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Protein
Structure
- large, complex molecules made up of amino acids
Found as essential components of all living cells
Made of carbon, oxygen, hydrogen and nitrogen
Structure is determined by DNA
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Amino acids
Proteins are made of amino acids (AA) bonded together in specific sequences (each can be hundreds of AAs long)
But there is only 20 different amino acids that are used in different combinations to make the hundreds of thousands of different proteins we use
9 of the 20 are ESSENTIAL amino acids (our body can not produce them, therefore we MUST get them from your diet)
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3. THE 20 AMINO ACIDS
9 essential amino acids: histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine.

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Amino Acid Structure
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2 Aas = dipeptide
Peptide bond
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After peptides are made they fold up because the AAs are attracted to each other and form weak intermolecular bonds
Sequence of AAs determines the 3D shape it will form
The 3D shape of a protein is what determines its function in the body
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HEMOGLOBIN - Protein found in red blood cells that carries oxygen molecules to the cells and carbon dioxide away from the cells
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8. Denaturation of Protein
Loss of shape of protein
This is caused by excess heat, pH changes, heavy metals, alcohol etc
Denatured proteins can’t work properly due to loss of 3D structure
Deficient AAs can limit protein synthesis
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9. Dietary Protein sources
Food Sources:
Meat, fish,eggs, poultry, dairy products, legumes, nuts and seeds. (Breads, cereals and vegetables also contain small amounts of protein.)
“high quality” proteins – contain all the essential amino acids
Mutual supplementation – foods can be combined to provide a complete source of protein (e.g. beans and rice), but should be during the same day, so protein synthesis is not limited
The incomplete proteins that are combined are called “complementary proteins”
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A complete protein
An incomplete protein
source is one that provides all of the essential amino acids. You may also hear these sources called high quality proteins. Animal-based foods; for example, meat, poultry, fish, milk, eggs, and cheese are considered complete protein sources.
source is one that is low in one or more of the essential amino acids.Complementary proteins are two or more incomplete protein sources that together provide adequate amounts of all the essential amino acids.
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Stomach
pH is low (1-3)
denature proteins
Pepsin
polypeptides amino acids +
smaller polypeptides
2. Duodenum
neutral pH
(because of sodium bicarbonate from the pancreas)
stops the action of pepsin
proteases
Peptide amino acid
peptidases
Proteases – from the pancreas
Peptidases – from the intestinal cells
3. Jejunum
– AAs are absorbed into the blood stream and travel to the liver
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Function of Proteins
Function in the Body:
Provides energy, but not the preferred energy source, but will be used if there is not enough carbs or fats
Cell growth, repair and maintenance.
Help to build, maintain, and repair body tissues.
Enzymes, antibodies, neutrotransmitters, haemoglobin, and some hormones (e.g. insulin) are made of protein
Maintain fluid and electrolyte levels
Proteins help to maintain acid-base balance in the blood
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13. Problems with excess dietary proteins
High cholesterol (high protein diets)
Bone loss (high protein diets – sulphur amino acids – pull Calcium from bones)
Kidney disease (diabetics) – too much urea production in the kidney
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