Protein

Protein

Protein is the macronutrient responsible for building, maintaining and repairing your body’s cells. 

Constructed from long chains of amino acids (chemical compounds that contain carbon, hydrogen, nitrogen and oxygen).  It is nitrogen that makes protein unique and essential to life. The body cant make nitrogen any other way.

Protein as a source of energy

In times of dire need, we can use protein for energy. 

The process is inefficient, and we must break down our own tissues to do it. 

Our bodies only use protein when no other energy source is available.

Amino Acids

Proteins are large polymers built up of amino acids. 80 amino acids exist.

The human body needs all 20 different types of amino acids. 12 can be made by the body, 8 have to be obtained through a protein diet these are known as essential amino acids (indispensable amino acids).

Thousands are joined together to make one protein. They combine to make:

Muscle protein, Nails, Hormones, Enzymes, Skin protein, Cell membranes, Antibodies, Haemoglobin.

Amino Acids

Combinations of amino acids can be joined in many different ways. As amino acids join together they form peptides.

As more amino acids are react with peptides, they form long chains called polypeptides.

E.g. insulin is a polypeptide built up from 51 amino acids molecules.

Different proteins

Each protein has its own chemical name. e.g.

Collagen in meat and fishElastin in meatGelatine in meat and fishGliadin in wheat

HBV vs LBV

Amino acids that are found in animal tissue and soya bean are known has High Biological Value (HBV).

Amino acids that are found in plants are known has Low Biological Value (LBV).

By mixing HBV and LBV amino acids:1. Ensures maximum intake2. Saves money (LBV are cheaper)3. Provides variety

How much is enough?

Health professionals suggest men should eat 55.5g protein a day and women 45g.

Protein deficiency is unlikely in Western World-people in fact eat too much excess protein. The body uses this excess protein for energy and if it’s not needed it is stored as fat.

Serving Size

You should eat two to three servings of protein every day from both plant and animal sources. Here are some examples of one serving (about the size of a standard pack of playing cards):

1. 100g boneless meat (eg lean beef, lamb or pork) 2. 100g boneless poultry (eg chicken or turkey breast) 3. 100g fish (eg salmon, sardines or tuna) 4. 2 medium eggs 5. 3 tablespoons of seeds (eg sunflower or pumpkin

seeds) 6. 3 tablespoons of nuts (eg almonds or walnuts)

Sources

- Almonds.- Beef.- Chicken.- Eggs.- Salmon.- Tuna.

How much is enough?How much is enough?

Estimated Average Requirement

EAR (protein) = 0.6 X Body Mass (kg)

Eg A woman who weighs 60kg would need

0.6 x 60 = 36g of Protein a day.

KWASHIORKORKWASHIORKORIn some parts of the world people are starving. The only foods available are cereals like rice and these are poor protein sources. Children develop a disease called Kwashiorkor because they do not have enough protein in their bodies. The muscles waste and the belly fills up with fluid.

Key terms

Amino acids: smallest unit of a protein Essential amino acids: can not be

made by the body HBV: contain essential amino acids LBV: do not contain essential amino

acids

Exam style questions

Which 4 chemical compounds make up protein? (4)

What are the proteins called which have to be taken in through the diet as the body can’t produce them? (1)

Amino acids join together they form…..(1) As more amino acids are react with ……, they

form long chains called………(1) Give 1 example of the chemical name of a

protein and where it is found (2)

Exam style answers

carbon, hydrogen, nitrogen and oxygenEssential amino acidsPeptidesPolypeptidesCollagen in meat and fish, Elastin in meat,

Gelatine in meat and fish, Gliadin in wheat