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Biology MCAT


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What two organelles do erythrocytes lack?
mitochondria and nuclei
Down's Syndrome is caused by:
nondisjunction of chromosome 21 during anaphase
If the ductus arteriosus is obstructed, where will blood supply increase to:
the fetal lungs
Muscle and kidneys are formed from what primary germ layer?
the mesoderm
The presence of a notochord beneath the ectoderm results in the formation of a neural tube. This is an example of what process?
induction; the initiation of cell differentiation in a developing embryo due to the influence of other surrounding cells
What is an example of induction in the formation of the eye?
the optic vesicles induce the ectoderm to thicken and form the lens, which in turn induces the optic vesicle to form the optic cup, which induces the lens to form the cornea and the lungs
Where does growth occur in long bones?
the epiphyseal plates
If someone takes a large overdose of antacid, what will be the effect of pepsin in the stomach?
pepsin will not function properly because it performs ideally in an acidic pH
What will cause an increase in breathing rate?
a high pCO2
The mitral valve sits between what two chambers of the heart? What does it prevent?
it is between the left atrium and left ventricle; it prevents the backflow of blood back into the atrium when the LV contracts
Piloerection, shivering, and vasoconstriction are all examples of what thermoregulatory process?
heat conservation
If a diabetic took an overdose of insulin, what would occur?
convulsions due to decrease in blood sugar
What does acetylcholinesterase do?
it removes acetylcholine from the synapse via hydrolysis to yield choline and acetate; without this enzyme, Ach will accumulate in the synapse
What is the main function of Ach?
it depolarizes the postsynaptic membrane of one neuron when released by the presynaptic terminal of another neuron
What is meant by DNA replication being semiconservative?
after one replication, the daughter strands will have one half the original parental strand and one half newly synthesized strand
What type of selection is most likely to induce speciation?
disruptive selection, the favoring of two extremes
What are some differences between steroid and peptide hormones?
1. PH's require second messengers
2. steroids are lipid derived, (usually from cholesterol) while PH's are amino acid derived
3. PH's act as 1st messengers
4. steroids pass through the PM bilayer easily and bind to DNA to regulate gene expression
What type of hormones are progesterone, estrogen, testosterone, aldosterone, and cortisol?
What do glucocorticoids do?
raise blood glucose levels and suppress immune system
What do mineralcorticoids do?
regulate blood levels of Na and K
What does epinephrine do?
stimulates the conversion of glycogen to glucose
What is the order of the taxonomic system?
Kingdom > Phylum > Class > Order > Family > Genus > Species
Which would cause an increase in the quantity of Ach released at the terminal?
a) increase in AP amplitude
b) increase in AP frequency
b; the action potential is an all or nothing response
In order for a drug to interact with an antibody, the drug's structure must be:
similar to the structure of the antibody
What common occurrances can be observed during the
a) 1st trimester
b) 2nd trimester
c) 3rd trimester
a) organ development, brain develops, cartilage turns to bone; heart beats
b) continued growth; toe and finger elongation
c) further brain development, antibodies are transferred
Increased [lactic acid], decreased pH, and decreased [ATP] are all signals of:
strenuous exercise associated with oxygen debt
During CPR, each time the rescuer relaxes the pressure on the sternum, the ventricles:
fill with blood
How can a virus first infect a host?
the host must have a receptor for the virus's specific protein coat
How can one stop certain viruses from inducing infections?
add complementary RNA to viral mRNA so that RNA base pairs with itself and prevents translation
A DNA has the sequence: TATAGCTATTGCC. What will the strand look like after RNA polymerase II activity?
no transcription will occur; remember that the 20-25 bases after the TATA box are not transcribed
How can one separate two amino acids using electrophoresis?
perform the electrophoresis at either of the isoelectric pH's of the amino acids
Sometimes athletes train at high altitudes before a big event. How does this benefit the athlete?
it increases oxygen capacity
What is cardiac output?
the volume of blood pumped by the LV into systemic circulation per minute
How is cardiac output calculated?
heart rate * stroke volume
Why is there a rise in both systolic and diastolic pressure during exercise?
Vasoconstriction of systemic blood vessels except for those in active muscle due to the sympathetic NS
If the cardiac output is very large, how does this affect lactic acid production during exercise?
it decreases lactic acid production because more O2 is pumped into systemic circulation per minute
Describe the repair mechanism excision.
Excision removes single bases or entire nucleotides by first unwinding DNA, introducing nicks on either side, and ligating a new, correct DNA fragment instead
The antigen binding site of an antibody represents which protein structure?
tertiary structure
A patient with insufficient ADH secretion will exhibit:
a) increased urine volume
b) increased urine osmolarity
a; more water will leave with the urine
What is an allosteric enzyme?
an enzyme that changes between activating and inactivating conformations
What is the difference between ribozymes and regular protein catalysts?
protein catalysts can have a greater variety of interactions with their substrates
Acetylation of histones...
relaxes DNA to allow binding
Does it take a short or long time for the effects of steroids to be observed?
long; the steroids have to go to DNA and regulate expression of certin genes; then transcription and translation have to occur before the effects are seen in the proteins
T/F: allosteric enzymes reaction velocities depend on the concentration of more than one compound, so it's graph will have an S shape
What occurs during southern blot?
RNA is reverse transcribed to DNA and then hybridized with a certain gene to form bands
T/F: the way mRNA is translated affects the results of the PCR
Blocking PTH receptors will induce the hypothalamus to do what?
increase Ca+2 production because the glands will think that [Ca+2] is always low
Endothelial cells in the digestive tract are said to be polarized because:
their have regions of the membrane that differ in their constituents
T/F: any water soluble protein will utilize a carrier protein
T/F: cholesterol requires a carrier protein
What is the correct sequence of events during inspiration of heavy breathing?
diaphragm contracts, rib cage expands, intrathoracic pressure drops, air enters lungs
What is pneumothorax?
a result from injury to the chest; air enters the intrapleual space, increasing pressure and collapsing lung; treated by inserting a needle and withdrawing air from the intrapleural space
What will occur to DNA during the loss of a restriction enzyme site?
the DNA will not be cleaved, and will not move as far up the gel during electrophoresis
What is a frameshift mutation?
a mutation that involves additions or deletions of nucleotides to yield different sequences of amino acids
What is a nucleotide made of?
a 5 carbon sugar, a phosphate group, and a purine or pyrimidine
What is a nonsense mutation?
a mutation where a premature stop codon is produced, and the result is a shorter polypeptide chain with a different MW than the normal polypeptide
What is a missense mutation?
a mutation where an incorrect amino acid is incorporated into the polypeptide chain; this can result in no change to the MW of the entire polypeptide
What is a silent mutation?
a mutation that causes no noticable effect
What is the primary NT in the sympathetic nervous system?
What is the primary NT in the parasympathetic nervous system?
What are the afferent nerves responsible for?
for delivering sensory information to the CNS; if destroyed, the pupils will not be able to respond to light
What will occur if one puts radioacetively labeled phosphorus on the membrane component of a NT vesicle?
the vesicle will fuse with the axon terminal membrane, and it's membrane will become incorporated with the axon's as the NT's are spilled into the synaptic cleft
Neurotransmitters that have inhibitory effects on the post synaptic neuron sometimes make it more difficult for the neuron to fire an action potential. Why?
the inhibitory NT's will cause opening of Cl- channels in post synaptic membrane, which will result in an influx of negative charge in the cell, making it more negative and causing hyperpolarization
T/F: the rate of a reaction depends on the concentration of the species in the RDS
T/F: the pO2 in the pulmonary arteries is equal to the pO2 in the systemic veins
An increase in respiration will affect the O2/Hb curve by:
shifting it to the right
A decrease in respiration will affect the O2/Hb curve by:
shifting it to the left
What is erythropoetin?
a hormone that intiates increase in Hb/erythrocytes
Which of the following will affect the O2/Hb dissociation curve?
a) [erythrocytes]
b) cardiac output
c) increase in mitochondria
d) none of the above
Which would be expected to contain an abundance of smooth ER?
a) adrenal cortical cells
b) adipose cells
c) endothelial cells
a; the smooth ER is the site of detoxification and lipid synthesis; corticoids are steroids that are made of cholesterol
What about DNA stabilizes it's double helix formation?
hydrogen bonding
If a scientist transplants embryonic cells from the arm bud of a frog to the head, and an arm still forms on the head, what can one deduce about the cells?
they were determined, not differentiated; differentiated cells are not considered differentiated until they form the body part; these were just the buds of the arm
Antibacterial soaps have led to resistant strains of bacteria. This is an example of what type of selection?
directional; which is selection that adapts to the changing environment
If TLC is used on an impurity, what is true about the Rf value?
there will be several Rf values because the impurities will separate
What is the most likely mechanism for protein reabsorption in the proximal tubule?
A drop in osmotic pressure will be interpreted as:
too much water in the body and no ADH or aldosterone secretion
What types of molecules are filtered through the glomerulus?
Na+, urea, amino acids, sugars; NOT RED BLOOD CELLS
Describe the composition of air in the dead spaces of the alveoli.
it is equivalent to the composition of the atmosphere; there will be a lower pCO2 and a higher pO2
What is secondary active transport?
transport against the concentration gradietnt of a substance without the direct use of ATP; uses energy from another favorable concentration gradient
One codon = "X" nucleotides.
What is the vasa recta?
capillaries that supply nutrients to the nephron
T/F: sodium reabsorption in the glomerulus is a passive process
Name three ways that materials can get across capillaries.
1. lipid soluble molecules can diffuse through capillary membrane, along with small, polar molecules
2. some nutrients are small enough to diffuse through capillary pores
3. endocytosis
Hydrostatic pressure forces fluids (into/out) of capillary, while osmotic pressure pushes fluid (into/out) of capillary.
out; into
Does blood or tissue have a higher solute concentration?
blood; that is why fluid is forced into capillaries; from higher [solute] to lower
What type of cells are capillaries made of?
How could one alter the arterial pressure as to increase blood pressure in the capillaries?
increase it
T/F: the plasma component of blood can cross the PM of the capillaries.
false; the plasma contains proteins, which are too large to cross capillary membrane
If endothelial cells were placed in water, the cell would:
a) lyse
b) shrink
c) stay the same
lyse; the cell will contain a higher [solute] than water, so osmosis will occur from the hypotonic to hypertonic environment
Why is carbon monoxide poisonous to humans?
Hb has a greater affinity for CO than for O2
People who go on a strict protein diet will lose weight fast. Why?
because of the sudden loss of glycogen
Are cytosolic proteins water soluble?
yes; they are polar and therefore water soluble b/c likes dissolve likes
In comparison to fit individuals, an obsese person will breathe more ____ due to:
slowly; increased air resistance and large amount of work it takes to breathe
What does somatostatin regulate and how is it increased?
somatostatin decreases insulin and glucagon secretion and is increased by high blood glucose levels
How does caffeine affect ADH secretion?
it inhibits ADH secretion and makes people have to urinate more often
What happens to lactic acid after recovery of strenuous exercise?
it gets converted back to glycogen
T/F: white blood cells and platlets lack nuclei
T/F: albumin can be typically found in plasma
Does nondisjunction involve a change in base sequence of DNA?
T/F: capillaries are made of muscle.

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