BIOCH200 Lecture Notes - Lecture 4: Disulfide, Phosphate, Myoglobin
1 May 2018
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Introduction to Biochemistry: What are Enzymes
Enzymes
❏Biological Catalysts that speed up chemical reactions without being consumed or changed.
❏Cofactors associated with enzyme maybe changed
❏Prosthetic groups;
❏Apo-Protein without cofactor → Myoglobin without heme.
❏Holo → Protein with cofactor → Myoglobin with heme.
General Properties of Enzymes versus non-biological catalysts
❏Higher reaction rates and milder reaction conditions.
❏Greater reaction specificity
❏Capacity for regulation → conformational change in protein structure to regulate activity →
Important in cooperativity.
Extracting Energy from Glucose
❏Glucose + 6 Oxygen → 6CO2 + 6H20 (Heat all released at once)
❏Multistep pathway releases energy slowly and a little at various stages.
Enzyme Specificity
❏A+B → C + D
❏A+B are substrates/Reactants (molecules acted upon by enzyme)
❏C+D are Products
❏Reverse Reaction would mean A+B are products and C+D are reactants/substrates.
Increasing Speed of Chemical Reactions
1. Heat → Incapable of using in human cells because they denature DNA and it is not specific →
speeds up multiple reactions.
2. Add a catalyst
a. Enzymes → Globular proteins that are biological catalysts
i. Same structures as others (1,2,3 structure, some 4 structure)
ii. Structure will determine and/or stabilized by same non-covalent interactions
(hydrophobic, H-bonds, ion pairs, some disulfide bridges).
iii. There are some RNA enzymes.
How do Enzymes Work?
1. They affect reaction rates → Speed up reactions.
Energy of Bonds
1. Phosphoanhydride Bonds → 2 Phosphates → “High Energy Bonds” (more than -25kJ/mol
released) → -30KJ/mol
a. ATP and ADP have phosphoanhydride bonds → High energy molecules.
b. AMP → No phosphoanhydride bond → Not high energy.
2. Phosphoester → Phosphate + Alcohol → -15 KJ/mol → Not a High energy molecule.
What are High Energy molecules?
❏Greater than -25KJ/mol → Goes from unstable to more stable when energy released.
❏Example; ATP to ADP → Decreased electrostatic repulsion + the inorganic phosphate released
has resonance stabilization → Increases entropy (more molecules = disorder).
❏Resonance Stabilization allows for increased bond stability, and entropy that drive the
reaction forward.
❏ATP + H20 → ADP + Pi + H+ E0=-30KJ/mol
Free Energy in Biological Systems
❏Only proceed if free energy of products is less than
Document Summary
Biological catalysts that speed up chemical reactions without being consumed or changed. Apo-protein without cofactor myoglobin without heme. Holo protein with cofactor myoglobin with heme. Higher reaction rates and milder reaction conditions. Capacity for regulation conformational change in protein structure to regulate activity . Glucose + 6 oxygen 6co2 + 6h20 (heat all released at once) Multistep pathway releases energy slowly and a little at various stages. A+b are substrates/reactants (molecules acted upon by enzyme) Reverse reaction would mean a+b are products and c+d are reactants/substrates: heat incapable of using in human cells because they denature dna and it is not specific . Increasing speed of chemical reactions speeds up multiple reactions: add a catalyst, enzymes globular proteins that are biological catalysts i. ii. iii. Same structures as others (1,2,3 structure, some 4 structure) Structure will determine and/or stabilized by same non-covalent interactions (hydrophobic, h-bonds, ion pairs, some disulfide bridges).
