Biochemistry MCQ Quiz - Objective Question with Answer for Biochemistry - Download Free PDF

The correct answer is Apoenzyme

Explanation:

• Enzymes are biological catalysts that speed up chemical reactions in living organisms without being consumed in the process.
• Enzymes are composed of two main parts: the protein portion and the non-protein portion.
• The protein portion of an enzyme is called an Apoenzyme, and it is inactive by itself.
• The non-protein part, which can either be a cofactor or coenzyme, binds to the apoenzyme to form an active enzyme known as a holoenzyme.

Holoenzyme = Apoenzyme + Coenzyme

Additional InformationCofactors are non-protein chemical compounds or metallic ions that are required for an enzyme's biological activity to occur. Cofactors can be broadly categorized into three main types:-

• Prosthetic Groups: Tightly bound, integral to the enzyme (Haem, FAD, Biotin).
• Coenzymes: Loosely bound, temporary carriers (NAD+, Coenzyme A, TPP).
• Metal Ions: Can be loosely or tightly bound, involved in structural and catalytic roles (Zinc, Magnesium, Iron).

• The protein portion of an enzyme, without its cofactor, is called an apoenzyme. It is inactive until the cofactor binds to it.

The correct answer is A-III, B-II, C-I, D-IV

Concept:

• Nucleoside is a compound formed by the union of a nitrogen base with a pentose sugar. It is a component of nucleotide.
• Each nucleotide is composed of three smaller units; a nitrogen base, a pentose sugar and a phosphate group

Explanation:

• A. Adenosine - III. Nucleoside: Adenosine is composed of adenine attached to a ribose sugar, making it a nucleoside.
• B. Adenylic acid - II. Nucleotide: Adenylic acid, also known as adenosine monophosphate (AMP), consists of three components: adenine (a nitrogenous base), ribose (a sugar), and a phosphate group.

• C. Adenine - I. Nitrogen base: Adenine is one of the nitrogenous bases found in DNA and RNA.

• D. Alanine - IV. Amino acid: Alanine is an amino acid used in the biosynthesis of proteins.

The correct answer is Catalase

Concept:

Cofactors are non-protein chemical compounds or metallic ions that are required for an enzyme's biological activity to occur. Cofactors can be broadly categorized into three main types:-

• Prosthetic Groups: Tightly bound, integral to the enzyme (Haem, FAD, Biotin).
• Coenzymes: Loosely bound, temporary carriers (NAD+, Coenzyme A, TPP).
• Metal Ions: Can be loosely or tightly bound, involved in structural and catalytic roles (Zinc, Magnesium, Iron).

Explanation:

Catalase:

• Catalase is an enzyme that contains haem as its prosthetic group.
• It plays a critical role in protecting cells from oxidative damage by decomposing hydrogen peroxide (H₂O₂).
• The haem group in catalase contains iron, which is essential for the enzyme's catalytic activity.
• The reaction catalyzed by catalase is:
  2H₂O₂ → 2H₂O + O₂
• This enzyme is highly efficient and critical for maintaining cellular health in aerobic organisms.

Other Options:

RuBisCo:

• RuBisCo (Ribulose-1,5-bisphosphate carboxylase-oxygenase) is a key enzyme involved in the Calvin cycle of photosynthesis.
• It catalyzes the fixation of carbon dioxide (CO₂) into organic compounds in plants.
• It does not contain haem; instead, it is a protein enzyme with no metalloprotein or haem group association.

Carbonic anhydrase:

• This enzyme catalyzes the reversible conversion of carbon dioxide (CO₂) and water (H₂O) into carbonic acid (H₂CO₃), which then dissociates into bicarbonate (HCO₃⁻) and protons (H⁺).
• It contains zinc (Zn²⁺) as a cofactor

Succinate dehydrogenase:

• This enzyme is part of the citric acid cycle (Krebs cycle) and the electron transport chain in mitochondria.
• It facilitates the oxidation of succinate to fumarate and contains iron-sulfur clusters and FAD (flavin adenine dinucleotide) as cofactors.

The correct answer is Transferase

Explanation:

Enzymes are divided into 6 classes each with 4-13 subclasses and named accordingly by a four-digit number.

• Transferases: Enzymes catalysing a transfer of a group, G (other than hydrogen) between a pair of substrate S and S’

S - G + S' → S + S' - G

• Hydrolases: Enzymes catalysing hydrolysis of ester, ether, peptide, glycosidic, C-C, C-halide or P-N bonds.
• Oxidoreductases/dehydrogenases: Enzymes which catalyse oxidoreduction between two substrates S and S’.
• Lyases: Enzymes that catalyse removal of groups from substrates by mechanisms other than hydrolysis leaving double bonds.
• Isomerases: Includes all enzymes catalysing inter-conversion of optical, geometric or positional isomers.
• Ligases: Enzymes catalysing the linking together of 2 compounds, e.g., enzymes which catalyse joining of C-O, C-S, C-N, P-O etc. bonds

The correct answer is All of the above

Concept:

• Non-protein constituents called co-factors are bound to the enzyme to make the enzyme catalytically active. The protein portion of the enzymes is called the apoenzyme.
• Three kinds of cofactors may be identified: prosthetic groups, co-enzymes and metal ions.

Explanation:

• Prosthetic groups are organic compounds and are distinguished from other cofactors in that they are tightly bound to the apoenzyme.
  • For example, in peroxidase and catalase, which catalyze the breakdown of hydrogen peroxide to water and oxygen, haem is the prosthetic group and it is a part of the active site of the enzyme.
• Co-enzymes are also organic compounds but their association with the apoenzyme is only transient, usually occurring during the course of catalysis.
• A number of enzymes require metal ions for their activity which form coordination bonds with side chains at the active site and at the same time form one or more coordination bonds with the substrate, e.g., zinc is a cofactor for the proteolytic enzyme carboxypeptidase

The correct answer is Primary Metabolites.

Key Points

• Metabolite is an intermediate or end product of metabolism
• They are the intermediate products produced during metabolism, catalyzed by various enzymes that occur naturally within cells
• The term metabolites are usually used for small molecules
• Functions of metabolites include; fuel, structure, signaling, catalytic activity, defense and interactions with other organisms.
• Metabolites are of two types:

1. Primary Metabolites
   • Chemical compounds produced during the growth and development processes
   • Required for growth and maintenance of cellular function
   • Same in every species because they are a part of basic cellular function occurring in all organisms
   • Involved in the primary metabolic processes of respiration and photosynthesis
   • They maintain the physiological functions of the body and are known as central metabolites
   • Produced at the growth phase
   • They are the intermediate products of anabolic metabolism, which are used by the cells for the formation of essential macromolecules
   • Produced in large amounts and easy to extract
   • e.g., Amino acids, vitamins, organic acids, carbohydrates
2. Secondary Metabolites
   • These compounds are produced by the organisms that are not required for primary metabolic processes
   • Secondary metabolites are considered to be the end products of primary metabolites
   • Involved in ecological functions
   • Produced at the stationary phase
   • Produced in small amounts and difficult to extract
   • Different in every species
   • e.g., Phenolics, steroids, antibiotics, pigments

The correct answer is Proteins.

Key Points

•  Proteins are known as bodybuilding food as they are essential for muscle growth and repair.
•  They contain amino acids that help in building and repairing muscles after a workout.
•  Protein-rich foods include chicken, fish, eggs, beans, lentils, and dairy products.
• Proteins are needed for the growth and repair of our body.
• Food containing proteins is called bodybuilding food.
• Examples of food rich in protein are beans, dal, meat, soybean.

Additional Information

•   Fats are important for providing energy and insulation to the body, but excessive fat consumption can lead to weight gain and health issues.
•  Carbohydrates are the primary source of energy for the body and are important for athletes, but too much carbohydrate consumption can lead to weight gain and insulin resistance.
• Vitamins are essential for overall health and well-being, but they do not directly contribute to muscle growth or repair. However, certain vitamins such as vitamin D and B12 can help in the absorption of protein and aid in muscle recovery.

The correct answer is option 2.

Key Points

Deoxyribonucleic Acid (DNA):

• It is an organic chemical of complex molecular structure that is found in all prokaryotic and eukaryotic cells and in many viruses. Hence statement 1 is correct.
• DNA codes genetic information for the transmission of inherited traits. Hence statement 3 is correct.
• The DNA molecule consists of two strands that wind around one another to form a shape known as a double helix. Hence statement 2 is incorrect.
• Each strand has a backbone made of alternating sugar (deoxyribose) and phosphate groups. Hence statement 4 is correct.
• Attached to each sugar is one of four bases--adenine (A), cytosine (C), guanine (G), and thymine (T).

Ribonucleic acid (RNA):

• Ribonucleic acid (RNA) is a molecule similar to DNA. 
• While the structure of DNA is a double-helix in eukaryotic cells, RNA is typically single-stranded and comes in various forms.
• The single-stranded structure of RNA allows this molecule to fold back on itself and form various stable secondary structures as necessary. 

The correct answer is Polyphenol oxidase

Key Points

• ​Polyphenol oxidases (PPOs) are a group of copper-containing enzymes that catalyze the o-hydroxylation of monophenols to o-diphenols 
•  any of several copper-containing enzymes (as laccase) that catalyze the oxidation especially of diphenols and polyphenols to quinones — compare phenol oxidase , tyrosinase.
• ​Polyphenol oxidases also known as tyrosinase, phenolase, catechol oxidase, monophenol oxidase, creso-lase, and catecholase, was first discovered in 1856 by Schoenbein (1856) in mushrooms.​​

Additional Information

• Bromelain
  • It is a group of enzymes found in the fruit and stem of the pineapple plant. Pineapple is native to the Americas but is now grown throughout the world in tropical and subtropical regions. 
•  Serrapeptase
  • ​It is used for conditions such as back pain, osteoarthritis, and rheumatoid arthritis, and for conditions generally associated with pain and swelling (inflammation), but there is no good evidence to support these uses..
• Papain
  • It is an enzyme found in the white fluid (latex) that occurs in raw papaya fruit. It is a protease, meaning it breaks down proteins. Papain contains substances that might help fight infection and heal wounds.

Concept:

• Nucleic acids are complex organic molecules with high molecular weights.
• Found in every living cell, nucleic acids play an important role in hereditary.
• There are two types: DNA and RNA.

Explanation:

Deoxyribonucleic acid (DNA):

• DNA is the genetic material found in nature along with RNA.
• DNA is responsible for the hereditary characteristics of an individual.
• A DNA molecule is made up of several nucleotides.
• Each nucleotide is made up of 3 parts:
  • A phosphate group
  • A 5-Carbon sugar - Deoxyribose in DNA and Ribose in RNA
  • A nitrogenous base.
• The pentose sugar is linked to a nitrogenous base which in turn is linked to the phosphate group.
• A phosphodiester linkage forms the backbone of a DNA molecule.
• It is a linkage between the 3'  carbon atom of a sugar molecule with the 5' carbon atom of another sugar molecule.

​

From the above-given information, the correct answer is option 2, Phosphodiester bonds.

Additional Information

•  Glycosidic Bonds: Glycosidic bonds are covalent bonds that are found between a carbohydrate and another group such as a different sugar group.
• Peptide bonds: Peptide bonds are covalent bonds that are formed between the carboxyl group of one amino acid and the amino group of another amino acid.
• Hydrogen bonds: Hydrogen bonds are weak bonds that are formed between a proton of one molecule and an electronegative atom of another by electrostatic attraction.

The correct answer is All of these

Concept:

• DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms and many viruses.
• The DNA chain is composed of nucleotides, each containing a phosphate group, a sugar molecule (deoxyribose), and a nitrogenous base.

Explanation:

• Phosphodiester Bond:
  • This type of bond forms the backbone of the DNA strand.
  • It connects the 5'-phosphate group of one nucleotide to the 3'-hydroxyl group of another nucleotide, creating a strong covalent linkage.
• Hydrogen Bond:
  • DNA is a double-stranded helical molecule. The two strands are complementary and anti-parallel.
  • The hydrogen bonds between the paired bases (A-T and G-C), repeated along the length of the DNA double helix, hold the two strands together in the double helix.
  • There are two hydrogen bonds between Adenine and Thymine base pair, whereas, there are three hydrogen bonds between Guanine and Cytosine base pair.

• Glycosidic Bond: This type of bond connects the nitrogenous base to the sugar molecule (deoxyribose) in a nucleotide.

Concept: 

• A nucleosome is a section of DNA that is wrapped around a core of proteins (histones).

• Nucleosomes are known as the fundamental subunit of chromatin.

• On the extension of chromatin under a microscope, the structure resembles beads on a string. 

​

Explanation: 

Statement a: 

Euchromatin is the loosely packed chromatin region. These are active during transcription.

Statement b:     

• Heterochromatin is transcriptionally inactive. 
• The tight packing makes them inaccessible to the protein involved in gene expression.
• They don't undergo crossing over.

Statement c:

• A nucleosome consists of DNA wrapped around a set of eight proteins called histones, which are known as histone octamer.
• Histone octamer is composed of two copies of each of the histone proteins H₂A, H₂B, H₃, and H₄.

• The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called a nucleosome.

Statement d: 

• Histones are rich in basic amino acid residues lysine and arginine.

Statement e: 

• A typical nucleosome contains 200 bp of DNA helix.
• Therefore option 3 is correct as it has the correct set of statements, i.e., statements a, c and d.

So, the correct answer is option 3.

The correct answer is Alanine.

Concept:

• An amino acid is a biomolecule that combines to form proteins.
• Amino acids are organic compounds with a carbon side chain, an amino group, and a hydroxyl group.
• All amino acids have the same fundamental structure, however, their carbon side chains differ.

Explanation:

Amino acids can be classified into three groups, namely essential amino acids, and nonessential amino acids.

Essential Amino Acids: 

• Amino acids which cannot be synthesized or produced by the body and are required from food supplements are called essential amino acids.
• There are 9 essential amino acids that include
  • Leucine,
  • Isoleucine,
  • Histidine,
  • Iysine,
  • Methionine,
  • Threonine,
  • Phenylalanine,
  • Tryptophan, and
  • Valine.

Non-Essential Amino Acids:

• Amino acids which are produced or synthesized by our bodies and are not taken up as food supplements are called nonessential amino acids.
• The non-essential amino acids are
  • Arginine,
  • Alanine,
  • Aspartic acid,
  • Asparagine,
  • Cysteine,
  • Glutamine,
  • Glutamic acid,
  • Proline,
  • Glycine,
  • Serine, and
  • Tyrosine.
• Without these amino acids, our body will find it hard to make up the proteins it needs which are required for the repair, growth, and maintenance of cells.

Key Points

• The first hormone discovered was a substance named secretin: CORRECT
  • The first hormone was discovered by English physician E.H. Starling in collaboration with physiologist W.M. Bayliss in 1902, while studying pancreatic secretions.
  • It was named secretin.
• The adrenal cortex arises from endoderm: INCORRECT
  • The adrenal gland has 2 parts: outer cortex and inner medulla.
  • The 2 layers originate from 2 different germinal layers.
  • Adrenal cortex arises from mesoderm, while adrenal medulla arises from ectoderm.
• Angiotensin II stimulates vasoconstriction, causing rise in blood pressure: CORRECT
  • Angiotensin II is a peptide hormone that plays an important role in the regulation of kidney function.
  • It is a part of the renin-angiotensin-aldosterone system or RAAS system.
  • Renin is released from the juxta-glomerular (JG) cells of the kidney.
  • It converts angiotensinogen to angiotensin I, which is further converted to angiotensin II.
  • Angiotensin II acts as a vasoconstrictor, causing increase in glomerular blood pressure.
  • It also stimulates the adrenal cortex to release aldosterone.
  • Aldosterone helps in reabsorption of Na⁺ and water, which also leads to an increase in blood pressure.
•  The posterior lobe of pituitary gland arises from pharyngeal epithelium as an invagination called Rathke's pouch: INCORRECT
  • The anterior and posterior lobes of pituitary gland have different embryological origins.
  • The posterior lobe or neurohypophysis arises from a finger-like evagination of the neural ectoderm growing downwards from the developing diencephalon.
  • The anterior lobe or adenohypophysis arises from the Rathke's pouch which is an upward protrusion of the ectoderm from the roof of the mouth.
  • Both the tissues grow into each other and get closely associated to function as the pituitary gland.
• Therefore, statements (a) and (c) are correct, as given in option 3.

The correct answer is glycogen.Key Points

• Carbohydrates are the primary source of energy for the body, and they are stored in the form of glycogen.
• Glycogen is a complex carbohydrate that is made up of many glucose molecules linked together in a highly branched structure.
• Glycogen is the main storage form of glucose in the body, and it is broken down into glucose when the body needs energy.
• Most glycogen in humans is stored in the liver and skeletal muscles.

Additional Information

• Amylopectin is a highly branched polysaccharide that is found in plants, particularly in starchy foods like potatoes, corn, and rice.
  • It is a type of complex carbohydrate that is broken down into glucose for energy.
• Amylose is also a polysaccharide found in plants, but it is a linear chain of glucose molecules rather than a branched structure like amylopectin.
  • It is also broken down into glucose for energy.
• Collagen is a fibrous protein that provides strength and elasticity to tissues in the body.
  • It is the most abundant protein in the body and is found in skin, bones, tendons, ligaments, and cartilage.
  • It is not a carbohydrate and is not used for energy.