1. 11/13/ :55 AM
Proteins
2.4
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2. Essential Idea: Proteins have a very wide range of functions in living organisms.
2.4
Proteins
Understandings:
Amino acids are linked together by condensation to form polypeptides
There are 20 different amino acids in polypeptides synthesized on ribosomes
Amino acids can be linked together in any sequence giving a huge range of possible polypeptides
The amino acid sequence of polypeptides is coded for by genes
A protein may consist of a single polypeptide or more than one polypeptide linked together
The amino acid sequence determines the three-dimensional conformation of a protein
Living organisms synthesize many different proteins with a wide range of functions
Every individual has a unique proteome
Applications:
Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk are examples of the range of protein functions
Denaturation of proteins by heat or by deviation of pH from the optimum
Skill:
Draw molecular diagrams to show the formation of a peptide bond

3. Protein Functions -Regulate reactions (enzymes)
-Transport molecules (hemoglobin)
-Chemical messengers (hormones, neurotransmitters)
-Channels and pumps in the cell membrane
-Cell-to-cell communication (transmit/receive signals)
-Fight disease (antibodies)
-Provide structure and support
-Contract to cause movement
The function of a protein is entirely dependent on its shape!!!
FORM FOLLOWS FUNCTION

5. Proteins (polypeptides) are polymers of amino acids
Basic amino acid structure:
Central Carbon
Amine group (NH2)
Carboxylic group (COOH)
Hydrogen atoms (H)
Variable side chain (R)
R groups give amino acids variability
-20 different amino acids used in virtually all organisms to build proteins
-11 can be made by the body
-9 must be ingested in food (“essential amino acids”)

7. Protein or polypeptide? What’s the difference?
Both are amino acids covalently bonded together, but a protein has done all its processing and folding and is ready to do its function

8. Polypeptides are formed by condensation reactions between amino acids – results in formation of peptide bonds
(Polypeptides are broken down by hydrolysis reactions)

9. Challenge: Draw the following polypeptide – met – ala- pro- arg - ser

10. Primary Protein Structure
Each polypeptide/protein has a unique sequence of amino acids (100s of amino acids long) that determines how it will fold
(*That sequence is coded for by a gene*)

11. Secondary Structure
-Carboxyl groups and Amine groups of the non-adjacent amino acids interact and form hydrogen bonds with each other, resulting in either alpha helix or beta pleated sheet
***Both types of secondary structure are generally found in all proteins

12. Tertiary Structure
-3-D folding created by bonds forming between the R groups of the various amino acids (hydrogen bonds, ionic bonds, disulfide bridges, and non-polar interactions are the most common)
-Can result in globular or fibrous structures

13. Quarternary Structure
-Some (not all!) proteins are composed of multiple polypeptides
-Can also associate with prosthetic groups (non-polypeptide molecules like iron, lipids, sugars, vitamins) – called conjugated proteins

14. Hemoglobin
Hemoglobin is an example of a protein with a quaternary structure (O2 carrying molecule in red blood cells)
Composed of 4 polypeptide chains (2 alpha, 2 beta)

16. Discuss
What would happen if the primary structure of a protein was not synthesized properly?
What would happen if proper folding did not occur?

17. ***Remember – quaternary structure is dependent on tertiary structure which is dependent on secondary structure which is dependent on primary structure – if you change the primary structure, you change the protein’s secondary, tertiary, and quarternary structure, making it unable to perform its function

18. Proteome
-Protein equivalent of a genome – the entire unique set of proteins that an individual is capable of producing

19. Factors that influence protein folding
- Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties

20. Factors that influence protein folding
-Temperature – increase in molecular motion puts stress on bonds of secondary and tertiary structure
-If primary structure is not disrupted, protein can return to normal shape once temperature decreases
Note: Human body temperature is 37° C, so that is the ideal temperature for most human enzymes

21. Factors that influence protein folding
-pH – proteins have an optimal pH, but addition of H+ or OH- ions (change in pH) causes amino acids to interact with the ions instead of forming the proper hydrogen bonds with other amino acids

22. Challenge
How do you think the ideal pH of an protein that works in your stomach compares to the ideal pH of an protein that works in your blood?

23. Brainstorm
As a group, come up with at least one question you would like answered or clarified.