1. PROTEINS

2. Recall:
Nutrients in the human body have three general functions:
They can supply energy for processes such as
growth, movement, electrical signalling, metabolism
2. They can regulate body processes such as
metabolism, growth, membrane transport,
cellular communication
3. They can provide the building blocks for making
the structures of our cells and our bodies `
Proteins in our diet serve all three functions

3. Proteins Proteins can supply energy:
Although cells of the body prefer to use
carbohydrates and lipids as sources of energy,
many cells can also use proteins as fuel molecules
if necessary.
That means that extra dietary protein can be
converted to carbohydrate or lipid molecules and
stored for future energy needs. 3

4. Proteins 2. Proteins can regulate cellular processes:
They help form “receptors” which
allow cells to respond to hormones

5. Proteins 2. Proteins can regulate cellular processes:
They help form “receptors” which
allow cells to respond to hormones
They form “channels” in the membrane
which allow things to get into and out of cells

6. Proteins 2. Proteins can regulate cellular processes:
They help form “receptors” which
allow cells to respond to hormones
They form “channels” in the membrane
which allow things to get into and out of cells
They form “junctions” on membranes
which allow cells to communicate with
each other.

7. Proteins 2. Proteins can regulate cellular processes:
They form enzymes which
catalyze cellular reactions

8. Proteins 2. Proteins can regulate cellular processes:
They form enzymes which
catalyze cellular reactions
They slide past each other to make
muscles contract

9. Proteins 2. Proteins can regulate cellular processes:
They form enzymes which
catalyze cellular reactions
They slide past each other to make
muscles contract
They fom the cytoskeleton which
holds organelles in place and moves them around in the cell

10. Proteins 2. Proteins can regulate cellular processes:
They form antibodies all
over the body, proteins in the
blood, and many hormones.

11. Proteins 3. Proteins can make structures our bodies need:
Proteins such as collagen form
tendons and ligaments

12. Proteins 3. Proteins can make structures our bodies need:
Proteins such as collagen form
tendons and ligaments
Collagen and another protein called
elastin form the dermis is the skin.
The protein keratin forms hair and
the top layer of the epidermis.

13. Proteins
All of these proteins in the body must constantly be replaced.
That means your diet must
contain the building blocks
of proteins, called amino acids 13

14. Proteins
Food sources Meat, Chicken, Fish Milk & cheese Eggs Beans, peas, grains, nuts, seeds, vegetables 14

15. Amino Acids 15

16. Amino Acids 16

17. Amino Acids
Amino acids bond together by a process called dehydration synthesis. 17

18. Amino Acids
Amino acids bond together by a process called dehydration synthesis.
Bonding two amino acids together forms a dipeptide 18

19. Amino Acids
Amino acids bond together by a process called dehydration synthesis.
Bonding two amino acids together forms a dipeptide
Bonding many amino acids together forms
a polypeptide
or protein 19

20. Amino Acids
While proteins are long, unbranching chains of amino acids, they do not remain straight.
Different side-groups cause the chain to bend and coil.
In fact, the three dimensional stucture of a protein is what gives it a specific function. 20

21. Amino Acids
Changing the three-dimensional shape of a protein is called denaturing, and changes the function of a protein, often permanently.
Proteins can be denatured
many ways: heat
alcohol
acids or alkalis
digestive enzymes
(“proteases”)
etc. 21

22. Protein Digestion Protein digestion begins in the stomach.
Hydochloric acid denatures the protein,
unfolding it so proteases can reach the amino acids to break the peptide bonds between them. 22

23. Protein Digestion
Along with the hydrochloric acid, one of these proteases, pepsin, begins protein digestion in the stomach. 23

24. Protein Digestion
It is then continued in the small intestine by proteases secreted by the pancreas and cells of the intestine. 24

25. Protein Digestion & Amino Acids
Individual amino acids are absorbed into the blood vessels in the mucosa of the small intestine.
They are carried first to the liver, which can remove excess amino acids, after which they enter the general circulation and become available to cells all around the body. 25

26. Amino Acids
All cells of the body have the ability to take those amino acids out of the blood and use them to build the proteins they need. 26

27. Amino Acids
All cells of the body also have the ability to break down proteins to release the individual amino acids back into the blood. 27

28. Amino Acids
Thus, there is a pool of amino acids available for building all of the proteins the body needs. 28

29. Amino Acids
Thus, there is a pool of amino acids available for building all of the proteins the body needs.
Some amino acids can be used to make other molecules such
as hormones, nucleotides, or neurotransmitters. 29

30. Amino Acids
Cells of the liver can break amino acids apart, separating the amino groups (nitrogen atom and two hydrogen atoms) from the rest of the amino acid molecules, called their “carbon skeleton”, which can be used to form lipids or carbohydrates which can be used to produce or store energy.
The amino groups are hooked together to form urea 30

31. Amino Acids
That urea can then safely travel to the kidneys, where it is removed and excreted in the urine. 31

32. Amino Acids
Your body needs to take in new amino acids from your diet, but this must be balanced by the excretion of nitrogen in the form of urea. 32

33. Amino Acids
Your body needs to take in new amino acids from your diet, but this must be balanced by the excretion of nitrogen in the form of urea.
If your liver can’t form enough urea, the nitrogen produced by the breakdown of amino acids can be toxic to the body.
This is called “nitrogen balance”:
Your intake of nitrogen (in the form of proteins)
must equal
Your output of nitrogen (in the form of urea in the urine) 33

34. Nitrogen Balance Nitrogen equilibrium
Nitrogen intake = nitrogen output
Healthy adults
Positive nitrogen balance
Nitrogen intake > nitrogen output
Necessary during growth; recovery from illness
Negative nitrogen balance
Nitrogen intake < nitrogen output
Results from injury and illness 34

35. Proteins in the Diet Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc 35

36. Proteins in the Diet Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day 36

37. Proteins in the Diet Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day
A 70 kg adult (154 pounds) should eat
70 x .8 = 56 grams of protein per day 37

38. Proteins in the Diet Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day
A 70 kg adult (154 pounds) should eat
70 x .8 = 56 grams of protein per day
A 90 kg adult (198 pounds) should eat
90 x .8 = 72 grams of protein per day 38

39. Proteins in the Diet Recommended protein intake:
Adult RDA = 0.8 gram per kilogram body weight
More in children, pregnancy, recovery from injury, etc
Thus: A 50 kg adult (110 pounds) should eat
50 x .8 = 40 grams of protein per day
A 70 kg adult (154 pounds) should eat
70 x .8 = 56 grams of protein per day
A 90 kg adult (198 pounds) should eat
90 x .8 = 72 grams of protein per day
In the United States: protein intake > protein needs 39

40. Proteins in the Diet
Excess protein can strain kidney function There are links between high-protein diets and Osteoporosis Obesity Heart disease Some forms of cancer 40

41. Proteins in the Diet
At the other extreme, it is possible to have too little protein in your diet. This can occur in diets which are not properly designed, but it is most often associated with extreme poverty, and occurs together with insufficient intake of fuel molecules such as carbohydrates or lipids.
Kwashiorkor and Marsmas 41

42. Proteins in the Diet
Not all dietary proteins are equally useful for the body. 42

43. Proteins in the Diet Tyrosine Serine Proline Valine Glycine Tryptophan
Glutamine
Threonine
Glutamic acid
Phenylalanine
Cysteine
Methionine
Aspartic Acid
Lysine
Asparagine
Leucine
Arginine
Isoleucine
Alanine
Histidine
Nonessential AA
Essential AA
Not all dietary proteins are equally useful for the body.
Of the 20 amino acids which are used to make proteins in the human body, only 11 of them can be synthesized. The remaining 9 must be obtained through the diet. 43

44. Proteins in the Diet Protein quality:
Complete proteins supply all of the essential amino acids
(e.g. animal proteins; soy proteins) 44

45. Proteins in the Diet Protein quality:
Complete proteins supply all of the essential amino acids
(e.g. animal proteins; soy proteins)
Incomplete proteins are low in one or more essential amino acid
( e.g. most plant proteins) 45

46. Proteins in the Diet Protein quality:
Complete proteins supply all of the essential amino acids
(e.g. animal proteins; soy proteins)
Incomplete proteins are low in one or more essential amino acid
( e.g. most plant proteins)
This can create problems for people on vegetarian or vegan diets, or for people on special diets low in meats, milk, eggs, etc. 46

47. Proteins in the Diet Protein quality:
You can ensure that you get all essential amino acids by combinig two or more incomplete proteins which are missing different ones.
These are called
complementary proteins 47

48. Proteins in the Diet
A healthy diet should include a variety of proteins from meats, eggs, dairy, soy products, legumes and other vegetables.
A vegetarian diet must include complementary proteins
such as those in - rice and beans
- whole grains and vegetables
- corn and beans
to ensure that all essential amino acids are available
Total protein intake should be moderated