NBME 7 BLOCK 1-4 (with Answers)

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Block 1
Block 2
Block 3

Block 3 NBME 7: BLOCK 2
Block 4





























1-Hemoglobin is an assembly of four globular protein subunits(polypeptide chains)....
2- Each subunit is composed of a protein chain tightly associated with a non-protein heme
group.
3-Each protein chain arranges into a set of alpha-helix structural segments connected together
in a globin fold arrangement,
4.Adult hemoglobin is made of 2 alpha and 2 beta chains
5-These four polypeptide chains are bound to each other and stabilized by
a- salt bridges...which is a noncovalent bonding...due to interaction between anionic carboxylate
(RCOO-) and cationic ammonium (RNH3+) in the amino acids
b-hydrogen bonds,
c- hydrophobic interactions....oil and water donot combine becuase of hydrophobic
interaction ...and hydrophobic interaction is a property of nonpolar molecules and this interaction
is also used in the case of protein folding where by most folded proteins have a hydrophobic
core in which side chain packing stabilizes the folded state, and charged or polar side chains on
the solvent-exposed surface where they interact with surrounding water molecules.
6-the hydrophobic effect is important to understand the structure of proteins that have
hydrophobic amino acids, such as alanine, valine, leucine, isoleucine, phenylalanine, and
methionine grouped together with the protein...and hydrophobic interaction is between individual
aminoacids
7-Ordinarily, the hemoglobin molecules exist as single, isolated units in the red cell, whether
they have oxygen bound or not...
8-Sickle hemoglobin exists as isolated units in the red cells when they have oxygen bound.
9-When sickle hemoglobin releases oxygen in the peripheral tissues, however, the molecules
tend to stick together and form long chains or polymers increases hydrophobic interactions ) ..and these hydrophobic interactions
stabilize the
polymerized sickle hemoglobin..
Let us see what happens in sickle cell anemia...glutamic acid(hydrophillic ) is replaced by
hydrophobic valine (which increases the number of hydrophobic aminoacids ...which inturn

A stroke on the right side
of the brain (especially parietal lobe), in addition to producing a homonymous
hemianopsia, may

Hemispatial neglect $















the question we are asked about heterogeneity(variability)
-The distances between the scores and the mean (Xi-M) are called deviations
-The greater the variety or heterogeneity of the scores, the greater the deviations













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pathway
decussates at the level of the spinal cord, rather than in the brainstem like the posterior column-