ورودثبت‌نام رایگان

Amino Acid Side-Chain Properties Flashcards: Polarity & Charge

56 flashcards on amino acid side-chain groups, charge at pH 7, and common property distinctions, with supplied-pKa reasoning and key exceptions.

نوشتهٔ Flashcards Open Source App

دربارهٔ این دسته

Practice amino acid side-chain properties with 56 original flashcards for learners who already recognize the 20 standard amino-acid names. The cards ask you to recall a named amino acid’s property group, identify an amino acid or a specified set from a functional-group clue, distinguish commonly confused properties, and infer predominant side-chain charge from supplied pH and pKa values.

The reference pH is 7. Charge means the R group alone, excluding backbone groups and peptide termini. Ordinary charge statements use a simple aqueous reference model, not a guarantee about a particular site inside a protein. The calculations supply their pKa assumptions; one cysteine example changes the pH to 9.3, and one histidine example supplies a shifted local pKa. You do not need to memorize exact pKa values.

This deck uses a four-group study convention: nonpolar (glycine, alanine, valine, leucine, isoleucine, methionine, proline, phenylalanine, tryptophan); polar and predominantly uncharged at pH 7 (serine, threonine, asparagine, glutamine, cysteine, tyrosine); acidic (aspartate, glutamate); and basic (lysine, arginine, histidine). These are broad labels. Tryptophan has a polar hydrogen-bond donor; cysteine can behave hydrophobically; tyrosine is both aromatic and polar. Histidine belongs to the basic family but is mostly neutral at pH 7 when its side-chain pKa is 6.0. Aromaticity, polarity, and charge are not mutually exclusive descriptors.

The sequence starts with charge scope and classification, introduces the 20 amino acids in an interleaved order, then moves through property clues, comparisons, and pH reasoning. Related recall directions are separated so a nearby answer is less likely to give away the next one. Glycine’s flexibility, proline’s ring and backbone donor exception, cysteine’s disulfides, aromatic side chains, and acid-versus-amide distinctions receive focused practice.

The deck does not test one-letter or three-letter codes, structure drawings, exact pKa memorization, pI calculations, codons, dietary requirements, clinical decisions, or full-course/exam coverage. Broad clues are only reversed when the requested answer is a clear amino acid or an explicitly requested set. Structure and code recognition are covered separately in the amino acid structures and codes deck.

The questions, answers, examples, sequence, and metadata were independently authored from common biochemical facts. Fact checks used EMBL-EBI’s side-chain chemistry and ionisation guidance, plus ChEBI’s chemical classification. No source passages, exercises, or diagrams were copied. The cover is an original AI-generated conceptual illustration, not a chemical model.

Original text, organization, metadata, and generated cover are offered under CC0 1.0 to the extent applicable rights exist. This dedication does not cover source materials or anyone else’s rights. This is an independent study resource, not affiliated with or endorsed by EMBL-EBI or any course or examination provider.

کارت‌های این دسته

  1. کارت ۱

    پرسش

    When a card asks for an amino acid’s side-chain charge, which charges should you leave out?

    پاسخ

    The backbone amino and carboxyl groups, including peptide termini. Count only the R group’s charge.

  2. کارت ۲

    پرسش

    Can an uncharged amino-acid side chain still be polar?

    پاسخ

    Yes. Uneven electron distribution can make a group polar without giving it a net charge; a hydroxyl group is an example.

  3. کارت ۳

    پرسش

    Are ‘aromatic,’ ‘polar,’ and ‘basic’ mutually exclusive amino-acid labels?

    پاسخ

    No. They describe different features. A ring can be aromatic while another feature makes the side chain polar or basic. Group labels are a study convention, not an exhaustive chemical description.

  4. کارت ۴

    پرسش

    Alanine side chain → polarity group?

    پاسخ

    Nonpolar. Its methyl group has no polar functional group.

  5. کارت ۵

    پرسش

    Serine side chain at pH 7 → polarity/charge group?

    پاسخ

    Polar, predominantly uncharged. It contains a hydroxyl group.

  6. کارت ۶

    پرسش

    Aspartate side chain at pH 7 → acid/base group and predominant charge?

    پاسخ

    Acidic; −1. The side-chain carboxyl group is predominantly deprotonated under the usual aqueous reference conditions.

  7. کارت ۷

    پرسش

    Valine side chain → polarity group?

    پاسخ

    Nonpolar. It is a branched hydrocarbon side chain.

  8. کارت ۸

    پرسش

    Glutamine side chain at pH 7 → polarity/charge group?

    پاسخ

    Polar, uncharged. Its amide group does not behave like glutamate’s carboxylate.

  9. کارت ۹

    پرسش

    Lysine side chain at pH 7 → acid/base group and predominant charge?

    پاسخ

    Basic; +1. Its terminal side-chain amino group is predominantly protonated under the usual aqueous reference conditions.

  10. کارت ۱۰

    پرسش

    Phenylalanine side chain → polarity group?

    پاسخ

    Nonpolar. Its benzyl group contains an aromatic ring.

  11. کارت ۱۱

    پرسش

    Glycine → polarity group in this deck’s convention?

    پاسخ

    Nonpolar. Its R group is just hydrogen; the grouping does not imply a large hydrophobic side chain.

  12. کارت ۱۲

    پرسش

    Threonine side chain at pH 7 → polarity/charge group?

    پاسخ

    Polar, predominantly uncharged. Its hydroxyl group contributes polarity despite the methyl group beside it.

  13. کارت ۱۳

    پرسش

    Glutamate side chain at pH 7 → acid/base group and predominant charge?

    پاسخ

    Acidic; −1. Its side-chain carboxyl group is predominantly deprotonated under the usual aqueous reference conditions.

  14. کارت ۱۴

    پرسش

    Leucine side chain → polarity group?

    پاسخ

    Nonpolar. It is a branched hydrocarbon side chain.

  15. کارت ۱۵

    پرسش

    Cysteine at pH 7 → group in this deck’s convention?

    پاسخ

    Polar, predominantly uncharged. The side-chain thiol is usually mostly protonated. Cysteine can also behave hydrophobically, so classification schemes differ.

  16. کارت ۱۶

    پرسش

    Arginine side chain at pH 7 → acid/base group and predominant charge?

    پاسخ

    Basic; +1. The guanidinium group is predominantly protonated under the usual aqueous reference conditions.

  17. کارت ۱۷

    پرسش

    Tryptophan → polarity group in this deck’s convention?

    پاسخ

    Nonpolar overall, with a polar feature. Its large aromatic indole group is hydrophobic, but its N–H can donate a hydrogen bond.

  18. کارت ۱۸

    پرسش

    Proline → polarity group in this deck’s convention?

    پاسخ

    Nonpolar. Its side chain also closes a ring with the backbone nitrogen, restricting backbone motion.

  19. کارت ۱۹

    پرسش

    Asparagine side chain at pH 7 → polarity/charge group?

    پاسخ

    Polar, uncharged. Its amide group is distinct from aspartate’s carboxylate.

  20. کارت ۲۰

    پرسش

    Isoleucine side chain → polarity group?

    پاسخ

    Nonpolar. It is a branched hydrocarbon side chain.

  21. کارت ۲۱

    پرسش

    Histidine → acid/base family?

    پاسخ

    Basic. Its imidazole can accept a proton. ‘Basic’ does not mean mostly +1 at pH 7: with a side-chain pKa of 6.0, most molecules have a neutral side chain.

  22. کارت ۲۲

    پرسش

    Tyrosine at pH 7 → group in this deck’s convention?

    پاسخ

    Polar, predominantly uncharged. Its phenolic hydroxyl adds polarity to an aromatic, partly hydrophobic side chain; other schemes group it with the aromatics.

  23. کارت ۲۳

    پرسش

    Methionine side chain → polarity group?

    پاسخ

    Nonpolar overall. Its sulfur is part of a thioether, not a thiol.

  24. کارت ۲۴

    پرسش

    Which standard amino acid has hydrogen as its R group and no chiral alpha carbon?

    پاسخ

    Glycine. Its small R group also permits more backbone conformations than most residues.

  25. کارت ۲۵

    پرسش

    Which two standard amino acids have side-chain amide groups?

    پاسخ

    Asparagine and glutamine. Their amides are polar and uncharged at pH 7.

  26. کارت ۲۶

    پرسش

    For a single ionizable side-chain group, what does pH below its pKa favor?

    پاسخ

    The protonated form. Whether that form is neutral or positive depends on the group.

  27. کارت ۲۷

    پرسش

    Which two standard amino acids have aliphatic alcohol side chains?

    پاسخ

    Serine and threonine. Tyrosine’s hydroxyl is phenolic, attached directly to an aromatic ring.

  28. کارت ۲۸

    پرسش

    Which standard amino acid supplies the side-chain sulfur atoms of a protein disulfide bond?

    پاسخ

    Cysteine. Oxidation of two cysteine thiols can produce a covalent S–S link.

  29. کارت ۲۹

    پرسش

    Which three standard amino acids are conventionally called the branched-chain amino acids?

    پاسخ

    Valine, leucine, and isoleucine. All three have nonpolar hydrocarbon side chains.

  30. کارت ۳۰

    پرسش

    Which two standard amino acids usually have negatively charged side-chain carboxylates at pH 7?

    پاسخ

    Aspartate and glutamate.

  31. کارت ۳۱

    پرسش

    Which standard amino acid closes its side chain back onto the backbone nitrogen?

    پاسخ

    Proline. The ring restricts backbone flexibility; an internal proline residue also lacks the usual peptide N–H donor.

  32. کارت ۳۲

    پرسش

    For a single ionizable side-chain group, what is the protonated:deprotonated ratio at pH = pKa?

    پاسخ

    1:1. Half is protonated and half is deprotonated in the simple two-state acid–base model.

  33. کارت ۳۳

    پرسش

    Which three standard amino acids form the usual ‘aromatic amino acids’ study group?

    پاسخ

    Phenylalanine, tyrosine, and tryptophan. Histidine’s imidazole is chemically aromatic too, but introductory grouping tables usually place histidine with the basic amino acids.

  34. کارت ۳۴

    پرسش

    Cysteine versus methionine: which side chain can make the usual protein disulfide link?

    پاسخ

    Cysteine. It has a thiol; methionine has a thioether and does not form this cysteine-type disulfide link.

  35. کارت ۳۵

    پرسش

    For a single ionizable side-chain group, what does pH above its pKa favor?

    پاسخ

    The deprotonated form. For a carboxyl group this is negative; for a protonated amine losing its proton, it is neutral.

  36. کارت ۳۶

    پرسش

    At pH 7, why is aspartate usually charged while asparagine is uncharged?

    پاسخ

    Aspartate has a side-chain carboxylate (−1); asparagine has a neutral amide. Similar names do not mean the same functional group.

  37. کارت ۳۷

    پرسش

    Which standard amino acid has an imidazole side chain that can switch between neutral and +1 forms?

    پاسخ

    Histidine. Its protonation depends on pH and its local pKa.

  38. کارت ۳۸

    پرسش

    Which standard amino acid combines a phenyl ring with a phenolic hydroxyl group?

    پاسخ

    Tyrosine. The hydroxyl makes this aromatic side chain more polar than phenylalanine’s.

  39. کارت ۳۹

    پرسش

    Glycine versus proline: which generally allows more backbone conformations?

    پاسخ

    Glycine. Its tiny R group imposes little steric restriction; proline’s ring constrains the backbone.

  40. کارت ۴۰

    پرسش

    Why can tryptophan donate a side-chain hydrogen bond despite being grouped as nonpolar overall?

    پاسخ

    Its indole N–H can donate a hydrogen bond. A large hydrophobic group can still contain a polar site.

  41. کارت ۴۱

    پرسش

    Must every nonpolar side chain lie inside a water-soluble globular protein?

    پاسخ

    No. Burial of nonpolar groups is a tendency, not a rule for every residue. Protein shape and local interactions also matter.

  42. کارت ۴۲

    پرسش

    Assume histidine’s side-chain pKa is 6.0. At pH 7.0, is its predominant side-chain charge 0 or +1?

    پاسخ

    0

    pH is one unit above pKa, so neutral:protonated is 10:1; about 9% is +1. This is a supplied-pKa model, not a universal protein value.

  43. کارت ۴۳

    پرسش

    Assume cysteine’s thiol pKa is 8.3. At pH 7.0, which form predominates: neutral thiol or negative thiolate?

    پاسخ

    Neutral thiol. pH is below pKa, so the protonated S–H form predominates.

  44. کارت ۴۴

    پرسش

    At pH 7, which has a predominantly −1 side chain: glutamate or glutamine?

    پاسخ

    Glutamate. Glutamine’s side-chain amide is neutral.

  45. کارت ۴۵

    پرسش

    Assume tyrosine’s phenolic pKa is 10.1. At pH 7.0, is its side chain predominantly neutral or negative?

    پاسخ

    Neutral. The phenolic hydroxyl is mostly protonated because pH is below pKa.

  46. کارت ۴۶

    پرسش

    Assume lysine’s side-chain pKa is 10.5. At pH 7.0, is its side chain predominantly neutral or +1?

    پاسخ

    +1. pH is below pKa, favoring the protonated amino group.

  47. کارت ۴۷

    پرسش

    Assume aspartate’s side-chain pKa is 3.9. At pH 7.0, is its side chain predominantly neutral or −1?

    پاسخ

    −1. pH is above pKa, favoring the deprotonated carboxylate.

  48. کارت ۴۸

    پرسش

    Can a standard aqueous pKa value determine a buried protein side chain’s charge with certainty?

    پاسخ

    No. Nearby charges, solvent exposure, and other local interactions can shift pKa. Use a value appropriate to that site when it is known.

  49. کارت ۴۹

    پرسش

    With a histidine side-chain pKa of 6.0, does the label ‘basic amino acid’ imply a predominantly +1 side chain at pH 7?

    پاسخ

    No. ‘Basic’ describes proton-accepting chemistry; the predominant charge at a stated pH follows the pKa. Here the side chain is mostly neutral.

  50. کارت ۵۰

    پرسش

    Does a predominantly neutral tyrosine side chain at pH 7 make tyrosine nonpolar in this deck’s grouping?

    پاسخ

    No. Its hydroxyl is polar even when uncharged. This deck groups tyrosine as polar, uncharged and also recognizes its aromatic character.

  51. کارت ۵۱

    پرسش

    Does an internal proline residue have the same backbone N–H hydrogen-bond donor as most peptide residues?

    پاسخ

    No. Its backbone nitrogen has no attached hydrogen in the peptide chain. This is a backbone consequence of its ring, not a side-chain charge.

  52. کارت ۵۲

    پرسش

    At pH = pKa, a side chain switches between 0 and +1. Is each individual side chain charged +0.5?

    پاسخ

    No. The two forms occur in equal proportions, giving an ensemble-average charge of +0.5. Each form still has charge 0 or +1.

  53. کارت ۵۳

    پرسش

    Assume cysteine’s thiol pKa is 8.3. At pH 9.3, what is its predominant side-chain charge?

    پاسخ

    −1. Deprotonated thiolate predominates; the thiolate:thiol ratio is 10:1 in the simple model.

  54. کارت ۵۴

    پرسش

    At pH 7, which pair is a plausible side-chain salt bridge: lysine–glutamate or leucine–valine?

    پاسخ

    Lysine–glutamate: their usual side-chain charges are +1 and −1. A salt bridge still requires suitable proximity and environment.

  55. کارت ۵۵

    پرسش

    A histidine site has a measured side-chain pKa of 8.0. At pH 7.0, which side-chain form predominates?

    پاسخ

    The protonated +1 form. pH is below this site’s pKa; use the supplied local value rather than a generic histidine value.

  56. کارت ۵۶

    پرسش

    Phenylalanine versus tyrosine: which has the side-chain hydroxyl that adds polarity?

    پاسخ

    Tyrosine. Phenylalanine lacks that hydroxyl; both contain an aromatic ring.

Abstract teal protein ribbon with colorful side branches on a dark blue background; conceptual illustration.

۵۶ کارت

Amino Acid Side-Chain Properties Flashcards: Polarity & Charge

این دسته را رایگان مطالعه کنید

Nibomo باز می‌شود تا بتوانید مطالعه را شروع کنید.