1. Proteins are involved in
Proteins are essential to the structures and activities of life
Proteins are involved in
structure
movement
defense
transport
communication
storage
regulation of chemical reactions ENZYMES!!
Structural proteins
Support: Silk from spiders, hair of mammals, fibers that make up tendons and ligaments
Contractile proteins
Provide muscular movement. Ex. actin/myosin
Storage proteins- storage of amino acid. Ex. casein, the protein of milk, stores amino acids for baby mammals.
Defensive proteins
Protection against disease. Antibodies combat bacteria and viruses.
Transport proteins
Transport of other substances. Hemoglobin
Signal proteins
Coordination of organism’s activities: Insulin, a hormone, helps regulate the concentration of sugar in the blood of vertebrates.
Enzymes
Serves as chemical catalyst (changes the rate of a reaction)
Promote and regulate virtually all chemical reactions in the cell
Mammalian hair is composed of structural proteins

2. Their diversity is based on different arrangements of amino acids
Proteins are the most structurally and functionally diverse of life’s molecules
Their diversity is based on different arrangements of amino acids
The key to variation is the sequence in which the monomers are strung together.

3. 20 Amino Acids used in Human Proteins

4. Each amino acid contains:
an alpha (α) carbon
a hydrogen
an amino group
a carboxyl group
an R group, which distinguishes each of the 20 different amino acids
Figure 3.12A
By having 20 amino acids, the monomers can join together in different combinations and create a wide variation of differing proteins.

5. Each amino acid has specific properties
Note the functional groups present.
Some are nonpolar, polar, acidic and basic.
Leucine (Leu)
Serine (Ser)
Cysteine (Cys)
HYDROPHOBIC
HYDROPHILIC
Figure 3.12B

6. Amino acids can be linked by peptide bonds
Cells link amino acids together by dehydration synthesis
The resulting covalent linkage is called a peptide bond
Product is called a dipeptide (2 amino acids)

7. Glycine: Dehydration Synthesis

8. Amino acids can be linked by peptide bonds
Cells link amino acids together by dehydration synthesis
The bonds between amino acid monomers are called peptide bonds
Carboxyl group
Amino group
PEPTIDE BOND
The resulting covalent linkage is called a peptide bond
Product is called a dipeptide (2 amino acids)
Dehydration synthesis
Amino acid
Amino acid
Dipeptide

9. Polypeptide Chains
Molecules formed by strings of hundreds of amino acids linked together by peptide bonds
Chain of amino acids = polypeptide
Range in length from a few monomers to a thousand or more
Peptide bond
Peptide bond
Peptide bond
Peptide bond
Peptide bond
Peptide bond

10. A protein’s specific shape determines its function!
A protein consists of polypeptide chain(s) folded into a unique 3-D shape = tertiary structure
The shape determines the protein’s function
A protein loses its specific function when its polypeptide(s ) unravels = denaturation = 
Each polypeptide has a unique sequence of amino acids and assumes a unique 3-D shape in a protein
Nearly all proteins must recognize and bind to some other molecule in order to function. Therefore their shape matters!
The function of each protein is a consequence of its specific shape, which is lost when a protein denatures.
The function of each protein is a consequence of its specific shape
During denaturation, polypeptide chains unravel, losing their specific shape and as a result, their function.
Denaturation may be causes by high temperatures or various chemical treatments.
Example: egg white cooking
Figure 3.14B

11. A protein’s primary structure is its amino acid sequence
For proteins to perform its specific function, it must have the correct collection of amino acids arranged in a precise order.
Primary structure is the sequence of amino acids forming its polypeptide chains
For proteins to perform its specific function, it must have the correct collection of amino acids arranged in a precise order.
Even a slight change in a protein’s primary structure may affect its overall shape and its ability to function
For example, a single amino acid change in hemoglobin (O2 carrying blood protein) causes sickle-cell disease
Figure 3.15, 16

12. A protein’s primary structure is its amino acid sequence The substitution of one amino acid for another at a particular position in hemoglobin causes sickle cell disease
Normal red blood cells are disk-shaped, but in sickle-cell disease, the abnormal hemoglobin molecules tend to crystallize, deforming some of the cells into a sickle shape.
Causes sickle cell crises which occur when the angular cells clog tiny blood vessels, impeding blood flow.

13. A protein’s primary structure is its amino acid sequence
Secondary structure is polypeptide coiling or folding produced by hydrogen bonding
Primary structure
Amino acid
Primary structure is the sequence of amino acids forming its polypeptide chains
For proteins to perform its specific function, it must have the correct collection of amino acids arranged in a precise order.
Secondary structure
Secondary structure: polypeptide coil or folds into local patterns
Coiling of a polypeptide chain results in an alpha helix
Folding of the polypeptide chain results in a pleated sheet.
Coiling and folds maintain the hydrogen bonds
Secondary structure
Hydrogen bond
Pleated sheet
Alpha helix

14. Secondary structure is polypeptide coiling or folding produced by hydrogen bonding
Both the oxygen and nitrogen atoms of the backbone are electronegative, with partial negative charges. The weakly positive hydrogen atom attached to the nitrogen atoms has an affinity for the oxygen atoms of a nearby peptide bond.
A helix: delicate coil held together by hydrogen bonding between every 4th amino acid.
B pleated: two or more regions of polypeptide chain lie parallel to eachother. Hydrogen bonds hold structure together.

15. Tertiary structure is the overall 3-D shape of a polypeptide
Polypeptide (single subunit of transthyretin)
Tertiary structure refers to the overall, 3-D shape of a polypeptide.
Contains both alpha helix and pleated sheet regions
This particular arrangement of coils and folds give the polypeptide the specific shape appropriate to its function
Hydrophobic side chains usually end up in the interior of the protein, away from water.
Hydrogen bonds between polar side chains and ionic bonds between positively and negatively charged side chains help stabilize tertiary structure.
Reinforced by strong, covalent bond called disulfide bridges. Disulfide bridges form when amino acids with sulfhydral groups (-SH) are brought close together by the folding of the protien.
Quartenary structure
Many proteins consist of 2 or more polypeptide chains or subunits
Figure 3.17, 18

16. Tertiary structure is the overall shape of a polypeptide
Hydrophobic side chains usually end up in the interior of the protein, away from water.
Hydrogen bonds between polar side chains and ionic bonds between positively and negatively charged side chains help stabilize tertiary structure.
Reinforced by strong, covalent bond called disulfide bridges. Disulfide bridges form when amino acids with sulfhydral groups (-SH) are brought close together by the folding of the protien.

17. Tertiary structure is the overall 3-D shape of a polypeptide
Quaternary structure is the relationship among multiple polypeptides of a protein
Tertiary structure
Polypeptide (single subunit of transthyretin)
Tertiary structure refers to the overall, 3-D shape of a polypeptide.
Contains both alpha helix and pleated sheet regions
This particular arrangement of coils and folds give the polypeptide the specific shape appropriate to its function
Hydrophobic side chains usually end up in the interior of the protein, away from water.
Hydrogen bonds between polar side chains and ionic bonds between positively and negatively charged side chains help stabilize tertiary structure.
Reinforced by strong, covalent bond called disulfide bridges. Disulfide bridges form when amino acids with sulfhydral groups (-SH) are brought close together by the folding of the protien.
Quartenary structure
Many proteins consist of 2 or more polypeptide chains or subunits
Quaternary structure
protein, with four identical polypeptide subunits
Figure 3.17, 18

18. Quaternary structure is the relationship among multiple polypeptides of a protein
Many (but not all) proteins consist of more than one primary chain.
Quaternary bonding is largely by polar and hydrophobic interaction.
Collagen- fibrous protein consisting of 3 helical polypeptides that are supercoiled to form a ropelike structure of great strength. Accounts for 40% of the protein in the human body, collagen strengthens connective tissues throughout the body. (connective tissue in skin, bone, tendons, ligaments)
Hemoglobin: Another good example of a protein with quaternary structure is hemoglobin: 4 polypeptide subunits, two of one kind (a chain) and two of another kind (b chains). Each subunit has a nonpolypeptide unit called a heme, with an iron atom that binds to oxygen.
Transthyretin, with four identical polypeptide subunits
Four Levels