Med’11 Biochemistry Enzymes
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| What are enzymes? | Biological catalysts
They permit reactions to “go” at conditions that the body can tolerate and can process millions of molecules every second
They are very specific – react with one or only a few types of molecules (substrates)
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| How do enzymes increase the reaction rates? | By providing an alternate, easier pathway for a reaction and lowering activation energy barrier
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| What is the transition state? | Unstable arrangement of atoms in which chemical bonds are in the process of being formed or broken
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| Define activation energy. | The energy required to reach the transition state from the ground state of the reactants
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| Formation of ES (raises/lessens) energy of S by bringing reactants together? | Raises
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| Enzymes _____ the transition state. | Stabilize
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| What is a prosthetic group? | Coenzyme or cofactor covalently linked or bound non-covalently very tightly to an enzyme
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| What is a substrate? | The molecule acted upon by the enzyme to form product
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| What is the product? | The substance that is produced by the action of the enzyme
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| What is an apoenzyme? | The protein portion of the enzyme which is catalytically inactive
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| What is a coenzyme? | An additional component to the enzyme to function properly .
Organic or organo-metallic molecule that assists an enzyme
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| What is a cofactor? | An additional component to the enzyme to function properly
Usually a metal ion or small organic molecule that is needed to activate the apoenzyme
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| What is an active site? | A particular arrangement of amino acids side-chain in the polypeptide, specific to bind a specific substrate, also contains the machinery involved in catalyzing the reaction
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| True or False: Enzymes are huge proteins, and all of the enzyme is used in the reaction. | False - Only a small part is involved in the reaction
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| What are the 2 components of the active site? | Binding Site
Catalytic Site
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| Enzymes are biological catalysts. They increase the rate of chemical reactions by: A. Raising the activation energy B. Temporarily increasing the temperature C. Covalently binding the substrate D. Lowering the activation energy | D Lowering the activation energy
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| What is a holoenzyme? | Holoenzyme: The apoenzyme + cofactor or prosthetic group
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| What is a proenzyme (zymogen)? | inactive precursor form of some enzymes (e.g. many digestive enzymes) that will be activated by cleavage of a specific peptide in its structure
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| What is an allosteric site? | A region of enzyme molecules (not at the active site) where small molecules bind & effect a change in the activity of the active site by change in the conformation of the enzyme.
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| Compare between enzymes and inorganic catalysts their natures. | Enzymes: Proteins
Inorganic Catalysts: Usually metals
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| Compare between enzymes and inorganic catalysts their effects of heat. | Enzymes: Heat labile
Inorganic Catalysts: Heat stable
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| Compare between enzymes and inorganic catalysts their molecular weights. | Enzymes: High
Inorganic Catalysts: Low
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| Compare between enzymes and inorganic catalysts their dialysis. | Enzymes: Non-dialysable
Inorganic Catalysts: Dialyasble
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| Compare between enzymes and inorganic catalysts their reversibility. | Enzymes: Most reactions are reversible
Inorganic Catalysts: Irreversible
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| Compare between enzymes and inorganic catalysts their specificity. | Enzymes: All highly specific
Inorganic Catalysts: Non-specific
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| What is the nomenclature of enzymes based on? | How it reacts
Add –ase ending
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| What is the basis of enzyme classification? | Based on type of reaction
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| What are the different classifications of enzymes? | Lyases break C-O, C-C or C-N bonds
Isomerases rearrange functional groups
Ligases join two molecules
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| What are the types of enzyme specificity? | Absolute -Reacts with a single substrate
Relative (linkage) specificity-Catalyze a specific combination of bonds
Group specificity-Work with similar molecules with the same functional grp
Stereochemical specificity-Work with the proper D- or L
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| What is a ribozyme? | RNA enzyme
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| List the activities of ribozymes. | Cleavage and rejoining of oligonucleotide substrate
Cleavage of DNA phosphodiester bonds
Cleavage of RNA at sequence-specific sites
Hydrolysis of esters
Formation of peptide bonds between amino acid
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