Biomolecules & Biochemistry — Part 2: 28 MCQs with Explanations

The proximal convoluted tubule (PCT) reabsorbs approximately 65-70% of filtrate, including all glucose, amino acids, vitamins, and most ions and water.

PCT reabsorbs ~65% of filtered water along with glucose, amino acids, and ions via active and passive transport.

Anaerobic respiration (e.g., lactic acid fermentation) yields net 2 ATP per glucose via substrate-level phosphorylation in glycolysis.

Primary succession begins on lifeless substrates without soil (e.g., bare rock, sand dunes); lichens are typical pioneer species.

Enzymes are biological catalysts that lower activation energy, remain unchanged after reaction, and show substrate specificity due to active site geometry.

Mutualism: Rhizobium fixes atmospheric nitrogen for legume; legume provides carbohydrates to bacteria—both benefit.

PCT reabsorbs approximately 65% of filtered water along with glucose, amino acids, and ions through active and passive transport mechanisms.

Vitamin C (ascorbic acid) is essential for collagen synthesis; its deficiency weakens connective tissues, causing scurvy symptoms.

Anaerobic respiration yields net 2 ATP per glucose via substrate-level phosphorylation in glycolysis; no additional ATP from Krebs cycle or ETC.

Fat-soluble vitamins (A, D, E, K) are stored in liver and adipose tissue; water-soluble vitamins (B-complex, C) are generally not stored and excess is excreted.

Primary succession starts on lifeless substrates; lichens and mosses are pioneer species that break down rock to form soil over centuries.

Enzymes have active sites with specific shape/charge complementary to substrates (lock-and-key or induced fit models); they lower activation energy and remain unchanged after catalysis.

Large intestine absorbs remaining water and electrolytes, forms and stores feces, and houses bacterial flora that produce vitamin K and some B vitamins.

Light-dependent reactions involve photosystems II and I, electron transport chain, and chemiosmosis to produce ATP and NADPH using solar energy.

Peptidyl transferase is a ribozyme (catalytic rRNA component of large ribosomal subunit) that forms peptide bonds between amino acids.

Codons in mRNA specify amino acids; 64 possible codons encode 20 amino acids plus start (AUG) and stop (UAA, UAG, UGA) signals.

Nitrogen fixation: Rhizobium (symbiotic) and Azotobacter (free-living) convert N₂ → NH₃ using nitrogenase enzyme requiring anaerobic conditions.

Liver detoxifies drugs/alcohol via cytochrome P450 enzymes, converts ammonia to urea, stores glycogen/vitamins, and produces bile.

Vitamin C (ascorbic acid) is water-soluble and not stored significantly in body; excess is excreted in urine. Fat-soluble vitamins (A, D, E, K) are stored in liver/adipose tissue.

Glycolysis yields gross 4 ATP but consumes 2 ATP in energy investment phase, resulting in net gain of 2 ATP plus 2 NADH per glucose molecule.

Lactobacillus bulgaricus and Streptococcus thermophilus ferment lactose to lactic acid, causing milk proteins to coagulate forming yogurt.

Theoretical maximum is 36-38 ATP per glucose: 2 from glycolysis, 2 from Krebs cycle, and 32-34 from oxidative phosphorylation (varies due to shuttle systems).

Ammonification: decomposers (bacteria/fungi) break down proteins/nucleic acids from dead organisms into ammonia (NH₃/NH₄⁺).

Simple diffusion occurs directly through phospholipid bilayer for small nonpolar molecules (O₂, CO₂); no carrier proteins or energy required.

Stroma contains enzymes for Calvin cycle including RuBisCO; ATP and NADPH from light reactions diffuse from thylakoids to stroma.

Enzymes provide alternative reaction pathway with lower activation energy barrier; they do not alter reaction equilibrium or get consumed.

Calvin cycle (dark reactions) uses ATP for phosphorylation and NADPH for reduction to convert CO₂ into glyceraldehyde-3-phosphate (G3P).

Substrate-level phosphorylation: enzymes directly transfer phosphate groups from substrates to ADP (e.g., phosphoglycerate kinase, pyruvate kinase).

An enzyme which converts a dipeptide into separate amino acids is an example of Hydrolase .

Variety among amino acids is produced due to R group .

Primary structure of proteins determines Amino acid sequence .

Which of the following carbohydrate is tasteless Polysaccharide .

During digesting the phagocytosed food particles vesicles formed from fusion of phagocytic vacuole with the enzymes secreted by Golgi apparantus are called Secondary lysosomes .

Inhibitors which block the enzyme by forming weak bond are called Both a and b .

A substance which binds at the active site of the enzyme but does not result in the formation of the products is called Competitive inhibitor .

A chemical substance which can react (in place of substrate) with the enzyme but is not transformed into product/s and thus blocks the active site temporarily or permanently is called Inhibitor .

Excessive increase in temperature of medium causes the enzyme molecule to Denatured .

If enzyme concentration is low than substrate pH and temperature values are equal to requirement then which of the following will increase rate of reaction increase in concentration of enzyme .

The structure of an enzyme is altered by Irreversible inhibitor .

If more substrate to already occurring enzymatic reaction is added and there is no effect on the rate of the reaction what is the form given to this situation Saturation .

The rate of reaction is directly proportional to the concentration of an enzyme which statement is incorrect in this respect This relation is for unlimited time period with unlimited enzyme concentration .

If the concentration of enzyme is kept constant and amount of substrate is increased a point is reached where increase in substrates concentration does not affect the reaction rate because of All the active sites on enzyme molecule are occupied .

Enzymes Decreases the activation energy of a chemical reaction.

Which one forms the raw material for coenzymes Vitamins .

Proteins and lipids are converted into glycolipids and glycoproteins by adding carbohydrates by Golgi apparatus .

Biological molecules (proteins) which catalyze a biochemical reaction and remain unchanged after completion of reaction are called Enzymes .

In which of the following location enzymes controlling cellular respiration are present Milochondria .

An activated enzyme consisting of polypeptide chain and a cofactor is called Both b and c .

Which statement about enzyme is incorrect All enzymes are fibrous Proteins. .

A three dimensional dcavity bearing a specific charge by which the enzyme reacts with its substrate is called Active site .

Ribonucleo-protein particles are the name of Eukaryotic ribosomes .

One which help in assembly of spindles during mitosis. is the correct answer to “Which of the following cytoskeletal fiber contain tubulin protein”. Items of this type are drawn from the Biomolecules & Biochemistry — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

A chemical substance that reacts with enzyme but is not transformed into product and thus blocking active site is called Inhibitor .

enzyme is bio catalyst .

The mechanism for ATP synthesis is Chemiosmosis .

Protein factory is ribosome .

Proteins are made from amino acids by the process of Dehydration synthesis .

vitamin is the correct answer to “Co-enzyme is often formed from”. Items of this type are drawn from the Biomolecules & Biochemistry — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Vitamin A is the correct answer to “Which Vitamin is needed for the formation of a light-sensitive pigment in the retina.”. Items of this type are drawn from the Biomolecules & Biochemistry — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

B.skin disease is the correct answer to “The Lake of Vitamin C creates which disease”. Items of this type are drawn from the Biomolecules & Biochemistry — Part 2 syllabus of Pakistani competitive exams, where the fact is tested verbatim.