Biochem 4.2 Enzyme Classification and Transferase Quiz
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Questions and Answers

Which class of enzymes primarily catalyzes the transfer of phosphate groups from ATP to substrates?

  • Hydrolases
  • Oxidoreductases
  • Phosphatases
  • Kinases (correct)

What is a major limitation of early enzyme classification based on the suffix --ase?

  • It fails to describe the catalytic mechanisms accurately. (correct)
  • It does not account for enzymes with mixed functions.
  • It ignores the substrate specificity of enzymes.
  • It mistakenly groups all enzymes under one category.

Which class of enzymes is responsible for breaking apart substrates by adding a phosphate group?

  • Ligases
  • Kinases
  • Phosphatases
  • Phosphorylases (correct)

How are the major classes of enzymes organized according to the Enzyme Commission classification system?

<p>Based on their catalytic mechanisms (D)</p> Signup and view all the answers

What was added to enzyme classification in 2018?

<p>A seventh class of enzymes (D)</p> Signup and view all the answers

Which of the following is NOT a function of oxidoreductases?

<p>Aiding in phosphorylation reactions (A)</p> Signup and view all the answers

What is the main reason enzymes may have been reclassified over time?

<p>Discovery of new catalytic mechanisms (A)</p> Signup and view all the answers

Which of the following correctly matches an enzyme class with its action?

<p>Kinases - Transfer phosphate groups (D)</p> Signup and view all the answers

What is the primary function of transferase enzymes?

<p>To catalyze the transfer of a functional group between two molecules. (B)</p> Signup and view all the answers

Which of the following statements is true regarding substrates in transferase reactions?

<p>One substrate acts as a donor and the other as an acceptor. (D)</p> Signup and view all the answers

How do transferases differ from hydrolases?

<p>Hydrolases involve water as an acceptor, while transferases do not. (D)</p> Signup and view all the answers

What distinguishes acyltransferases from other transferases?

<p>They move fatty acyl groups from one molecule to another. (D)</p> Signup and view all the answers

What is a common characteristic of transferase reactions?

<p>They produce two products after the transfer of functional groups. (C)</p> Signup and view all the answers

Which of the following is NOT an example of a transferase reaction?

<p>Hydrolase catalyzing the breakdown of a triglyceride. (C)</p> Signup and view all the answers

Which functional group is commonly transferred by methyltransferases?

<p>Methyl (–CH3) groups (D)</p> Signup and view all the answers

In transferase reactions, what role does the functional group donor play?

<p>It loses a functional group and may become oxidized. (B)</p> Signup and view all the answers

What is the primary function of receptor enzymes?

<p>To bind ligands and trigger intracellular effects (C)</p> Signup and view all the answers

What happens when an agonist binds to a receptor enzyme?

<p>It activates its intracellular catalytic domain (D)</p> Signup and view all the answers

Which type of residues do receptor tyrosine kinases (RTKs) phosphorylate when activated?

<p>Tyrosine residues (B)</p> Signup and view all the answers

What is an important feature of receptor tyrosine kinases regarding their structure?

<p>They typically become dimers upon agonist binding (D)</p> Signup and view all the answers

What allows phosphotyrosine (pTyr) to act as a potent intracellular signal?

<p>Its relative scarcity makes it a unique signal (C)</p> Signup and view all the answers

What process is involved in downstream signal propagation mediated by pTyr?

<p>Recruitment and activation of downstream effectors (A)</p> Signup and view all the answers

Which two types of enzymes do most receptor enzymes belong to?

<p>Kinases and guanylyl cyclases (B)</p> Signup and view all the answers

How does the catalytic domain of receptor enzymes typically behave until an agonist binds?

<p>It is inactive (C)</p> Signup and view all the answers

What do kinases primarily transfer to a substrate molecule?

<p>γ-phosphate group from ATP (D)</p> Signup and view all the answers

What is the main function of phosphorylases in biochemical reactions?

<p>To break apart molecules using phosphate groups (C)</p> Signup and view all the answers

Which of the following is an example of a reaction catalyzed by transaminases?

<p>Transfer of an α-amine group from an amino acid (A)</p> Signup and view all the answers

In the reaction catalyzed by glycogen phosphorylase, which compound acts as the acceptor?

<p>Inorganic phosphate (Pi) (D)</p> Signup and view all the answers

Which of the following statements best describes the behavior of polymerases?

<p>They transfer nucleotides onto a growing nucleic acid chain. (A)</p> Signup and view all the answers

What is the primary difference between phosphorolysis and hydrolysis?

<p>Phosphorolysis does not involve water. (C)</p> Signup and view all the answers

Which type of enzyme is involved in transferring the γ-phosphate group in the reverse reaction of phosphorylation?

<p>Kinases (A)</p> Signup and view all the answers

Why are transaminases considered transferases even though their reactions can be considered redox reactions?

<p>Their primary function is transferring the amine group. (D)</p> Signup and view all the answers

What reaction does a mutase catalyze?

<p>Transfer of a functional group within a molecule (C)</p> Signup and view all the answers

Which of the following describes configurational isomers?

<p>They have the same molecular formula but different atom placement (C)</p> Signup and view all the answers

What is a characteristic feature of protein disulfide isomerases?

<p>They move disulfide bonds within the same molecule (D)</p> Signup and view all the answers

What type of configuration do most peptide bonds favor?

<p>Trans configuration (A)</p> Signup and view all the answers

What is the role of phosphoglycerate mutase in glycolysis?

<p>It moves a phosphate group from one carbon to another on the same molecule (A)</p> Signup and view all the answers

Which statement about aldoses and ketoses is true?

<p>Isomerases catalyze their interconversion (B)</p> Signup and view all the answers

Why can proline residues in peptide bonds exist in both cis and trans configurations?

<p>They possess a unique ring structure that allows flexibility (B)</p> Signup and view all the answers

What is a typical feature of a redox process facilitated by certain isomerases?

<p>They involve the transfer of disulfide bonds within a single molecule (B)</p> Signup and view all the answers

What type of reaction do hydrolases catalyze?

<p>Reaction that involves breaking bonds using water (A)</p> Signup and view all the answers

Which of the following statements about proteases is correct?

<p>Some proteases have common names that do not end in --ase. (C)</p> Signup and view all the answers

How can hydrolases typically be identified?

<p>By examining the chemical equations of the reactions they catalyze (B)</p> Signup and view all the answers

What differentiates polymerases from ligases?

<p>Polymerases incorporate nucleotides while ligases use them independently. (B)</p> Signup and view all the answers

Which enzyme is specifically known for hydrolyzing phosphate groups?

<p>Phosphatase (A)</p> Signup and view all the answers

Which of the following best describes the action of kinases?

<p>They add a phosphate group to substrates. (A)</p> Signup and view all the answers

What is a characteristic of most hydrolases in terms of naming?

<p>They indicate the substrate they act on also with the suffix --ase. (B)</p> Signup and view all the answers

Which reaction is an example of a hydrolysis reaction catalyzed by hydrolases?

<p>Breaking down a disaccharide into two monosaccharides. (C)</p> Signup and view all the answers

Flashcards

Enzyme Classification

Enzymes are grouped based on the type of chemical reaction they catalyze.

Kinases and Phosphatases

Enzymes ending in '-kinase' add a phosphate group to a molecule, while those ending in '-phosphatase' remove a phosphate group.

Enzyme Classification System

The Enzyme Commission created six major classes of enzymes, with a seventh class added in 2018.

Oxidoreductases

Oxidoreductases catalyze reactions involving the transfer of electrons (oxidation-reduction reactions).

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Transferases

Transferases catalyze the transfer of functional groups between molecules.

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Hydrolyases

Hydrolyases break down molecules by adding water.

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Lyases

Lyases break down molecules without adding water.

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Isomerases

Isomerases rearrange atoms within a molecule to create an isomer.

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Functional Group Donor

The molecule that donates the functional group in a transferase reaction.

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Functional Group Acceptor

The molecule that receives the functional group in a transferase reaction.

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Acyltransferases

Transferases that move fatty acyl groups from one molecule to another.

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Glycosyltransferases

Transferases that transfer carbohydrates (glycosyl groups) from one molecule to another.

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Phosphatases

Transferases that remove a phosphate group from a molecule.

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Hydrolysis vs. Transferase

Reactions involving enzymes like transferases that use water as an acceptor of a functional group are classified as hydrolysis reactions and are catalyzed by hydrolases, not transferases.

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What are kinases?

Kinases are a type of transferase that catalyzes the transfer of a phosphate group, typically from ATP, to a substrate molecule.

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What are phosphorylases?

Phosphorylases are transferases that use phosphate groups to break down molecules. This process is called phosphorolysis, similar to the way hydrolases break down molecules using water.

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What are transaminases?

Transaminases, also known as aminotransferases, are enzymes that transfer amine groups (NH2) from one molecule to another.

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What are polymerases?

Polymerases are transferases that catalyze the addition of nucleotides to a growing nucleic acid chain. DNA polymerases use dNTPs, while RNA polymerases use NTPs.

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Do kinases only work in one direction?

Kinases can also catalyze the reverse reaction, transferring a phosphate group from a substrate molecule to ADP.

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How are phosphorylases similar to hydrolases?

Phosphorylases are similar to hydrolases in their function of breaking down molecules, but they differ in their use of phosphate instead of water.

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Why are transaminases important?

Transaminases are important in amino acid metabolism, facilitating the transfer of amine groups to synthesize or breakdown amino acids.

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What is the key role of polymerases?

Polymerases play a crucial role in DNA replication and RNA transcription, ensuring the accurate copying of genetic information.

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What are transferases?

Enzymes that catalyze reactions involving the transfer of functional groups between molecules, with one molecule donating and the other accepting the functional group.

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What are phosphatases?

Enzymes that catalyze the reverse reaction of kinases, removing a phosphate group from a phosphorylated substrate.

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What are hydrolases?

Enzymes that break down molecules by using water to cleave a chemical bond.

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What are proteases?

Enzymes that break down peptide bonds between amino acids, essentially digesting proteins.

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What are hydrolysis reactions?

Reactions that involve the breaking of a bond using water to add a functional group to one of the resulting fragments.

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What are isomerases?

Enzymes that rearrange atoms within a molecule to create a new isomer.

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What are receptor enzymes?

Receptor enzymes are membrane proteins that bind extracellular ligands (signals) and activate their intracellular catalytic domain as a result. This triggers a signaling cascade within the cell.

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What are the two key domains of receptor enzymes?

They possess an extracellular binding domain for ligand interaction and an intracellular catalytic domain that acts like an enzyme.

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How are receptor enzymes activated?

Upon ligand binding, the receptor enzyme undergoes a conformational change that activates its catalytic domain. This is similar to allosteric regulation of enzymes.

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What is the common catalytic activity of receptor enzymes?

Many receptor enzymes are kinases, which transfer phosphate groups to target molecules, usually proteins. This phosphorylation often triggers a signaling cascade.

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What are receptor tyrosine kinases (RTKs)?

Receptor tyrosine kinases (RTKs) are a significant subclass of receptor kinases that specifically phosphorylate tyrosine residues on target proteins.

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Why is autophosphorylation important in RTKs?

RTKs often exist as dimers, meaning two subunits bind together. Binding of a ligand can bring these subunits closer, allowing them to phosphorylate each other.

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What is the role of phosphotyrosine in RTK signaling?

Phosphotyrosine (pTyr) acts as an intracellular signal, attracting downstream proteins that bind to it and continue the propagation of the signal.

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How is the signal propagated downstream of RTKs?

RTK signaling pathways involve a chain of events where each activated protein interacts with and activates the next, like dominos falling.

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What does phosphoglycerate mutase do?

Phosphoglycerate mutase is an enzyme that plays a key role in glycolysis. It transfers a phosphate group between the C3 and C2 positions of glyceric acid.

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What are protein disulfide isomerases?

Protein disulfide isomerases are enzymes that catalyze the movement of disulfide bonds within a protein molecule. They transfer a disulfide bond from one pair of cysteines to another pair of cysteines within the same protein.

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What are configurational isomers?

Configurational isomers are molecules that have the same atoms connected in the same order, but differ in the spatial arrangement of those atoms. It's like having two different versions of the same Lego model built with the same pieces but arranged differently.

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What are cis/trans isomers?

Cis/trans isomers occur around a double bond, where the substituents are on the same (cis) or opposite (trans) sides of the double bond.

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What are R/S isomers?

R/S isomers occur around a chiral carbon, where the substituents are arranged in a specific way (R or S configuration). It's like having a left hand and a right hand, which are mirror images of each other but can't be superimposed.

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How do peptide bonds exhibit cis/trans configuration?

Due to the partial double bond character of peptide bonds, they exhibit a cis or trans configuration with respect to the adjacent α-carbons.

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Study Notes

Enzyme Classification

  • Enzymes catalyze a wide range of biochemical reactions on various substrates, producing diverse products.
  • Enzyme classification groups enzymes based on the type of reaction they catalyze.
  • An early system named enzymes based on their reaction and added the suffix "-ase".
  • This system has limitations, as it doesn't always clearly categorize enzymes with similar reactions but different mechanisms.
  • In 1961, the Enzyme Commission classified enzymes into six major classes based on their catalytic mechanism.
  • A seventh class was added in 2018.
  • Enzyme classification is important for understanding the catalytic mechanisms of enzymes.

Oxidoreductases

  • Oxidoreductases catalyze oxidation-reduction reactions, transferring electrons between molecules.
  • These enzymes are multisubstrate, requiring both an electron donor and acceptor.
  • Redox cofactors or coenzymes (e.g., NAD+/NADH, FAD/FADH2) often change oxidation state during the reaction.
  • Crucial in many metabolic pathways.
  • The name often reflects the substrate changed.

Transferases

  • Transferases catalyze the transfer of a functional group from one molecule (donor) to another (acceptor).
  • They typically require two substrates (donor and acceptor).
  • Water cannot be the acceptor.
  • Includes kinases (transfer phosphate groups), acyltransferases (transfer fatty acyl groups) and glycosyltransferases (transfer carbohydrates).
  • Important for metabolic processes involving functional group transfer.

Hydrolases

  • Hydrolases catalyze the cleavage of a bond with the addition of water.
  • The reaction involves breaking a bond and adding water.
  • Important in many metabolic pathways for breaking down large molecules.
  • Named after the substrate or the functional group acted upon (e.g., esterases, glycosidases).

Lyases

  • Lyases catalyze the addition or removal of a functional group to/from a double bond.
  • Do not use hydrolysis or redox rxns.
  • Include mechanisms involving elimination reactions or addition across double bonds.
  • Examples include enzymes involved in, glycolysis, fumarate hydratase.

Isomerases

  • Isomerases catalyze reactions that change the structure of a single substrate without altering its net composition and type of atoms.
  • These reactions can result in constitutional or configurational isomers.
  • Examples include triose phosphate isomerase, mutases.

Ligases

  • Ligases catalyze the joining of two molecules using the hydrolysis of ATP (or other nucleoside triphosphates).
  • This reaction involves joining two molecules (synthases).
  • Important in processes requiring energy investment to create a new bond between two molecules (e.g., in DNA repair or synthesis).
  • Names frequently include "synthetase" or "ligase."

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Test your knowledge on enzyme classification, particularly focusing on transferases and their functions. This quiz covers key concepts, limitations, and updates in enzyme classification systems. Perfect for students studying biochemistry or related life sciences.

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