ACS BIOCHEMISTRY PRACTICE FINAL BEHARRY
EXAM REVIEW STUDY NOTES
◉ Normal blood pH range.
Answer: 7.35-7.45
◉ The Hydrophobic Effect.
Answer: 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.
Answer: 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?.
Answer: When [HA]= [A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and
vice versa:
◉ Blood Buffering.
Answer: 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.
Answer: 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.
Answer: Between the C and N of C=O and N-H of two adjacent amino
acids.
◉ What wavelength is indicative of aromatic amino acids?.
Answer: 280 nm, with tryptophan absorbing more, tyrosine
absorbing a bit less, and phenylalanine absorbing a lot less.
◉ Stereochemistry of amino acids.
Answer: 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.
Answer: 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.
Answer: 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
**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!)**
EXAM REVIEW STUDY NOTES
◉ Normal blood pH range.
Answer: 7.35-7.45
◉ The Hydrophobic Effect.
Answer: 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.
Answer: 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?.
Answer: When [HA]= [A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and
vice versa:
◉ Blood Buffering.
Answer: 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.
Answer: 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.
Answer: Between the C and N of C=O and N-H of two adjacent amino
acids.
◉ What wavelength is indicative of aromatic amino acids?.
Answer: 280 nm, with tryptophan absorbing more, tyrosine
absorbing a bit less, and phenylalanine absorbing a lot less.
◉ Stereochemistry of amino acids.
Answer: 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.
Answer: 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.
Answer: 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
**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!)**
