1. Amino Acids and Proteins
Larry Scheffler
Lincoln High School
Portland OR 1

2. Amino Acids Amino acids have both a carboxyl group -COOH
an amino group
-NH2
in the same molecule..  2

3. Amino Acid Structure
The general formula of an amino acid is shown here
The group designated by R is usually a carbon chain but other
structures are also
possible 3

4. Amino Acid Structure
Amino acids may be characterized as a, b , or g amino acids depending on the location of the amino group in the carbon chain.
a are on the carbon adjacent to the carboxyl group.
b are on the 2nd carbon
g on the 3rd carbon from the carboxyl group 4

5. Amino Acids - Proteins
Amino acids are the building blocks of proteins. Proteins are natural polymers of successive amino acids
There are 20 different amino acids that make up human proteins 5

6. a- amino acids
Amino acids found in proteins are a- amino acids. The amino group is always found on the carbon adjacent to the carboxyl group 6

7. Amino Acid Functions Amino acids are the building blocks of proteins
Some amino acids and their derivatives function as neurotransmitters and other regulators
Examples Include
L-dopamine
Epinephrine
Thyroxine
Histidine 7

8. Amino Acids and Proteins
Amino acids forming proteins may be characterized as Acidic, Basic, or neutral depending on the character of the side chain attached. 8

9. Acidic Amino Acids There are two acidic amino acids.
There are two carboxyl groups and only one amino group per molecule
(asp)
(glu) 9

10. Basic Amino Acids I
These amino acids are basic. They have more amino groups than carboxyl groups 10

11. Basic Amino Acids II
These amino acids are also basic. They have more amino groups than carboxyl groups 11

12. Neutral Amino Acids I
These amino Acids are considered neutral. There is one carboxyl group per amino group
(ala)
(gly)
((leu) 12

13. Neutral Amino Acids II
(Ser)
(Tyr)
(Val)
(Trp)
(Cys)
(Met) 13

14. Neutral Amino Acids III
(Ile)
(Thr)
(Asp)
(Phe)
(Gln)
(Pro) 14

15. Amino Acids and Optical Isomers
Except for glycine, all amino acids have a chiral carbon atom. Therefore they can have optical isomers
The amino acids found in proteins are all levarotatory or L forms. 15

16. Amino Acids are Amphoteric
Amino acids are amphoteric. They are capable of behaving as both an acid and a base, since they have both a proton donor group and a proton acceptor group.
In neutral aqueous solutions the proton typically migrates from the carboxyl group to the amino group, leaving an ion with both a (+) and a (-) charge. 16

17. The Zwitterion
This dipolar ion form is known as a Zwitterion. 17

18. Essential Amino Acids
Of the 20 amino acids that make up proteins 10 of them can be synthesized by the human body
The other 10 amino acids must be acquired from food sources. These amino acids are known as essential amino acids 18

19. Essential Amino Acids Essential amino acids Arginine Histidine
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
Non-Essential amino acids
Alanine (from pyruvic acid)
Asparagine (from aspartic acid)
Aspartic Acid (from oxaloacetic acid)
Cysteine
Glutamic Acid (from oxoglutaric acid)
Glutamine (from glutamic acid)
Glycine (from serine and threonine)
Proline (from glutamic acid)
Serine (from glucose)
Tyrosine (from phenylalanine) 19

20. Essential Amino Acids Complete protein Incomplete protein
Contains all 10 essential amino acids
Proteins derived from animal sources are complete proteins
Beans contain some complete protein as well
Incomplete protein
Lack one of more of the essential amino acids
Most vegetable proteins are incomplete proteins
Beans are an exception to this generalizations 20

21. Peptide Bond
When two amino acids combine, there is a formation of an amide and a loss of a water molecule
+ H2O 21

22. Proteins- Levels of Structure
Amino acids can undergo condensation reactions in any order, thus making it possible to form large numbers of proteins.
Structurally, proteins can be described in four ways.
Primary
Secondary
Tertiary
Quaternary structure. 22

23. Primary Structure
The primary structure of a protein is defined by the sequence of amino acids, which form the protein. This sequence is determined by the base pair sequence in the DNA used to create it. The sequence for bovine insulin is shown below 23

24. Secondary Structure
The secondary structure describes the way that the chain of amino acids folds itself due to intramolecular hydrogen bonding
Two common secondary structures are
the a-Helix 
and the b- sheet  24

25. Tertiary Structure
The tertiary structure maintains the three dimensional shape of the protein.
The amino acid chain (in the helical, pleated or random coil form) links itself in places to form the unique twisted or folded shape of the protein. 25

26. Tertiary Structure
There are four ways in which parts of the amino acid chains interact to stabilize its tertiary shape.. They include:
-- Covalent bonding, for example disulfide bridges formed when two cysteine molecules combine in which the –SH groups are oxidized:
-- Hydrogen bonding between polar groups on the side chain.
-- Salt bridges (ionic bonds) formed between –NH2 and –COOH groups
-- Hydrophobic interactions. 26

27. Quaternary Structure Many proteins are not single strands
The diagram below shows the quaternary structure of an enzyme having four interwoven amino acid strands 27

28. Denaturing Proteins
The natural or native structures of proteins may be altered, and their biological activity changed or destroyed by treatment that does not disrupt the primary structure.
Following denaturation, some proteins will return to their native structures under proper conditions; but extreme conditions, such as strong heating, usually cause irreversible change. 28

29. Denaturing Proteins Heat Ultraviolet Radiation Strong Acids or Bases
hydrogen bonds are broken by increased translational
and vibrational energy.(coagulation of egg white albumin on frying.)
Similar to heat (sunburn)
salt formation; disruption of hydrogen bonds. (skin blisters and burns, protein precipitation.)
competition for hydrogen bonds. (precipitation of soluble proteins.)
(e.g. ethanol & acetone) change in dielectric constant and hydration of ionic groups. (disinfectant action and precipitation of protein.)
shearing of hydrogen bonds. (beating egg white albumin into a meringue.)
Heat
Ultraviolet Radiation
Strong Acids or Bases
Urea
Some Organic Solvents
Agitation 29

30. Sickle Cell Anemia
A small change in the sequence of the primary structure can have a significant impact on protein structure
In sickle cell anemia a glutamic acid is replaced by a valine in the amino acid sequence 30

31. Ninhydrin Reaction
Triketohydrindene hydrate, commonly known as ninhydrin, reacts with amino acids to form a purple colored imino derivative, This derivative forms a useful test for amino acids, most of which are colorless. 31

32. Protein Tests: Biuret
Biuret reagent is a light blue solution containing Cu2+ ion in an alkaline solution. Biuret turns purple when mixed with a solution containing protein. The purple color is formed when copper ions in the biuret reagent react with the peptide bonds of the polypeptide chains to form a complex. 32

33. Xanthroprotic Test
Concentrated Nitric acid will form a yellow complex with tryptophan and Tyrosine side chains in proteins 33

34. Disulfide Bridge Test
Disulfide bridges will react with Pb2+ ion from lead acetate in an acidfied solution. A black precipitate indicates the presence of disulfide-bonded cysteine in proteins. 34