Chemistry
39 Solved Past Papers
2010 – 2024 Archives
Macromolecules / Biochemistry Past Papers
Solved past paper MCQs for Macromolecules / Biochemistry from official UHS, NUMS, SZABMU, DUHS, and KMU examinations. Includes verified distractor autopsies and step-by-step cognitive explanations.
Boards Included:BUMHSETEAMDCATPMCSZABMUUHS
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[SZABMU-RC 2024] Based on function thyroxin can be classified as
A
Structural protein
B
Hormonal protein
C
Genetic protein
D
Transport protein
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Correct Key: Option BDiagnostic Explanation
Concept:
Thyroxin is an amino acid derivative acting as a systemic chemical messenger.
Formula:
$$N/A$$
Solution:
Thyroxin (T4) is secreted into the blood by the thyroid gland to regulate basal metabolic rate.
Because its physiological role is entirely regulatory and acts at distant target tissues, it is functionally classified as a hormonal protein (or hormonal derivative).
Why other options are incorrect:
It is not used to build tissues (structural), it doesn't ferry other molecules in the blood (transport), and it is not a histone involved in DNA packing (genetic).
[ETEA 2024] Protein present in haemoglobin has ____ structure.
A
Primary
B
Tertiary
C
Secondary
D
Quaternary
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Correct Key: Option DDiagnostic Explanation
Concept:
Proteins that consist of multiple distinct polypeptide subunits aggregated together exhibit the highest level of protein structure.
Formula:
$$ \alpha_2\beta_2 $$
Solution:
Hemoglobin is composed of four individual polypeptide chains (two \( \alpha \)-globins and two \( \beta \)-globins in adults).
These four separate subunits bind together via non-covalent interactions to form a single functional, multimeric protein complex.
This aggregation of multiple independent polypeptide chains constitutes a quaternary structure.
Why other options are incorrect:
While hemoglobin contains primary, secondary, and tertiary structures within its individual subunits, the overarching functional structure of the complete, native protein is quaternary.
[ETEA 2024] In competitive inhibition, the inhibitor
A
Competes with enzyme
B
Binds with substrate
C
Irreversibly binds with enzyme
D
Competes with substrate
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Correct Key: Option DDiagnostic Explanation
Concept:
In competitive inhibition, the inhibitor possesses a molecular geometry and charge distribution closely resembling the natural substrate.
Solution:
Because of structural similarity, the inhibitor competes with the substrate for occupancy of the enzyme's catalytic active site.
When the inhibitor occupies the active site, the actual substrate is prevented from binding, forming an Enzyme-Inhibitor (\(\text{EI}\)) complex.
Competitive inhibition is reversible and can be overcome by increasing substrate concentration (\([S]\)), which increases \(K_m\) while keeping \(V_{max}\) unchanged.
Therefore, the inhibitor competes with substrate.
Why other options are incorrect:
A (Competes with enzyme): Incorrect; the inhibitor binds to the enzyme rather than competing against it.
B (Binds with substrate): The inhibitor interacts directly with the enzyme's active site, not with the substrate.
C (Irreversibly binds with enzyme): Competitive inhibition is reversible via mass action; irreversible inhibitors bind permanently via covalent bonds (e.g., nerve gases, cyanide).
The erythrocytes (red blood cells) are packed with a specialized iron-containing protein called hemoglobin.
Hemoglobin binds oxygen tightly in the high-oxygen environment of the lungs and releases it in the lower-oxygen environment of peripheral tissues.
Why other options are incorrect:
While hemoglobin is a protein, "Proteins" is far too broad of an answer. Hormones regulate physiology, and liquids (like blood plasma) carry only a negligible amount of dissolved oxygen compared to hemoglobin.
[DUHS 2024] Deficiency of ____ causes loss of weight, appetite, and taste: (out of syllabus)
A
P
B
Zn
C
Fe
D
K
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Correct Key: Option ADiagnostic Explanation
Concept:
Trace minerals and macronutrients play crucial roles in physiological homeostasis. Phosphorus (P) is vital for ATP, bone structure, and cellular signaling.
Formula:
$$N/A$$
Solution:
According to the provided explanatory notes for this specific exam, a deficiency of Phosphorus (P) is linked to a cluster of symptoms including loss of weight, appetite, and taste.
Note: In clinical medicine, Zinc (Zn) deficiency is most classically famous for causing loss of taste (ageusia) and appetite. However, strictly following the provided board curriculum/key, Phosphorus is the indicated answer.
Why other options are incorrect:
Iron (Fe) deficiency causes anemia (fatigue, pale skin). Potassium (K) deficiency causes muscle weakness and fatigue. Zinc (Zn) causes skin rashes and diarrhea according to the provided text.
[UHS 2023] Competitive inhibitors stop an enzyme from working by:
A
Changing the shape of the enzyme
B
Merging with the substrate instead
C
Blocking the active site of the enzyme
D
Combining with the product of the reaction
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Correct Key: Option CDiagnostic Explanation
Concept:
Enzyme inhibition occurs when molecules interfere with catalysis. The mechanism defines the type of inhibition.
Formula:
$$N/A$$
Solution:
A competitive inhibitor is structurally similar to the enzyme's natural substrate.
Because of this mimicry, it binds directly to the active site, physically preventing the actual substrate from entering.
Thus, it stops the enzyme from working by blocking the active site of the enzyme.
Why other options are incorrect:
Changing the shape of the enzyme (allosteric shift) is characteristic of non-competitive inhibition. Inhibitors bind to the enzyme, not the substrate or the product.
By the time dietary proteins reach the brush border of the small intestine for absorption, pancreatic and gastric proteases have aggressively cleaved them.
However, they are not strictly reduced to single amino acids; rather, the intestinal lumen contains a mixture of free amino acids and small polypeptides (dipeptides and tripeptides).
These di- and tripeptides are absorbed by enterocytes alongside free amino acids.
Why other options are incorrect:
Digestion does not perfectly yield 'only' amino acids in the lumen before absorption. Conversely, saying it is 'only' polypeptides ignores the massive amount of free amino acids produced. Ammonia is a metabolic waste product of deamination in the liver, not a product of digestive tract hydrolysis.
[SZABMU 2023] The two functional groups present in all amino acids are:
A
Carboxylic acid and amino
B
Amino and aldehyde
C
Ether and carboxylic acid
D
Aldehyde and carboxylic acid
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Correct Key: Option ADiagnostic Explanation
Concept:
An \( \alpha \)-amino acid has a specific, highly conserved core structure surrounding a central chiral carbon atom.
Formula:
$$ \text{H}_2\text{N-CH(R)-COOH} $$
Solution:
Every amino acid has a central \( \alpha \)-carbon bonded to a hydrogen atom and an R-group side chain.
Crucially, it is bonded to a basic amino group (\( \text{-NH}_2 \)) and an acidic carboxyl group (\( \text{-COOH} \)).
Hence, the two defining functional groups are carboxylic acid and amino groups.
Why other options are incorrect:
Aldehydes and ethers are not part of the standard amino acid backbone. While some specific R-groups might contain complex functionalities, only the amino and carboxyl groups are universally present in all amino acids.
Enzymes are biological catalysts produced by living cells to facilitate biochemical reactions.
Formula:
$$ k = A e^{-\frac{E_a}{RT}} $$
Solution:
By providing an alternative reaction pathway with a lower activation energy (\( E_a \)), enzymes allow more substrate molecules to convert into product per unit time.
Therefore, they fundamentally increase the rate of chemical reaction.
Why other options are incorrect:
Enzymes do not decrease or stop reactions (that is the role of inhibitors). Since life depends on rapid metabolic processes, claiming they have "no effect" is biologically false.
[ETEA 2023] The inhibition in which or inhibitor does not combine directly with the enzyme but binds to the enzyme substrate complex is called:
A
Reversible inhibition
B
Competitive inhibition
C
Uncompetitive inhibition
D
Non-competitive inhibition
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Correct Key: Option CDiagnostic Explanation
Concept:
In enzyme kinetics, inhibitors can bind to the free enzyme, the enzyme-substrate (ES) complex, or both. The specific binding target defines the kinetic pattern.
If an inhibitor exclusively binds to the Enzyme-Substrate (ES) complex (and has zero affinity for the free enzyme), it locks the substrate inside and prevents product formation.
This specific mechanism is defined as uncompetitive inhibition.
Why other options are incorrect:
Competitive inhibitors bind only to the free enzyme. Non-competitive inhibitors can bind to both the free enzyme AND the ES complex equally. Reversible inhibition is a broad category that includes all of these.
[KPK 2023] Trypsinogen can be activated by the action of:
A
HCl
B
Enterokinase
C
Glucokinase
D
Amylase
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Correct Key: Option BDiagnostic Explanation
Concept:
Proteases are secreted as inactive zymogens (proenzymes) to prevent them from digesting the organs that synthesize them. They require a specific activator in the gut.
[DUHS 2023] Enzyme show optimum activity between 37°C to 50°C. it however works
A
Below 37°C
B
Above 50°C
C
It loses activity permanently below 37°C
D
It loses activity permanently above 50°C
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Correct Key: Option DDiagnostic Explanation
Concept:
Enzymes are proteinaceous catalysts that rely on a specific 3D folded structure. High temperatures impart excess kinetic energy, breaking the weak non-covalent bonds holding this structure together.
Formula:
$$N/A$$
Solution:
As temperature increases up to 50°C, enzyme activity typically increases (reaching an optimum).
However, pushing temperatures above this optimum range (typically above 50°C - 60°C for human enzymes) violently disrupts hydrogen bonds and hydrophobic interactions.
This leads to thermal denaturation, unfolding the active site. Because the protein coagulates and unfolds irreversibly, it loses activity permanently above 50°C.
Why other options are incorrect:
Below 37°C, enzyme activity decreases due to low kinetic energy, but it does NOT lose activity permanently (it regains activity when warmed). It definitely does not "work" above 50°C once denatured.
Among the choices, aspartic acid (aspartate) is one of the standard 20 naturally occurring \( \alpha \)-amino acids used to synthesize proteins.
Its R-group is a \( \text{-CH}_2\text{-COOH} \) group, making it an acidic amino acid.
Why other options are incorrect:
Palmitic acid is a 16-carbon saturated fatty acid. Benzoic acid is an aromatic carboxylic acid. Aniline is an aromatic amine (phenylamine). None of these possess the dual amino-carboxyl backbone of an amino acid.
[BUMHS 2023] Protein content of human milk is about:
A
1.4 %
B
3.4 %
C
2.4 %
D
4.4 %
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Correct Key: Option CDiagnostic Explanation
Concept:
The biochemical composition of human breast milk is specifically tailored for slow infant growth, containing primarily water, lactose, lipids, and proteins.
Formula:
$$N/A$$
Solution:
Cow's milk contains a relatively high protein content (around 3.4%) for rapid calf muscle growth.
In contrast, human breast milk is optimized for brain development and easier digestion, containing roughly 1.0% to 1.5% protein initially, but standard textbook values often cite the total solid protein fraction dynamically or refer to specific comparative charts.
According to the official explanatory notes provided for this specific past paper, the protein content of human milk is marked as 2.4%.
Why other options are incorrect:
Values like 3.4% and 4.4% are much closer to bovine (cow) or other mammalian milks. The 2.4% figure reflects the established answer key for this specific board curriculum.
[BUMHS 2023] For every reaction occurring in human body there is at least one type of:
A
Protein
B
Enzyme
C
Amino acid
D
Vitamin
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Correct Key: Option BDiagnostic Explanation
Concept:
Biological systems maintain homeostasis and rapid metabolism at low body temperatures by using highly specific biological catalysts.
Formula:
$$N/A$$
Solution:
Without catalysis, biochemical reactions in the human body would occur far too slowly to sustain life at 37°C.
To overcome activation energy barriers, enzymes are utilized.
Enzymes are highly specific; thus, for virtually every discrete metabolic reaction in the body, there exists a specific enzyme to catalyze it.
Why other options are incorrect:
While all enzymes are proteins (and thus made of amino acids), saying "protein" is too broad, as many proteins (like keratin) do not catalyze reactions. Vitamins act as coenzymes, but not every reaction requires a vitamin coenzyme.
[UHS 2022] When food reaches stomach, the action of which of the following come to an end due to acidic pH?
A
Amylase
B
Lipase
C
Maltase
D
Hydrolase
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Correct Key: Option ADiagnostic Explanation
Concept:
Enzymes have a strict optimum pH range. Deviating drastically from this pH alters the active site's ionization state and denatures the enzyme.
Formula:
$$N/A$$
Solution:
Digestion of carbohydrates begins in the mouth with salivary amylase (ptyalin), which functions optimally at a nearly neutral pH (approx 6.8).
When the swallowed food bolus reaches the stomach, it encounters gastric juice containing hydrochloric acid (pH 1.5 - 2.5).
This highly acidic environment immediately denatures salivary amylase, bringing its carbohydrate-digesting action to an end.
Why other options are incorrect:
Gastric lipase actually functions in the acidic environment of the stomach. Maltase acts later in the slightly alkaline environment of the small intestine. 'Hydrolase' is a broad class of enzymes, some of which (like pepsin) thrive in acidic pH.
[UHS 2022] Which of the following proteins acts as carrier of Cu in blood plasma?
A
Ceruloplasmin
B
Haemoglobin
C
Glycoprotein
D
Histone
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Correct Key: Option ADiagnostic Explanation
Concept:
Specific transport proteins in the blood plasma are responsible for safely carrying metal ions to prevent toxicity and facilitate systemic delivery.
Formula:
$$N/A$$
Solution:
Copper (Cu) is a vital trace mineral, but free copper ions are highly toxic.
In the blood plasma, over 90% of circulating copper is bound to a specific transport and ferroxidase protein called ceruloplasmin.
Why other options are incorrect:
Haemoglobin carries oxygen and contains iron (Fe), not copper. Histones are nuclear proteins that pack DNA. Glycoprotein is a broad structural category (though ceruloplasmin is technically a glycoprotein, 'ceruloplasmin' is the exact, specific carrier name).
[SZABMU 2022] Based on function, thyroxin can be classified as
A
Transport protein
B
Structural protein
C
Hormonal protein
D
Genetic protein
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Correct Key: Option CDiagnostic Explanation
Concept:
Biomolecules (including amino acid derivatives) are classified by their physiological roles, such as transport, structure, or regulation.
Formula:
$$N/A$$
Solution:
Thyroxin (T4) is secreted by the thyroid gland and travels through the bloodstream to target organs, regulating base metabolic rate.
Because it functions as a chemical messenger regulating body processes, it falls under the functional classification of a hormonal protein (or biologically active amino acid derivative).
Why other options are incorrect:
It does not provide physical structure (structural), transport molecules like oxygen (transport), or interact directly with DNA packaging (genetic).
Enzymes are biological catalysts produced by living cells to facilitate biochemical reactions.
Formula:
$$ k = A e^{-\frac{E_a}{RT}} $$
Solution:
By providing an alternative reaction pathway with a lower activation energy (\( E_a \)), enzymes allow more substrate molecules to convert into product per unit time.
Therefore, they fundamentally increase the rate of chemical reaction.
Why other options are incorrect:
Enzymes do not decrease or stop reactions (that is the role of inhibitors). Since life depends on rapid metabolic processes, claiming they have "no effect" is biologically false.
[ETEA 2022] The linear arrangement of amino acid units in proteins is called:
A
Primary structure
B
Secondary structure
C
Tertiary structure
D
Quaternary structure
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Correct Key: Option ADiagnostic Explanation
Concept:
Protein architecture is organized from simple 1D sequences up to complex 3D multi-subunit structures.
Formula:
$$N/A$$
Solution:
The most basic level of protein structure is the simple, straight-chain sequence of amino acids linked end-to-end by covalent peptide bonds.
This specific linear arrangement is termed the primary structure.
Why other options are incorrect:
Secondary structure involves coiling into helices/sheets. Tertiary structure involves 3D folding of those helices/sheets. Quaternary involves the aggregation of multiple folded chains.
Nylon-6,6 is synthesized from two monomers: adipic acid (hexanedioic acid) and hexamethylenediamine (1,6-diaminohexane).
Both monomers contain 6 carbon atoms, hence the name "6,6".
Water is eliminated during bond formation, making it a condensation polymer of hexandioic acid & 1,6-diaminohexane. (While D is technically true, A is the most specific and accurate description).
Why other options are incorrect:
Addition polymers form without the loss of small molecules (e.g., polyethylene). Nylon contains amide bonds (\( \text{-CO-NH-} \)), so it is a polyamide, not a polyester.
[DUHS 2022] In protein amino acid molecule are linked by:
A
Peptide linkage
B
Glycosidic linkage
C
Glucoacidic linkage
D
Ethane linkage
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Correct Key: Option ADiagnostic Explanation
Concept:
Macromolecules utilize specific covalent bonds to link their respective monomers.
Formula:
$$ \text{-CO-NH-} $$
Solution:
The carboxyl group of one amino acid reacts with the amino group of another, releasing water.
The resulting amide bond (\( \text{-CO-NH-} \)) in biochemistry is universally called a peptide linkage.
Why other options are incorrect:
Glycosidic linkages join monosaccharides together to form carbohydrates. Glucoacidic is not a standard biochemical term. Ethane linkages imply carbon-carbon alkane bonds, which do not link amino acid backbones.
Macromolecules are composed of repeating monomeric units. Proteins are one of the four major classes of biological macromolecules.
Formula:
$$N/A$$
Solution:
Proteins are complex, high-molecular-weight organic compounds.
They are built from chains of amino acids connected by peptide bonds. Hence, amino acids are the monomers of proteins.
Why other options are incorrect:
Glucose is the monomer of carbohydrates (like starch and cellulose). Nitrogenous bases are components of nucleotides (the monomers of nucleic acids). While proteins contain nitrogen atoms, "nitrogen atoms" themselves are not polymeric units.
The question states that globulins yield only amino acids (or their direct derivatives) upon hydrolysis and do not yield any non-protein prosthetic groups.
By definition, macromolecules that yield only amino acids upon hydrolysis are classified as simple proteins.
Why other options are incorrect:
Compound and conjugated proteins are synonymous; both yield non-protein prosthetic groups (like lipids or carbohydrates) alongside amino acids. Derived proteins are denatured or partially broken-down proteins, whereas globulins are native functional proteins.
[PMC 2021] Regular coiling and twisting of polypeptide chain caused by H-bonding in between NH and CO occurs ____
A
Tertiary structure
B
Primary structure
C
Secondary structure
D
Quaternary structure
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Correct Key: Option CDiagnostic Explanation
Concept:
Protein structure is organized hierarchically into primary, secondary, tertiary, and quaternary levels.
Formula:
$$N/A$$
Solution:
The primary structure is the linear sequence of amino acids (covalent peptide bonds).
When this linear chain begins to fold, it forms regular local patterns such as \( \alpha \)-helices (coiling) and \( \beta \)-pleated sheets (twisting/folding).
This localized folding is entirely stabilized by regular hydrogen bonds between the \( \text{N-H} \) and \( \text{C=O} \) groups of the peptide backbone. This level is defined as the secondary structure.
Why other options are incorrect:
Primary structure involves no H-bonding. Tertiary structure is the overall 3D folding stabilized by R-group interactions (disulfide, ionic, hydrophobic). Quaternary structure involves multiple polypeptide chains assembling together.
[PMC 2021] The substances which reduce the activity of enzyme action are called ____?
A
Activators
B
Promotors
C
Reducers
D
Inhibitors
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Correct Key: Option DDiagnostic Explanation
Concept:
Enzyme activity can be modulated by various small molecules that bind to the enzyme.
Formula:
$$N/A$$
Solution:
Chemical substances that bind to an enzyme (either at the active site or an allosteric site) and subsequently decrease or halt its catalytic activity are termed inhibitors.
Inhibition can be competitive, non-competitive, or uncompetitive.
Why other options are incorrect:
Activators and promoters increase enzyme activity or gene expression, respectively. Reducers are chemical agents that donate electrons in redox reactions, not a term used specifically for reducing enzyme kinetics.
[NMDCAT 2020] Based on function, thyroxin can be classified as:
A
Structural protein
B
Transport protein
C
Hormonal protein
D
Genetic protein
View Answer & Propolis Autopsy
Correct Key: Option CDiagnostic Explanation
Concept:
Proteins/amino acid derivatives perform vastly different functional roles in the body, such as structure, transport, catalysis, or signaling.
Formula:
$$N/A$$
Solution:
Thyroxin (T4) is an iodine-containing hormone derived from the amino acid tyrosine.
It is secreted by the thyroid gland and circulates in the blood to regulate metabolism.
Functionally, because it acts as a chemical messenger regulating physiological processes, it is classified functionally under the category of hormonal proteins (or amino-acid derived hormones).
Why other options are incorrect:
Structural proteins (like collagen) provide physical support. Transport proteins (like hemoglobin) move molecules. Genetic proteins (like histones) bind to DNA. Thyroxin performs none of these functions; it is purely regulatory/hormonal.
L-asparaginase breaks down the amino acid L-asparagine.
Normal cells can synthesize their own L-asparagine, but certain leukemic (blood cancer) cells in children cannot.
Administering L-asparaginase depletes circulating L-asparagine, starving the cancer cells and causing their death. Thus, it is highly effective in treating childhood blood cancer (acute lymphoblastic leukemia).
Why other options are incorrect:
Jaundice is related to bilirubin processing. Rickets is caused by Vitamin D/calcium deficiency. Heart disease is treated with other agents (like tissue plasminogen activator). None of these involve L-asparaginase.
Saliva contains an enzyme called salivary amylase, historically and specifically referred to as ptyalin.
Ptyalin accelerates the breakdown of the polysaccharide starch into simpler sugars (like maltose and dextrins).
Why other options are incorrect:
Pepsin is a protease found in the stomach that digests proteins. Thrombin is involved in blood clotting. Fumarase is an enzyme in the Krebs cycle. None of these act on starch in the saliva.
[MDCAT 2019] Which of the following bond is responsible for joining the amino acids in proteins?
A
Peptide Bond
B
Metallic Bond
C
Di sulfide bond
D
Ionic Bond
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Correct Key: Option ADiagnostic Explanation
Concept:
The primary structure of a protein is defined by the linear sequence of amino acids linked together by covalent bonds.
Formula:
$$ \text{-CO-NH-} $$
Solution:
During translation in ribosomes, amino acids undergo a condensation reaction.
The carboxyl group of one amino acid reacts with the amino group of the next, releasing water and forming a covalent amide linkage known specifically as a peptide bond.
Why other options are incorrect:
Disulfide bonds connect cysteine residues to stabilize tertiary structure but do not form the main primary backbone between all amino acids. Ionic and metallic bonds are not the linkages that polymerize amino acids.
[MDCAT 2018] The stability in the following structure is due to the
Protein Secondary Structure (α-Helix Hydrogen Bonding Stability)
A
Hydrogen bonding between NH group of one peptide with another peptide
B
Disulfide bridges
C
Weak vander Waal's forces
D
Presence of unpaired electron in the structure
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Correct Key: Option ADiagnostic Explanation
Concept:
The secondary structure of proteins (like the \( \alpha \)-helix or \( \beta \)-pleated sheet) is stabilized by specific non-covalent interactions along the polypeptide backbone.
Formula:
$$ \text{>C=O} \cdots \text{H-N<} $$
Solution:
The given structure (\( \alpha \)-helix) maintains its coiled shape because of regular hydrogen bonds.
These hydrogen bonds form between the carbonyl oxygen (\( \text{C=O} \)) of one amino acid residue and the amide hydrogen (\( \text{N-H} \)) of another residue four positions down the chain.
Why other options are incorrect:
Disulfide bridges are covalent bonds that stabilize tertiary structure. Van der Waals forces contribute to tertiary packing, but H-bonds specifically define secondary structure. Unpaired electrons are irrelevant here.
[MDCAT 2018] Amino acids react with each other such that -COOH group of one amino acid reacts with the another amino acid to give a condensed structure as shown below. What is the name of circled part of this structure?
Peptide Bond Linkage Formation (-CONH-)
A
Ester linkage
B
Azide linkage
C
Peptide linkage
D
Carbide linkage
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Correct Key: Option CDiagnostic Explanation
Concept:
Proteins are formed through dehydration condensation reactions between amino acids, resulting in a specific amide bond.
The reaction between the carboxylic acid group (\( \text{-COOH} \)) of one amino acid and the amino group (\( \text{-NH}_2 \)) of a second amino acid releases a water molecule.
The resulting \( \text{-CO-NH-} \) bond linking the two amino acids is biochemically referred to as a peptide linkage (or peptide bond).
Why other options are incorrect:
Ester linkages (\( \text{-COO-} \)) are found in lipids, linking fatty acids to glycerol. Azide (\( \text{-N}_3 \)) and carbide are entirely different chemical groups not found in the protein backbone.
[MDCAT 2018] Role of a catalyst in a chemical reaction is to
A
Decrease rate of a reaction
B
Increase rate of a reaction
C
Decrease yield of a reaction
D
Increase yield of product
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Correct Key: Option BDiagnostic Explanation
Concept:
Catalysts (including biological enzymes) affect the kinetics of a chemical reaction without altering its thermodynamics.
Formula:
$$ k = A e^{-\frac{E_a}{RT}} $$
Solution:
A catalyst provides an alternative reaction pathway with a lower activation energy (\( E_a \)).
By lowering \( E_a \), a larger proportion of reactant molecules possess sufficient kinetic energy to react, thereby increasing the rate of the reaction.
It does not change the equilibrium constant or the final yield of the products.
Why other options are incorrect:
Catalysts do not decrease the reaction rate (that is the role of an inhibitor). They also cannot change the thermodynamic yield of the reaction; they only help the reaction reach equilibrium faster.
[MDCAT 2017] Phosphoprotein comes under the type of proteins
A
Simple protein
B
Conjugated
C
Derived protein
D
Both A & B
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Correct Key: Option BDiagnostic Explanation
Concept:
Conjugated proteins consist of an amino acid chain (protein part) attached to a non-protein prosthetic group.
Formula:
$$N/A$$
Solution:
Phosphoproteins yield amino acids and phosphoric acid upon hydrolysis.
Because phosphoric acid serves as a non-protein prosthetic group covalently bound to the protein, phosphoproteins are classified as conjugated proteins.
Why other options are incorrect:
Simple proteins lack a prosthetic group entirely. Derived proteins are altered or degraded forms of native proteins. Therefore, 'Both A & B' is also incorrect.
[MDCAT 2012] Macromolecules are described as large molecules built up from small repeating units called
A
Monomers
B
Metamers
C
Isomers
D
Tautomers
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Correct Key: Option ADiagnostic Explanation
Concept:
Polymer chemistry involves the formation of large macromolecules from smaller fundamental building blocks.
Formula:
$$N/A$$
Solution:
A macromolecule (or polymer) is synthesized by covalently bonding many smaller, repeating structural units together.
These fundamental repeating units are called monomers (from Greek mono meaning 'one' and meros meaning 'part').
Why other options are incorrect:
Metamers, isomers, and tautomers are types of molecules with the same molecular formula but different structural arrangements; they do not refer to the repeating units of a polymer.
[MDCAT 2011] A polymer in which the number of amino acid residue is greater than 100 or the molecular mass is greater than 10,000 is called
A
Polypeptide
B
Tripeptide
C
Dipeptide
D
Protein
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Correct Key: Option DDiagnostic Explanation
Concept:
Amino acids polymerize via peptide bonds. The nomenclature (peptide vs. protein) depends on the length of the chain and molecular weight.
Formula:
$$N/A$$
Solution:
A dipeptide has 2 amino acids, a tripeptide has 3, and a polypeptide typically has up to 100 amino acids.
By biochemical definition, a macromolecule with more than 100 amino acid residues or a molecular mass exceeding 10,000 Daltons (10 kDa) is officially termed a protein.
Why other options are incorrect:
A polypeptide refers to chains shorter than 100 amino acids. Dipeptides and tripeptides consist of only 2 and 3 amino acids, respectively.
Proteins are classified into simple, conjugated, and derived proteins based on their composition and hydrolysis products. Simple proteins yield only amino acids upon hydrolysis.
Formula:
$$N/A$$
Solution:
Collagen (a structural protein in connective tissues) and albumin (a globular blood protein) consist entirely of amino acid sequences.
Upon hydrolysis, they yield only amino acids and no non-protein (prosthetic) groups, making them simple proteins.
Why other options are incorrect:
Derived proteins are products of partial hydrolysis of proteins (like peptones). Polyamides can be synthetic (like nylon), and polysaccharides are carbohydrates, not proteins.
[MDCAT 2010] Glucose is converted into ethanol by the enzyme present in the yeast:
A
Zymase
B
Urease
C
Invertase
D
Sucrase
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Correct Key: Option ADiagnostic Explanation
Concept:
Alcoholic fermentation is a biochemical process in which sugars such as glucose, fructose, and sucrose are converted into cellular energy, producing ethanol and carbon dioxide as metabolic waste.
Yeast naturally contains an enzyme complex called zymase.
Zymase catalyzes the fermentation of simple sugars like glucose into ethanol and carbon dioxide.
Why other options are incorrect:
Invertase catalyzes the hydrolysis of sucrose into fructose and glucose. Urease catalyzes the hydrolysis of urea into carbon dioxide and ammonia. Sucrase is similar to invertase in breaking down sucrose.
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