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.
Mayelana naleli qoqo
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.
Amakhadi akuleli qoqo
Ikhadi 1
Umbuzo
When a card asks for an amino acid’s side-chain charge, which charges should you leave out?
Impendulo
The backbone amino and carboxyl groups, including peptide termini. Count only the R group’s charge.
Ikhadi 2
Umbuzo
Can an uncharged amino-acid side chain still be polar?
Impendulo
Yes. Uneven electron distribution can make a group polar without giving it a net charge; a hydroxyl group is an example.
Ikhadi 3
Umbuzo
Are ‘aromatic,’ ‘polar,’ and ‘basic’ mutually exclusive amino-acid labels?
Impendulo
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.
Ikhadi 4
Umbuzo
Alanine side chain → polarity group?
Impendulo
Nonpolar. Its methyl group has no polar functional group.
Ikhadi 5
Umbuzo
Serine side chain at pH 7 → polarity/charge group?
Impendulo
Polar, predominantly uncharged. It contains a hydroxyl group.
Ikhadi 6
Umbuzo
Aspartate side chain at pH 7 → acid/base group and predominant charge?
Impendulo
Acidic; −1. The side-chain carboxyl group is predominantly deprotonated under the usual aqueous reference conditions.
Ikhadi 7
Umbuzo
Valine side chain → polarity group?
Impendulo
Nonpolar. It is a branched hydrocarbon side chain.
Ikhadi 8
Umbuzo
Glutamine side chain at pH 7 → polarity/charge group?
Impendulo
Polar, uncharged. Its amide group does not behave like glutamate’s carboxylate.
Ikhadi 9
Umbuzo
Lysine side chain at pH 7 → acid/base group and predominant charge?
Impendulo
Basic; +1. Its terminal side-chain amino group is predominantly protonated under the usual aqueous reference conditions.
Ikhadi 10
Umbuzo
Phenylalanine side chain → polarity group?
Impendulo
Nonpolar. Its benzyl group contains an aromatic ring.
Ikhadi 11
Umbuzo
Glycine → polarity group in this deck’s convention?
Impendulo
Nonpolar. Its R group is just hydrogen; the grouping does not imply a large hydrophobic side chain.
Ikhadi 12
Umbuzo
Threonine side chain at pH 7 → polarity/charge group?
Impendulo
Polar, predominantly uncharged. Its hydroxyl group contributes polarity despite the methyl group beside it.
Ikhadi 13
Umbuzo
Glutamate side chain at pH 7 → acid/base group and predominant charge?
Impendulo
Acidic; −1. Its side-chain carboxyl group is predominantly deprotonated under the usual aqueous reference conditions.
Ikhadi 14
Umbuzo
Leucine side chain → polarity group?
Impendulo
Nonpolar. It is a branched hydrocarbon side chain.
Ikhadi 15
Umbuzo
Cysteine at pH 7 → group in this deck’s convention?
Impendulo
Polar, predominantly uncharged. The side-chain thiol is usually mostly protonated. Cysteine can also behave hydrophobically, so classification schemes differ.
Ikhadi 16
Umbuzo
Arginine side chain at pH 7 → acid/base group and predominant charge?
Impendulo
Basic; +1. The guanidinium group is predominantly protonated under the usual aqueous reference conditions.
Ikhadi 17
Umbuzo
Tryptophan → polarity group in this deck’s convention?
Impendulo
Nonpolar overall, with a polar feature. Its large aromatic indole group is hydrophobic, but its N–H can donate a hydrogen bond.
Ikhadi 18
Umbuzo
Proline → polarity group in this deck’s convention?
Impendulo
Nonpolar. Its side chain also closes a ring with the backbone nitrogen, restricting backbone motion.
Ikhadi 19
Umbuzo
Asparagine side chain at pH 7 → polarity/charge group?
Impendulo
Polar, uncharged. Its amide group is distinct from aspartate’s carboxylate.
Ikhadi 20
Umbuzo
Isoleucine side chain → polarity group?
Impendulo
Nonpolar. It is a branched hydrocarbon side chain.
Ikhadi 21
Umbuzo
Histidine → acid/base family?
Impendulo
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.
Ikhadi 22
Umbuzo
Tyrosine at pH 7 → group in this deck’s convention?
Impendulo
Polar, predominantly uncharged. Its phenolic hydroxyl adds polarity to an aromatic, partly hydrophobic side chain; other schemes group it with the aromatics.
Ikhadi 23
Umbuzo
Methionine side chain → polarity group?
Impendulo
Nonpolar overall. Its sulfur is part of a thioether, not a thiol.
Ikhadi 24
Umbuzo
Which standard amino acid has hydrogen as its R group and no chiral alpha carbon?
Impendulo
Glycine. Its small R group also permits more backbone conformations than most residues.
Ikhadi 25
Umbuzo
Which two standard amino acids have side-chain amide groups?
Impendulo
Asparagine and glutamine. Their amides are polar and uncharged at pH 7.
Ikhadi 26
Umbuzo
For a single ionizable side-chain group, what does pH below its pKa favor?
Impendulo
The protonated form. Whether that form is neutral or positive depends on the group.
Ikhadi 27
Umbuzo
Which two standard amino acids have aliphatic alcohol side chains?
Impendulo
Serine and threonine. Tyrosine’s hydroxyl is phenolic, attached directly to an aromatic ring.
Ikhadi 28
Umbuzo
Which standard amino acid supplies the side-chain sulfur atoms of a protein disulfide bond?
Impendulo
Cysteine. Oxidation of two cysteine thiols can produce a covalent S–S link.
Ikhadi 29
Umbuzo
Which three standard amino acids are conventionally called the branched-chain amino acids?
Impendulo
Valine, leucine, and isoleucine. All three have nonpolar hydrocarbon side chains.
Ikhadi 30
Umbuzo
Which two standard amino acids usually have negatively charged side-chain carboxylates at pH 7?
Impendulo
Aspartate and glutamate.
Ikhadi 31
Umbuzo
Which standard amino acid closes its side chain back onto the backbone nitrogen?
Impendulo
Proline. The ring restricts backbone flexibility; an internal proline residue also lacks the usual peptide N–H donor.
Ikhadi 32
Umbuzo
For a single ionizable side-chain group, what is the protonated:deprotonated ratio at pH = pKa?
Impendulo
1:1. Half is protonated and half is deprotonated in the simple two-state acid–base model.
Ikhadi 33
Umbuzo
Which three standard amino acids form the usual ‘aromatic amino acids’ study group?
Impendulo
Phenylalanine, tyrosine, and tryptophan. Histidine’s imidazole is chemically aromatic too, but introductory grouping tables usually place histidine with the basic amino acids.
Ikhadi 34
Umbuzo
Cysteine versus methionine: which side chain can make the usual protein disulfide link?
Impendulo
Cysteine. It has a thiol; methionine has a thioether and does not form this cysteine-type disulfide link.
Ikhadi 35
Umbuzo
For a single ionizable side-chain group, what does pH above its pKa favor?
Impendulo
The deprotonated form. For a carboxyl group this is negative; for a protonated amine losing its proton, it is neutral.
Ikhadi 36
Umbuzo
At pH 7, why is aspartate usually charged while asparagine is uncharged?
Impendulo
Aspartate has a side-chain carboxylate (−1); asparagine has a neutral amide. Similar names do not mean the same functional group.
Ikhadi 37
Umbuzo
Which standard amino acid has an imidazole side chain that can switch between neutral and +1 forms?
Impendulo
Histidine. Its protonation depends on pH and its local pKa.
Ikhadi 38
Umbuzo
Which standard amino acid combines a phenyl ring with a phenolic hydroxyl group?
Impendulo
Tyrosine. The hydroxyl makes this aromatic side chain more polar than phenylalanine’s.
Ikhadi 39
Umbuzo
Glycine versus proline: which generally allows more backbone conformations?
Impendulo
Glycine. Its tiny R group imposes little steric restriction; proline’s ring constrains the backbone.
Ikhadi 40
Umbuzo
Why can tryptophan donate a side-chain hydrogen bond despite being grouped as nonpolar overall?
Impendulo
Its indole N–H can donate a hydrogen bond. A large hydrophobic group can still contain a polar site.
Ikhadi 41
Umbuzo
Must every nonpolar side chain lie inside a water-soluble globular protein?
Impendulo
No. Burial of nonpolar groups is a tendency, not a rule for every residue. Protein shape and local interactions also matter.
Ikhadi 42
Umbuzo
Assume histidine’s side-chain pKa is 6.0. At pH 7.0, is its predominant side-chain charge 0 or +1?
Impendulo
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.
Ikhadi 43
Umbuzo
Assume cysteine’s thiol pKa is 8.3. At pH 7.0, which form predominates: neutral thiol or negative thiolate?
Impendulo
Neutral thiol. pH is below pKa, so the protonated S–H form predominates.
Ikhadi 44
Umbuzo
At pH 7, which has a predominantly −1 side chain: glutamate or glutamine?
Impendulo
Glutamate. Glutamine’s side-chain amide is neutral.
Ikhadi 45
Umbuzo
Assume tyrosine’s phenolic pKa is 10.1. At pH 7.0, is its side chain predominantly neutral or negative?
Impendulo
Neutral. The phenolic hydroxyl is mostly protonated because pH is below pKa.
Ikhadi 46
Umbuzo
Assume lysine’s side-chain pKa is 10.5. At pH 7.0, is its side chain predominantly neutral or +1?
Impendulo
+1. pH is below pKa, favoring the protonated amino group.
Ikhadi 47
Umbuzo
Assume aspartate’s side-chain pKa is 3.9. At pH 7.0, is its side chain predominantly neutral or −1?
Impendulo
−1. pH is above pKa, favoring the deprotonated carboxylate.
Ikhadi 48
Umbuzo
Can a standard aqueous pKa value determine a buried protein side chain’s charge with certainty?
Impendulo
No. Nearby charges, solvent exposure, and other local interactions can shift pKa. Use a value appropriate to that site when it is known.
Ikhadi 49
Umbuzo
With a histidine side-chain pKa of 6.0, does the label ‘basic amino acid’ imply a predominantly +1 side chain at pH 7?
Impendulo
No. ‘Basic’ describes proton-accepting chemistry; the predominant charge at a stated pH follows the pKa. Here the side chain is mostly neutral.
Ikhadi 50
Umbuzo
Does a predominantly neutral tyrosine side chain at pH 7 make tyrosine nonpolar in this deck’s grouping?
Impendulo
No. Its hydroxyl is polar even when uncharged. This deck groups tyrosine as polar, uncharged and also recognizes its aromatic character.
Ikhadi 51
Umbuzo
Does an internal proline residue have the same backbone N–H hydrogen-bond donor as most peptide residues?
Impendulo
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.
Ikhadi 52
Umbuzo
At pH = pKa, a side chain switches between 0 and +1. Is each individual side chain charged +0.5?
Impendulo
No. The two forms occur in equal proportions, giving an ensemble-average charge of +0.5. Each form still has charge 0 or +1.
Ikhadi 53
Umbuzo
Assume cysteine’s thiol pKa is 8.3. At pH 9.3, what is its predominant side-chain charge?
Impendulo
−1. Deprotonated thiolate predominates; the thiolate:thiol ratio is 10:1 in the simple model.
Ikhadi 54
Umbuzo
At pH 7, which pair is a plausible side-chain salt bridge: lysine–glutamate or leucine–valine?
Impendulo
Lysine–glutamate: their usual side-chain charges are +1 and −1. A salt bridge still requires suitable proximity and environment.
Ikhadi 55
Umbuzo
A histidine site has a measured side-chain pKa of 8.0. At pH 7.0, which side-chain form predominates?
Impendulo
The protonated +1 form. pH is below this site’s pKa; use the supplied local value rather than a generic histidine value.
Ikhadi 56
Umbuzo
Phenylalanine versus tyrosine: which has the side-chain hydroxyl that adds polarity?
Impendulo
Tyrosine. Phenylalanine lacks that hydroxyl; both contain an aromatic ring.
amakhadi angu-56
Amino Acid Side-Chain Properties Flashcards: Polarity & Charge
I-Nibomo iyavuleka ukuze uqale ukufunda.