Unit 2A Human Form & Function Cells, metabolism & regulation Nutrition

Further information Further information about this topic can be found in Our Human Species (3 rd edtn) Chapter 2, section 2 Chapter 15, section 1

Nutrients Nutrients are the chemical compounds that make up foods and which are essential for life. Nutrients include: Carbohydrates Lipids Proteins Vitamins Minerals

Carbohydrates

Typical examples are sugars & starches. They all contain the elements C, H, O roughly in the proportion of 1C:2H:1O. The building blocks are simple (monosaccharide) sugars (e.g. glucose).

Main uses Carbohydrates are used mainly as an energy source for cellular respiration. Some combine with other substances – e.g. glycoproteins in the cell membrane. Can be stored in the liver and in muscle cells as glycogen.

Sugars Sugars are relatively small carbohydrate molecules – either a single sugar molecule (monosaccharides or simple sugars) or double sugar molecules (disaccharides or double sugars). Sugars are water soluble and most are sweet.

Sugars Examples of monosaccharide sugars - glucose (dextrose), fructose, galactose and ribose. Examples of disaccharide sugars - sucrose, maltose and lactose.

Polysaccharides Starch is a good example of a polysaccharide (glycogen is a polysaccharide that occurs in animals). Polysaccharides are long chains (or polymers) of simple sugars. Polysaccharides are not sweet and do not dissolve in water. Starch represents a large part of our carbohydrate intake.

Carbohydrate –rich foods Foods rich in starch – Cereal-based foods (e.g. bread, pastry, pasta, noodles, rice) Some vegetables (e.g. potatoes, beans & corn), nuts. Foods rich in sugars – cakes, biscuits, lollies, many processed foods, fruit (dried fruit, stone fruit, bananas, citrus), sweetened drinks (fruit juice, flavoured milk, carbonated drinks).

Lipids

Typical examples are fats & oils. They all contain the elements C, H, O - a smaller proportion of O than in carbohydrates. The building blocks are fatty acids & glycerol. Some fatty acids (e.g. omega-3 & omega- 6) are essential fatty acids.

Triglycerides Most lipids are triglycerides – i.e. one glycerol molecule attached to three fatty acid molecules. The way in which the C & H atoms in the fatty acids are bonded determines whether a fat is ‘saturated’ or ‘unsaturated’. GlycerolFatty acids

Lipid classification Low density lipids (LDL) carry cholesterol from the liver to the tissues. LDL can start the formation of plaque and increased levels are associated with cardiovascular disease. For this reason, cholesterol inside LDL is often called ‘bad’ lipids. High density lipids (HDL) collect cholesterol from the tissues, and bring it back to the liver. Sometimes referred to as the ‘good’ lipids.

Main uses An energy source – lipids contain twice as much energy as carbohydrates Energy storage Insulation Protection of organs Structural functions (e.g. cell membrane, myelin sheath Metabolic functions (e.g. cholesterol, steroids) Chemical messengers (e.g. prostaglandin, hormones)

Lipid-rich foods Dairy foods (e.g. cream, butter, cheese), pastry, fried foods, meat (fat on), poultry (skin on), oily fish, avocado, olives, nuts.

Proteins

They all contain the elements C, H, O, N – (some contain elements such as iron, sulphur and phosphorus). The building blocks are amino acids.

Main uses Structural functions (e.g. actin & myosin in muscles, collagen in connective tissues) Metabolic functions (e.g. enzymes) Oxygen transport (haemoglobin) Protection (antibodies, blood clotting) Energy source (in emergencies).

Essential amino acids Essential amino acids are the eight (possibly nine) amino acids that cannot be produced by the body and must therefore be obtained from the diet.

Complete proteins (animal proteins, such as most meats, eggs & milk) contain the full range of amino acids. Incomplete proteins (mainly plant proteins, such as grains & legumes) contain low levels of one or more of the essential amino acids.

Protein-rich foods Dairy foods (e.g. milk, cheese, yoghurt) Eggs Lean meats, fish, and poultry Soy milk Beans, tofu, lentils, and other legumes Grains, including bread and pasta Nuts and seeds

Vitamins Vitamins are organic substances essential in small quantities for normal health. Most vitamins act as coenzymes or help regulate metabolic processes. There are 13 known vitamins, most of which are present in foods - some are produced within the body.

Solubility Vitamins are often classified as water soluble or fat soluble. Vitamins B & C are water soluble. These are easily excreted from the body. Vitamins A, D, E & K are fat soluble and are absorbed from the gut with the help of lipids.

Vitamin deficiency diseases A – night blindness B1 – beriberi B3 – pellagra B6 & B12 – anaemia B9 – (folic acid) miscarriage, neural tube defect C – scurvy D - rickets

Dietary minerals Dietary minerals are the chemical elements required by living organisms, in addition to the four elements, carbon, hydrogen, nitrogen, and oxygen. Dietary minerals occur in all natural foods.

Macrominerals & trace minerals Macrominerals are those, such as Na, Mg, K, Ca, Fe, P, S & Cl, required in relatively large amounts. Trace minerals are those required in relatively small amounts.

Functions Dietary minerals have many functions e.g.: Ca is needed in bones and muscles Na & K are important electrolytes Fe is needed in haemoglobin P is an essential element in nucleic acids (DNA & RNA).

A balanced diet USDA food pyramid

Study Guide Read: Our Human Species Chapter 2, section 2 Chapter 15, section 1 Complete: Workbook Topic 2, Nutrition