Official Guide to the MCAT Exam
with Complete Solutions
What is the difference between Type I and Type II muscle fibers?
Understand the difference between Type I and Type II Muscle fibers.
Type I (slow-twitch) - mitochondria rich, slow twitch (slow conduction
velocity), slow contraction speed, aerobic, long, low power, long duration,
fatigue-free.
Type II fibers - two types, Type IIA, and Type IIB. Type IIA are intermediate
between I and IIB.
Type IIB are white, fast contraction speed, fast-twitch (fast conduction
velocity), anaerobic, short, easily fatigue, power, ATP from creatine
phosphate.
QUESTION 1:
The muscle subtype represented by Culture C is LEAST likely to be characterized by:
A. a fast rate of muscle contraction.
B. the ability to engage in oxidative and anaerobic respiration.
C. the presence of medium-sized motor units.
D. low densities of mitochondria and capillaries.
D. got this wrong because i did not understand which culture (A, B or C) related to
which muscle type in the table in the passage.
Don't be fooled by this answer choice. Even though in the "Activity used for" section
it states anaerobic. The type IIA muscle fiber still exhibits "high oxidative capacity"
which means it would be able to perform BOTH anaerobic and aerobic processes.
Based on the passage, it can be inferred that Culture B is I, Culture A is
Type IIx. Further, Culture C is then Type IIa. There are many clues to figure
this out. If this is the case, Type IIa will have HIGH density of mitochondria
for oxidative phosporylation (which is indicated as being high for IIA).
make sure to look at LEAST likely in the passage.
,QUESTION 2:
Which steps involved in the contraction of a skeletal muscle require binding and/or
hydrolysis of ATP?
I. Dissociation of myosin head from actin filament
II. Attachment of myosin head to actin filament
III. Conformational change that moves actin and myosin filaments relative to one
another
IV. Binding of troponin to actin filament
V. Release of calcium from the sarcoplasmic reticulum
VI. Reuptake of calcium into the sarcoplasm
A. I, II, and III only
B. II, III, and IV only
C. I, III, and VI only
D. III, IV, and VI only
C. got it wrong, chose A, bc did not know that ca reuptake required ATP
Also known as "cross bridge dissociation". This occurs after the power stroke to put
the myosin head into a low energy position II. Calcium is required to expose the
myosin binding sites through the conformational change in tropomyosin III. The
conformational change among actin and myosin requires the hydrolysis of ATP
which is what allows the power stroke a.k.a. the muscle contraction caused when
myosin pulls actin towards the middle of the sarcomere VI. Reuptake of calcium
requires ATP because the ions are moving against their concentration gradient into
the SR
What are the steps for muscle contraction?
QUESTION 3:
,Does the release of Ach in skeletal muscle cells, cause depolarization or
hyperpolarization?
The addition of acetylcholine to the medium most likely induced:
a. depolarization of the cell membrane that resulted in contraction.
b. repolarization of the cell membrane that resulted in relaxation.
c. hyperpolarization of the cell membrane that resulted in contraction.
d. depolarization of the cell membrane that resulted in relaxation.
A. because we know ach causes contractions also according to the passage it states
that ach caused a cell culture to retain contractile activity for longer than 30 mins.
Acetylcholine is released at the neuromuscular junction where it binds to receptors
on the muscle cells and, depending on the type of muscle cell, causes
depolarization or hyperpolarization of the cell membrane. In skeletal muscles,
acetylcholine binds to its receptors, which leads to depolarization of the
muscle cell membrane and muscle contraction.
QUESTION 4:
The terminal electron acceptor in lactic acid fermentation is:
a. pyruvate.
b. oxygen.
c. NAD+.
d. water.
A.
I chose C but thats wrong bc NADH reduces pyruvate to produce lactate and
regenerate NAD+ so glycolysis can continue.
You have to know the key difference between fermentation and aerobic respiration
for this question. In aerobic respiration, oxygen is an electron acceptor while in
fermentation, pyruvate is an electron acceptor to regenerate NAD+, so glycolysis
can continue. In this process, NADH reduces pyruvate to produce lactate.
Therefore, pyruvate serves as the electron acceptor in production of
lactate.
Remember, 2 ATP produced in fermentation process per mol of glucose (which
occurs when no O2 present in eukaryotes)! In glycolysis, however, 32 ATP is
produced per mol of glucose. This is a vast difference.
QUESTION 5:
What control experiment was necessary to ensure that the apparent subcellular
locations of the cat6xbs and lacY6xbs transcripts were NOT skewed by the location
preference of the bound MS2–GFP?
, a. Determination of expression of MS2–GFP in cells that lacked the 6xbs insertion
upstream of the cat and lacY genes
b. Use of E. coli cells that expressed only MS2 instead of the MS2–GFP fusion protein
c. Insertion of the 6xbs region upstream of both the cat and lacY genes in the same
cells
d. Determination of expression of both MS2 and GFP as separate proteins rather
than as a fusion protein
A. got this correct but because i guessed. I did not understand the terminology but
rationalizing it out, if you are trying to test that the location of MS2 did not affects
the locations of cat and lac then you must take out cat and lac and see where MS2
is and then add cat and lac back in and see where it is.
QUESTION 6:
Which other cellular components are likely to be located near the lacY6xbs
transcript in the cell membrane?
A.Proteins and glycolipids
B. Glycolipids and sterols
C. Sterols and phospholipids
D. Phospholipids and proteins
D. got this correct but because I did was thinking of cell membrane components but
needed to recognize that the passage was about E.coli (a prokaryote).
The passage states lacY is located near the cell membrane, so the answer
will have to be the cell components of an E.coli membrane (a prokaryote).
E.coli is a gram negative cell. Gram negative cells have a thin
peptidoglycan layer and a outer cell wall (which contains LPS). E.coli
membranes, like all cells, have plasma membranes (inner most) and this
plasma membrane contains 75% protein, and 25% phospolipids. Typically,
these are the major two components of all cell membranes
Prokaryotes CM: do not contain sterols, glycolipids or glycoproteins do
have phospholipids, proteins, sphinglolipids (see below in extra info)
Eukaryotes CM: contain sterols (cholesterol for fluidity), glycolipids and
glycoproteins (serve as recognition molecules)
Extra Info: Most prokaryotes cell membranes also do contain include spingolipids
(which can be a phospolipid when head group contain a phosphates - this is then
called a spingomyelin. The other types of spingolipids are eramide (OH head group),
or glycolipids (sugar head group) such as cereboside (one sugar), globoside (2+
sugar), and ganglisoide (oligosacharide with NANA/Salic acid)
QUESTION 7:
