Unit 1: Biochemistry - #5 Structure and Function of Macromolecules: Proteins

Proteins

• Make up 50% of the dry mass of most cells 

• Structural value: Collagen (tendons, bones) and keratin(hair, nails) 

• Enzymes that are used as catalysts in chemical reactions 

• Transport materials throughout the body like oxygen and carbon dioxide 

• Produce antibodies that destroy foreign bacteria and viruses 

• Form structures that allow transport across the membrane

Structure

• Proteins are large polymer units made up of amino acids monomers 

• The overall shape of a protein is determined by the amino acids that it is composed from 

• The structure of a protein is important in determining its overall function. It has to be the EXACT fit because if the shape changes, then the protein may not be able to perform its function properly

Structure of Amino Acids

• Consist of a central carbon bonded to four different covalent partners 

• Hydrogen atom 

• Carboxyl 

• Amino group 

• R group

• There are 20 different R groups which results in 20 different amino acids 

• R groups give amino acids their properties (polar, non-polar, acidic, etc) 

• 8 amino acids are considered essential - only obtained through diet

Amino Acid Linkages

• Amino acids are linked together through condensation (dehydration synthesis) reactions 

• The carboxyl group of one amino acid bonds to the amino group of a second amino acid to form a peptide bond. 

• When two amino acids bond, the resulting molecule is called a diepeptide.

The chain of more than 50 aa’s(amino acids) is called polypeptide

Primary Structure

• Unique linear sequence of amino acids in a polypeptide chain 

• Changing a single amino acid will alter the overall structure of the protein 

• Unlimited combos of primary structure, specific to each protein (20 combos for each spot of the chain)

Secondary Structure

Results from hydrogen bonding between carboxyl group of one amino acid and the amino group of a neighboring amino acid

𝛂-helix

Coil structure held together by h-bonds between every fourth amino acids

ꞵ-pleated sheet

• Two separate polypeptide strands that run parallel to each other interact due to H bonds, an accordion shape appears 

• Ex. Strength of silk

Tertiary Structure

• The polypeptide chain continues to bend, fold and contort itself as a result of the interaction between the “R” groups. 

• Polar, non-polar and ionic “R” groups interact to form hydrogen, covalent, and ionic bonds 

• Forms a large globular arrangement 

EG. Amino acid cysteine contains a sulfur atoms that will form a disulphide bridge with another cysteine atom

Quaternary Structure

• Some proteins consist of two or more polypeptide chains combined into one functional macromolecule 

• Same types of bonds/interactions as tertiary structure 

• The final structure of a protein (confirmation) is critical as its orientation and shape is directly related to its function. Many diseases and disorders are a result of an improperly functioning protein.

Protein Denaturation

• Results from changes in the 3D shape caused by temperature, PH or ionic concentration changes 

• Protein unravels and looses conformation 

• If peptide bonds break the protein is destroyed 

• Enzymes function best within a narrow range of the above conditions