MCAT AAMC OUTLINE 2025 EXPERT
VERIFIED | ACE THE TEST
Content Category 1A: Structure and function of proteins and their
constituent amino acids - 🧠 ANSWER ✔✔
1A.1) amino acids - 🧠 ANSWER ✔✔
* description - 🧠 ANSWER ✔✔- Amino acids contain two functional groups,
an amino group (-NH2) and a carboxyl group (-COOH)
- Alpha amino acids are those where both functional groups are attached to
the same carbon.
- Side chain/R group and hydrogen atom are also attached to alpha carbon.
,- Side chain determines the properties of amino acids and its functions.
Absolute configuration at the α position - 🧠 ANSWER ✔✔* Alpha carbon is
usually a chiral center since it has four different groups attached to it.
- Thus most amino acids are optically active
- Glycine is the only exception since it has a hydrogen as its R group.
* All chiral amino acids are L-amino acids, which means that the amino
group is drawn on
the left side for the Fischer projection.
- Translates to an (S) absolute configuration for almost all chiral amino
acids.
- Cysteine is the only amino acid that has an L-amino acid configuration but
has an (R) absolute configuration. This is because the carboxyl group is not
the highest priority functional group.
hydrophobic and hydrophilic amino acids - 🧠 ANSWER ✔✔* Amino acids
with long alkyl side chains - alanine, isoleucine, leucine, valine, and
phenylalanine - are strongly hydrophobic, and are thus more likely to be
found in the interior of proteins
,* All amino acids with charged side chains - histidine, arginine, lysine,
glutamate, and aspartate - are hydrophilic
- So are the amides asparagine and glutamine
* Remaining amino acids are somewhere in the middle between being
philic and phobic.
Acid Base Chemistry of Amino Acids - 🧠 ANSWER ✔✔* Amino acids are
an amphoteric species since they have an acidic carboxyl group and a
basic amino group.
* Ionizable groups tend to gain protons under acidic conditions and lose
them under basic conditions.
- i.e. at low pH an ionizable group will be protonated
* The pKa of a group is the pH at which half of the molecules of the species
are deprotonated or [HA]=[A-]
- If pH is lower than pKa then the majority of the species will be protonated.
protonation and deprotonation - 🧠 ANSWER ✔✔* All amino acids have at
least two pKa values.
COPYRIGHT©NINJANERD 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
STATEMENT. ALL RIGHTS RESERVED
3
, - pKa1 is the pKa of the carboxyl group and is usually around 2
- pKa2 is the pKa of the amino group and is usually around 9-10
* If the amino acid has an ionizable side chain, then there will be three pKa
values.
positively charged under acidic conditions - 🧠 ANSWER ✔✔- At pH below
1, the pKa is far below that of the amino group, so the amino group is fully
protonated (-NH3+)
- Additionally, the carboxylic acid group is fully protonated (-COOH)
- At very acidic pH values, amino acids tend to be positively charged.
zwitterions at intermediate pH - 🧠 ANSWER ✔✔At pH of 7.4, carboxylic
acid pKa has been moved past. As such, you will not find amino acids with
their carboxylate group protonated and the amino group unprotonated
- Amine group stays protonated since the pKa still is not high enough.
- Resulting molecule has both a positive charge and a negative charge, but
is overall
neutral.
VERIFIED | ACE THE TEST
Content Category 1A: Structure and function of proteins and their
constituent amino acids - 🧠 ANSWER ✔✔
1A.1) amino acids - 🧠 ANSWER ✔✔
* description - 🧠 ANSWER ✔✔- Amino acids contain two functional groups,
an amino group (-NH2) and a carboxyl group (-COOH)
- Alpha amino acids are those where both functional groups are attached to
the same carbon.
- Side chain/R group and hydrogen atom are also attached to alpha carbon.
,- Side chain determines the properties of amino acids and its functions.
Absolute configuration at the α position - 🧠 ANSWER ✔✔* Alpha carbon is
usually a chiral center since it has four different groups attached to it.
- Thus most amino acids are optically active
- Glycine is the only exception since it has a hydrogen as its R group.
* All chiral amino acids are L-amino acids, which means that the amino
group is drawn on
the left side for the Fischer projection.
- Translates to an (S) absolute configuration for almost all chiral amino
acids.
- Cysteine is the only amino acid that has an L-amino acid configuration but
has an (R) absolute configuration. This is because the carboxyl group is not
the highest priority functional group.
hydrophobic and hydrophilic amino acids - 🧠 ANSWER ✔✔* Amino acids
with long alkyl side chains - alanine, isoleucine, leucine, valine, and
phenylalanine - are strongly hydrophobic, and are thus more likely to be
found in the interior of proteins
,* All amino acids with charged side chains - histidine, arginine, lysine,
glutamate, and aspartate - are hydrophilic
- So are the amides asparagine and glutamine
* Remaining amino acids are somewhere in the middle between being
philic and phobic.
Acid Base Chemistry of Amino Acids - 🧠 ANSWER ✔✔* Amino acids are
an amphoteric species since they have an acidic carboxyl group and a
basic amino group.
* Ionizable groups tend to gain protons under acidic conditions and lose
them under basic conditions.
- i.e. at low pH an ionizable group will be protonated
* The pKa of a group is the pH at which half of the molecules of the species
are deprotonated or [HA]=[A-]
- If pH is lower than pKa then the majority of the species will be protonated.
protonation and deprotonation - 🧠 ANSWER ✔✔* All amino acids have at
least two pKa values.
COPYRIGHT©NINJANERD 2025/2026. YEAR PUBLISHED 2025. COMPANY REGISTRATION NUMBER: 619652435. TERMS OF USE. PRIVACY
STATEMENT. ALL RIGHTS RESERVED
3
, - pKa1 is the pKa of the carboxyl group and is usually around 2
- pKa2 is the pKa of the amino group and is usually around 9-10
* If the amino acid has an ionizable side chain, then there will be three pKa
values.
positively charged under acidic conditions - 🧠 ANSWER ✔✔- At pH below
1, the pKa is far below that of the amino group, so the amino group is fully
protonated (-NH3+)
- Additionally, the carboxylic acid group is fully protonated (-COOH)
- At very acidic pH values, amino acids tend to be positively charged.
zwitterions at intermediate pH - 🧠 ANSWER ✔✔At pH of 7.4, carboxylic
acid pKa has been moved past. As such, you will not find amino acids with
their carboxylate group protonated and the amino group unprotonated
- Amine group stays protonated since the pKa still is not high enough.
- Resulting molecule has both a positive charge and a negative charge, but
is overall
neutral.
