Test d'ingresso Semmelweis: simulazione 1 con soluzioni

Risposta: D

Quaternary structure is the arrangement of several polypeptide chains (subunits) in one protein, as in haemoglobin's α₂β₂ tetramer. Primary structure is a chain's amino acid sequence, secondary its local α-helices and β-sheets, and tertiary the folding of a single chain in three dimensions.

Risposta: A

Allosteric regulators bind to a regulatory (allosteric) site distinct from the active site and change the enzyme's conformation, making it more or less active. A molecule that occupies the active site in place of the substrate is a competitive inhibitor, not an allosteric regulator.

Risposta: A

Each of glycerol's three hydroxyl groups forms an ester bond with a fatty acid, giving a triacylglycerol, the body's main energy store. Glycerol with two fatty acids and a phosphate group is a phosphoglyceride, the main lipid of membranes; sphingosine is the backbone of sphingolipids.

Risposta: C

Niacin (nicotinic acid and nicotinamide) provides the nicotinamide ring of NAD⁺ and NADP⁺. Riboflavin is the precursor of FAD and FMN, thiamine of thiamine pyrophosphate, and cobalamin is itself a coenzyme for a few reactions such as methionine synthesis.

Risposta: A

A competitive inhibitor competes with the substrate for the active site, so more substrate is needed to reach half-maximal velocity (a higher apparent Km). Enough substrate outcompetes it, so Vmax is unchanged. Lowering Vmax with Km unchanged is the pattern of non-competitive inhibition, and permanent covalent binding is irreversible inhibition.

Risposta: B

Replication is semiconservative: each parental strand serves as a template and stays paired with its new partner, so after one round every molecule is a hybrid of one old (¹⁵N) and one new (¹⁴N) strand. This is what Meselson and Stahl found. The first option describes conservative replication and the last dispersive replication, both ruled out by that experiment.

Risposta: B

RNA polymerase II transcribes protein-coding genes into pre-mRNA. RNA polymerase I makes most ribosomal RNA (in the nucleolus) and RNA polymerase III makes tRNA and the small 5S rRNA. DNA polymerases replicate DNA; they do not transcribe it.

Risposta: D

Pre-mRNA is capped at its 5′ end, given a poly(A) tail at its 3′ end and spliced to remove introns before it leaves the nucleus. The AUG start codon is kept: translation begins at it, in the cytoplasm.

Risposta: B

Glycolysis reduces NAD⁺ to NADH. Without oxygen the respiratory chain cannot reoxidise NADH, so lactate dehydrogenase uses it to reduce pyruvate to lactate, regenerating the NAD⁺ glycolysis needs to keep making its 2 ATP. The reaction itself makes no ATP and releases no CO₂; lactate is turned back into glucose in the liver (the Cori cycle), not in the muscle.

Risposta: A

The enzymes of the citrate (Krebs) cycle are in the mitochondrial matrix, apart from succinate dehydrogenase, which is bound to the inner membrane. Glycolysis is the part of glucose oxidation that happens in the cytosol.

Risposta: D

The respiratory chain uses the energy of electron transfer to pump protons from the matrix into the intermembrane space. ATP synthase lets them flow back, and that proton flow turns the enzyme and drives ATP synthesis (chemiosmosis). Electrons do not pass through ATP synthase, and oxygen is the final electron acceptor at complex IV, not a ligand of the synthase.

Risposta: A

RNA can store information in its base sequence and, as ribozymes (including the peptidyl transferase of the ribosome), catalyse reactions, so a world based on RNA alone could have both copied and run itself before DNA and proteins took over those roles. RNA is in fact less stable than DNA, is found in every cell, and contains uracil, not thymine.

Risposta: D

The nucleolus is where rRNA genes are transcribed and the rRNA is combined with proteins into the small and large ribosomal subunits, which then leave the nucleus. Lipids are made in the smooth endoplasmic reticulum, and glycosylation takes place in the ER and the Golgi apparatus.

Risposta: C

Lysosomal enzymes are acid hydrolases: a proton pump keeps the lysosome at about pH 5, where they work best. This also protects the cell, because enzymes that leak into the cytosol (pH about 7.2) are much less active. They are made on the rough ER and sent to lysosomes through the Golgi apparatus.

Risposta: B

Mitochondria are inherited through the egg; the sperm's mitochondria do not normally survive in the embryo. So an affected mother passes the mutation to all her children, sons and daughters, while an affected father passes it to none. How severely each child is affected can vary, because cells carry different proportions of mutant mitochondria.

Risposta: D

p53 is a transcription factor that accumulates when DNA is damaged; it switches on genes that halt the cycle at the G1 checkpoint (so the damage can be repaired) or, if the damage is too great, trigger apoptosis. Many cancers carry mutations in the gene for p53.

Risposta: A

Steroids are lipid-soluble, so they cross the plasma membrane and bind receptors in the cytoplasm or nucleus; the hormone-receptor complex binds DNA and changes the transcription of target genes. Water-soluble hormones such as adrenaline or glucagon cannot cross the membrane and use cell-surface receptors and second messengers instead.

Risposta: A

The sinoatrial node in the wall of the right atrium depolarises spontaneously fastest, so it sets the heart rate (the pacemaker). The impulse spreads across the atria, is delayed in the atrioventricular node, then travels down the bundle of His and the Purkinje fibres to the ventricles.

Risposta: C

Ca²⁺ binds troponin C; the troponin complex then shifts tropomyosin away from the myosin-binding sites on actin, so cross-bridges can form. Tropomyosin is the tempting answer, but it is moved by troponin rather than binding calcium itself. (In smooth muscle, calcium acts through calmodulin instead.)

Risposta: C

Reverse transcriptase is an RNA-dependent DNA polymerase: it copies the viral RNA genome into DNA, which another viral enzyme, integrase, inserts into the host cell's genome. Making RNA from DNA is ordinary transcription, done by the host's RNA polymerase.

Risposta: B

Sodium has 11 electrons: 2 fill 1s, 2 fill 2s, 6 fill 2p and the eleventh goes into 3s. That single 3s electron is easily lost, which is why sodium forms Na⁺. A 2p subshell holds at most six electrons, so 2p⁷ is impossible; 3s² would describe magnesium.

Risposta: A

Oxygen is far more electronegative than sulfur, so the O–H bonds are strongly polar and water molecules form hydrogen bonds with one another; more energy is needed to separate them. Covalent bonds hold atoms together within a molecule, not molecules to each other, and dispersion forces are weaker in water than in the larger H₂S.

Risposta: C

Water self-ionises slightly: in pure water at 25 °C, [H⁺] = [OH⁻] = 1 × 10⁻⁷ mol/L, so their product is 1 × 10⁻¹⁴. 10⁻⁷ is each ion's concentration (giving pH 7), not their product; pH + pOH = 14 follows from Kw but is not Kw itself.

Risposta: B

Moles needed: 0.20 mol/L × 0.500 L = 0.10 mol. Mass: 0.10 mol × 180 g/mol = 18 g. Forgetting to halve for 500 mL gives 36 g.

Risposta: C

AgCl ⇌ Ag⁺ + Cl⁻, so if s mol/L dissolves, Ksp = s × s = s². Then s = √(1.6 × 10⁻¹⁰) ≈ 1.3 × 10⁻⁵ mol/L. Taking Ksp itself as the solubility, or halving it, forgets that two ion concentrations are multiplied.

Risposta: D

NaOH is a strong base, so [OH⁻] = 0.010 = 10⁻² mol/L and pOH = 2. At 25 °C pH = 14 − pOH = 12. pH 2 would be the answer for a 0.010 mol/L strong acid.

Risposta: C

A buffer is a weak acid with its conjugate base (or a weak base with its conjugate acid): acetic acid neutralises added base and acetate ions take up added acid, so the pH changes little. A strong acid or base with its salt cannot buffer, because the strong acid is fully dissociated and its anion is too weak a base to take up H⁺.

Risposta: D

K is +1 and each O is −2, so +1 + x + 4(−2) = 0, which gives x = +7. That high oxidation state is why permanganate is such a strong oxidising agent; in acid it is reduced to Mn²⁺.

Risposta: B

Copper has the higher reduction potential, so Cu²⁺ is reduced at the cathode and zinc is oxidised at the anode. E°cell = E°cathode − E°anode = 0.34 − (−0.76) = +1.10 V. A working galvanic cell has a positive potential; 0.42 V comes from adding the two values without changing a sign.

Risposta: A

Oxygen binds reversibly to iron(II), Fe²⁺, held in the heme ring. When the iron is oxidised to Fe³⁺ the protein becomes methaemoglobin, which cannot carry oxygen, which is why that oxidation is harmful.

Risposta: B

ΔH < 0 means the products have less enthalpy than the reactants, so the difference is released as heat: the reaction is exothermic. Whether a reaction is spontaneous depends on ΔG = ΔH − TΔS, not on ΔH alone, and exothermic reactions still need activation energy to start.

Risposta: D

ΔG = ΔH − TΔS. With ΔH negative and ΔS positive, both terms make ΔG negative whatever the temperature. With ΔH > 0 and ΔS < 0 the reaction is never spontaneous; in the other two cases the sign of ΔG depends on the temperature.

Risposta: B

A catalyst, such as an enzyme, offers an alternative reaction pathway with a lower activation energy, so more collisions have enough energy to react. It speeds up the forward and reverse reactions equally, so it changes neither the equilibrium position nor ΔH.

Risposta: C

Benzene is a planar ring of six carbons with six delocalised π electrons, which is what makes it aromatic and unusually stable. Cyclohexane and hexane are saturated, and cyclohexene has one isolated double bond, not a delocalised ring system.

Risposta: A

Oxidising a primary alcohol removes two hydrogens and gives an aldehyde (ethanol gives ethanal, acetaldehyde); further oxidation gives the carboxylic acid. Secondary alcohols are oxidised to ketones, tertiary alcohols resist oxidation, and losing water (dehydration) rather than hydrogen would give an alkene.

Risposta: C

The middle carbon carries a C=O bonded to two other carbons, a ketone (oxo) group, and the end carbon is a carboxyl group, so pyruvic acid is an α-keto acid. An amino group and a carboxyl group together would make an amino acid; transamination indeed turns pyruvate into alanine.

Risposta: A

The nitrogen of an amine has a non-bonding electron pair, which can take up H⁺ to form an ammonium ion (R–NH₃⁺); that is a Brønsted base by definition. Amines contain no OH⁻ to release, and a carboxyl group would make the molecule acidic.

Risposta: D

A phosphate group forms ester bonds with the 3′ carbon of one sugar and the 5′ carbon of the next, a phosphodiester bond, making the sugar-phosphate backbone. The glycosidic bond attaches each base to its sugar, and hydrogen bonds pair bases between strands.

Risposta: A

Two cysteine thiol (–SH) groups are oxidised to a disulfide (–S–S–) bond, which stabilises the tertiary or quaternary structure, as in insulin and antibodies. Methionine contains sulfur too, but as a thioether that cannot form disulfides.

Risposta: C

Adenine and guanine are purines, with a double ring; cytosine, thymine and uracil are pyrimidines, with a single ring. In the double helix a purine always pairs with a pyrimidine (A with T, G with C), which keeps the helix the same width throughout.

Risposta: A

The first paragraph says the view began to change when recordings revealed recurring periods of rapid eye movement during which the brain was "almost as active as when awake". The memory experiments come later, in the second paragraph, and the third paragraph says that learning from night-time recordings failed.

Risposta: D

The passage says that "those who slept between learning and testing generally recall more than those who stayed awake for the same length of time". Nothing is said about how fast they learned.

Risposta: B

Recurring means happening again and again, so repeated. The context supports it: periods of rapid eye movement return several times during a night's sleep.

Risposta: C

The paragraph rejects learning in one's sleep ("attempts ... have repeatedly failed") and ends: sleep seems to strengthen what was learned while awake, "not to replace the effort of learning it". The first and last options say the opposite of what the paragraph reports.

Risposta: B

This is a third conditional, about an unreal situation in the past: if + past perfect (had known), then would have + past participle (would have told). "Knew" belongs in a second conditional (If I knew, I would tell you).

Risposta: B

With neither ... nor, the verb agrees with the nearer subject. "The teacher" is singular and the sentence is in the past, so "was". (Neither the teacher nor the students were aware would be correct, because "the students" would then be the nearer subject.)

Risposta: C

The analysis was finished before another past event (the inspector's arrival), so the past perfect is needed, and since the samples did not analyse anything themselves, it must be passive: had already been analysed. The other options are active, which would make the samples do the analysing.

Risposta: B

With the present perfect, "since" introduces the starting point (since 2019) and "for" a length of time (for six years). "From" needs an end point (from 2019 to 2023), and "during" refers to a period within which something happens.

Risposta: D

"Each" is singular, so the verb is singular (has), while "of the" is followed by a plural noun (of the patients). "Each" directly before a noun takes the singular: each patient.

Risposta: A

"Where" introduces a relative clause about a place, standing for "in which" (the hospital in which my sister was born). "Which" alone would need a preposition, "who" refers to people, and "what" cannot introduce a relative clause after a noun.

Risposta: B

After a reporting verb in the past (said), the tense usually moves one step back: present simple "am" becomes past simple "was". "Is" can be used when the statement is still true at the time of reporting, but it is not among the options; "is being", "will be" and "has been" change the meaning.

Risposta: B

After the verb "to be" an adjective is needed: effective. "Effect" is a noun, "effectively" an adverb, and "affect" a verb (to affect something).

Risposta: C

The negative prefix in- becomes il- before a word starting with l: legible, illegible (likewise legal, illegal; logical, illogical). The other forms do not exist.

Risposta: A

Inconclusive results do not settle the question, which is why the experiment had to be repeated. Indifferent describes a lack of interest, inevitable means bound to happen and inhabited means lived in; none of them explains the need to repeat it.

Risposta: C

To alleviate is to relieve or lessen: painkillers alleviate pain. It does not mean removing the pain completely, only making it less severe.

Risposta: D

In English, experiments are carried out (or conducted, performed, done). "Make an experiment" is a common error, often carried over from other languages.

Risposta: B

The noun is analysis (plural analyses), from Greek like diagnosis and synthesis. The other words do not exist.

Risposta: B

"Suggest" and "may" are hedging words: they present the finding as likely rather than certain, which is right when evidence is limited. The other sentences state the effect as universal or proven.

Risposta: C

The second clause adds a drawback that contrasts with the benefit in the first, so a contrasting linker is needed: however. "Therefore" would present dizziness as a result of lowering blood pressure, and "because" and "so that" cannot follow a semicolon like this.

Risposta: D

Contamination is the cause and discarding the results the effect, so "because" must introduce the contamination. The other three sentences reverse cause and effect.

Risposta: B

Hyper- means above or excessive: hyperglycaemia is a blood glucose level above normal. Its opposite is hypo- (hypoglycaemia, below normal); peri- means around and a- or an- without.

Risposta: A

-itis means inflammation: appendicitis is inflammation of the appendix and hepatitis of the liver. Surgical removal is -ectomy (appendectomy), enlargement -megaly (hepatomegaly) and a tumour -oma.

Risposta: B

Uni- means one, so a unicellular organism consists of one cell, like an amoeba or a bacterium. Lacking a nucleus describes prokaryotes, which are all unicellular, but many unicellular organisms, such as amoebae and yeasts, do have a nucleus; living inside another organism describes a parasite or symbiont.

Risposta: C

Cardiac (from Greek kardia) refers to the heart. Hepatic refers to the liver, renal to the kidney and pulmonary to the lungs.

Risposta: A

A mutation is a heritable change in the DNA sequence, from a single base to a whole chromosome. Making protein from mRNA is translation, and exchange between homologous chromosomes in meiosis is crossing over.

Risposta: C

Homo- means same: a homozygote carries two identical alleles (AA or aa). Two different alleles (Aa) make a heterozygote (hetero-, different), and a homozygote can just as well carry two recessive alleles.

Risposta: A

The phenotype is what can be observed or measured, from eye colour to blood group or enzyme activity, produced by the genotype together with the environment. The full set of genes is the genotype (or genome).

Risposta: D

To transcribe is to copy into another form: in transcription, RNA polymerase makes RNA from a DNA template. Copying DNA into DNA is replication, making protein from mRNA is translation, and removing introns is splicing.

Risposta: C

Tachy- means fast: tachycardia is a resting heart rate above normal, usually over 100 beats per minute. A slow heart rate is bradycardia (brady-, slow), an irregular one an arrhythmia, and a heart attack a myocardial infarction.

Risposta: A

Hypo- means below and tension here means blood pressure, so hypotension is low blood pressure; high blood pressure is hypertension. Low body temperature is hypothermia, and low blood glucose hypoglycaemia.

Risposta: D

Renal refers to the kidney (Latin ren). The liver's arterial supply is the hepatic artery, the lungs receive the pulmonary arteries and the brain the carotid and vertebral arteries.

Risposta: C

Haemato- means blood and -poiesis making, so haematopoiesis is the formation of blood cells, mainly in the red bone marrow in adults. Breakdown of red blood cells is haemolysis, clotting is coagulation and blood loss haemorrhage.

Risposta: A

Patho- means disease and -gen producing: a pathogen is anything that causes disease, such as a bacterium, virus, fungus or parasite. Antibodies are made by plasma cells, and a drug that kills bacteria is an antibiotic (bactericidal).

Risposta: B

An antigen is any molecule, or part of one, that antibodies or T- and B-cell receptors recognise, often a protein or polysaccharide on a microbe. The protein made by B cells (plasma cells) to bind it is the antibody, which is the mix-up the first option tests.

Risposta: A

Nosocomial (from Greek nosokomeion, hospital) means acquired during care in a hospital, also called a hospital-acquired or healthcare-associated infection. Infection passed from mother to child is vertical or congenital, and infection carried by insects is vector-borne.

Risposta: A

Hydro- means water and -phobic fearing: hydrophobic substances, such as fats and the tails of membrane lipids, are non-polar and do not mix readily with water. Substances that dissolve easily in water are hydrophilic, and breaking a bond with water is hydrolysis.

Risposta: C

Catabolic pathways break molecules down, as glycolysis breaks down glucose, and release energy, much of it captured as ATP. Building large molecules from smaller ones is anabolism; together the two make up metabolism.

Risposta: D

Iso- means equal: an isotonic solution exerts the same osmotic pressure as the cell, so water moves in and out equally and the cell keeps its volume. 0.9% saline is isotonic to red blood cells. A hypertonic solution draws water out and a hypotonic one lets it flow in.

Risposta: D

"For instance" (like "for example" or "such as") introduces an example. "In contrast" and "nevertheless" introduce a contrast, and "consequently" a result.

Risposta: D

To inhibit is to slow down or prevent an activity. The sentence describes feedback inhibition: when ATP is plentiful, an enzyme of an ATP-producing pathway is slowed down. The opposite would be "activated" or "stimulated".