Aminosyrequiz: de 20 standardaminosyrer
- 15 spørgsmål
- Cirka 15 min.
- Gratis
Testens spørgsmål er på engelsk.
Which pair of one-letter codes belongs to glutamine and glutamic acid (glutamate), in that order?
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Om denne test
Den her gratis aminosyrequiz har 15 spørgsmål skrevet af StudyPDF-teamet. Den dækker koderne med ét bogstav, sidekædernes klasser, ladning ved fysiologisk pH, essentielle aminosyrer, kiralitet, det isoelektriske punkt og de særtilfælde, der dukker op i biokemi og i eksamener i MCAT-stil, som prolin, cystein og histidin. Svar på alle 15, se så din score og læs forklaringen til hvert spørgsmål.
Alle 15 spørgsmål i overblik
Vil du hellere læse, før du går i gang? Alle spørgsmål i smagsprøven står herunder. Svar og forklaringer er foldet sammen, indtil du åbner dem.
1.Which pair of one-letter codes belongs to glutamine and glutamic acid (glutamate), in that order?
- A. E and Q
- B. Q and E
- C. N and D
- D. D and N
Svar: B. Q and E
Glutamine is Q and glutamic acid is E. Asparagine (N) and aspartic acid (D) are the same amide and acid pair with a side chain one carbon shorter, so N and D belong to a different pair of amino acids. The trap here is the order: E and Q has the right letters in the wrong order, and D and N is the shorter pair in reverse.
2.Which pair of amino acids has side chains that are positively charged at physiological pH?
- A. Aspartate and glutamate
- B. Serine and threonine
- C. Valine and leucine
- D. Lysine and arginine
Svar: D. Lysine and arginine
The lysine side chain ends in an amino group with a pKa near 10.5, and the arginine side chain ends in a guanidinium group with a pKa near 12.5. Both are far above 7.4, so both are protonated and positive in the body. Aspartate and glutamate carry negative carboxylates, serine and threonine are polar but uncharged, and valine and leucine are nonpolar. Histidine is mostly neutral at 7.4 because its pKa is near 6, so it does not belong in this pair even though it is classed as basic.
3.Which of these amino acids have nonpolar side chains?
Vælg alle, der passer.
- A. Valine
- B. Serine
- C. Leucine
- D. Asparagine
- E. Methionine
Svar: A. Valine, C. Leucine, E. Methionine
Valine and leucine have branched hydrocarbon side chains with nothing to form hydrogen bonds. Methionine has a thioether, with sulfur bonded to two carbons, and that sulfur is a poor hydrogen-bond partner, so methionine counts as nonpolar too. Serine has a hydroxyl group and asparagine has an amide, so both are polar and uncharged. Nonpolar residues tend to sit in the interior of a folded protein, away from water.
4.Complete the sentence.
The one-letter code for lysine is _____, and lysine has a _____ side chain.
Muligheder for felt 1: L, K, Y, R
Muligheder for felt 2: basic, acidic, nonpolar, polar but uncharged
Svar: K, basic
Lysine is K. L is already leucine, Y is tyrosine and R is arginine. A common memory aid is that K sits right next to L in the alphabet, and L already belongs to leucine. The side chain ends in an amino group that picks up a proton at physiological pH, which makes it basic and positively charged. Lysine, arginine and histidine are the basic three.
5.Which of these side chains has a pKa closest to physiological pH (about 7.4), so small pH shifts can switch it between protonated and deprotonated?
- A. Aspartate
- B. Lysine
- C. Arginine
- D. Histidine
Svar: D. Histidine
The imidazole ring of histidine has a pKa near 6, the closest of these four to the pH of the body and the one textbooks single out as a physiological buffer. Near that pH it can pick up and give back protons, which is why histidine is common in enzyme active sites and in buffering proteins such as hemoglobin. Aspartate (about 3.9) is deprotonated and negative well below 7.4, while lysine (about 10.5) and arginine (about 12.5) stay protonated and positive well above it.
6.Glycine has an alpha-carboxyl pKa of about 2.3 and an alpha-amino pKa of about 9.6, and its side chain has no ionizable group. What is its approximate isoelectric point (pI)?
- A. 5.95
- B. 2.3
- C. 7.0
- D. 9.6
Svar: A. 5.95
The pI is the pH at which the net charge is zero. With no ionizable side chain, it sits halfway between the two pKa values: (2.3 + 9.6) / 2 = 5.95. Around that pH the molecule is mostly the neutral zwitterion, with a positive amino group and a negative carboxylate. For an acidic amino acid, average the two lowest pKa values instead, and for a basic one the two highest. The answers 2.3 and 9.6 are single pKa values, and 7.0 is not special for an amino acid.
7.Complete the sentence.
In a solution whose pH is below an amino acid's pI, the molecule carries a net _____ charge, so in an electric field it moves toward the _____.
Muligheder for felt 1: negative, zero, positive, variable
Muligheder for felt 2: positive electrode, negative electrode, neither electrode, both electrodes at once
Svar: positive, negative electrode
Lowering the pH below the pI means more protons are around, so the groups hold on to them: the amino group stays positive and the carboxyl group loses its negative charge. The net charge is positive, and a positive molecule migrates toward the negative electrode, the cathode. Above the pI the opposite happens, the net charge is negative and the molecule moves toward the anode. At the pI itself it has no net charge and does not move.
8.In nearly every L-amino acid the alpha carbon has the S configuration. Which of these is the exception, with an R alpha carbon?
- A. Serine
- B. Alanine
- C. Cysteine
- D. Methionine
Svar: C. Cysteine
R and S come from the Cahn-Ingold-Prelog priority rules, not from the L or D family. In cysteine, the CH2SH group outranks the carboxyl group because sulfur has a higher atomic number than oxygen, so the same spatial arrangement that is labeled S in serine, alanine or methionine is labeled R. L-cysteine and its neighbors have the same three-dimensional layout. Only the priority order changes, which is why L does not simply mean S.
9.Complete the sentence.
_____ is the only one of the 20 standard amino acids with no chiral center, and the amino acids built into proteins are the _____ stereoisomers.
Muligheder for felt 1: Alanine, Glycine, Proline, Serine
Muligheder for felt 2: D, racemic, L, meso
Svar: Glycine, L
The side chain of glycine is just a hydrogen, so its alpha carbon has two identical hydrogens and no mirror-image form. Every other standard amino acid has four different groups on the alpha carbon, so each can exist as an L or a D form. Ribosomes build proteins from the L form. D-amino acids do exist in nature, for example in bacterial cell walls, but they are not what the genetic code builds into proteins.
10.What makes proline structurally unusual among the 20 standard amino acids?
- A. Its side chain loops back onto the backbone nitrogen, forming a ring
- B. It is the only one with a sulfur atom in its side chain
- C. It is the only one with an aromatic ring
- D. It is the only one without a chiral alpha carbon
Svar: A. Its side chain loops back onto the backbone nitrogen, forming a ring
The three-carbon side chain of proline bonds to the alpha carbon and to the backbone nitrogen, which closes a five-membered ring. That makes its nitrogen a secondary amine with no N-H to donate to a backbone hydrogen bond, and the ring limits rotation. So proline often starts turns and interrupts alpha helices. Sulfur is in cysteine and methionine, aromatic rings are in phenylalanine, tyrosine and tryptophan, and glycine is the one without a chiral center. Proline's alpha carbon is chiral.
11.Two cysteine residues in a folded protein are oxidized and joined. What is the covalent link called?
- A. A peptide bond
- B. A hydrogen bond
- C. A disulfide bond
- D. A salt bridge
Svar: C. A disulfide bond
The thiol groups (-SH) of two cysteines are oxidized to form an S-S bond, and the oxidized pair is called cystine. Disulfide bonds help stabilize the tertiary and quaternary structure of many secreted proteins, such as antibodies and insulin. The inside of a cell is a reducing environment, so most cysteines there stay as free thiols. A peptide bond joins neighboring backbone atoms, and a hydrogen bond and a salt bridge are noncovalent.
12.Which amino acids have a side chain that a protein kinase can phosphorylate?
Vælg alle, der passer.
- A. Serine
- B. Valine
- C. Threonine
- D. Alanine
- E. Tyrosine
Svar: A. Serine, C. Threonine, E. Tyrosine
Serine, threonine and tyrosine each carry a hydroxyl group on the side chain, and a kinase transfers a phosphate from ATP onto it. Serine and threonine kinases act on the first two, and tyrosine kinases on the third. Adding a phosphate adds negative charge and can switch an enzyme or a signaling protein on or off. Valine and alanine have hydrocarbon side chains with nothing to accept the phosphate.
13.Which of these amino acids are essential in the adult diet?
Vælg alle, der passer.
- A. Leucine
- B. Alanine
- C. Lysine
- D. Serine
- E. Tryptophan
Svar: A. Leucine, C. Lysine, E. Tryptophan
Leucine, lysine and tryptophan are three of the nine on the usual adult list, which also has histidine, isoleucine, methionine, phenylalanine, threonine and valine. Essential means the body cannot make enough of it. Alanine and serine are made from common metabolic intermediates (alanine from pyruvate, serine from 3-phosphoglycerate), so they are nonessential. Arginine, cysteine, glutamine, glycine, proline and tyrosine are the conditionally essential ones. Course lists vary a little, so use yours. This is exam content, not dietary advice.
14.Which of these is NOT one of the 20 standard amino acids that the genetic code specifies for proteins?
- A. Arginine
- B. Ornithine
- C. Asparagine
- D. Glutamine
Svar: B. Ornithine
Ornithine is an intermediate of the urea cycle, made from arginine by the enzyme arginase, and no codon specifies it. Arginine, asparagine and glutamine are all standard. Selenocysteine and pyrrolysine are found in the proteins of some organisms through special recoding, but they are not among the 20 of the standard codon table either.
15.A peptide bond joins two amino acids. Which groups react, and what is released?
- A. The side chains of the two residues, releasing carbon dioxide
- B. The alpha carbon of one and the side chain of the next, releasing hydrogen
- C. The carboxyl group of one and the amino group of the next, releasing water
- D. The amino groups of both residues, releasing ammonia
Svar: C. The carboxyl group of one and the amino group of the next, releasing water
A peptide bond is an amide link formed in a condensation (dehydration) reaction: the carboxyl group of one amino acid joins the amino group of the next and a molecule of water leaves. Side chains stay out of the backbone. A chain has a free amino group at one end, the N-terminus, and a free carboxyl group at the other, the C-terminus, and peptides are written from the N-terminus to the C-terminus.
De 20 aminosyrer: klasser, koder og listen over essentielle
Alle 20 standardaminosyrer har samme rygrad: et centralt alfa-kulstof bundet til en aminogruppe, en carboxylgruppe, et hydrogenatom og en sidekæde, skrevet R. Det er kun sidekæden, der er forskellig, og derfor afgør den næsten alt det, en quiz spørger om: klassen, ladningen ved fysiologisk pH, om resten sidder inde i et protein eller på overfladen, og hvad den kan i et enzym. Lærebøger deler normalt de 20 op i fem grupper. Upolære alifatiske: glycin, alanin, valin, leucin, isoleucin, methionin og prolin. Aromatiske: phenylalanin, tyrosin og tryptofan. Polære uladede: serin, threonin, cystein, asparagin og glutamin. Sure: aspartat og glutamat. Basiske: lysin, arginin og histidin. Kilderne er uenige om nogle grænsetilfælde, for eksempel om tyrosin regnes som aromatisk eller polær, så brug den inddeling, der er i dit eget kursus.
Du skal også kunne to sæt bogstaver. Koder med tre bogstaver og koder med ét bogstav, i alfabetisk rækkefølge: Ala A, Arg R, Asn N, Asp D, Cys C, Gln Q, Glu E, Gly G, His H, Ile I, Leu L, Lys K, Met M, Phe F, Pro P, Ser S, Thr T, Trp W, Tyr Y, Val V. De par, der snubler flest, er glutamin (Q) mod glutamat (E) og asparagin (N) mod aspartat (D).
Ni aminosyrer er opført som essentielle for voksne, og det betyder, at kroppen ikke kan danne nok af dem, så de skal komme fra maden: histidin, isoleucin, leucin, lysin, methionin, phenylalanin, threonin, tryptofan og valin. Arginin, cystein, glutamin, glycin, prolin og tyrosin kaldes ofte betinget essentielle, fordi kroppen danner dem, men kan komme til kort under sygdom, hurtig vækst eller stress. Listerne varierer lidt mellem kurser, især for arginin og histidin, så følg den, din underviser har givet dig.
Sådan bruger du quizzen, og hvad du skal lære i hvilken rækkefølge
De 15 spørgsmål fordeler sig sådan: tre om navne og koder, tre om sidekædens klasse og ladning, to om pI og nettoladning, to om kiralitet, ét om listen over essentielle, tre om særlige aminosyrer (prolin, cystein og de aminosyrer, som kinaser fosforylerer) og ét om peptidbindingen. De fleste spørger hvorfor, ikke kun hvilken. Hvorfor buffer histidin tæt på neutral pH, mens lysin ikke gør? Hvorfor er cystein R, når dens naboer er S? Hvorfor bryder prolin en helix? Det er de forklaringer, der kan bruges på et spørgsmål, du aldrig har set.
Tag den én gang uden at slå noget op, og læs så forklaringen til hvert spørgsmål, også dem du svarede rigtigt på. Behandl en fejl som et emne. Hvis du missede pI-spørgsmålet og nettoladningsspørgsmålet, er hullet sandsynligvis ideen om, at ladningen følger pH i forhold til hver enkelt pKa, ikke to adskilte fakta. De pKa-værdier, der står i spørgsmålene, er omtrentlige og afviger lidt mellem lærebøger, så quizzen giver dig altid de tal, den skal bruge. Den beder dig ikke om at tegne strukturer, så skitsér hver sidekæde på papir undervejs, for det er tegningen, der får klasserne til at sidde fast.
Hvis du hellere vil arbejde på papir, så brug knappen Hent prøven som PDF over spørgsmålene. Filen har alle 15 spørgsmål med en facitliste på sidste side, og den kræver en gratis StudyPDF-konto, mens det er gratis at spille online. Spørgsmålene er originale og skrevet ud fra almindeligt biokemistof på første semester. De er ikke taget fra en lærebog, en eksamen eller et forberedelsesfirmas bank, og intet her er kostvejledning.
Sådan bygger StudyPDF aminosyreøveprøver ud fra dine egne noter
Femten spørgsmål kan vise dig, hvilken del af emnet der er usikker. De kan ikke gøre dig klar alene, og en generel quiz matcher sjældent de strukturer, pKa-tabeller og grupperinger, som dit biokemikursus faktisk bruger.
StudyPDF tager i stedet udgangspunkt i dit eget materiale. Upload kapitler fra din lærebog, din undervisers slides eller dine forelæsningsnoter, tryk på Nyt materiale, og StudyPDF bygger øveprøver og flashcards ud fra præcis de sider. Hvert spørgsmål bygger på dit materiale, og hver forklaring henviser til, hvor svaret kommer fra, så du kan gå direkte tilbage til siden, når et trin ikke giver mening. Diagrammer og tabeller i dine filer kan også dukke op i spørgsmålene.
Du behøver ikke uploade noget for at komme i gang. Nævn i stedet et emne, for eksempel aminosyrers sidekæder eller det isoelektriske punkt, og Bo sætter det op med nøglebegreberne, så du kan bygge quizzer og flashcards om det. Dine resultater viser, hvilke begreber du bliver ved med at ramme forkert, så næste øveprøve kan målrette dem. Det er gratis at starte.
Skrevet af StudyPDF-teamet. Sidst opdateret 19. august 2026.
Godt at vide
Er den her aminosyrequiz gratis?
Ja. Alle 15 spørgsmål, scoreskærmen og hver forklaring er gratis, og quizzen kører i din browser. Du skal bruge en gratis StudyPDF-konto for at hente prøven som PDF med facitliste eller for at bygge flere quizzer og flashcards ud fra dine egne noter.
Hvem har skrevet spørgsmålene?
StudyPDF-teamet har skrevet hvert spørgsmål og hver forklaring ud fra almindeligt biokemistof på første semester. De er originale opgaver, ikke taget fra en lærebog, en eksamen eller et forberedelsesfirmas bank, og StudyPDF er ikke tilknyttet AAMC eller nogen eksamensudbyder. Opgaverne om essentielle aminosyrer er eksamenstræning, ikke kostvejledning.
Dækker quizzen alle 20 aminosyrer, og hvad med selenocystein?
Femten spørgsmål kan ikke spørge om hver enkelt rest, så quizzen prøver de ideer, der afgør de fleste spørgsmål: koder, klasser, ladning, pI, kiralitet og særtilfældene. Vil du have fuld dækning af alle navne, koder og strukturer, så byg flashcards ud fra dine egne noter. Selenocystein og pyrrolysin bliver bygget ind i proteiner i nogle organismer ved en særlig omkodning, men de hører ikke til de 20 standardaminosyrer, så quizzen holder sig til de 20.
Kan jeg få quizzer og flashcards bygget ud fra mit eget kursusmateriale?
Ja. Upload kapitler fra din lærebog, slides eller forelæsningsnoter til StudyPDF, så kan du bygge øveprøver og flashcards ud fra præcis de sider, med forklaringer knyttet til dine kilder. Har du ikke noget at uploade, så nævn et emne som aminosyrers sidekæder eller det isoelektriske punkt i stedet.