UEE Biology (ЭЕШ Биологи) (Mongolia)

Which organelle features an inner membrane folded into cristae to maximize the surface area for ATP synthase and electron transport chain complexes?

• APeroxisome
• BGolgi apparatus
• CEndoplasmic reticulum
• DMitochondrion

What structural characteristic differentiates prokaryotic ribosomes from the cytosolic ribosomes of eukaryotic cells?

• AProkaryotic ribosomes are 80S complexes composed of 40S and 60S subunits
• BProkaryotic ribosomes are 70S complexes composed of 30S and 50S subunits
• CProkaryotic ribosomes lack ribosomal RNA and consist entirely of basic proteins
• DProkaryotic ribosomes are enclosed within a double-membrane ribonucleoprotein envelope

Which organelle maintains an acidic internal lumen (pH 4.5–5.0) via proton pumps and contains hydrolytic enzymes responsible for autophagy and heterophagy?

• ACentrosome
• BGlyoxysome
• CLysosome
• DRibosome

Which of the following functions is primarily attributed to the smooth endoplasmic reticulum rather than the rough endoplasmic reticulum?

• ASynthesis of secretory proteins targeted for the plasma membrane
• BAddition of initial N-linked oligosaccharide cores to nascent polypeptides
• CLipid and steroid hormone biosynthesis, and intracellular calcium storage
• DAssembly of amino acids into peptide chains via membrane-bound 80S ribosomes

Which sequence lists the main taxonomic ranks correctly, from the most inclusive (broadest) to the least inclusive?

• AKingdom → Phylum → Class → Order → Family → Genus → Species
• BKingdom → Class → Phylum → Order → Family → Genus → Species
• CKingdom → Phylum → Order → Class → Family → Genus → Species
• DKingdom → Phylum → Class → Order → Genus → Family → Species

Where are the photosynthetic pigment-protein complexes and the light-driven ATP synthase localized within a chloroplast?

• AStroma matrix
• BThylakoid membrane
• COuter chloroplast envelope
• DIntermembrane space

Which of the following structures is found in both typical Gram-negative eubacteria and eukaryotic plant cells?

• AMitochondria
• BNuclear envelope
• CCell wall
• DEndoplasmic reticulum

How does cholesterol influence the physical properties of animal plasma membranes at varying physiological temperatures?

• AIt permanently solidifies the lipid bilayer into an impermeable crystalline gel regardles…
• BIt dissolves transmembrane proteins to allow free unrestricted lipid lateral diffusion
• CIt acts as a bidirectional fluidity buffer, restraining phospholipid motion at warm tempe…
• DIt hydrolyzes sphingolipids into free glycerol and inorganic phosphate during cold shock

When a living plant cell with an internal solute concentration of 0.3 M is placed into a hypertonic sucrose solution (0.8 M), what physiological phenomenon occurs?

• ASucrose molecules rush inward across the plasma membrane by facilitated diffusion, genera…
• BWater enters the cell rapidly until osmotic pressure causes the cellulose cell wall to ly…
• CActive proton efflux ceases completely, causing immediate cytoplasmic alkalosis and swell…
• DWater leaves the vacuole and cytoplasm by osmosis, causing the protoplast to shrink away…

What is the precise ionic stoichiometry and directionality of the primary active transport cycle mediated by the animal cell Na+/K+-ATPase?

• A3 Na+ ions pumped out of the cell and 2 K+ ions pumped into the cell per ATP hydrolyzed
• B2 Na+ ions pumped out of the cell and 3 K+ ions pumped into the cell per ATP hydrolyzed
• C3 Na+ ions pumped into the cell and 2 K+ ions pumped out of the cell per ATP hydrolyzed
• D1 Na+ ion and 1 K+ ion cotransported outward simultaneously per ATP hydrolyzed

Which of the following carbohydrates consists of unbranched chains of D-glucose units linked by beta-1,4-glycosidic bonds, forming high-tensile microfibrils via extensive hydrogen bonding?

• AAmylose
• BCellulose
• CGlycogen
• DAmylopectin

How do unsaturated fatty acids chemically differ from saturated fatty acids, and how does this affect their physical state at room temperature?

• AUnsaturated fatty acids possess max-hydrogen saturation, creating straight chains that pa…
• BUnsaturated fatty acids contain alternating peptide bonds that permit rapid esterificatio…
• CUnsaturated fatty acids lack hydrocarbon tails and are entirely hydrophilic, dissolving c…
• DUnsaturated fatty acids contain one or more carbon-carbon double bonds, creating kinks th…

What covalent linkage is formed between the alpha-carboxyl group of one amino acid and the alpha-amino group of an adjacent amino acid during protein synthesis on a ribosome?

• APhosphodiester bond
• BPeptide bond
• CGlycosidic bond
• DDisulfide cross-link

Which level of protein structural organization remains intact when a globular protein undergoes thermal denaturation without the action of proteolytic enzymes?

• ASecondary structure
• BTertiary structure
• CPrimary structure
• DQuaternary structure

In complementary base pairing within double-stranded DNA, how many hydrogen bonds form between cytosine and guanine, and between adenine and thymine?

• ATwo hydrogen bonds between C and G; three hydrogen bonds between A and T
• BThree hydrogen bonds between C and G; two hydrogen bonds between A and T
• COne covalent bond between C and G; two covalent bonds between A and T
• DFour ionic interactions between C and G; two ionic interactions between A and T

How do biological enzymes accelerate biochemical reaction rates without shifting the overall equilibrium constant (Keq)?

• ABy supplying thermal energy directly into the covalent bonds of substrate molecules
• BBy altering the standard free energy change (Delta G) of products relative to reactants
• CBy lowering the activation energy barrier (Ea) required to achieve the transition state
• DBy permanently incorporating their catalytic residues into the final chemical products

In Michaelis-Menten enzyme kinetics, how does the addition of a reversible competitive inhibitor affect the observed parameters Km and Vmax?

• AApparent Km decreases, while Vmax decreases proportionately due to irreversible active si…
• BKm remains unchanged, while Vmax decreases because the inhibitor binds exclusively to the…
• CBoth Km and Vmax increase simultaneously by shifting the cooperative Hill coefficient
• DApparent Km increases, while Vmax remains unchanged because high substrate concentrations…

What is the primary regulatory mechanism when the end product of a multi-step biosynthetic pathway binds to an allosteric site on the first committed pathway enzyme to suppress its activity?

• AFeedback inhibition
• BCompetitive dephosphorylation
• CIrreversible proteolytic degradation
• DZymogen activation

During the cytoplasmic glycolytic breakdown of one molecule of glucose into two molecules of pyruvate, what is the net yield of ATP and reduced electron carriers?

• ANet yield of 4 ATP and 4 FADH2
• BNet yield of 2 ATP and 2 NADH
• CNet yield of 32 ATP and 2 NADPH
• DNet yield of 0 ATP and 1 NADH

In the aerobic eukaryotic mitochondrion, which reaction directly links cytosolic glycolysis to the citric acid cycle?

• ACondensation of oxaloacetate and malate to produce citrate via citrate synthase
• BOxidative decarboxylation of pyruvate to acetyl-CoA by the pyruvate dehydrogenase complex
• CPhosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate by phosphofructokina…
• DCleavage of succinyl-CoA into succinate and GTP by succinyl-CoA synthetase

What is the direct thermodynamic driving force that powers ATP synthesis by the mitochondrial F0F1-ATP synthase during oxidative phosphorylation?

• ADirect high-energy phosphate transfer from phosphoenolpyruvate to ADP in the matrix
• BActive sodium efflux across the outer mitochondrial membrane mediated by secondary sympor…
• CThe electrochemical proton gradient (proton motive force) across the inner mitochondrial…
• DSpontaneous exothermic hydrolysis of molecular oxygen into superoxide radicals

Under anaerobic conditions in human skeletal muscle during intense sprint exercise, why must pyruvate be converted into lactate by lactate dehydrogenase?

• ATo directly synthesize two additional molecules of ATP via substrate-level phosphorylation
• BTo reoxidize NADH back to NAD+, replenishing the pool needed for glycolysis to continue g…
• CTo generate molecular oxygen internally to support mitochondrial electron transport
• DTo prevent dangerous alkaline shifts in the cytoplasmic pH of skeletal myocytes

During the light-dependent reactions of oxygenic photosynthesis, which process directly replenishes the electrons lost by the reaction center P680 chlorophyll molecules of Photosystem II?

• ACyclic electron transfer from ferredoxin to cytochrome b6f
• BOxidation of NADPH to NADP+ by ferredoxin-NADP+ reductase
• CSplitting of carbon dioxide into carbon monoxide and nascent singlet oxygen
• DPhotolysis of water molecules at the oxygen-evolving manganese-calcium cluster

In the stroma of chloroplasts, which enzyme catalyzes the initial carbon-fixation reaction by combining atmospheric CO2 with ribulose-1,5-bisphosphate (RuBP)?

• ARibulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO)
• BPhosphoenolpyruvate carboxylase (PEP carboxylase)
• CGlyceraldehyde-3-phosphate dehydrogenase (GAPDH)
• DPhosphofructokinase-1 (PFK-1)

At which phase of the eukaryotic mitotic cell cycle are sister chromatids separated and pulled toward opposite spindle poles by shortening kinetochore microtubules?

• AMetaphase
• BProphase
• CTelophase
• DAnaphase

According to Gregor Mendel's Law of Segregation, what happens to the two alleles of a single gene locus during gamete formation in a diploid organism?

• AThey replicate simultaneously and remain paired within every mature haploid gamete
• BThey recombine with non-homologous autosomes to produce hybrid gametic chromosomes
• CThey separate from each other during anaphase I of meiosis so that each gamete carries on…
• DThey fuse covalently into a single functional allele before meiotic cytokinesis

In a classic Mendelian dihybrid cross between two individuals heterozygous for two unlinked, autosomal traits showing complete dominance (AaBb x AaBb), what is the expected phenotypic ratio among the F2 offspring?

• A9 : 3 : 3 : 1
• B1 : 2 : 1 : 1
• C3 : 1
• D12 : 3 : 1

To determine whether an organism exhibiting a dominant phenotype is homozygous dominant (AA) or heterozygous (Aa), with which genotype must it be crossed in a standard Mendelian testcross?

• AA homozygous dominant individual (AA)
• BA known heterozygous individual (Aa)
• CA triploid tester organism (AAA)
• DA homozygous recessive individual (aa)

When true-breeding red-flowered snapdragons (CRCR) are crossed with true-breeding white-flowered snapdragons (CWCW), all F1 progeny have pink flowers (CRCW). If two pink-flowered F1 plants are self-crossed, what phenotypic ratio is expected in the F2 generation?

• A3 red : 1 white
• B1 red : 2 pink : 1 white
• C9 red : 6 pink : 1 white
• DAll pink flowers

In the human ABO blood group system governed by alleles IA, IB, and i, a woman with type A blood whose father was type O has children with a man with type AB blood. What are the possible blood types and their probabilities among their offspring?

• A50% type A, 50% type O
• B100% type AB
• C50% type A, 25% type B, 25% type AB
• D25% type A, 25% type B, 25% type AB, 25% type O

Hemophilia A is an X-linked recessive bleeding disorder in humans. If a phenotypically unaffected woman whose father had hemophilia marries an unaffected male, what is the probability that their first son will be affected by hemophilia?

• A50%
• B0%
• C25%
• D100%

Which pattern of genetic transmission accounts for continuous phenotypic variation in traits such as human skin pigmentation and adult height, displaying a bell-shaped normal distribution curve across a population?

• ASingle-gene pleiotropy
• BMaternal cytoplasmic mitochondrial inheritance
• CComplete autosomal dominance at a single locus
• DPolygenic inheritance involving the additive effects of multiple independent gene loci

In Labrador retrievers, black coat color (B) is dominant to brown (b), but homozygous recessiveness at an independent locus (ee) prevents pigment deposition in the hair shafts, resulting in a yellow coat regardless of the B locus. In a cross between two dihybrids (BbEe x BbEe), what phenotypic ratio of black, brown, and yellow puppies is produced?

• A9 black : 3 brown : 3 yellow : 1 albino
• B9 black : 3 brown : 4 yellow
• C12 black : 3 brown : 1 yellow
• D15 black : 1 yellow

In Drosophila melanogaster, a testcross of a female heterozygous for two linked genes producing 400 total offspring yields 162 wild-type, 158 double mutant, 42 recombinant class 1, and 38 recombinant class 2. What is the map distance between these two loci on the chromosome?

• A8.0 map units (cM)
• B40.0 map units (cM)
• C20.0 map units (cM)
• D50.0 map units (cM)

Down syndrome (trisomy 21) in humans is most commonly caused by which cellular error during gametogenesis?

• ANondisjunction of homologous chromosomes or sister chromatids during meiotic division
• BTerminal deletion of the short p-arm of chromosome 5
• CReciprocal balanced translocation between chromosome 9 and chromosome 22
• DReplication slippage causing trinucleotide CAG repeat expansion

Which feature correctly describes the structural architecture of the Watson-Crick B-form DNA double helix?

• ABoth phosphodiester strands run in parallel 5' to 3' directions with purines pairing excl…
• BThe ribose-phosphate backbones are positioned along the interior axis surrounded by nitro…
• CAdjacent nitrogenous bases within a single strand are joined by high-energy phosphodieste…
• DTwo antiparallel polynucleotide chains coil around a central axis, with sugar-phosphate b…

In the landmark 1958 Meselson-Stahl experiment using 15N and 14N isotopic density-gradient centrifugation in E. coli, what result conclusively ruled out the conservative model of DNA replication after one generation of growth in 14N?

• AA single broad band corresponding entirely to heavy 15N/15N DNA
• BA single intermediate hybrid band of DNA with a density between 15N and 14N
• CTwo distinct bands: one at the heavy 15N density and one at the light 14N density
• DThree bands representing dispersive fragmentation of parental strands

During replication fork progression in prokaryotes, which enzyme relieves the positive supercoiling and torsional strain generated ahead of the advancing replication fork by transiently cutting and resealing DNA strands?

• ADNA helicase
• BSingle-stranded DNA-binding protein (SSB)
• CDNA topoisomerase (DNA gyrase)
• DDNA polymerase I

Why must the lagging strand of a replication fork be synthesized discontinuously as a series of Okazaki fragments?

• ABecause DNA polymerases can synthesize new polynucleotide chains only in the 5' to 3' dir…
• BBecause RNA primase cannot bind to single-stranded lagging templates
• CBecause DNA helicase unwinds only one of the two parental strands at a time
• DBecause Okazaki fragments contain ribose sugars that prevent continuous polymerase progre…

During bacterial DNA replication, which catalytic activity enables DNA polymerase III to excise incorrectly paired nucleotides immediately after incorporation, ensuring high replication fidelity?

• A5' to 3' exonuclease activity
• BEndonuclease restriction activity
• CTopoisomerase ligating activity
• D3' to 5' exonuclease proofreading activity

What is the primary function of the promoter region, such as the TATA box in eukaryotic gene promoters, during transcription?

• AIt encodes the 5' untranslated leader sequence of the mature polypeptide
• BIt serves as the specific DNA sequence recognized and bound by transcription factors and…
• CIt signals the spliceosome to excise the first intervening sequence
• DIt binds the poly-A polymerase enzyme to attach adenine nucleotides to the pre-mRNA

Which three critical post-transcriptional modifications convert eukaryotic primary pre-mRNA transcripts into mature mRNA ready for nuclear export and translation?

• ADNA methylation, histone acetylation, and promoter silencing
• BCleavage of 5' leaders, attachment of CCA trinucleotide, and base modification to pseudou…
• CAddition of a 5' 7-methylguanosine cap, addition of a 3' poly-A tail, and spliceosomal ex…
• DRibosomal subunit assembly, chaperone folding, and signal peptide cleavage

How does alternative splicing of eukaryotic pre-mRNA transcripts contribute significantly to proteomic complexity in complex multicellular organisms?

• AIt allows a single pre-mRNA transcript to produce multiple distinct mature mRNA variants…
• BIt alters the genomic DNA sequence inside somatic cell chromosomes permanently
• CIt changes the universal genetic code so that stop codons encode standard amino acids
• DIt directs ribosomes to synthesize polypeptides without initiating at an AUG start codon

What is meant by the statement that the biological genetic code is 'degenerate' (redundant)?

• AEach three-nucleotide codon can specify multiple distinct amino acids depending on cellul…
• BThe code rapidly breaks down and degrades into free nucleotides after transcription
• CCodons overlap along the mRNA strand, sharing common purine bases
• DMost amino acids are encoded by more than one triplet codon

Which codon functions universally as the initiation (start) codon for translation in eukaryotic cytosol, and which amino acid does it specify?

• AUAA, specifying STOP
• BAUG, specifying Methionine
• CUGA, specifying Tryptophan
• DUAG, specifying Phenylalanine

During translation elongation on the ribosome, what is the role of the ribosomal A (aminoacyl) site?

• AIt anchors the mRNA 5' cap to the 40S subunit during initial scanning
• BIt houses the uncharged deacylated tRNA immediately prior to its exit into the cytosol
• CIt receives incoming aminoacyl-tRNA molecules whose anticodons match the mRNA codon being…
• DIt holds the peptidyl-tRNA that carries the growing polypeptide chain