Elementary Biochemistry

Transcription

1 Elementary Biochemistry To grow, respire and allow cells to function properly, we need a number of substances in our diet. These can be divided into organic (contain carbon) and inorganic (no carbon) substances. Organic Inorganic Carbohydrates (fibres/roughage) Vitamins Lipids Minerals Proteins Water Nucleic acids Carbohydrates general formula is CH 2 0 Glucose C 6 H 12 O 6 - Provides energy for the body when they are respired. - 17KJ/g - This energy is often supplied quickly and easily as they are easy to break down. - Contain: Carbon, Hydrogen and Oxygen Proteins - made of amino acids - used for growth, repair and replacement of cells and tissues - also make enzymes and some hormones - can be used to provide energy when carbohydrate and lipids are unavailable. However, this causes muscle wastage person is probably starving - composed of Carbon, Hydrogen, Oxygen and Nitrogen or Sulphur or Phosphate - building blocks of proteins are called amino acids. - There are 20 common amino acids, which can be joined in many different ways and make different length chains. - These chains can be joined together in different ways. - Consequently, there are thousands of different ways. - This gives a huge variety of structural diversity in the body. AA AA dipeptide AA AA AA AA AA AA Polypeptide join to make proteins Foods rich in protein are: Meat, fish, milk, cheese and eggs - animal sources - most rich Peanuts, Soya beans - plant sources

2 Lipids - made of Glycerol - composed of fats and oils - plant sources are usually liquid at room temperature(e.g. olive oil, sunflower oil) - animal sources are usually solid at room temperature(e.g. lard, butter) - All lipids are composed of 2 substrates (building blocks) - Provide 39KJ/g of energy - Provide insulation by fat under skin - Provides waterproofing by oil on skin/feathers. Fatty acids Glycerol Triglyceride Water Most cells contain about 75% of water and will die if their water content falls much below this. Water is a good solvent and many substances move around the cell in a watery solutions. Water molecules take part in many vital chemical reactions (e.g. photosynthesis). In plants, it is the water pressure in the vacuoles, which keep the cells turgid. The physical and chemical properties of water differ from other liquids but make it uniquely effective in supporting living activities. For example, water has a high capacity for heat which means that it can absorb a lot of heat without its temperature rising to high levels. However, because water freezes at 0 o C, most cells are damaged if their temperature falls below this and ice forms in the protoplasm. Oddly, quick-freezing of cells in liquid nitrogen (-196 o C) does not harm them.

3 Nucleic Acids These are the building blocks of DNA in the nucleus and of another compound called RNA. There are four types. All are similar but one component alters the base. P S B B Base P Phosphate S Carbon sugar (pentose) There are 4 possible bases: Ademine Thymine Cytosine Guonine (A) (T) (C) (G) Minerals/Salts Iron Calcium Iodine Phosphorous Where they are found Eggs, Red meat, Vegetables, Red blood cells (haemoglobin) Blood plasma, Milk, Cheese, Hard water, Bread Sea fish, Vegetables, Salt Cheese, Meat, Fish, Milk What they are used for Needed in muscles, Carry oxygen round the body in haemoglobin. Make muscles contract. Transmit nerve impulses. Healthy blood, and teeth. Help blood clot. Essential part of thyroxine which speed up respiration in cells. Calcium phosphate for bones and teeth. ATP and DNA production. Important in membranes Deficiency disease Anaemia Bones and teeth will be brittle. Nerves will be slow. Neck swelling Lower respiration speed Brittle bones and teeth. Cells begin to breakdown. Reduction in growth.

4 Vitamins Vitamins are only needed in small quantities, but are essential. Vitamin Found in Used for Deficiency disease Keeps cells lining Infections of the breathing system butter breathing system, healthy. cheese carrots Night blindness, A (retinol) Needed to make red egg yolk cells in the eye. cod liver oil Long term liver deficiency can lead Allows vision in dim to total blindness. light. Scurvy Ascorbic Acid Healthy immune Citrus foods:- system Ascorbic Acid Bleeding gums and oranges Vitamin C joints vegetables Keeps cells and potatoes tissues healthy Can be fatal wholemeal bread Involved in many Beri Beri Vitamin B liver chemical reactions in e.g. riboflavin, brown rice the body Muscular weakness niacin yeast extract e.g. respiration and paralysis butter egg yolk Helps calcium and Vitamin D Rickets: bones do phosphate to make Calciferol not develop properly made by body in healthy bones sunlight

5 Food Tests Benedicts test for reducing sugars (e.g. glucose) Set up a water bath by half-filling the 250cm 3 beaker with tap water. Bring the water to the boil and turn down the Bunsen flame to maintain a steady boil. Take a test tube and add about 2 cm 3 of the food solution. Add about 1 cm 3 of Benedicts solution. Heat the test tube in the water bath for 2-3 minutes. The appearance of an orange coloured precipitate indicates that a reducing sugar is present. The presence of glucose may be also tested by use of the Clinistix. Iodine test for starch At room temperature add several drops of iodine solution (I 2 in KI) to a sample of the food solution to be tested. A blue/black colour indicates the presence of starch. Biuret test for proteins At room temperature, put about 2 cm 3 of the food solution into a test tube. Add an equal volume of Biuret 1 (10% Sodium Hydroxide - with care!) then add Biuret 2 solution drop by drop, mixing the solutions by gently shaking the tube. A purple colour confirms the presence of protein. The presence of proteins may be detected by use of the Albustix. Emulsion test for fats Mix equal quantities of the solution to be tested and absolute ethanol in a test tube and shake together vigorously. Add an equal volume of cold water. A cloudy white suspension indicates the presence of fats. Place one drop of the solution to be tested onto greaseproof and/or brown paper. The presence of fat is indicated by the paper appearing more transparent.

6 A Balanced Diet A balanced diet contains the following components in the right proportions: 1. Carbohydrates 2. Proteins 3. Lipids 4. Vitamins 5. Minerals 6. Water 7. Roughage or Fibre The relative proportions of the components in a balanced diet varies with age, gender and amount of activity. Description Energy Requirements (KJ) Notes 0-1 years 3,200 Childhood 7,500 Adolescence Boys: 12,000 Girls: 9,600 Adult Female 9,000 Pregnancy 10,000 Lactation 11,500 Adult male: Deskbound office worker Adult male: Building site worker 10,000 14,000 Extra calcium needed for growth of bone Extra calcium, iron and protein needed for growth Extra calcium, iron and protein needed for growth and development of foetus Extra calcium, iron and protein needed for growth and development of baby Extra protein needed for muscle development

7 Food additives Food additives have been used in increasing numbers and volumes over the last few decades and in the UK their use is now regulated by the European Community. Additives are used for four main reasons: a) to enhance the flavour of food b) to colour food c) as a preservative d) to improve the texture of food In the EEC, food additives are given a designated E number, which enables lists of additives to be given on food packets without the need to write out all the names of ingredients in full. Food additives can be of benefit to the consumer longer shelf life for food and the availability of convenience foods but some additives have an undesirable side effects on some individuals. Additive Advantages Disadvantages Sugar Salt Sweetens food Preservative Good energy source Improves flavour Preservative Can lead to obesity (and therefore high blood pressure) Can lead to tooth decay Too much can lead to high blood pressure E102 Tartrazine (yellow dye) E621 Monosodium glutamate E250 Sodium nitrite E122 Carmosine Gives colour to orange squash, and crisps etc. Provides meaty flavour in crisps, stock cubes meat pies etc. Helps preserve bacon, ham, corned beef etc. Colours food red (e.g. jelly, sweets and packed soups) Hyperactivity in children Can make asthma worse Can cause Chinese Restaurant Syndrome headaches, dizziness, vomiting, muscle tightening and heart palpitations May cause cancer (from nitrosamine in gut). Also causes dizziness and vomiting in some cases Can cause skin rashes and produce adverse reactions with asthmatics.

8 Starvation and Malnutrition General lack of food or not enough food leads to starvation. Body uses up all stored reserves: 1. Glycogen stores glucose respired energy 2. Fat reserves respired 3. Protein respired muscle wastage death Protein energy malnutrition Kwashiorkor Diet contains plenty or enough carbohydrates but not enough proteins. Seen in children and causes bloated abdomen. Also means that cells are not repaired or replaced. Growth is limited. Immune system fails. Western Diets Too much sugar - causes tooth decay - obesity Too much fat - blockage of arteries - coronary heart attack - the more cholesterol, the more chance of getting heart attack. - saturated fatty acids cause fatty deposits in artery Too little fibre - constipation - disorders and diseases of the intestine possibly cancer. - fibre stops you eating may lead to obesity Too much of everything - surplus fat obesity - high blood pressure - diabetes - coronary heart disease