Test: Enzymes - Grade 12 MCQ

• Kinases, endonucleases and ligases are proteins in nature.
• They are made out of repeating units of amino acids.
• However, ribozymes are not proteins but are nucleic acids that act as enzymes.

In order to catalyze a reaction, the substrate must bind to enzyme at its active site. Following this, an enzyme-substrate complex is formed which ultimately leads to the formation of the product.

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.

Restriction endonucleases are enzymes which scan the DNA molecule for a particular nucleotide sequence. These are called recognition sequences. Once the endonuclease finds this sequence it halts and cuts the strand. Thus the correct answer is option C.

Dehydrogenases are the enzymes which catalyze oxidation-reduction reactions by addition or removal of electrons. These reactions are used to synthesize reduced coenzymes like NADH₂ and FADH₂. For example phosphoglyceraldehyde dehydrogenase.

Yes because ex, enzyme hexokinase which catalysis glucose to glucose 6 phosphate is inhibited by glucose 6 phosphate called feedback allosteric inhibitor.

Feedback inhibition is the process by where the end product terminates the reaction. The accumulation of the end product interferes with the enzymatic activity by changing the shape of its active site. On changing the shape of the active site, the substrate does not attach to the active site and thus the reaction terminates. During glycolysis, the glucose changes to glucose 6 phosphates in presence of hexokinase. When the amount of glucose 6 phosphate exceeds it deactivate hexokinase.

So, the correct answer is option B.

Proteins that are enzymes form only a subset of the total protein population. Non-enzymatic proteins include structural proteins and receptors, among others.

While most enzymes are indeed proteins, there are some that are not. These are the enzymatic RNAs, also known as ribozymes.

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

• Definition: Isoenzymes are multiple forms of enzymes that catalyze the same reaction but have slightly different amino acid sequences and structures.



• Function: Despite their structural differences, isoenzymes perform the same biological function in the body.



• Examples: Examples of isoenzymes include lactate dehydrogenase, which has different forms in different tissues, and creatine kinase, which has different forms in muscle and brain tissue.



• Diagnostic Use: Isoenzymes are often used in clinical diagnostics to identify specific diseases or conditions. For example, measuring different forms of enzymes in the blood can help diagnose heart attacks or liver disease.



• Regulation: Isoenzymes can be regulated differently in response to various stimuli or conditions in the body, allowing for fine-tuning of metabolic pathways.

• Enzymes are primarily made of proteins: Enzymes are biological molecules that act as catalysts, speeding up chemical reactions in living organisms. The vast majority of enzymes are proteins, which are made up of long chains of amino acids.


• Proteins are composed of amino acids: Amino acids are the building blocks of proteins. There are 20 different amino acids that can be combined in various sequences to form a wide variety of proteins, including enzymes.


• Unique structure of enzymes: Enzymes have a unique three-dimensional structure that allows them to bind to specific molecules, called substrates, and facilitate chemical reactions. This structure is crucial for the function of enzymes in biological systems.


• Other components: While proteins are the main component of enzymes, they may also contain non-protein components such as cofactors or coenzymes that are necessary for their function. These additional components help enzymes catalyze reactions efficiently.

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.

Hydrolases are the enzymes which break large molecules into smaller ones with the help of hydrogen and hydroxyl groups of water molecules, this phenomenon is known as hydrolysis. Amylase is the enzyme produced by the salivary gland and is found in saliva. It breaks starch into glucose. Thus, the correct answer is A.

A competitive inhibitor is one which competes with the substrate molecules for the active site of the enzyme. Competitive inhibitor resembles the natural substrate and combines reversibly to the free enzyme at the active site. This results in the competition between the substrate and inhibitor for the active site of the enzyme. Malonate inhibits succinate dehydrogenase activity. The structure of malonate is similar to succinate. This is an example of competitive inhibition. 
Thus, the correct answer is option C.

• Enzymes are organic catalysts or biocatalysts.
• However, inorganic catalysts work at high temperatures and high pressures efficiently.
• Enzymes, being proteinaceous in nature, get denatured under such conditions.