1. Protein Lancelot McLean, PhD lmclean@llu.edu

2. Proteins More complex than carbohydrates or fats Twenty amino acids
Different characteristics
Essential amino acids
Cannot be synthesized (or produced in sufficient amounts) by the body
Must be obtained from diet
Nonessential amino acids
Can be synthesized in sufficient amounts by the body

3. 20 Amino acids

4. Essential and Nonessential Amino Acids

5. Primary Structure
The linear sequence of amino acids in a protein is called the primary structure of the protein.

6. Secondary Structure
The structure brought about by the formation of hydrogen bonds between the C=O and N-H groups of the amino acids in the polypeptide chain.
Consists of several repeating patterns.

7. Tertiary structure
A description of the way the polypeptide chain folds itself into its final 3-dimensional shape.
Held together by interactions between the side chains ( R groups).
1) Hydrogen bonds
2) Disulfide bonds
3) Ionic interactions
4) Hydrophobic interactions

8. Quaternary structure
The 3D structure formed by interaction of more than one polypeptide chain
Subunits are held together by noncovalent interactions (e.g. H-bonds, ionic bonds and hydrophobic interactions
Subunits may either function independently or cooperatively

9. Proteins Denaturation Disruption of stability Uncoil and lose shape
Stomach acid as well as heat can cause denaturation

10. Protein Digestion Mouth Stomach Small intestine Crushed and moistened
Hydrochloric acid denatures proteins
Pepsin cleaves proteins to smaller polypeptides and some free amino acids
Small intestine
Hydrolysis reactions breaks down polypeptides to shorter tripeptides, dipeptides and amino acids
Peptidase enzymes split tripeptides and dipeptides into single amino acids

11. Protein Digestion

12. Breaking Down Nutrients for Energy
Amino acids can be used for
a) energy
b) to synthesize needed compounds

13. Protein Synthesis

14. Roles of Proteins Growth and maintenance
Building blocks for most body structures
Muscles, blood, skin, bone, teeth etc.
Replacement of dead or damaged cells
Skin cell lifespan is about 30 days
GI tract cells about a few days
Enzymes
Break down, build up, and transform substances
Catalysts

15. Roles of Proteins Hormones Messenger molecules
Transported in blood to target tissues
Regulatory molecules
Acid base regulators
Proteins have negative charges, attract H+ ions thereby maintaining acid base balance
Fluid balance regulators
Proteins attract water – plays role in edema

16. Roles of Proteins Transporters Hemoglobin carries O2
Lipoproteins transport lipids
Special transport proteins carry vitamins and minerals

17. Roles of Proteins Antibodies Defend body against disease Specificity
Immunity – memory
Source of energy and glucose
During starvation and insufficient carbohydrate intake

18. Nitrogen Balance
Nitrogen balance occurs when the amount of nitrogen consumed equals that of the nitrogen excreted in the urine, sweat, and feces.
Most healthy adults are normally in nitrogen balance
Positive nitrogen balance
Negative nitrogen balance

19. Nitrogen Balance
Adequate protein intake in adults yields a Nitrogen Balance
In children or in individuals undergoing healing, there is a net increase in the amount of nitrogen in the body. Positive Nitrogen Balance
In wasting or degeneration there is a Negative Nitrogen Balance

20. Quality of protein
The quality of a dietary protein is a measure of its ability to provide the essential amino acids required for tissue maintenance
Proteins from animal sources have a high quality because they contain all the essential amino acids in proportions similar to those required for synthesis of human tissue proteins
Meat, poultry, milk and fish
Proteins from plant sources have a lower quality than do animal proteins. However, proteins from different plant sources may be combined in such a way that the result is equivalent in nutritional value to animal protein
Soy protein, legumes, nuts, grains, vegetables

21. Quality of protein Proteins from plant sources
Combing 2 incomplete proteins that have complementary amino acid
deficiencies results in a mixture with a higher biologic value
Isoleucine
Lysine
Methionine
Tryptophan
Legumes + -
Grains
Together

22. Recommended intakes for protein
10-35% of energy intake
Some individuals may require more
People who exercise strenuously on a regular basis e.g. athletes
Women who are pregnant or lactating
Infants to support growth

23. Consumption of excess protein
Protein consumed in excess of the body’s needs is deaminated, and the resulting carbon skeletons are metabolized to provide energy or acetyl CoA for fatty acid synthesis
When excess protein is eliminated from the body as urinary nitrogen, it is often accompanied by increased urinary calcium, increasing the risk of nephrolithiasis (kidney stones) and osteoporosis

24. Negative Health Effects of High-Protein
High-protein diets
Osteoporosis
Calcium excretion increases when protein intake is high
Some research suggests that animal protein may be more detrimental than plant protein

25. Negative Health Effects of High-Protein
High-protein diets
Heart disease
Animal-protein intake
Rich in saturated fats
Homocysteine levels
Associated with increased oxidative stress and inflammation
Coffee’s role in heart disease has been controversial
Research suggests it is among the most influential factors in raising homocysteine levels
Homocysteine

26. Negative Health Effects of High-Protein
High-protein diets
Cancer
Protein-rich foods
Red meat and processed meats
Cancer of the colon
Kidney disease
Acceleration of kidney deterioration
Due to excretion of end products of protein metabolism
Especially in people with kidney disease

27. Negative Effects of too little protein
When carbohydrate intake is low, amino acids are deaminated to provide carbon skeletons for the synthesis of glucose that is needed as a fuel by the CNS
When carbohydrate intake is low, substantial amounts of protein are metabolized to provide precursors for gluconeogenesis

28. Negative Effects of too little protein
Protein energy malnutrition (PEM)
In developed countries PEM is most frequently seen in patients with medical conditions that decrease appetite or alter how nutrients are digested or absorbed, or in hospitalized patients with major trauma or infections
In developing countries, an inadequate intake of protein and/or energy is the primary cause of PEM

29. Negative Effects of too little protein
Protein Energy Malnutrition (PEM)
Affected individuals show a variety of symptoms, including a depressed immune system with a reduced ability to resist infection
Death from secondary infection is common
Two extreme forms of PEM are kwashiorkor and marasmus

30. Protein Energy Malnutrition (PEM)
Kwashiorkor
Results from a sudden and recent deprivation of food (acute)
Mainly caused by
Protein deficiency
Illness such as infection
Protein deprivation is associated with severely decreased synthesis of visceral protein
Frequently seen in children after weaning between 18 months and 2 years of age, when their diet consists predominantly of carbohydrates

31. Protein Energy Malnutrition (PEM)
Kwashiorkor
Typical symptoms include stunted growth, edema, skin lesions, depigmented hair, anorexia
Edema results from the lack of adequate plasma proteins to maintain the distribution of water between blood and tissues

32. Protein Energy Malnutrition (PEM)
Marasmus (chronic)
Results from severe deprivation of food over a long time (chronic)
Occurs mostly in children from 6 – 18 months of age in impoverished areas of the world
Learning disability
Brain normally grows to almost full adult size within first 2 years of life

33. Protein Energy Malnutrition (PEM)
Marasmus (chronic)
Typical symptoms include arrested growth, extreme muscle wasting, weakness, and anemia