Macronutrients are needed in large amounts by the body to supply structural materials or energy.They include:
- Water: you can only survive a few days without water. Water is needed to carry nutrients in the blood and to control body temperature. Roughly half the water you need comes from the food you eat, the rest you have to drink.
- Carbohydrates: are the main energy source for the body. Bread, rice, pasta, fruits and vegetables contain carbohydrates either as sugars or as starch. Animals store carbohydrates as glycogen.
- Proteins: contain the amino acids that are needed to build the cells in the body. Good sources of protein include meat, fish, eggs, beans, nuts, milk and cheese. Protein deficiency is extremely rare in this country.
- Fats: are used for long term energy storage, particularly in animals (plants store mainly carbohydrates). Meat, oil, butter, nuts and milk contain fat.
Saturated fats have no double bonds (only single bonds); straight molecules; solids; found in animals; eg butter.
Eating a lot of saturated fat increases your risk of heart attack.
Unsaturated fats have 1 or more double bonds; bent molecules; liquids; in plants; eg corn oil, olive oil. Unsaturated fats are more healthy for you than saturated.
Some foods, like margarine, cookies and snack foods are hydrogenated (have hydrogen added to them) to make them more solid. This produces trans fat which is as bad for you as saturated fat. Since 2006 food labels have been required to list any trans fat in the food.
Micronutrients
Micronutrients are needed in very small amounts and include vitamins and minerals. Vitamins often act as coenzymes (see below) and are found in a variety of meat, vegetables, fruit and milk (don't learn all the details in Table 3.1). High doses of certain vitamins may be harmful.
Minerals are inorganic and are essential to keep the body healthy. They include calcium, iron, potassium and sodium.
Whole foods such as wholewheat bread and brown rice are healthier for you than processed foods (white bread, white rice). Avoid eating a lot of foods that contain mainly fructose or other sugars (like candy and soda). Fruits and vegetables are particularly healthy.
Enzymes
Enzymes control chemical reactions in the cell. Enzymes are proteins. They act as catalysts ( speed up chemical reactions by lowering the activation energy ).
Enzymes are specific ( each affects a particular substrate ).
They have an active site that the substrate molecule fits. Fig 3.6.
Enzymes work very rapidly (up to 100,000 chemical reactions per minute) so are only needed in tiny quantities.
Enzymes
The speed of enzymes can be affected by :
a) environmental conditions ( temp, pH ).
Human enzymes work best at about 37o C ( body temp). Above about 40o C enzymes become denatured.
Cold temperatures slow enzymes.
Siberian surgery : by cooling down a patient's body, surgeons can do heart surgery without a heart/lung machine.
Most human enzymes work best close to pH 7 (for example trypsin in the intestines works best around pH 8). There are a few exceptions: pepsin in the stomach works best around pH 2.
Generally, however acids act as preservatives, as they slow or stop enzymes.
b) coenzymes ( vitamins )
Vitamins are needed in very small amounts. Large amounts of vitamins can actually be toxic:
Vitamin A toxicity.
Recently folate (folic acid) was added to flour and other basic foods, because it was the only vitamin that people generally were deficient in. During pregnancy, a folate deficiency increases the risk of birth defects.
The law on marketing vitamins and other nutritional supplements is very lax: companies do not have to prove the supplements are effective, or even safe.
c) inhibitors ( toxins ) : inhibitors stop an enzyme from working.
Commercially, enzyme inhibitors are important in pesticides, and some medications, such as HIV drugs and aspirin, are inhibitors.
Movement of Chemicals
Passive transport : the cell uses no energy to move chemicals.
- diffusion and osmosis.
Diffusion : the movement of molecules from high concentration to low concentration ( liquid or gas ).
Osmosis : the diffusion of water through a selectively permeable membrane.
Isotonic solution : has the same water concentration as the cell, eg blood.
Cells in isotonic solution stay the same size
Hypotonic solution : has more water than inside the cell, eg freshwater.
Cells in hypotonic solution swell (plants, animals) and may burst (animals)
Hypertonic solution : has less water than inside the cell, eg seawater.
Cells in hypertonic solution shrink (dehydrate)
Active transport : requires energy ( ATP ) There are three types of active transport: pumps, exocytosis and endocytosis.
Pumps : membrane proteins that transport chemicals.
Endocytosis : large molecules are pulled into the cell.
Exocytosis: large molecules are pushed out of the cell
example : tears, milk.
Health Problems
Body mass index uses height and weight to estimate how much body fat a person has (Table 3.4). Anyone with a BMI of 30 or more is considered obese. Calculate your own BMI. In many countries obesity is an increasing problem. Obesity contributes to several diseases including:
- Diabetes: where the body does not respond to the hormone insulin. Diabetes
- Hypertension (or high blood pressure): increases the risk of heart attack by six times.
- Heart attack: occurs when the arteries going to the heart get blocked. It is the most common cause of death for both men and women. Risk factors include obesity, high blood pressure, smoking, high cholesterol and lack of exercise. Risk