BIOL10002 Lecture Notes - Lecture 5: Reaction Rate, Hydrophile, Peptide
Lecture 5
Proteins & Enzymes
Amino Acids – 20 in total
- Can be polar but uncharged (hydrophilic), charged (hydrophilic), or non - polar (hydrophobic)
- Some have special properties (e.g. cysteine links two amino acids by forming disulphide bonds) S - S
Proteins
- Proteins are formed by condensation of amino acids
- Linear chain of amino acids connected by peptide bonds (polypeptide)
- Variable length and order of amino acids
Four Structural Levels:
1. Primary - amino acid sequence, peptide bonds
2. Secondary - Conformation changed due to formation of electrostatic and
hydrogen bonds between amino acids
- α helix or β pleated sheet formation
3. Tertiary - Reaches the configuration of minimal free energy
4. Quaternary - Association of individual polypeptide chains in proteins,
composed in multiple subunits
Denatured proteins: lose structure e.g. cooked egg whites
Enzymes
- Catalysts
- Typically proteins (some RNA molecules have enzyme activity)
- Increase reaction rate but do not alter final equilibrium, decreases Ea
- Do not alter Δ G
- Recyclable (not used up in the reaction)
- Enzyme for almost every cellular reaction, multiple copies of each enzyme
- Active site - “lock and key” type fit for each substrate
Regulation of Enzymes:
- Competitive inhibitors: inhibitor binds to active site.
- Non-competitive inhibitors: inhibitor binds elsewhere on enzyme and changes the shape of the active site.
- Allosteric inhibitors (negative modulators): Binds elsewhere on enzyme, making it less likely for active form of
enzyme to occur
- Allosteric activators (positive modulators): Binds elsewhere on enzyme, making it more likely for active form of
enzyme to occur
- Feedback loops
Substrate channels/pathways: enzymes can be physically linked, so that step by step a substrate is turned into the
desired product
Enzyme partners:
- Vitamins (needed in diet)
- Metal ions (e.g. Mg2+)
- Temporary electron holders (e.g. NAD/NADH)
- ATP
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Document Summary
Can be polar but uncharged (hydrophilic), charged (hydrophilic), or non - polar (hydrophobic) Some have special properties (e. g. cysteine links two amino acids by forming disulphide bonds) s - s. Proteins are formed by condensation of amino acids. Linear chain of amino acids connected by peptide bonds (polypeptide) Variable length and order of amino acids. Four structural levels: primary - amino acid sequence, peptide bonds, secondary - conformation changed due to formation of electrostatic and hydrogen bonds between amino acids. Helix or pleated sheet formation: tertiary - reaches the configuration of minimal free energy, quaternary - association of individual polypeptide chains in proteins, composed in multiple subunits. Denatured proteins: lose structure e. g. cooked egg whites. Typically proteins (some rna molecules have enzyme activity) Increase reaction rate but do not alter final equilibrium, decreases e a. Recyclable (not used up in the reaction) Enzyme for almost every cellular reaction, multiple copies of each enzyme.
