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Alle 15 spørsmål i oversikt

Vil du heller lese før du spiller? Alle spørsmålene i smakebiten står listet under. Svar og forklaringer er skjult til du åpner dem.

1. 1. A globular protein folds in water. Which amino acid side chain is most likely to end up buried in the hydrophobic core?

   • A. Aspartate
   • B. Lysine
   • C. Valine
   • D. Serine
   Vis svar og forklaring

   Svar: C. Valine

   Folding in water pushes nonpolar side chains inward and leaves charged and polar ones on the surface where they can interact with water. Valine has a branched hydrocarbon side chain with nothing to hydrogen bond, so the core is where it costs the least energy. Aspartate and lysine carry charges at physiological pH and serine has a hydroxyl group, so all three prefer the surface.

2. 2. A competitive inhibitor is added to an enzyme assay. What happens to the apparent Km and the Vmax?

   • A. Km increases and Vmax is unchanged
   • B. Km decreases and Vmax is unchanged
   • C. Km is unchanged and Vmax decreases
   • D. Km increases and Vmax decreases
   Vis svar og forklaring

   Svar: A. Km increases and Vmax is unchanged

   A competitive inhibitor binds the active site, so it fights substrate for the same spot. That means you need more substrate to reach half maximal velocity, which shows up as a higher apparent Km. Enough substrate still outcompetes the inhibitor completely, so Vmax is untouched. Pure noncompetitive inhibition is the mirror image: Vmax falls and Km stays put.

3. 3. Complete the sentence.

   In oxidative phosphorylation, the electron transport chain uses the energy released by electron transfer to pump protons into the _____. ATP synthase then makes ATP as those protons flow back down their gradient into the _____.

   Alternativer for luke 1: mitochondrial matrix, intermembrane space, cytosol

   Alternativer for luke 2: mitochondrial matrix, intermembrane space, cytosol

   Vis svar og forklaring

   Svar: intermembrane space, mitochondrial matrix

   The electron transport chain is a series of redox reactions, and the energy it releases is stored as a proton gradient across the inner mitochondrial membrane rather than as ATP directly. ATP synthase is the only part that turns that gradient back into chemical energy. This is why an uncoupler that lets protons leak across the membrane keeps electron transport and oxygen consumption running while ATP output collapses.

4. 4. A buffer is made from a weak acid and its conjugate base. Its buffering capacity is greatest when:

   • A. The solution pH is two units below the pKa
   • B. The solution pH is two units above the pKa
   • C. The solution pH equals the pKa
   • D. The weak acid is present in large excess over the conjugate base
   Vis svar og forklaring

   Svar: C. The solution pH equals the pKa

   The Henderson-Hasselbalch equation says pH equals pKa plus the log of the base to acid ratio, so pH equals pKa exactly when that ratio is one. With equal amounts of both forms the buffer has the most room to absorb either added acid or added base before one form runs out. Practically, a buffer is useful roughly one pH unit on either side of its pKa, which is why bicarbonate and phosphate cover different ranges in the body.

5. 5. Which statements about eukaryotic gene expression are correct?

   Velg alle som passer.

   • A. Introns are spliced out of the primary transcript before the mature mRNA leaves the nucleus
   • B. The genetic code is degenerate, so several codons can specify the same amino acid
   • C. RNA polymerase requires a primer to begin synthesis
   • D. A missense mutation changes a codon so a different amino acid is inserted
   • E. Ribosomes read the mRNA from the 3 prime end toward the 5 prime end
   Vis svar og forklaring

   Svar: A. Introns are spliced out of the primary transcript before the mature mRNA leaves the nucleus, B. The genetic code is degenerate, so several codons can specify the same amino acid, D. A missense mutation changes a codon so a different amino acid is inserted

   Splicing, capping and polyadenylation all happen in the nucleus, and only the processed mRNA is exported. Degeneracy is why the third base of a codon often tolerates a change with no effect on the protein, which is the definition of a silent mutation, while a missense mutation swaps the amino acid and a nonsense mutation creates a stop codon. RNA polymerase can start a chain from scratch, unlike DNA polymerase, and ribosomes read mRNA 5 prime to 3 prime.

6. 6. In the proximal tubule of the nephron, glucose crosses the apical membrane into the cell against its own concentration gradient by moving together with sodium. This is best described as:

   • A. Simple diffusion
   • B. Facilitated diffusion
   • C. Primary active transport
   • D. Secondary active transport
   Vis svar og forklaring

   Svar: D. Secondary active transport

   Secondary active transport means the carrier itself burns no ATP. It rides an ion gradient that some other pump paid for. Here the sodium potassium ATPase on the basolateral side spends ATP to keep intracellular sodium low, and the sodium glucose cotransporter uses that inward sodium gradient to drag glucose uphill. Block the ATPase and the sodium gradient collapses, and glucose reabsorption stops even though the cotransporter is untouched.

7. 7. Complete the sentence.

   In an infrared spectrum, a broad absorption centered near 3300 reciprocal centimeters points to an _____ bond, while a strong sharp band near 1700 reciprocal centimeters points to a _____.

   Alternativer for luke 1: O to H, C to H, C to C double

   Alternativer for luke 2: carbon carbon double bond, carbonyl group, nitrile group

   Vis svar og forklaring

   Svar: O to H, carbonyl group

   Infrared spectroscopy reports bond vibrations, and the two most useful signals for a first pass are the broad hydroxyl stretch and the sharp carbonyl stretch. The hydroxyl band is broad because hydrogen bonding gives the bond a range of strengths across the sample. Seeing both a broad hydroxyl band and a carbonyl band in one spectrum is the classic hint that you are looking at a carboxylic acid.

8. 8. Which carboxylic acid derivative is most reactive toward nucleophilic acyl substitution?

   • A. An acyl chloride
   • B. An ester
   • C. An amide
   • D. A carboxylate ion
   Vis svar og forklaring

   Svar: A. An acyl chloride

   Reactivity in this family tracks two things: how good the leaving group is and how much the attached atom donates electron density into the carbonyl. Chloride is a weak base and a good leaving group, and it donates very little, so the acyl chloride sits at the top. Nitrogen donates strongly, which makes amides the most stable of the neutral derivatives, and a carboxylate is already deprotonated and negatively charged, so a nucleophile has little reason to attack it.

9. 9. A reaction has a negative delta G under the given conditions. Which statements are correct?

   Velg alle som passer.

   • A. The reaction must proceed quickly
   • B. The reaction is spontaneous as written under those conditions
   • C. The reaction must be exothermic
   • D. An enzyme could speed it up without changing the value of delta G
   • E. Under standard conditions, a negative standard delta G means the equilibrium constant is greater than one
   Vis svar og forklaring

   Svar: B. The reaction is spontaneous as written under those conditions, D. An enzyme could speed it up without changing the value of delta G, E. Under standard conditions, a negative standard delta G means the equilibrium constant is greater than one

   Delta G is about thermodynamics, not speed. A spontaneous reaction can take years if the activation energy is high, and a catalyst lowers that barrier without touching the free energy difference between reactants and products. Spontaneity also does not require heat release, since a positive entropy change at high enough temperature can make delta G negative for an endothermic reaction. Standard delta G is related to the equilibrium constant by delta G naught equals minus RT ln K, so a negative value puts K above one.

10. 10. Circulating thyroid hormone rises because the thyroid gland itself is overproducing. In an intact feedback loop, what happens to TSH released by the anterior pituitary?

    • A. It rises, because hormone levels and TSH move together
    • B. It falls, because the high hormone level suppresses the pituitary and the hypothalamus
    • C. It stays the same, because TSH is regulated only by the hypothalamus
    • D. It rises first and then stays permanently elevated
    Vis svar og forklaring

    Svar: B. It falls, because the high hormone level suppresses the pituitary and the hypothalamus

    The hypothalamus releases TRH, the anterior pituitary releases TSH, and the thyroid releases its hormones, which then feed back to shut down the two levels above. When the gland at the end of the chain is the source of the excess, the feedback signal is strong and TSH goes down. That inverse pattern is the point of a negative feedback loop, and the same logic runs the hypothalamus, pituitary and adrenal axis with cortisol.

11. 11. A vessel behaves as a rigid tube with steady laminar flow. If its radius drops to half while the pressure difference across it stays the same, the flow rate becomes about:

    • A. One half of the original
    • B. One quarter of the original
    • C. One eighth of the original
    • D. One sixteenth of the original
    Vis svar og forklaring

    Svar: D. One sixteenth of the original

    Poiseuille's law says flow rate is proportional to the fourth power of the radius for a given pressure difference, viscosity and length. Halving the radius therefore divides flow by two to the fourth, which is sixteen. That fourth power dependence is why radius changes dominate resistance in the circulation, and why small changes in vessel diameter matter far more than changes in length or viscosity.

12. 12. A student has a headache, takes a painkiller, and the headache goes away. She now reaches for the painkiller sooner whenever a headache starts. In operant terms this is:

    • A. Positive reinforcement
    • B. Negative reinforcement
    • C. Positive punishment
    • D. Classical conditioning
    Vis svar og forklaring

    Svar: B. Negative reinforcement

    In operant conditioning, reinforcement means the behavior becomes more frequent and punishment means it becomes less frequent. Positive and negative describe whether something was added or taken away, not whether it felt good. Here an unpleasant stimulus was removed and the behavior increased, which is negative reinforcement by definition. Classical conditioning would involve pairing two stimuli to produce an involuntary response, not strengthening a voluntary action by its consequence.

13. 13. The smallest change in a stimulus that a person can detect half of the time is called the:

    • A. Absolute threshold
    • B. Signal detection criterion
    • C. Difference threshold
    • D. Point of sensory adaptation
    Vis svar og forklaring

    Svar: C. Difference threshold

    The difference threshold, also called the just noticeable difference, is about telling two stimuli apart, while the absolute threshold is the smallest stimulus that can be detected at all half the time. Weber's law adds that the difference threshold is a constant proportion of the original stimulus rather than a fixed amount, so a heavier weight needs a bigger change before you notice it. The signal detection criterion is a separate idea about how willing someone is to say yes when they are unsure.

14. 14. Researchers record the diets of 2,000 healthy adults, then follow the same people for 20 years and record who develops heart disease. Which statements about this study are correct?

    Velg alle som passer.

    • A. It is a prospective cohort study
    • B. Participants were randomly assigned to a diet
    • C. Participants dropping out over the 20 years can bias the result
    • D. It can measure how many new cases of heart disease appear in each diet group
    • E. It shows that diet causes heart disease
    Vis svar og forklaring

    Svar: A. It is a prospective cohort study, C. Participants dropping out over the 20 years can bias the result, D. It can measure how many new cases of heart disease appear in each diet group

    The exposure was measured before the outcome appeared and the group was followed forward, which makes this a prospective cohort study. That design can measure incidence, meaning new cases over time, which case control studies cannot do directly. What it cannot do is establish causation, because nobody assigned the exposure and people who eat differently may differ in many other ways. Attrition matters because the people who leave a long study are often not a random sample of those who stay.

15. 15. Complete the sentence.

    Blaming a stranger's rudeness on their personality while ignoring what is going on around them is the _____. Explaining your own good grade by your ability but your own bad grade by an unfair test is the _____.

    Alternativer for luke 1: fundamental attribution error, self-serving bias, just world hypothesis

    Alternativer for luke 2: actor observer bias, self-serving bias, halo effect

    Vis svar og forklaring

    Svar: fundamental attribution error, self-serving bias

    Attribution questions turn on two axes: whether the cause is placed inside the person or in the situation, and whether the person being judged is you or somebody else. The fundamental attribution error is over-weighting personality when explaining other people. The self-serving bias protects your own self-image by taking internal credit for success and external blame for failure. Both are on the MCAT because they shape how patients and clinicians read each other.

Dette spør de tre naturvitenskapelige delene faktisk om

MCAT har fire deler. Tre av dem er naturvitenskapelige: Chemical and Physical Foundations of Biological Systems, Biological and Biochemical Foundations of Living Systems, og Psychological, Social, and Biological Foundations of Behavior. Den fjerde er Critical Analysis and Reasoning Skills, som er ren lesing og har sin egen side. Hver naturvitenskapelig del har nå 59 spørsmål på 95 minutter, og omtrent 15 av de 59 er frittstående spørsmål som står på egne bein uten tekst. Delpoengene går fra 118 til 132, og de fire delene summerer seg til en total mellom 472 og 528, med 500 midt på skalaen. AAMC kan endre formatet, så bekreft de gjeldende tallene på aamc.org før du bygger en plan rundt dem.

Selve innholdet kommer fra innholdskategoriene AAMC publiserer. Det som overrasker folk flest er hvor mye biokjemi som dukker opp, og at det dukker opp i to forskjellige deler. Aminosyrer, enzymkinetikk og metabolisme kan testes i biologidelen og igjen i kjemi- og fysikkdelen. Fysikken er smal og anvendt, mest væsker og trykk, termodynamikk, optikk og kretser, og den er nesten alltid rammet inn i et levende system framfor en kloss som sklir ned et skråplan.

Delen om psykologi og sosiologi er en ekte innholdsdel med sitt eget fagspråk, ikke en del du klarer på sunn fornuft, og det går folk i baret. Betinging, hukommelsessystemer, persepsjonsterskler, attribusjonsteori og forskningsdesign har alle presise definisjoner, og spørsmålene står og faller på de definisjonene. På tvers av alle tre delene er de fleste oppgavene ikke enkel gjenkalling. De gir deg et scenario, en graf eller et sett resultater og spør hva som følger av det, så det å kunne et begrep er bare halvparten av det du trenger.

Slik bruker du denne smakebiten

Hvert spørsmål under er et frittstående spørsmål med hensikt. Frittstående spørsmål er den reneste testen på om du faktisk kan innholdet, fordi det ikke ligger noen tekst ved siden av som stille gir deg konteksten. Klarer du de frittstående kaldt, blir tekstoppgavene mye lettere. Klarer du dem ikke, vil øving på tekstoppgaver skjule hullet framfor å tette det. De to quizene som er lenket under dekker den blandede tekststilen og lesedelen, så ta alle tre og sammenlign hvor du mister poeng.

Ta den i én økt uten notater, med rundt 90 sekunder per spørsmål, og les så forklaringen til hver oppgave, også de du fikk riktig. Å gjette riktig og å kunne er ikke det samme, og bare det ene overlever prøvedagen. Behandle hver bom som et tema framfor et faktum. Bommet du på bufferspørsmålet og termodynamikkspørsmålet, repeter syre-base og likevekt sammen, for det er det samme resonnementet brukt på to forskjellige størrelser.

En merknad om hva disse spørsmålene er. StudyPDF-teamet har skrevet alle 15 ut fra innholdskategoriene AAMC publiserer. De er ikke AAMC-oppgaver, de er ikke kopiert fra noen spørsmålsbank eller repetisjonsbok, og StudyPDF er ikke tilknyttet AAMC. De er eksamensøving, ikke medisinsk veiledning, og ingenting på denne siden skal brukes til å ta en avgjørelse om en ekte pasient.

Slik bygger StudyPDF fullengdes øvingsprøver fra ditt eget materiale

Femten spørsmål kan vise deg hvilken innholdskategori som er svak. De kan ikke bære en hel MCAT-plan, og en generell spørsmålsbank treffer sjelden vektleggingen i repetisjonsbøkene og forelesningsnotatene du faktisk leser fra.

StudyPDF jobber fra ditt eget materiale i stedet. Du laster opp kapittelet fra repetisjonsboka, lysarkene fra biokjemiforelesningen eller sammendraget av reaksjonsveiene du lagde selv, så skriver Bo, studieagenten, fullengdes øvingsprøver fra akkurat de sidene. Hvert spørsmål er forankret i ditt materiale og hver forklaring viser hvor svaret kommer fra, så når noe ser galt ut kan du gå rett til kilden og sjekke. Du kan lage nye prøver så ofte du vil, snevre dem inn til ett område som enzymkinetikk eller forskningsdesign, og følge med på hvilke begreper du stadig bommer på.

Du trenger ingen fil for å komme i gang. Har du ingenting å laste opp, oppgi et tema i stedet, for eksempel sitronsyresyklusen eller operant betinging, så skriver Bo et øvingssett fra det. Gratis å komme i gang.