Chapter 2 - Protein (Notes)

2.1 Functions Of Protein

·      To build, repair and maintain of the body tissue

·      As acid-base balance

·      Structural component of the body e.g. DNA, hair, skin

·      Make enzymes and hormones

·      Act as antibodies to fight infection

·      Transport iron, fats, mineral and oxygen

·      Provide energy as last resort

·      Helps blood clots (fibrinogen)

2.2 Protein Structure

·      Known as amino acid, link by peptide bond. 2 amino acids known as dipeptide and more than 3 amino acids known as polypeptide.

R

COOH          C         NH3

H

*R – sidechain, COOH – acidic, H – backbone, NH3 – nitrogen-containing compound. This structure known as an amphoteric.

2.3 22 Known Amino Acids

      i.         9 essential/ indispensible amino acids e.g. histidine, lycine, leucine, valine

o   known as high quality protein

o   need to obtained from food, cannot be produced by human body

o   cannot be synthesized in sufficient quantity by human body

o   can be divided into 2:

a.     Complete protein – contain all 9 essential amino acids e.g. from animal and soya.

b.     Incomplete protein – contain less than 9 essential amino acids e.g. from plants food. Need to combine few protein foods or mutual supplementation.

     ii.         13 non-essential amino acids e.g. serine, glycine, cysteine, proline.

o        Known as low quality protein

o        Can be produced by human body

2.4 Four Structures of Protein

·      Primary protein – number and sequence

·      Secondary protein – bending and coiling, involves attraction and repulsion forces e.g. hair

·      Tertiary protein – loop and fold, compact structural/ globule e.g. hemoglobin

·      Quaternary protein – combination of few tertiary protein structures

Denaturation – protein loses its shape and ability to function. It caused by high temperature, high salt concentration, acid/ base, UV radiation or mechanical action.

Coagulation – process after denaturation in which reforming the structure e.g. fried eggs. It is irreversible.

2.5 Protein and Health

·      Eating too much protein – excessive kcal, excessive fat if eating too much high-fat animal foods, Ca loss.

·      High intake of animal protein associates with colon cancer.

·      Eating too little protein – slowing down rebuilding and repairing process, weaken the immune system. It may lead to protein energy malnutrition (PEM).

·      PEM is a disorder caused by inadequate intakes of protein and energy. There are 2 diseases associates with PEM:

o   Kwashiokor – resulting from extreme low protein intake. The symptoms include weight loss and muscle wasting, peeling skin, retarded growth and development, protruding abdomen due to edema.

o   Marasmus – resulting from severe inadequate intake of protein, energy and other substances. The symptoms include stunted physical growth and brain development, anemia, severe wasting of muscle tissue.

·      Proper protein intake depends on activity level, age and health status.

·      Dietary References for protein is 0.8g/ kg of body weight.

o   NH3 balance – same NH3 intake as lose in which means 0 NH3 balance.

o   Positive NH3 balance – condition in which the body excretes less protein than taken in. It occurs during pregnancy and growth.

o   Negative NH3 balance - condition in which the body excretes more protein than taken in. It occurs during starvation and illness.