NUTRITION NUTRIENTS chemicals in food biomolecules WHAT’S IN THE FOOD YOU EAT? CARBOHYDRATE LIPIDS COMPONENTS OF FOOD PROTEINS VITAMINS MINERALS LABORATORY EXPERIMENT NUTRITION • Nutrition, for living organisms, refers to the processes of obtaining energy and matter in order to survive. • Energy and matter are found together in chemicals called nutrients which are found in foods. • Organisms are not able to grow, move, reproduce or do anything without food. • The energy and materials contained within food are needed for metabolism and continuity. THERE ARE TWO METHODS OF NUTRITION: • Autotrophic nutrition: where food is made from inorganic nutrients and, usually, sunlight energy. The formation of organic nutrients always requires an energy input – generally plant use light to make their own food by photosynthesis. • Heterotrophic nutrition, where existing foods are broken down to provide ready-made nutrients. Animals obtain their food by eating existing matter; foods that they find in their habitat. NUTRIENTS Nutrients are grouped according to whether or not they contain the element carbon (chemical symbol C); • • • • Organic nutrients contain carbon and originate from other living organisms. Examples include: proteins, fats and oils (lipids), carbohydrates, vitamins. • • • • Inorganic nutrients do not contain carbon (except for carbon dioxide). Examples include: dissolved salts (sodium chloride, calcium phosphate), trace elements (iron, copper, zinc), carbon dioxide (CO2), water (H2O). THE CHEMICALS PRESENT IN FOOD • Bio-molecules are the basic chemical structure found within most organic chemicals. They are found in food and in the bodies of living organisms. • Foods contain many different chemical elements: some in large amounts, but many in tiny amounts, i.e. traces. • Originally all these elements are gathered by plants and then passed along the food chains for all other organisms. • The six common bio-elements in food are: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur. • Food also contains: sodium, magnesium, chlorine, potassium and calcium – all are present as salts dissolved in water. • There are also traces, tiny amounts of iron, copper, zinc and other elements. • All bio-molecules are constructed around carbon atoms which form the “skeleton” of every organic chemical. • The carbon atoms can join to form chains, rings or branched structures. • Carbon is able to form up to four chemical bonds at one time. • The joining is called condensation, and breaking the units apart is termed hydrolysis. COMPONENTS OF FOOD • • • • • Carbohydrates Lipids Proteins Vitamins Minerals CARBOHYDRATES • Carbohydrates include: glucose, sucrose, lactose, ribose, starch, glycogen, cellulose and chitin. • All carbohydrates contain the elements carbon, hydrogen and oxygen. Hydrogen and oxygen are always in a ratio of 2:1. • The general formula can be written: Cx( H2O)y, The chemical formula of glucose is:C6( H2O)6 and of sucrose is C12( H2O)11 Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides: • Monosaccharides contain single sugar molecules with some carbon atoms: (glucose, fructose, ribose). • Disaccharides, are made from pairs of single sugar bio-molecules that are joined: (sucrose, lactose, maltose). • Polysaccharides are made from long chains of many sugar bio-molecules joined together: (glycogen, cellulose, starch). Where do you find carbohydrates? Why do you need them? Foods rich in carbohydrates are: grapes, honey (glucose); sweet fruit (fructose); cakes, biscuits (sucrose); milk (lactose); potatoes, flour, pasta, rice (starch); meat, liver (glycogen); cereals, vegetables (cellulose). Carbohydrates function as: • Fuel: they have a high energy content and release their energy quickly during respiration. They are primary sources of energy for cell metabolism. • Support: they can form the cell walls in plants, or be the supporting framework of a DNA molecule. LIPIDS • Lipids include: fats, oils, waxes, phospholipids. • They contain carbon, hydrogen and oxygen atoms but with a different ratio of hydrogen : oxygen atoms. • Most lipids are constructed from glycerol molecules and fatty acid molecules joined together. • The smallest fat is called a triglyceride. • Fatty acids are a major component of lipids. They contain long chains of carbon atoms and are described as either saturated or unsaturated. • Saturated fatty acids are found in animal fats, and they are solid at room temperature (butter, lard). • Unsaturated fatty acids are found in plant fats and they are liquid at room temperature (oils). • All fats are insoluble in water, but they do dissolve in organic solvents such as alcohol, ether, or chloroform. Why do you need them? Where can you find lipids? • Foods rich in animal fats: butter (margarine), milk, cheese, egg yolk… • Food rich in plant oils: sunflower oil, maize oil, nuts, olives … • • • • The functions consist of: Fuel: they have twice the energy of carbohydrates, they are primary sources of energy. Protection: fats protect human and animals from falls and bruising Insulation: fat stored adipose tissue is a heat insulator Structural: phospholipids are used to form all cell membranes. PROTEINS • Examples of proteins are: collagen in skin, ligaments and bone; keratin in hair and nails; myosin in muscle; albumin in egg white, all enzymes and antibodies. • Proteins are constructed from amino acids of which there are about 20 different kinds occurring in nature. The amino acids are joined in chains to form proteins. • Proteins have a complicated overall structure, with chains linked, folded or branched. This means that there are unlimited variations. • This huge variation is necessary because an organisms requires thousands of different enzymes (which are proteins) in order to maintain itself. • The correct structure in enzymes is extremely important. For example, the enormous amount of information contained in a DNA molecule is concerned with the instructions for joining amino acids in the correct order to produce enzymes. Where do you find proteins? • Plants can synthesise their own amino acids from simple chemicals; animals assemble the proteins and enzymes they need from the amino acids in their diet. • There are nine essential amino acids, that are not easily made by animals and must be included in their diet. They are found in first class proteins which come from animal sources (meat, fish, eggs)… • There are also non-essential amino acids: they can be synthesised from any protein including plant proteins. These are second class proteins. • No single plant protein contains all of the essential amino acids, but a mixture of plant proteins does. Why do you need them? Proteins function as: • Metabolic regulators: almost all enzymes are proteins, every chemical process in biology is directed and regulated by a specific enzyme. • Fuel: they are secondary sources of energy for cell metabolism. They give up their energy only in case of extreme starvation. • Structural: they give strength and support, for example collagen in skin, hair, nails, tendons. • Movement: actin and myosin produce movement in muscles. • Communication: many hormones are formed from proteins. • Growth and repair: amino acids are needed for growth and to maintain almost all tissues. VITAMINS • Vitamins are needed only in tiny amounts, but they are essential for all living organisms. • They are synthesised by all plants and are required in the diet of all animals. • They are named with letters and numbers. • Vitamins A, D, E and K are fat-soluble, while the B group vitamins and vitamin C are watersoluble. Vitamin C Vitamin D • is found in citrus fruits and green vegetables. • is found in fish, liver oil, milk, eggs and diary products. • is needed for the formation of connective tissue. • is needed for absorbing calcium and phosphorus from food, for hardening bones, and for aiding blood clotting. MINERALS • are found in: soil, water and in almost all foods material. • are inorganic nutrients obtained from mineral salts. • are common metalcontaining compounds often dissolved in water. • tend to have two-part names such as calcium phosphate. their functions are: • to form parts of rigid structures (e.g. calcium in bones, and teeth) • to form soft tissues • to function in cellular and body fluids LABORATORY EXPERIMENT: QUALITATIVE TESTS FOR COMMON NUTRIENTS • Various food samples can be tested in the science laboratory in order to test for substances (chemicals) in food, such as: starch, fats, reducing sugars or proteins. • You will do a test to identify whether there is glucose or fructose in fruit. • Objective: test for reducing sugar. • Materials: samples of fruit, reducing sugar solution, Benedict’s solution or Fehling’s solution I and II, water, (DCPIP solution dichlorophenolindophenol -for the optional test). • Resources: test tubes, heat source, microscope, slide holders, dropping pipettes. • Introduction: prepare a chart to show the results and carry out a control experiment with water rather than food to check and compare the results. Procedure: • Place about 2 cm of food sample in a test tube and add an equal amount of Benedict’s reagent or Fehling’s solution I and II. • Warm the test tube gently – do not boil. • A brown or brick-red precipitate indicates reducing sugar. • A green colour indicates relatively little sugar. • As a control experiment repeat with water and compare. Results and conclusion: • Look for changes in colour and check the results. • A brick red colour is positive for glucose or other reducing sugars. • Make notes of your results on a chart. AN OPTIONAL TEST • • • • You can also test for the presence of vitamin C in your food sample: Add 2 cm. of DCPIP solution to a test tube. Drip the food solution into the tube and observe. Watch for a change from blue to pink and then to colourless. Repeat with water and compare as a control experiment.