Proteins Flashcards
Functions
Catalyze chemical reactions, provide structural support, transports substances in body, enables movement (muscle contractions), regulates cellular processes, defends against disease (antibodies)
Structure
Amino acids: made up of central carbon, amino group, hydrogen, carboxyl group, and R group
- 20 different R groups/amino acids, 8 essential
- Based on R group, can be polar, non-polar, or charged
Polypeptides
Polymer of amino acids, bonded via peptide bonds/amide linkages –> sequence determines 3D shape and function
Levels of Structure
Primary and secondary are linear/fibrous - narrow strands
Tertiary and quaternary are globular - rounded and compacted
Primary (1°)
Sequences of amino acids determined by genes in DNA –> one change in amino acid could alter entire final shape and function
Secondary (2°)
Polypeptide coils and folds as length increases –> H-bonding occurs between carboxyl and amino (+ other intermolecular forces)
- a-helix (H-bonds every 4 peptide bonds)
- b-pleated sheets (H-bond between adjacent strands)
Tertiary (3°)
Polypeptide undergoes additional folding due to strong forces of attraction and repulsion –> may use chaperone proteins to assist in folding
Tertiary Structure Interactions
Stabilized by R-group interactions:
- Amino acids with hydrophobic R-groups congregate away from water
- H-bonds, ionic bonds, prolines (kinks), disulphide bridge (with sulphur containing R-groups)
Quaternary (4°)
2 or more polypeptides join to form a functional protein
Factors Affecting Shape/Folding
1° structure, temperature, pH, ionic concentration
Denaturation
Change in protein’s 3D shape, changing its function (denatured proteins do not carry out functions)
- May function again if denaturing agent is removed
- Protein will be destroyed if 1° structure is altered
Denaturation Examples
Fever: increase in body temperature can denature proteins, causing seizures
Pickling: pH denatures enzymes in bacteria that spoil food
