Exam (elaborations)
ACS Biochemistry Exam A Questions and Answers 2024
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ACS Biochemistry Exam A
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ACS Biochemistry Exam AMetabolism (catabolism and anabolism) - answer 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 - answer 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? - answerHydrogen bonding
The unique properties of water (specific heat, heat of vaporization, solubility) - answer1)
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 - answerAt 25 degrees C:
Keq= Kw= [OH-][H3O+]= 1*10^-14
In pure water:
[OH-]=[H3O+]= 1*10^-7
Calculation for pH and pKa - answerpH= -log[H3O+]
pKa= -log(Ka)
Normal blood pH range - answer7.35-7.45
The Hydrophobic Effect - answerWhen 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 - answerComposed 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? - answerWhen [HA]=
[A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and vice versa:
Blood Buffering - answerComponents:
,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 - answerthe 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 - answerBetween the C and N of C=O and N-H of two adjacent amino
acids.
What wavelength is indicative of aromatic amino acids? - answer280 nm, with
tryptophan absorbing more, tyrosine absorbing a bit less, and phenylalanine absorbing
a lot less.
Stereochemistry of amino acids - answerEvery 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 - answerEach 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 - answerthe 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
**At PI, amino acid or peptide cannot migrate through an electric field, so this is a way
we can separate amino acids (by PI via electric field!)**
, How to calculate PI, or isoelectric pint - answerAverage pKa values involving the neutral
species
For glycine, that only has COOH and NH3 pKa's, the PI is the average between 2.34
and 9.60, so 5.97!
Essential Amino Acids - answerThose that cannot be made in the body and thus must
be obtained via the diet. Some can be made from others, so it isn't a hard line, but:
Histidine, Isoleucine, Leucine, Lysine, Methionine, Phenylalanine, Threonine,
Tryptophan, and Valine are all essential.
**Cysteine can be made from methionine, tyrosine can be made from phenylalanine,
etc.**
Amino acid name post-peptide bond - answerresidues
Peptide directionality - answerFrom N to C
Protein makeup - answerOne or more polypeptide chains, and optional prosthetic
groups that make a conjugated protein.
The folding of the chains is what delineates function of the protein itself.
4 protein structure levels, and their components - answerPrimary structure: amino acid
reside sequences
Secondary structure: alpha helix and beta sheet folded segments
Tertiary structure: polypeptide chains in 3-D shapes
Quaternary structure: Assembled subunits comprised of multiple chains
Amino Acids with ionizable side chains - answerTerminal carboxyl group: pKa of 3.1
Aspartic Acid/Glutamic Acid: pKa of 4.1
Histidine: pKa of 6.0
Terminal amino group: pKa of 8.0
Cysteine: pKa of 8.3
Tyrosine: pKa of 10.9
Lysine: pKa of 10.8
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