between cells (e.g. haemoglobin is involved in the movement of oxygen from the lungs to cells around the body).
• Structural proteins typically the largest of the protein groups. They are typically found in body tissues that require tensile strength which is provided by the long and fibrous structural proteins. Some examples are collagen and keratin.
• Hemoglobin is fund in red blood cells  and is responsible for the transport of oxygen around the body. It consists of 4 polypeptides subunits, 2 alpha helixes and 2 beta sheets. Each subunit contains a heme group. High oxygen binding affinity results in the formation ox oxyhemoglobin in the lungs
• Enzymes speed up reactions by lowering the activation energy required for the reaction to occur. They hold substrate molecules in a way that makes the reaction more likely to occur.
• Catalase is an enzyme consisting of 4 polypeptide chains. It is found in the liver and breaks down harmful hydrogen peroxide into oxygen and water. 
• Protein hormones are typically globular in shape and water soluble. Function by binding to receptors on the outside of a cell and causing a change to occur inside the cell.
• Insulin is a hormone protein made in the pancreas. After eating, blood glucose levels rise stimulating the production of insulin. Insulin travels through the blood and stimulates muscle, fat and liver cells to take up and store the glucose as glycogen. This ensures that blood sugar levels are kept relatively constant.