Protein

- Many substances attach themselves to protein to help transport in the body e.g. Haemoglobin carries oxygen. - Transport proteins also carry substances across cell membranes e.g. During absorption in the digestive tract. - Transferrin transports iron and lipoproteins transport fat and cholesterol.

How is transport a function of protein?

Nitrogen balance is the difference between nitrogen input and nitrogen output. It is the overall indicator of protein metabolism in the body.

Define the term nitrogen balance?

- Almost all enzymes are proteins. - Proteins are instrumental in facilitating most of the chemical reactions in the body, including digestion of nutrients and regulation of energy production in cells.

How is the formation of enzymes a function of protein?

The value of food may be judged by its protein content and the number and amounts of indispensable amino acids present in the food. Biological value of protein is used as a measure of protein quality. It is therefore the percentage of absorbed protein which is converted into body protein and can be used for growth, repair and maintenance.

Explain the term biological value.

Mostly from animal sources. Referred to as complete proteins as they contain all the indispensable amino acids in the correct proportion required by the human body. Sources include soya beans, egg, meat and milk.

Explain the term high biological value.

Mostly from plant sources. Low biological proteins are deficient in one or more of the indispensable amino acids and are therefore referred to as incomplete proteins. The amino acid that is in shortest supply is known as the limiting amino acid. Sources include gelatine, peas, nuts and wheat.

Explain the term low biological value.

- Each cell contains protein in the cell membrane and cytoplasm. - Muscles, bones, connective tissue and organs all contain protein. - Protein is synthesised during growth, repaired, maintained and replaced during life. - Protein in the body is in a constant state of flux, changing, repairing, renewing, etc.

How is structure a function of protein?

- 1 gram provides 17KJ (4 kcal). - Secondary source of energy as it's primary function is the growth and repair of body cells. - Protein is used as an energy source if there is not an adequate supply of carbohydrate or fat available.

How is being an energy source a function of protein?

- Several proteins found in blood plasma play a key role in blood clotting. - E.g. Fibrinogen is a protein found in blood plasma. If the body fails to synthesise fibrinogen then prolonged bleeding could occur, which could be fatal.

How is blood clotting a function of protein?

- Form major components of hair and nails as well as structural framework of bones.

How is hair, nails and bones a function of protein?

- The body must be kept in a constant state. - Hormones - consist of amino acids. Act as messengers carried in the circulation and control the internal environment. - Immunity - antibodies are composed of amino acids. - Acid-Base Balance - proteins act as a buffer. They maintain a constant pH in the blood and bodily fluids. - Fluid Balance - proteins in plasma exert an osmotic effect that holds fluid within the circulation.

How is homeostasis a function of protein?

- Red meat - White meat - Seafood - Dairy foods - Eggs

What are examples of animal sources of protein?

- Soya beans and soya bean products - Quorn - Tofu - TVP (textured vegetable protein)

What are examples of novel sources of protein?

- Pulses - Nuts and seeds - Wholegrains

What are examples of plant sources of protein?

- Structure - Formations of enzymes - Hoemeostasis - Transport - Blood clotting - Energy source - Hair, nails and bones

What are the functions of protein?

Nitrogen output is greater than nitrogen input. A negative nitrogen balance can be a sign of inadequate protein consumption and malnutrition. A negative balance can occur because there isn't enough protein being consumed to meet the body's needs or because of catabolism (using protein as a secondary energy source).

What does negative nitrogen balance mean?

The amount of nitrogen taken in is equal to the amount of nitrogen being excreted. This is generally a normal for healthy adults eating a balanced diet.

What does nitrogen equilibrium mean?

Nitrogen input is greater than nitrogen output. More protein is being consumed than the body needs. A positive balance indicates that protein is being retained in the and is being used for protein synthesis.

What does positive energy balance mean?

If a food is of low biological value it lacks one or more of the indispensable amino acids. The amino acid in shortest supply is known as the limiting amino acid. Low biological foods can be combined in the same meal so that the limiting amino acids in each food are compensated for by the other low biological foods. This is known as the complementary action of proteins. This is particularly important in countries where protein intakes are low and for vegans or vegetarians who avoid high biological value proteins.

What is protein complementation?

Dispensable amino acids do not have to be provided by the diet. This is because the amino group of these amino acids can be transferred to another amino acid with a different amino group by a process called transamination. Due to this the body is able to make some amino acids itself (dispensable amino acids). Indispensable amino acids have to be provided by the diet as they cannot be made by the body.

What is the difference between dispensable and indispensable amino acids?