MCAT Biology Missed Problems
Synthesis of antibody proteins in eukaryotic cells is associated with what organelle? A. Nucleus B. Mitochondria C. Endoplasmic reticulum D. Golgi apparatus
C Note that this question is asking about synthesis, not exportation.
The germ cells of a newly discovered diploid organism divide without the DNA replication step that normally occurs prior to meiosis. For this organism, which type of chromosome is found at the metaphase plate during meiosis I? A. Tetrads, consisting of two pairs of sister chromatids B. Dyads, consisting of a single pair of sister chromatids C. Monads, consisting of a single chromatid D. Bivalents, consisting of four pairs of sister chromatids
C Sister chromatids is a result from DNA replication. This is not to be confused with homologous chromosome pairs. As in this problem DNA replication is missing, there will not be any sister chromatid pairs.
Which of the following associations of a primary germ layer and an adult organ is correct? A. Endoderm--cardiac muscle B. Endoderm--lens of the eye C. Ectoderm--fingernails D. Mesoderm--lining of a digestive tract
C The ectoderm becomes integument (outer protective layer including skin, nails, hair), surface linings (mouth, ear, anal canal), and the eyes and nervous system. The mesoderm forms musculoskeletal system, circulatory system, and the excretory system. Endoderm becomes internal epithelial linings and digestive system (liver, pancreas, thyroid, bladder)
Certain ovarian tumors called granulosa cell tumors are known to produce excessive levels of estrogen. A physician who diagnose a granulosa cell tumor should look for a secondary cancer in which of the following parts of the reproductive tract? A. Fallopian tube B. Cervix C. Endometrium D. Vagina
C The ovaries are connected with the endometrium by the fallopian tube. An excess of estrogen stimulates growth of endometrial layer in the uterus.
Which statement provides the most plausible explanation for the fact that there are 63 possible codons, but only 20 amino-acyl tRNA synthase enzymes? A. Production of 63 different tRNAs would overwhelm cellular energy resources. B. Synthesis of 63 different amino-acyl tRNA synthases would overwhelm cellular energy resources. C. Wobble in genetic code allows more than one amino acid to be paired to the same tRNA molecule. D. Wobble in the genetic code allows for the same amino acid to be paired with multiple tRNA molecules.
D Beware that choice like A and B are common illogical distractors. There are more than 20 tRNAs in human, and one amino acid can be assembled with multiple codons. Which is made possible by the third base (wobble) in the codon.
All of the following will lead to smooth muscle relaxation EXCEPT: A. pumping calcium into the sarcoplasmic reticulum. B. activating the Na-Ca exchanger that moves calcium out of the cells while bringing Na into an intracellular compartment. C. inhibiting the action of inositol triphosphate. D. activating calmodulin within smooth muscle cells.
D Calcium is released FROM sarcoplasmic reticulum during activation, therefore pumping Ca into SR will lead to relaxation. Removing Ca and inhibiting IP3 have the same effect. However, calcium-calmodulin-myosin kinase complex phosphorylates the light chains of myosin and allows cross-bridge cycling and contraction of muscles.
Sarin is a potent organophosphate that can be used in chemical warfare. As an inhibitor of acetylcholinesterase, sarin causes excessive buildup of acetylcholine in all synapses where it is the neurotransmitter. Which of the following symptoms would most likely be seen in an individual with sarin poisoning? A. Increased urination and increased sweating B. Increased urination and decreased sweating C. Decreased urination and increased sweating D. Decreased urination and decreased sweating
A Acetylcholine is used as a neurotransmitter for all parasympathetic neurons, preganglionic sympathetic neurons, and postganglionic sympathetic neurons. The postganglionic sympathetic neurons innervate sweat glands, and the parasympathetic neurons innervate detrusor muscle that stimulates urination. Therefore hyperactivity of cholinergic receptors would result in increased urination and sweating.
Bile acids facilitate the intestinal absorption of lipids. During this stage of digestion, bile acids function as: A. emulsifiers. B. buffers. C. carrier proteins. D. lipases.
A Bile acids are not proteins, eliminating choice C and D. Bile acids are amphipathic molecules and therefore allows them to interact with both polar and nonpolar structural components of lipids to form an emulsion. Buffers in digestion is mainly bicarbonate, which is synthesized by the pancreas duct cells and released into the duodenum.
Consuming a meal high in fat is likely to cause an increase in the: I. discharge of bile by the gall bladder II. activity of pancreatic lipase in the small intestine III. absorption of triglycerides into villi capillaries A. I and II only B. I and III only C. II and III only D. I,II, and III
A Discharge of bile is stimulated by the presence of fat in the duodenum. Pancreatic lipase is the primary enzyme for breaking down of lipids in the small intestine. Villi capillaries collects amino acids and sugars, instead of triglycerides. Therefore only statement I and II are true.
Some studies suggest that, in patients who have Alzheimer's disease, there is a defect in the way the spindle apparatus attaches to the kinetochore fibers. At which stage of mitotic division would one first expect to be able to visualize this problem? A. Prophase B. Metaphase C. Anaphase D. Telophase
A Do not mix centrosome and centromere. The centrosome is formed in prophase, radiating spindles connected to kinetochore fibers. The centromere is connected by spindles during metaphase where they align in the middle of the cell.
A bacterial cell is noted to be resistant to penicillin. The bacterium is transferred to a colony that lacks the fertility factor, and the rest of the colony does not become resistant to penicillin. However, the penicillin-resistant cell has also started to exhibit other phenotypic characteristics, including secretion of a novel protein. Which of the following methods of bacterial recombination is NOT likely to account for this change? A. Conjugation B. Transformation C. Transduction D. Infection with a bacteriophage
A In this problem, the critical information is the fertility factor (factor F) that is necessary for conjugation to transfer genetic material.
In the human "knee-jerk" reflex, the knee is struck and the lower leg jerks forward. Which of the following represents the complete pathway that the nerve impulse travels in effecting this response? A. Sensory neuron, motor neuron B. Sensory neuron, brain, motor neuron C. Sensory neuron, associative neuron, brain, associative neuron, motor neuron D. Sensory neuron, associative neuron, motor neuron, associative neuron, motor neuron
A Knee-jerk reflex is a simple monosynaptic stretch reflex, the antagonist muscle relaxation involves a interneuron in the spinal cord but is not the main impluse. Associative neuron is also known as interneuron.
Melanosomes most likely move along microtubules that originate in and radiate from the: A. centrosome. B. kinetochores. C. Golgi apparatus. D. microfilaments under the plasma membrane.
A Microtubules are cellular structures that originate from centrosomes, they attach chromosomes by forming mitotic spindle during metaphase at kinetochore on each chromosome. Microtubules also shuttle vesicles containing neurotransmitter in nerve cells. Cilia and flagella are also composed of microtubules.
Anencephaly is a rare physiological abnormality in which the cerebrum fails to develop. During which trimester of pregnancy would this disorder manifest? A. First trimester B. Second trimester C. Third trimester D. Any trimester
A The first trimester is the formation of most organs in the fetus; the second trimester marks rapid size growth, facial development, and fetal movement in the amniotic fluid; the third trimester includes further brain maturation, size growth, and active antibody transport from mother's body via the umbilical chord.
At venous end of a capillary bed, the osmotic pressure: A. is greater than the hydrostatic pressure. B. results in a net outflow of fluid. C. is significantly higher than the osmotic pressure at the arterial end. D. causes proteins to enter the interstitium.
A The osmotic (oncotic) pressure the the pressure due to different osmolarity and tends to absorb water into the vessel. Hydrostatic pressure is the pressure that comes from fluid within the blood. They sum together to determine the Sterling force. A hydrostatic pressure higher than osmotic pressure will cause blood to leak out of vessels.
Diabetic nephropathy is commonly detected by finding protein in the urin of a patient. In such a disease, where is the likely defect in the nephron? A. Glomerulous B. Proximal convoluted tubule C. Loop of Henle D. Collecting duct
A The urea originates from the filtration at the glomerulous (Bowman's space). It should only allows passage of small molecules like water, Sodium, Potassium, Chloride, monosaccharides, acids and bases. If large molecules like protein is detect in urine, the problem must be with glomerulous.
Spiral arteries provide placental blood flow during pregnancy. Vasoconstriction of spiral arterioles is most likely to cause: A. low fetal oxygen levels. B. fetal oxidative stress. C. excessive fetal blood perfusion. D. decreased maternal blood perfusion
A Vasoconstriction will result in less blood flowing through a tissue and result in less oxygen transferred to the fetus.
Which of the following does NOT describe connective tissue cells? A. They account for most cells in muscles, bones, and tendons B. They secrete substances to form the extracellular matrix C. In organs, they tend to form the stroma D. In organs, they provide support for epithelia cells
A While bones and tendons are mostly made of connective tissue cells, muscle cells form muscle tissues.
Respiratory acidosis occurs from retention of CO₂ due to depressed respiratory function. Which of the following is a way for kidneys to compensate? A. Increased retention of H⁺ B. Increased retention of HCO₃⁺ C. Decreased secretion of H⁺ D. Decreased secretion of nitrogenous waste
B Acidosis of blood is a result of increased amount of H⁺ and lowered pH. To compensate that, kidneys should either increase secretion of H⁺ or reabsorption of basic molecules. In this case, bicarbonate is a weak base and should be reabsorbed.
In an experiment, enteropeptidase secretion was blocked. As a direct result, levels of all of the following active enzymes would likely be affected EXCEPT: A. trypsin B. aminopeptidase C. chymotrypsin D. carboxypeptidase A
B Both trypsinogen and procarboxypeptidases A/B are activated by enteropeptidase. Once activated, trypsin and activate chymotrypsinogen. Aminopeptidase is a brush-border peptidase secreted by the cells lining the duodenum; it does not require enteropeptidase for activation.
A patient presents with muscle weakness, slow movement, and calcium deposits in some tissues. A blood test reveals very low calcium levels in the blood. Administration of which of the following would be an appropriate treatment for the blood test findings? A. Calcitonin B. Parathyroid hormone C. Aldosterone D. Thymosin
B Calcitonin decreases blood calcium level. Parathyroid hormone would raise blood calcium concentration via gut absorption and bone. Aldosterone is involved in RAAS and regulates blood pressure. Thymosin is released by the thymus for T cell regulation.
Which experimental result from the study of transgenic rats predisposed to AD would most strongly support the theory that a reduction in the number of dendritic spines causes AD? A. The number of dendritic spines on cortical neurons is inversely correlated with the severity of AD symptoms. B. Increasing the dosage of a drug that promotes dendritic spine formation is associated with a significant decrease in AD symptoms. C. Symptom-free rats with a reduced number of dendritic spines on their cortical neurons eventually develop AD. D. A drug that inhibits dendritic spine formation on cortical neurons is associated with a significant increase in AD symptoms.
B Choices A and C suggests correlation, instead of causal relations. B is a better choice as it also includes dosage effect.
Division of the zygote into blastomeres begin about 30 hours after fertilization. These mitotic division normally occurs as the zygote passes through the fallopian tube to the uterus. The process by which subsequent division forms progressively smaller blastomeres is called: A. compaction B. cleavage C. blastulation D. gastrulation
B Cleavage is the division of cells that didn't change total volume and it happens before blastrulation, resulting in smaller cells and larger N:C ratio. Blastrulation forms the hollow sphere of cells with fluid inside. Blastomere is the small product cell of cleavage.
A patient with liver disease is found to have a bleeding disorder that causes coagulation to occur slowly or not at all. Which of the following explanation is most likely? A. Elevation of liver enzyme due to liver damage interferes with function of clotting factors B. Damage to liver cells diminish production of clotting factors C. Liver disease cause diminished total protein and changes the oncotic pressure of blood D. Elevation of liver enzyme due to liver damage interferes with production of clotting factors
B Clotting factors are produced by liver cells. Liver enzymes only represent the activity of liver cells but do not affect production of clotting factors.
Which of the following most accurately describes the effect of decreasing circulating levels of carbon dioxide? A. Bicarbonate increases and the blood become more basic B. Hydrogen ions decrease and the blood become more basic C. Bicarbonate decreases and the blood become more acidic D. Hydrogen ions increase and the blood become more acidic
B Decreasing carbon dioxide level will lead to increase in pH, due to the reduced H+ level. Bicarbonate is basic but the effect is weaker than protons.
Rab27a protein on the melanosome membrane facilitates this transfer by interacting with melanophilin protein, which in turn binds myosin Va, a motor protein on microfilaments. Based on the passage, myosin Va most likely directly binds: A. tubulin. B. actin. C. melanin. D. Rab27a.
B Myosin Va is a motor protein. Motor proteins such as myosin Va move along microfilaments through interaction with actin. Microfilaments are made of solid polymerized rods of actin, and actin filaments can use ATP to generate movement by interacting with myosin.
Pyloric stenosis is a condition that occurs in newborns when the pyloric sphincter is too narrow. This is characterized by forceful, non-bilious projectile vomiting. Which of the following metabolic abnormalties is like to result from this condition? A. Blood pH too low B. Blood pH too high C. Blood sodium too low D. Blood sodium too high
B Vomiting results in an outflow of HCl, which leads to an increase in blood pH
To facilitate the process of birth, an infant's head is somewhat flexible. This flexibilities due in part to the two fontanelles, which are soft spots of connective tissue in the infant's skull. With time the fontanelles will close through a process known as: A. endochondral ossification. B. intramembranous ossification. C. bone reabsorption. D. longitudinal growth.
B Ossification is the formation of bones. Endochondral ossification is the replacement of cartilage with bones, forming a long bone; intramembranous ossification is the formation of bones from undifferentiated connective tissue (mesenchyme) and occurs mostly in fusion of skull. Bone reabsorption is the break down of bone by osteoclasts. Longitudinal growth is the elongation of bones from physeal.
A particular gene is said to be fully penetrant but with variable expressivity. Which of the following is true regarding this gene? A. The gene is rarely expressed when present, but appears with the same exact phenotype when expressed. B. The gene is always expressed when present, but not necessarily with the same phenotype. C. The gene is rarely expressed when present, but when expressed, the phenotypes may vary. D. The gene is always expressed when present with thee same exact phenotype.
B Penetrance is the percentage of individuals in a population carrying an allele who actually express the phenotype associated with it. Fully penetrant is equivalent to dominant gene. Variable expressivity means the expression of the gene is not constant. Therefore the phenotype is not always the same.
In mothers with preeclampsia, the fetus experiences oxidative stress during ischemia-reperfusion cycles. The reperfusion portion of this cycle causes: A. increased oxygen to the fetus during vasoconstriction. B. increased blood flow to the fetus. C. decreased oxygen to the fetus during vasoconstriction. D. decreased blood flow to the fetus.
B Reperfusion is increased blood flow to the fetus after a period of relative ischemia. Vasoconstriction will result in reduced oxygen and leads to ischemia.
Which experimental method(s) are appropriate for assessing whether mutations occurred within p53 gene? I. Sanger sequencing II. Southern blotting III. SDS-PAGE A. I only B. I and II only C. II and III only D. I, II, and III
B Sanger sequencing obviously can detect mutations by sequencing the isolated, amplified DNA fragments. The three blotting techniques (with their target molecules) are Southern (DNA), Northern (RNA), and Western (protein) blotting. Southern blotting uses fluorescent labelled DNA probe (nucleic acid with complementary sequence) and will not bind if there is a mutation. SDS-PAGE is a gel electrophoresis method that can only be used to compare the molecular weight of proteins, and is used by Western blot to detect prescence of a particular protein using specific antibodies.
Which of the following is true regarding pancreatic somatostatin? A. Its secretion is increased by low blood glucose B. It is always inhibitory C. It is regulated by cortisol levels D. Is stimulates insulin and glucagon secretion
B Somatostatin is released by pancreatic δ cells when glucose and amino acid levels are high. It suppresses glucagon and insulin secretion.
Which of the following is the correct sequences of the development of a mature sperm cell? A. Spermatid→1°spermatocyte→spermatogonium→2°spermatocyte→spermatozoa B. Spermatogonium→1°spermatocyte→2°spermatocyte→spermatid→spermatozoa C. Spermatozoa→1°spermatocyte→2°spermatocyte→spermatogonium→spermatid D. Spermatogonium→1°spermatocyte→2°spermatocyte→spermatozoa →spermatid
B Spermatogonia (2n) first differentiate into primary spermatocytes, then undergo meiosis to yield four spermatids. The spermatids undergo a series of changing to become the mature sperm, or spermatozoa.
Which of the following is/are true about sphingolipids? I. They are all phospholipids. II. They all contain a sphingosine backbone. III. They can have either phosphodiester or glycosidic linkages to their polar head groups. A. I only B. III only C. II and III only D. I, II, and III
B Sphingolipids can either have a phosphodiester or a glycosidic bond, making them either phospholipids or glycolipids. The backbone of sphingolipids could be sphingosine or sphingoid.
A diagram of the ATP synthase enzyme is shown. A toxic compound that blocks the α subunits of ATP synthase must enter which region of the mitochondria to function? A. Cristae B. Matrix C. Intermembrane space D. Outer mitochondrial membrane
B The mitochrondrial structure, from inner most to outer most, includes matrix, inner membrane, intermembrane space, outer membrane. The high proton concentration at intermembrane space creates a electric gradient across inner membrane, and give rise to ATP production.
From which of the following layers does the notochord form? A. Ectoderm B. Mesoderm C. Endoderm D. Archenteron
B The notochord later forms the spine, and is part of the musculoskeletal system that mesoderm gives rise to. Archenteron is the opening of gastrula that becomes the gut.
The danger posed by S. aureous virus infections would likely be most decreased by reducing the length of which of the following phases of its growth cycle? A. lag phase B. log phase C. lytic phase D. death phase
B These phases describes the cycle of a bacteria population, with log phase showing exponential growth. Therefore shortening this phase will limit the expansion of this colony.
Based on Figure 1 and the passage, which of the following cells are most important in the exchange of O2 between the blood and the surrounding tissues? A. Pericytes B. Endothelial cells C. Smooth-muscle cells D. Fibroblasts
B This is a trick question that it only refers to the following figure, which states that only endothelial cells have contact with the blood. Data from figure 2 are just distractors.
The histones released by ischemic neurons were primarily found in which cellular location prior to the ischemic trauma? A. Dendrites B. Soma C. Synaptic end plate D. Axon
B This question simply tests on the function of histones. Histones are proteins that DNA wrap around in the cell nucleus, therefore histones should be in soma prior to trauma.
Addision's disease is characcterized by primary adrenal gland insufficiency, when adrenal glands are targeted by the immunes system and secrets insufficient hormones. Normally, a hypothalamic factor stimulates the release of adrenocorticotropic hormone (ACTH) from the pituitary gland. In a patient with Addison's disease, the secretion of the hypothalamic factor will: A. be lower than normal. B. be higher than normal. C. be unchanged. D. increase before disease onset and decrease thereafter.
B This question tests upon the negative feedback loop of endocrine regulation. A hypothalamic factor stimulates adrenal gland, and irresponsive adrenal gland will result in extra hypothalamic factor secretion.
Given data in the following table, what can be concluded regarding p53 levels and skin de-pigmentation? A. p53 is upregulated in de-pigmented tissues relative to pigmented tissues. B. p53 is downregulated in de-pigmented tissues relative to pigmented tissues. C. Relative to normal, p53 is upregulated in both de-pigmented and adjacent tissues. D. Relative to normal, p53 is downregulated in both de-pigmented and adjacent tissues.
C A difference of 16-20 can be considered significant enough in such problems.
What is the most probable impact of a point mutation that substitutes the terminal guanine of a 5' exon with an alternate nucleotide? A. The mRNA will be prematurely terminated. B. The protein will be nonfunctional due to an amino acid change. C. The intron will not be spliced from the mRNA transcript. D. There will be no effect, because this is a silent mutation
C A guanine at 5' end is required for RNA splicing. A point mutation will replace the stop codon and the intron will not be spliced out. See more at transcription.
Ftt is an obligate intracellular bacterium. An antibody response can still be effective against Ftt because antibodies: A. enhance the rate of phagocytosis of Ftt B. bind to Ftt plasma B-cells, stimulating antibody production C. bind to Ftt and prevent it from entering the cell D. cross the Ftt cell membrane and prevent translation of Ftt proteins.
C Antibodies are often released into extracellular space and is not effective in enhancing phagocytosis for a obligate intracellular bacteria. It can bind to membrane proteins and opsonize the bacteria, preventing it from entering host cell.
Which fo the following would NOT likely lead to elevated levels of bilirubin in the blood? A. Cholangiocarcinoma, a cancer of the bile ducts that can ultimately lead to full occlusion of the duct lumen B. Autoimmune hemolytic anemia, a disease in which the red blood cells are attacked by antibodies and are lysed C. Menetrier's disease, in which rugae thicken and overlying glands lose secretory ability D. Acetaminophen (Tylenol) overdose, in which the accumulation of toxic metabolites can cause rapid liver failure
C Bilirubin comes from the breakdown of hemoglobin and is one of the main components of biles. Elevated bilirubin is a result of blockage to bile flow or overproduction of bile. Occlusion of duct lumen, increased RBC lysis, and liver failure (unable to produce bile). Rugae are the folds in the stomach wall. Lack of gastric function would not have much effects on bilirubin levels.
Excessive levels of dopamine in the brain are associated with psychosis. Accordingly, many antipsychotic medications block dopamine receptors. Which of the following effects may be seen in an individual taking antipsychotics? A. Increased secretion of growth hormone B. Decreased secretion of growth hormone C. Increased secretion of prolactin D. Decreased secretion of prolactin
C Dopamine in endocrine system is related to hypothalamic secretion. It suppresses anterior pituitary secretion of prolactin. Therefore blocking dopamine receptors increases prolactin secretion.
Which of the following is NOT a difference between prokaryotic and eukaryotic transcription? A. Eukaryotic ribosomal subunits are larger than prokaryotic ribosomal subunits. B. Translation and transcription are directly coupled in prokaryotic cells only. C. The 5' cap and poly-A tail are found only in mature prokaryotic mRNA. D. Introns must be spliced out of the pre-mRNA transcript in eukaryotes only.
C Eukaryotic ribosomes (80S) are larger than prokaryotes' (70S), eliminating choice A. Prokaryotes differ from eukaryotes in that mRNA is transcribed immediately as it's copied from DNA, and splicing of introns and alternative splicing of exons are unique features of prokaryotes eliminating choice B and D. Therefore only C is the correct choice, as 5' cap and poly-A tail are only found in eukaryotes. The 5' cap is used for recognition in translation, and poly-A tail prevents it from being degraded, which are not found in prokaryotes.
Which of the following statements regarding fetal circulation is FALSE? A. In the umbilical cord, there are more arteries than veins. B. The foramen ovale is the only shunt that connects two chambers of the heart. C. Blood flow in the ductus arteriosus is from the aorta to the pulmonary artery. D. The ductus venosus is the only shunt that bypasses the liver.
C In fetus, blood flow is from pulmonary artery to aorta. Fetal circulation bypasses the lung via foramen ovale and ductus arteriosus to avoid high pressure in the lung.
The final electron acceptor during alcohol fermentation in S. cerivisiae is acetaldehyde. Is this process analogous to anaerobic respiration in humans? A. Yes, because acetaldehyde is the final electron acceptor. B. Yes, because oxygen is the final electron acceptor. C. No, because pyruvate is the final electron acceptor. D. No, because oxygen is the final electron acceptor.
C In human anaerobic respiration, pyruvate is the final electron acceptor whereas lactate is the final product. For the two process to be analogous they need to have identical final electron acceptor in this problem. Review topic on oxidative phosphorylation and electron transport chain to get more detail.
An individual undergoes a rapid constriction of the musculature within the bronchioles in response to an airborne substance. Which of the following cells is likely for this response. A. Type II pneumocytes B. Macrophages C. Mast cells D. Epithelial cells
C Mast cells have antibodies at their cell surface and triggers immune response upon activation. It is the cell in lungs that causes allergies. Macrophages phagocytose and is not involved in muscle constriction. Epithelial cells lines the airway and secretes mucus.
During which phase of the menstrual cycle does progesterone concentration peak? A. Follicular phase B. Ovulation C. Luteal phase D. Menses
C Mistaken progesterone for LH. In the menstrual cycle, FSH and LH peaks at ovulation, which is caused by estrogen concentration getting above threshold. After that progesterone production maximizes, suppressing secretion of FSH and LH.
A single-cell diploid organism acquires a deleterious point mutation before entering mitosis. If one of the daughter cells reproduces asexually, and the other daughter cell goes through meiosis to produce gametes that fuse with gametes from other individuals, which cell lineage will be most evolutionarily successful? A. Neither cell lineage will have an advantage because both cell lines carry the deleterious mutation. B. The asexually-reproducing cell lineage, because only one copy of the mutation is present per cell. C. The sexually-reproducing linage, because crossing over events will eventually erase the mutation. D. The sexually-reproducing lineage, because only one-half of the offspring will have the mutation.
D Deleterious point mutation on only one chromatid will not kill the cell directly. However all asexually reproduced progenies will keep one copy of this deleterious mutation. Choice C is incorrect because crossing over doesn't delete a mutation.
Tay-Sachs disease is an autosomal recessive disorder characterized by defective hexosaminidase A. Proteomic analysis of a cell affected by this condition revealed a shortened protein with an abnormal amino acid sequence at the C-terminus. Based on this information, which mutation is mostly likely? A. Silent mutation B. Missense mutation C. Nonsense mutation D. Frameshift mutation
D In nucleotide-level mutations: silent mutation means no change in AA sequence; missense leads to change in single AA at point of mutation; nonsense mutation results in a stop codon; and frameshift will result in many effects such as change of AA sequence and length of peptide.
Enterococcus faecium is a Gram-positive bacteria responsible for many hospital-based infections. Which plant extract is likely to be most effective against an E. faecium infection? A. Hymenelobium petraeum B. Ptychopetalum olacoides C. Enterococcus faecalis D. Vatairea guianenis
D In the table, E. faecalis is NOT the same bacteria as E. faecium. However, the question gives cue that E. faecium is Gram-positive bacteria and we can thus use IZ Size in the table for Gram-positive bacteria.
To perform the immunocytochemistry measurement, researchers dissolved an experimental antibody in aqueous solution, then added thge solution to the cell culture where it bound the target p53 protein. p53 most likely associated with the antibody as a result of: A. covalent bonds B. hydrophobic interactions C. the overlap of π orbitals D. hydrogen bonds
D Interaction between proteins and antibodies are often non-covalent interactions. However as the environment is aqueous, hydrophobic interactions are not likely. Hydrophobic interactions are more likely occur inside large proteins that are away from water molecules.
Red bone marrow is involved in erythrocyte formation. In contrast, yellow bone marrow: A. is involved in leukocyte formation. B. is responsible for drainage of lymph. C. causes the formation of spicules. D. contains predominantly adipose tissues.
D Red bone marrow contains hematopoietic stem cells that give rise to both erythrocyte and leukocytes. Lymph is drained through the epiphyseal just like blood. Yellow bone marrow are mainly made of fat and contains stem cells that can become cartilage, fat, or bone cells.
Which of the following INCORRECTLY pairs a type of muscle fiber with a characteristic of that fiber? A. Red fibers--rich in mitochondria B. Red fibers--high levels of myoglobin C. White fibers--fast twitching D. White fibers--predominantly use aerobic respiration
D Red fibers (Type I fiber) are slow-twitching fibers that have high levels of myosin (which makes them red) and mitochondria; they are often fatigue-resistant. White fibers (Type II fiber) have lower mitochondria and myosin levels, faster onset and shorter duration; they are often fatigable, with Type IIa more enduring than Type IIb. Primary energy source for muscle fibers are ATP. However, as white fibers have less mitochondria and myoglobin, they rely primarily on anaerobic respiration.
Which of the following statements concerning the somatic division of the peripheral nervous system is INCORRECT? A. Its pathways innervate skeletal muscle. B. Its pathways are usually voluntary. C. Some of its pathways are referred to as reflex arcs. D. Its pathways always involve more than two neurons.
D Somatic division of PNS involve sensory and motor neurons and controls voluntary muscle movement. It can involve only two neurons therefore choice D is incorrect.
Many lipid-soluble toxins are metabolized by cytochrome P-450 (cP450). The role of cP-450 in the metabolism of toxins may be exemplified by the a case in which a chronic alcoholic died of a barbiturate overdose: While sober, the alcoholic was having trouble falling asleep and, therefore, took the recommended dosage of sleeping pills (barbiturates). When no drowsiness was felt, the alcoholic consumed more sleeping pills, then drank an alcoholic beverage. Severe respiratory depression and death soon followed caused by an overdose of barbiturates. No drowsiness was initially felt by the alcoholic because the previous abuse of alcohol had: A. denatured the cP-450. B. inhibited the cP-450. C. reduced the cP-450. D. induced the cP-450.
D The interaction between cP450 and barbiturates is that cP450 metabolizes barbiturates, reducing its effect. Reduced drowsiness results in barbiturates overdose. Therefore there's an increased amount of cP450, meaning it's induced by alcohol.
When the pH of the blood is high, which substance is likely to be excreted in larger quantities in the urine? A. Urea B. Ammonia C. Hydrogen ions D. Bicarbonate ions
D The kidney regulates pH of blood by controlling the secretion and reabsorption of H⁺ and HCO₃⁺. Ammonia is toxic and is usually converted to urea in the liver. To lower blood pH, kidney should increase secretion of basic HCO₃⁺ and reabsorption of H⁺.
Researchers overexpressed a CLdn6 cytoplasmic tail deletion in the suprabasal (upper) compartment of the transgenic mouse epidermis. No gross phenotypic abnormalities were observed at birth, but with aging, chronic dermatitis appeared with a concomitant barrier dysfunction manifested as increased trans-epidermal water loss. A disruption in the expression of Cldn6 is LEAST likely to affect which layer of the epidermis? A. Stratum corneum B. Stratum granulosum C. Stratum spinosum D. Stratum basale
D The provided information indicates that layers above the basal layer are affected by Cldn6 gene disruption, therefore the Stratum basale (the basal layer) is least likely to be affected.
Viruses can be classified based on various characteristics. Which is NOT an example of how virus could be classified? A. Viruses can be classified by their genomic content B. Viruses can be classified by their external surface C. Viruses can be classified by their size and shape D. Viruses can be classified by the symptoms they cause
D Viral classification can be based on genomic content (DNA/RNA), external surface (capsid only/capsid and lipid membrane called envelope), and shape (coronavirus etc.) However, many viruses cause similar symptoms and is hard to classify.
Wild poliovirus (WPV) is made of four structural proteins: VP1, VP2, VP3, and VP4. The antigen binding sites were identified as A1, A2, and A3. Shown in the following table. Among the genes that code for the amino acid sequences, what is the likelihood of two genes being separated by a cross-over during Prophase one of meiosis? A. The A1 and A2a genes are most likely to be separated. B. The A2a and A2b genes are most likely to be separated. C. Both the A2a and A3a genes, and the A1 and A2b genes, are equally likely to be separated. D. None of the genes in table 1 are likely to be separated.
D Virus replication doesn't involve meiosis and therefore will not have cross-over events.