4.foodnutritionbasics_module2.pdf

Food and Nutrition Basics Module 2 / Protein, Carbohydrate and Fat  Module 2 / Protein Section 1 Protein - Section 1 Objectives Upon completion of...

Food and Nutrition Basics Module 2 / Protein, Carbohydrate and Fat  Module 2 / Protein Section 1 Protein - Section 1 Objectives Upon completion of this section you should Name the basic units of protein be able to: State the major functions of protein Name the amino acids essential for adults State the main dietary sources of protein Explain the difference between complete and incomplete proteins Recognise the concept of amino acid complementarity 2/3 Additional Information Notes: Amino acids and polypeptides R H O N C C H OH H amino group carboxyl group – The above is the general formula of an amino acid in which R represents the rest of the molecule. Amino acids join together to form a chain when the amino group of one amino acid reacts with the car- boxyl group of another. The resulting linkage is called a peptide bond. R R H O H O N C C N C C H OH H OH H H Amino Acid Amino Acid R O H R H O N C C N C C +H2 O H OH H H Peptide Bond Two amino acids joined together form a dipeptide; three amino acids form a tripeptide etc., and many amino acids joined together form a polypeptide. When more than 50 amino acids are joined together, this is generally considered to be a protein. The hormone insulin, which contains 51 amino acids is, therefore, considered to be a small protein and not a polypeptide. Different polypeptide chains can also be linked to each other by chemical bonds other than a peptide bond (e.g., hydrogen and sulphur linkages). This enables the formation of different three dimensional structures such as coils, sheets and globules. It is the specific shape of a protein which gives it its unique biological function.  Module 2 / Protein, Section 1 The Importance of Protein Amino Acids On average the human body is composed of All protein, whether in the body or in the 60% water and 40% dry matter – protein, fat, food we eat, is made up of individual units carbohydrate and minerals (including trace known as amino acids which are joined elements). When looking at the dry matter in together like links in a chain. more detail, protein and fat are the major com- ponents, each comprising about 40% of the The chemical linkage by which amino acids total. This is followed by minerals, which con- join together is called a peptide bond. As pro- stitute about 15% of the total, and last but not teins are made up of many different amino least, carbohydrates which account for less acids linked together they are, chemically than 5%. speaking, polypeptides. Linking up amino acids to form proteins is Body composition of a non-obese man similar to letters of the alphabet making (proximate % of dry matter) words. The difference is that words are very much smaller – on average 4-5 letters – Protein 40% Minerals 15% whereas the average length of a protein is 1000 Fat 40% Carbohydrate