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Wednesday, December 7, 2011

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.


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