Proteins are complex molecules found in all living things that contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. They are made up of combinations of amino acids, which vary in their side chains. There are essential amino acids that must be obtained through food, and non-essential ones that the body can produce. High quality proteins contain all essential amino acids and are highly digestible, while lower quality proteins lack some essential amino acids or digestibility. Proteins are important for growth, repair, enzymes, hormones, fluid balance and more. However, very high protein intake, especially from animal sources, may increase risk of heart disease, bone loss and kidney disease due to saturated fat and acid content.

1. PROTEINS
Proteins are large, complex molecules found in the cells of all
living things.
 In addition to the carbon, hydrogen, and oxygen also found in
carbohydrates and lipids, proteins contain a special form of
nitrogen that the body can readily use.
In addition, two amino acids, cysteine and methionine, also
contain sulfur

2. Proteins
• The proteins in our bodies are made from a combination of building blocks called
amino acids, molecules composed of a
1. Central carbon atom connected to four other groups:
2. Amine group (NH2)
3. An acid group (COOH)
4. A hydrogen atom
5. A side chain

3. STRUCTURE OF AMINO-ACID
COOH
H C-----R( group)
NH2
NB: Variations in the structure of the R group give each amino
acid its distinct properties.

4. Types of amino acids.
They are subdivided into two categories:
i. Essential (indispensable) amino acids
ii. Non-essential (dispensable) amino acids.

5. 1. Essential amino acids
Amino acids not produced by the body or not
produced in sufficient amounts so that they must be
obtained from food.
They are 9 in number.
NB; CHECK EXAPLES FROM THE NOTES

6. 2. Non-essential amino acids
Amino acids that can be manufactured by the body in
sufficient quantities and therefore do not need to be
consumed regularly in our diet.
They are 11 in number
NB; CHECK EXAPLES FROM THE NOTES

7. Types of proteins
1. Complete proteins
Foods that contain all nine essential amino acids.
2. Incomplete proteins
Foods that do not contain all of the essential amino
acids in sufficient amounts to support growth and health.

8. Types of proteins
3. Complementary proteins
Proteins contained in two or more foods that together contain all
nine essential amino acids necessary for a complete protein.
It is not necessary to eat complementary proteins at the same
meal.

9. Proteins
Mutual supplementation
 The process of combining two or more incomplete
protein sources to make a complete protein.

10. PROTEIN QUALITY
Protein quality is affected by ;
i. Amino acid content
ii. Digestibility

11. I. Amino acid content
The quantity of essential amino acids in a protein determines its
quality:
1. Higher-protein quality foods
 Are those that contain more of the essential amino acids in
sufficient quantities needed to build proteins.
2. Lower-protein-quality foods
 Contain fewer essential amino acids.

12. II. Digestibility
 Digestibility, or how well the body can digest a protein.
The Protein Digestibility Corrected Amino Acid
Score (PDCAAS) uses the chemical score and a
correction factor for digestibility to calculate a value for
protein quality.

13. II. Digestibility
Proteins with higher digestibility are more complete.
 Animal protein sources such as meat and dairy products
are highly digestible, as are many soy products; we can
absorb more than 90% of these proteins.

14. II. Digestibility
Legumes are also highly digestible (about 70% to 80%).
Grains and many vegetable proteins are less digestible,
with PDCAAS values ranging from 60% to 90%.

15. PROTEIN QUALITY
These measures of protein quality are useful when
determining the quality of protein available to
populations of people.

16. Roles of proteins
i. Proteins Contribute to Cell Growth, Repair and
Maintenance
ii. Proteins Act as Enzymes and Hormones- examples
include insulin, a hormone that acts on cell
membranes to facilitate the transport of glucose into
cells; glucagon, which responds to conditions of low
blood glucose, and thyroid hormone, which helps
control our resting metabolic rate.

17. Roles of proteins
iii. Proteins Help Maintain Fluid and Electrolyte
Balance
iv. Proteins Help Maintain Acid–Base Balance

19. Roles of proteins
• Proteins Serve as an Energy Source
• Proteins Assist in the Transport and Storage of Nutrients-
lipoproteins contain (lipids bound to proteins) which allows
the transport of hydrophobic lipids through the watery
medium of blood.

20. Another example of a transport protein is transferrin,
which carries iron in the blood.
Ferritin, in contrast, is an example of a storage protein
which is the compound in which iron is stored in the
liver.

21. Roles of proteins
Proteins Help Maintain a Strong Immune System e.g.
antibodies.
Their production is prompted by the presence of bacteria, viruses, toxins,
and allergens.

22. Disorders associated with proteins
High protein intake may increase the risk of health problems.
Three health conditions that have received particular attention include
1. Heart disease
2. Bone loss
3. Kidney disease.

23. Disorders associated with proteins
High-protein diets composed of predominantly
animal sources are associated with higher blood
cholesterol levels.
This is probably due to the saturated fat in animal
products, which is known to increase blood
cholesterol levels and the risk of heart disease.

24. Disorders associated with proteins
• High Protein Intake May Contribute to Bone Loss because they
increase calcium excretion. This may be because animal products
contain more of the sulfur amino acids (methionine and cysteine).
Metabolizing these amino acids makes the blood more acidic, and
calcium is pulled from the bone to buffer these acids.

25. Disorders associated with proteins
3. High Protein Intake Can Increase the Risk for Kidney
Disease

26. PROTEIN SOURCES
ANIMAL SOURCES
PLANT