All questions of Enzymes (BC, BIO) for MCAT Exam

Adenosine triphosphate, also known as molecular unit of currency, is a coenzyme of vast importance in the transfer of chemical energy derived from biochemical oxidations and it also transports energy within cells for metabolism. Thus, option 'B' is the right answer.

Restriction Endonucleases are enzyme which scan DNA molecules for a particular nucleotide sequence. These are called Recognition Sequences.Once the Endonuclease finds this sequence it halts ans cuts the strand.Thus,the correct option is "C".

A lysosome is a membrane-bound organelle found in nearly all animal cells. They are spherical vesicles that contain hydrolytic enzymes that can break down many kinds of biomolecules.

Transaminase are the enzymes concerned with transfer of atoms or group of atoms or electrons.. so, option B is correct not A

Hydrolase are the enzyme which breaks down the large molecules into smaller ones with the help of hydrogen and hydroxyl groups of water molecule this phenomena is known as hydrolysis. Amylase is the enzyme produced by the salivary gland and helps in breaking down the starch into glucose. Amylase catalysis the hydrolysis of starch into sugar (glucose).
Amylase is also found in germinating seeds.

Enzymes with slightly different molecular structure but performing identical activity are called isoenzymes.

Explanation:
Enzymes are biological catalysts that facilitate and speed up biochemical reactions in living organisms. They are usually proteins with a specific three-dimensional structure that allows them to bind to specific substrates and convert them into products. However, enzymes can also have slightly different molecular structures while performing the same catalytic activity. These enzymes are called isoenzymes.

Definition of Isoenzymes:
Isoenzymes, also known as isozymes, are enzymes that catalyze the same chemical reaction but have slightly different amino acid sequences or molecular structures. They are encoded by different genes but perform identical functions in the same organism or different tissues. Isoenzymes are often found in multiple forms and can be distinguished from each other through various methods such as electrophoresis or immunoassay.

Reasons for Different Molecular Structures:
1. Genetic Differences: Isoenzymes are encoded by different genes, which can result in variations in the amino acid sequence and overall structure of the enzyme.
2. Post-translational Modifications: Isoenzymes may undergo different post-translational modifications, such as phosphorylation or glycosylation, which can alter their structure and function.
3. Tissue-Specific Expression: Different tissues within an organism may require slightly different versions of an enzyme to perform the same activity optimally. These tissue-specific isoenzymes may have distinct molecular structures.

Importance of Isoenzymes:
1. Diagnostic Tool: Isoenzymes can be used as diagnostic markers for certain diseases or conditions. For example, the measurement of different forms of creatine kinase isoenzymes can help diagnose heart attacks.
2. Tissue-Specific Function: Isoenzymes may have different kinetic properties or substrate specificities, allowing them to perform specialized functions in specific tissues.
3. Evolutionary Adaptation: Isoenzymes can evolve to perform similar functions under different conditions or in different organisms, allowing for adaptation and survival in diverse environments.

In conclusion, isoenzymes refer to enzymes with slightly different molecular structures but identical catalytic activities. They play important roles in various biological processes and have diagnostic and evolutionary significance.

Explanation:

Enzymes are biological catalysts that speed up chemical reactions in living organisms. They are typically protein molecules, but there are exceptions.

Ribozymes
Ribozymes are RNA molecules that exhibit catalytic activity. Unlike most enzymes, which are proteinaceous, ribozymes are composed of RNA. They were first discovered in the 1980s and have since been found to play important roles in various biological processes. Ribozymes can catalyze a wide range of reactions, including cleavage, ligation, and isomerization reactions.

Endonucleases
Endonucleases are enzymes that cleave the phosphodiester bonds within a nucleic acid chain. They are involved in processes such as DNA replication, repair, recombination, and transcription. Endonucleases can be either proteinaceous or ribozymes.

Ligases
Ligases are enzymes that catalyze the joining of two molecules by forming a new chemical bond, usually in the presence of ATP. They are involved in DNA repair, DNA replication, and the synthesis of RNA and proteins. Ligases are proteinaceous enzymes.

Kinases
Kinases are enzymes that catalyze the transfer of a phosphate group from ATP to a substrate molecule, a process known as phosphorylation. This phosphorylation can regulate the activity of the substrate molecule. Kinases are proteinaceous enzymes.

Conclusion
Among the enzymes listed, ribozymes are not proteinaceous. Ribozymes are RNA molecules that exhibit catalytic activity and can perform a wide range of enzymatic reactions. This discovery challenged the long-held belief that all enzymes are proteinaceous. Ribozymes have since been found to play important roles in various biological processes, contributing to our understanding of the diversity and complexity of enzymatic reactions in living organisms.

 Coenzyme is an organic nonprotein molecule that associates with an enzyme molecule in catalsying biochemical reactions. It usually participates in the substrate-enzyme interaction by donating or accepting certain chemical groups.                            Holoenzyme is a complex comprising of enzyme molecule and its cofactor. The enzyme is catalytically active in this state.      Apoenzyme is an inactive enzyme that must associate with a specific cofactor molecule in order to function.                           Isoenzyme or isozyme is one of the several forms of an enzyme that catalyse the same reaction but differ from each other in such properties as substrate affinity and maximum rates of enzyme-substrate reaction.

It's protein

Active site:
The substrate fits into the active site of an enzyme. The active site is a specific region on the enzyme where the substrate binds and undergoes a chemical reaction. This site has a unique shape and chemical properties that complement the structure of the substrate molecule.

Key points:
- The active site is like a lock and key, where the substrate (key) fits into the active site (lock) with precision.
- The active site provides a microenvironment that is conducive to the chemical reaction between the enzyme and substrate.
- The binding of the substrate to the active site induces a conformational change in the enzyme, which helps facilitate the reaction.
- The active site may contain specific amino acid residues that directly participate in the catalytic process.
In conclusion, the substrate fits into the active site of an enzyme, where it undergoes a chemical reaction facilitated by the enzyme's specific structure and properties.

Oxygenases can be classified as either monooxygenases or dioxygenases.

• Monooxygenases incorporate one atom of an oxygen molecule into the substrate.
• Dioxygenases incorporate both atoms of an oxygen molecule into the substrate.

Phase 1 xenobiotic reactions, particularly hydroxylation, are primarily catalysed by a group of enzymes known as monooxygenases or cytochrome P450s.

Reversible covalent modifications include

• Phosphorylation
• Dephosphorylation
• ADP Ribosylation
• Methylation
• Acetylation

Irreversible covalent modifications consist of

• Zymogen activation
• Partial proteolysis

B. coenzyme

Coenzyme is an organic nonprotein molecule that associates with an enzymes molecule in catalysing biochemical reactions. It usually participates in the substrate-enzyme interaction by donating or accepting certain chemical groups.
Apoenzyme is an inactive enzyme that must associate with a specific cofactor molecule in order to function.
Isoenzyme or isozyme is one of the several forms of an enzyme that catalyse the same reaction but differ from each other in such properties as substrate affinity and maximum rates of enzymes-substrate reaction.

Zymogen activation represents a case of irreversible covalent alteration.

Induction refers to the process of regulating the amount of enzymes. The regulation of enzymes can be categorised into:

• Regulation of Enzyme Quality (Intrinsic Catalytic Efficiency)
• Allosteric Regulation
• Covalent Modification

Covalent modification includes:

• Phosphorylation/dephosphorylation (the most prevalent covalent modification)
• Methylation
• Adenylation
• ADP ribosylation
• Acetylation

The regulation of enzyme quantity involves:

• Control of Enzyme Synthesis through Induction and Repression
• Control of Enzyme Degradation

Enzymes are broken down via the Ubiquitin-Proteasome pathway.

Yes option B is correct

when the end products levels are more,products will bind to enzymes and reduces its activity.After the body utilises products and the level decreases and becomes zero means then enzymes become free from inhibitors(products) and then again the enzymes catalyse the reaction and form products

Oxidoreductases can include:

• Dehydrogenase
• Oxygenase
• Monooxygenase
• Dioxygenase
• Oxidase
• Catalase
• Peroxidase

Dehydrogenases facilitate the removal of hydrogen from the substrate. They do not utilise oxygen as a hydrogen acceptor. Oxidases remove hydrogen from a substrate with oxygen acting as the hydrogen acceptor, including:

• Monoamine Oxidase
• Cytochrome Oxidase
• Xanthine Oxidase

Oxygenases catalyse the direct transfer and incorporation of oxygen into a substrate molecule. Monooxygenases, also known as Mixed Function Oxidases or Hydroxylases, integrate one atom of molecular oxygen into the substrate, such as:

• Phenylalanine Hydroxylases
• 7 alpha Hydroxylases
• Cytochrome p450

Dioxygenases incorporate both atoms of molecular oxygen into the substrate. The fundamental reaction is represented below:

• A + O₂ → AO₂

Examples of dioxygenases include:

• Homogentisate oxidase
• Tryptophan Pyrrolase (Dioxygenase)
• Nitric Oxide Synthase

Cyclooxygenase is referred to as a 'suicide enzyme.' The deactivation of prostaglandin activity is partially due to an exceptional characteristic of cyclooxygenase, which is its ability for self-catalysed destruction; in other words, it acts as a 'suicide enzyme.' Quick overview of cyclooxygenase:

• Cyclooxygenase (COX), also known as prostaglandin H synthase
• Plays a role in the synthesis of prostanoids (prostaglandins, thromboxane, and prostacyclin)
• Exhibits two activities: cyclooxygenase and peroxidase
• Exists as two isoenzymes: COX-1 and COX-2

Drugs that act as inhibitors of COX include:

• NSAIDs:
  • Aspirin: Inhibits both COX-1 and COX-2
  • Indomethacin and ibuprofen: Inhibit cyclooxygenases by competing with arachidonate
• Coxibs: Selectively inhibit COX-2; however, some have been withdrawn or suspended from the market due to adverse side effects and safety concerns

Anti-inflammatory corticosteroids:

• Completely inhibit the transcription of COX-2, but not COX-1