12 Questions
What is a characteristic of a nucleophile?
Electron rich and negatively charged
What occurs in a heterolytic cleavage reaction?
A carbanion and a hydride ion are formed
What is the term for the structure that is between the reactants and products in a nucleophilic substitution reaction?
Transition state
What is the result of oxidation in a redox reaction?
The compound loses electrons
What is the term for the addition of oxygen to a molecule in a biological system?
Oxidation
What is the term for the molecule that binds to the enzyme in a catalytic reaction?
Ligand
What type of amino acids are present in the active site of the enzyme?
Both hydrophobic and polar amino acids
What is the mechanism of acid-base catalysis?
Donation or gain of proton
Which amino acid is responsible for facilitating acid-base catalysis?
Histidine
What is the difference between specific and general acid-base catalysis?
Specific involves OH and H, while general involves other groups
What is the net result of the covalent catalysis reaction?
A–X + B → A + B–X
What is the role of the enzyme in covalent catalysis?
It forms a covalent bond with the substrate
Study Notes
Nucleophilic Substitution
- A nucleophile is electron-rich, negatively charged, and seeks electrons.
- An electrophile is electron-poor, positively charged, and seeks electrons.
- High electronegativity leads to a more stable intermediate state, but not stable enough, as electrons are shared between carbon and oxygen.
- To restabilize, electrons on oxygen move between oxygen and carbon, breaking one bond and re-establishing a double bond, and forming a leaving group.
Cleavage Reactions
- Heterolytic cleavage forms a carbanion and a hydride ion, carrying the shared electrons.
- Homolytic cleavage breaks a bond, each compound taking one electron, forming highly reactive free radicals.
Oxidation-Reduction Reactions
- Oxidation involves electron transfer, resulting in the oxidized compound losing electrons.
- Reduction involves electron gain, resulting in the reduced compound gaining electrons.
- OIL RIG: Oxidation Is Loss, Reduction Is Gain.
Biological Oxidation
- Addition of oxygen, removal of electrons, or dehydrogenation (removing hydrogen, resulting in hydride ions).
Chemical Catalysis
- Enzyme: a protein that aids chemical reactions.
- Substrate: the molecule on which the enzyme acts.
- Active site: the enzyme's binding site, containing hydrophobic amino acids and polar amino acids facilitating acid-base or covalent catalysis.
Types of Catalysis
- Acid-base catalysis: donation or gain of protons, increasing the reaction rate through catalytic proton transfer.
- Covalent catalysis: covalent bond formation between the substrate and enzyme.
Acid-Base Catalysis
- Histidine's imidazole group, with a pKa close to the solution's pH, donates/accepts protons, facilitating the reaction.
- Base catalysis removes protons, indirectly participating in bond cleavage.
- Acid catalysis involves proton donation.
Covalent Catalysis
- Substrate binds covalently to the enzyme (E), enabling covalent catalysis.
- Example: Sucrose phosphorylase facilitates the reaction sucrose + Pi → glucose-1-P + fructose.
Learn about nucleophilic substitution reactions, including the roles of nucleophiles and electrophiles, intermediate states, and transition states.
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