PROTEINS ARE NUTRIENTS Food can be tasty but enjoying its flavors is not the main reason that people eat People eat because they need nutrients Nutrients are what a body requires to move grow and stay alive All living things need nutrients to function Plants make some nutrients and take in others from the air and soil Animals such as humans get nutrients from the foods they eat Proteins carbohydrates fats minerals Protein is one of several nutrients that the human body needs 4
Protein keeps your body strong About one-sixth of the body’s total weight is protein Compare and Contrast How is protein like the other kinds of nutrients How is it different vitamins and water are all nutrients Proteins are needed for body tissue to grow and repair itself After water and possibly fat protein is the most abundant material in the human body Carbohydrates supply most of the energy the body needs Fats store extra energy for the body Minerals and vitamins keep the body healthy Water has many uses in the body It makes up most of the body’s weight 5
AMINO ACIDS SALIVARY GLAND TONGUE TEETH SALIVARY GLANDS The human body has many types of proteins which it uses in several ways Proteins are involved in the processes of growth movement reproduction repair digestion and aging Proteins are made up of groups of molecules called amino acids A molecule is the smallest unit of a substance that has all the properties of that substance For instance a water molecule ESOPHAGUS STOMACH LIVER GALLBLADDER PANCREAS LARGE INTESTINE SMALL INTESTINE APPENDIX RECTUM The digestive system is made up of the parts of the body that break down food into forms that the body can use 6
This scientist is holding a model of a molecule of the amino acid alanine is the smallest unit that is still water Molecules are made of even smaller bits called atoms Amino acid molecules consist of atoms of carbon hydrogen oxygen nitrogen and sometimes sulfur More than 100 kinds of amino acids are found in nature However only twenty kinds are the building blocks of all proteins in living things Amino acids combine in various patterns to make different proteins Much of the protein-making protein-making in the body happens in the liver Compare and Contrast How are molecules similar to atoms How are they different 7
