ACS BIOCHEMISTRY EXAM | Actual Questions and Answers Latest
Updated 2024/2025 (Graded A+)
Metabolism (catabolism and anabolism) - ✔✔Metabolism: sum of total chemical reactions in an
organism, also the method by which cells extract and use energy from their environment.
Catabolism: The process by which stored nutrients and ingested foods are converted to a usable form of
energy. It produces simple products CO2, H2O, NH3, and building blocks such as sugars and fats that are
used in anabolism.
Anabolism: the process by which simple products and building blocks of catabolism are used to create
complex biological products that contribute to organismal growth and development. It also uses the
energy produced in catabolism to do biological work.
Properties of cells - ✔✔Metabolism: undergoing catabolic and anabolic processes.
Reproduction: cell populations grow via asexual reproduction.
Mutation: during growth and reproduction, cells sometimes make mistakes, leading to mutations and
evolution.
Respond to environment: metabolic pathways respond to signals, including light, touch, hormones, and
nutrients, that can turn the pathways on or off.
Speed and efficiency: cell operations are highly specific to maximize targeting and efficiency.
Similar building blocks: most species are very similar at the cellular level.
What accounts for water's unique properties? - ✔✔Hydrogen bonding
The unique properties of water (specific heat, heat of vaporization, solubility) - ✔✔1) high specific heat,
or heat required to raise the temperature of the unit mass of a given substance by one degree.
,For water to increase in temperature, water molecules must be made to move faster, or get higher KE,
and doing this requires breaking hydrogen bonds, which absorbs heat. So, as heat is applied, most of it
goes to breaking the bonds not upregulating KE, thus making water harder to heat than substances
where no bonds need to be broken.
2) High heat of vaporization, or the amount of heat needed to turn one g of a liquid into vapor, without
a temperature rise in the liquid. Important for sweat because it ensures that when the liquid evaporates
from our skin, the heat required for the transition is kept in the gas, causing a net cooling effect on the
skin.
3) Unique solubility properties: "like dissolves like". Water dissolves polar molecules and ions, and can
act as an H-bond donor or receptor
4) Amphoteric, it can act as an acid (donating electrons) or a base (accepting electrons). The conjugate
acid of water is the hydronium ion, H3O+, and the conjugate base of water is the hydroxide ion, OH-.
Keq for water at 25 degrees C and in pure water - ✔✔At 25 degrees C:
Keq= Kw= [OH-][H3O+]= 1*10^-14
In pure water:
[OH-]=[H3O+]= 1*10^-7
Calculation for pH and pKa - ✔✔pH= -log[H3O+]
pKa= -log(Ka)
Normal blood pH range - ✔✔7.35-7.45
The Hydrophobic Effect - ✔✔When non-polar molecules aggregate in the presence of water, minimizing
the entropy decrease water must go through to order themselves around the border of the non-polar
molecule. Reducing the surface area water must organize around increases entropy, which is favorable.
,The aggregation is responsible for the formation of a variety of lipid structures in the body, including cell
membranes.
Buffers - ✔✔Composed of a weak acid (HA) and its conjugate base (A-). Added acid reacts with A-, and
added base reacts with HA, giving a limited overall pH change.
Two main reactions:
1) When excess base is added:
OH-+HA-->H2O+A-
2) When excess acid is added:
H+ + A- -->HA
**So, the net result is more of the weak acid and its conjugate base**
When are buffers optimal? What equation can we use for this? - ✔✔When [HA]= [A-], occurring when
pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and vice versa:
Blood Buffering - ✔✔Components:
1) carbonic acid (H2CO3) (weak acid). pKa= 6.1.
2) Bicarbonate Ion (HCO3-), conjugate base of carbonic acid
3) H+ (hydrogen ion)
If OH- (base) is added, Carbonic acid buffers it into bicarbonate ion and water.
If H+ (acid) is added, bicarbonate ions and H+ buffer it to carbonic acid.
Amino Acids, peptides, and polypeptides - ✔✔the building blocks of proteins, a chain of which is called a
peptide. There are 20 standard amino acids that act as the monomers to make protein polymers!
, A long peptide is called a polypeptide!
Proteins are composed of one or more polypeptide chain.
Peptide bonds - ✔✔Between the C and N of C=O and N-H of two adjacent amino acids.
What wavelength is indicative of aromatic amino acids? - ✔✔280 nm, with tryptophan absorbing more,
tyrosine absorbing a bit less, and phenylalanine absorbing a lot less.
Stereochemistry of amino acids - ✔✔Every carbon except for glycine is a chiral center, giving two
possible structures for each: L and D (except for glycine).
L is the only one found in nature.
Acid-Base properties of amino acids - ✔✔Each has at least two ionizable protons (from the COOH and
NH3 groups), but most have others.
COOH pKa: 2.34
NH3 pKa: 29.60
PI - ✔✔the isoelectric point, or the pH at which an amino acid or peptide has no net charge.
- At pH= PI, the predominant species is the zwitterion
- At pH<PI, the predominant species is net positive
- At pH>PI, the predominant species is net negative
Updated 2024/2025 (Graded A+)
Metabolism (catabolism and anabolism) - ✔✔Metabolism: sum of total chemical reactions in an
organism, also the method by which cells extract and use energy from their environment.
Catabolism: The process by which stored nutrients and ingested foods are converted to a usable form of
energy. It produces simple products CO2, H2O, NH3, and building blocks such as sugars and fats that are
used in anabolism.
Anabolism: the process by which simple products and building blocks of catabolism are used to create
complex biological products that contribute to organismal growth and development. It also uses the
energy produced in catabolism to do biological work.
Properties of cells - ✔✔Metabolism: undergoing catabolic and anabolic processes.
Reproduction: cell populations grow via asexual reproduction.
Mutation: during growth and reproduction, cells sometimes make mistakes, leading to mutations and
evolution.
Respond to environment: metabolic pathways respond to signals, including light, touch, hormones, and
nutrients, that can turn the pathways on or off.
Speed and efficiency: cell operations are highly specific to maximize targeting and efficiency.
Similar building blocks: most species are very similar at the cellular level.
What accounts for water's unique properties? - ✔✔Hydrogen bonding
The unique properties of water (specific heat, heat of vaporization, solubility) - ✔✔1) high specific heat,
or heat required to raise the temperature of the unit mass of a given substance by one degree.
,For water to increase in temperature, water molecules must be made to move faster, or get higher KE,
and doing this requires breaking hydrogen bonds, which absorbs heat. So, as heat is applied, most of it
goes to breaking the bonds not upregulating KE, thus making water harder to heat than substances
where no bonds need to be broken.
2) High heat of vaporization, or the amount of heat needed to turn one g of a liquid into vapor, without
a temperature rise in the liquid. Important for sweat because it ensures that when the liquid evaporates
from our skin, the heat required for the transition is kept in the gas, causing a net cooling effect on the
skin.
3) Unique solubility properties: "like dissolves like". Water dissolves polar molecules and ions, and can
act as an H-bond donor or receptor
4) Amphoteric, it can act as an acid (donating electrons) or a base (accepting electrons). The conjugate
acid of water is the hydronium ion, H3O+, and the conjugate base of water is the hydroxide ion, OH-.
Keq for water at 25 degrees C and in pure water - ✔✔At 25 degrees C:
Keq= Kw= [OH-][H3O+]= 1*10^-14
In pure water:
[OH-]=[H3O+]= 1*10^-7
Calculation for pH and pKa - ✔✔pH= -log[H3O+]
pKa= -log(Ka)
Normal blood pH range - ✔✔7.35-7.45
The Hydrophobic Effect - ✔✔When non-polar molecules aggregate in the presence of water, minimizing
the entropy decrease water must go through to order themselves around the border of the non-polar
molecule. Reducing the surface area water must organize around increases entropy, which is favorable.
,The aggregation is responsible for the formation of a variety of lipid structures in the body, including cell
membranes.
Buffers - ✔✔Composed of a weak acid (HA) and its conjugate base (A-). Added acid reacts with A-, and
added base reacts with HA, giving a limited overall pH change.
Two main reactions:
1) When excess base is added:
OH-+HA-->H2O+A-
2) When excess acid is added:
H+ + A- -->HA
**So, the net result is more of the weak acid and its conjugate base**
When are buffers optimal? What equation can we use for this? - ✔✔When [HA]= [A-], occurring when
pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and vice versa:
Blood Buffering - ✔✔Components:
1) carbonic acid (H2CO3) (weak acid). pKa= 6.1.
2) Bicarbonate Ion (HCO3-), conjugate base of carbonic acid
3) H+ (hydrogen ion)
If OH- (base) is added, Carbonic acid buffers it into bicarbonate ion and water.
If H+ (acid) is added, bicarbonate ions and H+ buffer it to carbonic acid.
Amino Acids, peptides, and polypeptides - ✔✔the building blocks of proteins, a chain of which is called a
peptide. There are 20 standard amino acids that act as the monomers to make protein polymers!
, A long peptide is called a polypeptide!
Proteins are composed of one or more polypeptide chain.
Peptide bonds - ✔✔Between the C and N of C=O and N-H of two adjacent amino acids.
What wavelength is indicative of aromatic amino acids? - ✔✔280 nm, with tryptophan absorbing more,
tyrosine absorbing a bit less, and phenylalanine absorbing a lot less.
Stereochemistry of amino acids - ✔✔Every carbon except for glycine is a chiral center, giving two
possible structures for each: L and D (except for glycine).
L is the only one found in nature.
Acid-Base properties of amino acids - ✔✔Each has at least two ionizable protons (from the COOH and
NH3 groups), but most have others.
COOH pKa: 2.34
NH3 pKa: 29.60
PI - ✔✔the isoelectric point, or the pH at which an amino acid or peptide has no net charge.
- At pH= PI, the predominant species is the zwitterion
- At pH<PI, the predominant species is net positive
- At pH>PI, the predominant species is net negative
