1. Proteins

2. Extremely important molecule in the body
About 50% of a cell’s dry weight is protein
Polymers made up of monomer units called amino acids

3. Important functions of Proteins
enzymes (speed up chemical reactions)
hormones
storage (egg whites of birds, reptiles; seeds)
transport (hemoglobin)
contractile (muscle)
protective (antibodies)
membrane proteins (receptors, membrane transport)
structural
toxins (botulism, diphtheria)

4. Amino Acids The building blocks of proteins
There are 20 different amino acids, each with a unique R-group (what makes the amino acid distinct)
Each amino acid contains
An amino group (NH2)
A carboxyl group (COOH)
A central carbon attached to a hydrogen
A side chain (R group)

5. Amino Acid Structure Carboxyl Group Functional Group
Central
Carbon
Functional Group
(gives properties)
Amino Group

6. Amino acids may be polar, non-polar, acidic or basic depending on the nature of their side-chains
There are 8 essential amino acids that the body cannot synthesize; these must be obtained from the diet

7. Polypeptides
Amino acids are joined by peptide bonds into long chains called polypeptides
This bond is formed by a condensation reaction between the amino group on one amino acid and the carboxyl group of another amino acid
Two amino acids = dipeptide
Three amino acids = tripeptide

9. Polypeptides
Always have an amino group on one end and a carboxyl group on the other end
Several amino acids together will produce a repeating sequence of atoms along the chain
N-C-C-N-C-C-N-C-C

10. Proteins consist of one or more amino acid polymers that have twisted and coiled into a specific shape
The final shape (conformation) of the polypeptide is determined by the sequence of amino acids it contains
A protein’s conformation is critical to its function
There are four levels of organization for proteins

11. Levels of Organization
Structural name
Structural Description
Bonding Characteristics
Primary
Sequence of amino acids
Covalent peptide bonds
Secondary
Alpha helix
Hydrogen bonds
Beta pleated sheet
Tertiary
Complex folding
R-group-R-group interactions (H-bonds, ionic bonds, hydrophobic interactions), disulfide bridges
Quaternary
Several polypeptides in tertiary structure interacting with one another
R-group-R-group interactions between globular polypeptide chains

13. Primary and Secondary Structure
Primary Structure
refers to the sequence of amino acids found in a protein.
Secondary Structure
The oxygen or nitrogen atoms of the peptide bond are capable of hydrogen- bonding with hydrogen atoms elsewhere on the molecule. This bonding produces two common kinds of shapes seen in protein molecules, coils (helices) and pleated sheets

14. Tertiary Structure
Tertiary structure refers to the overall 3-dimensional shape of the polypeptide chain.
Hydrophobic interactions with water molecules are important in creating and stabilizing the structure of proteins. Hydrophobic (nonpolar) amino acids aggregate to produce areas of the protein that are out of contact with water molecules.
Hydrophilic (polar and ionized) amino acids form hydrogen bonds with water molecules due to the polar nature of the water molecule.
Hydrogen bonds and ionic bonds form between R groups to help shape the polypeptide chain.
Disulfide bonds are covalent bonds between sulfur atoms in the R groups of two different amino acids. These bonds are very important in maintaining the tertiary structure of some proteins.

15. How polypeptides are held in place!

16. Quaternary Structure
Some proteins contain two or more polypeptide chains that associate to form a single protein. These proteins have quaternary structure. For example, hemoglobin contains four polypeptide chains

18. https://www.youtube.com/watch?v=qBRFIMc xZNM

19. A proteins shape is also determined by the environmental conditions in which it is found
The structure is sensitive to pH, temperature, salt, concentration and chemicals
If any of the conditions fall outside favourable range, a protein’s shape and therefore function is altered

20. Denaturation and Inactivation
Denaturation of a protein occurs when the normal bonding patterns are physically broken causing the shape of the protein to change. This can be caused by increased temperature
Inactivation occurs when the temperature is too low for a protein to function properly
Chaperone proteins are molecules that can assist a protein fold properly after it has been slightly damaged or unfolded