NBME Biochemistry 2024 UPDATED
EXAM QUESTIONS AND CORRECT
ANSWERS || GRADED A+
Isoelectric point (pI) - ANSWER pH at which the number of
positive charges equals the number of negative charges, and the
overall charge on the AA is zero?
1st pKa= carboxyl group (pKa ~2)
2nd p...
Isoelectric point (pI) - ANSWER ✔ pH at which the number of
positive charges equals the number of negative charges, and the
overall charge on the AA is zero?
1st pKa= carboxyl group (pKa ~2)
2nd pKa= side chain (if the side chain is ionizable)
3rd pKa= amino group (pKa ~9) - ANSWER ✔ Titration curves of
amino acids:
1st pKa corresponds to?
2nd pKa corresponds to?
3rd pKa corresponds to?
1. The atoms involved in a peptide bond form a *rigid* planar unit
(due to partial double bond character)
*No freedom of rotation*
2. Extremely stable: cleavage generally involves the action of
proteolytic enzymes. - ANSWER ✔ Characteristics of a peptide
bond:
,-Rigid or free to rotate?
-Stability?
Cathode (-)
Anode (+)
**At the isoelectric point, the net charge is zero and the protein
does not migrate. - ANSWER ✔ Positively charged proteins will
migrate towards the __________
Negatively charged proteins will migrate towards the
____________
Four
Side chains of AAs extend outward from the central axis of the
alpha helix - ANSWER ✔ An Alpha-Helix is generated when each
carbonyl of a peptide bond forms a hydrogen bond with the -NH of
a peptide bond ______ amino acid residues further along in the
chain.
Proline
**disrupts alpha-helix structures, due to ring imposing geometric
constraints. - ANSWER ✔ Amino acid known as a "Helix
Breaker"?
Hydrogen bonding occurs between the carbonyl of one peptide
bond and the NH of another peptide bond.
**amino acid side chains are trans to one another and alternate
above and below the plane of the sheet - ANSWER ✔ Hydrogen
,bonding between beta pleated sheets occurs between what two
functional groups of the amino acids?
When oxygen binds, Hb changes from the tight (T) form to the
relaxed (R) form. - ANSWER ✔ When oxygen binds, Hb changes
from the ______ form to the _______ form.
Positive cooperativity: Binding of 02 to one heme group in
hemoglobin increases the affinity of 02 for its other heme groups.
- ANSWER ✔ What property of Hb causes the oxygen saturation
curve of Hb to be sigmoidal?
Two alpha subunits; Two beta subunits.
Two alpha subunits; two gamma subunits. - ANSWER ✔ What
are the 4 subunits in adult Hb?
What are the 4 subunits of fetal Hb?
1. H+ (Bohr effect)
2. CO2
3. 2,3-BPG - ANSWER ✔ 3 molecules that decrease Hb affinity to
02 at the tissues?
Fetal Hb has a lower affinity for 2,3-BPG than adult Hb.
Therefore, fetal Hb has a higher affinity for 02 than adult Hb -
ANSWER ✔ Why does fetal Hb have a higher affinity than adult
Hb.
As P50 decreases, Hb 02 affinity increases. - ANSWER ✔ What
happens to Hb 02 affinity as P50 decreases?
, Sickle Cell anemia.
**Deoxygenated aggregates of HbS aggregate, RBCs form sickle
shape, and undergo hemolysis, resulting in anemia.* - ANSWER
✔ Hemoglobinopathy that results from the Beta-chain containing
a hydrophobic valine instead of a glutamine, allowing
deoxygenated molecules of HbS to polymerize.
Collagen - ANSWER ✔ Protein that consists of 3 peptide chains
that wind around each other to form a triple helix?
Glycine
**Also significant amounts of proline, hydroxyproline, and
hydroxylysine. - ANSWER ✔ 1/3 of the approx 1000 amino acids
in collagen are this amino acid?
On the rough ER
"pre" sequence is cleaved here as well. - ANSWER ✔ Where is
preprocollagen synthesized?
Pro-collagen.
**"Pro" segments are cleaved off, causing collagen to form into
long fibers - ANSWER ✔ Collagen is secreted from the cell in
what form?
Vitamin C - ANSWER ✔ What vitamin is required as a cofactor
for hydroxylation of lysine and proline residues on collagen?
Hydroxylysine and Hydroxyproline are needed for cross linking of
the alpha particles, generating the triple helix. - ANSWER ✔ What
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