Biology Subject Review

Question 1

Why does rainwater have low salinity when the large bodies of water on Earth, such as seas and oceans, are very saline?

a. Most of the salt in the precipitates remains in the oceans.

b. Most of the salt in the precipitates remains in the clouds.

c. Most of the salt in the vapors is dissolved in the air.

d. Most of the salt in the vapors is converted to energy.

Answer 1

a. Most of the salt in the precipitates remains in the oceans.

Question 2

Intracellular changes are necessary to initiate embryonic stem cell differentiation. In certain cell types, reduced activity of the Na+–H+ exchanger (which normally brings Na+ in and H+ out of a cell) plays a major role in creating the proper intracellular conditions for differentiation.

Based on this information, what intracellular change is needed to initiate differentiation in these cells?

a. Decreased translation

b. Decreased intracellular pH

c. Increased apoptosis

d. Increased intracellular pH

Answer 2

b. Decreased intracellular pH

Question 3

What makes RNA less stable and more reactive than DNA?

a. DNA can only be double-stranded.

b. DNA has stronger bonds than RNA.

c. Proteins can bind RNA tighter than DNA.

d. RNA contains an extra hydroxyl group.

Answer 3

d. RNA contains an extra hydroxyl group.

Question 4

Carbon is an important element that serves as a backbone for all life. Which part of our bodies contains the lowest percentage of carbon?

a. Brain

b. Hair

c. Lung surfactant

d. Vitreous humor

Answer 4

d. Vitreous humor

Question 4

Case:
Trace evidence retrieved in a crime scene revealed 2 distinct monosaccharides upon infrared spectroscopic analysis. The victim was a scientist who was working with an enzyme that cleaves disaccharides. The spectroscopic analysis from the crime lab exactly matched the last entry on the victim’s electronic notebook. During their investigation, the forensics team analyzed carbohydrate samples from 4 suspects who had entered the crime scene in the past 24 hours. Each of the suspects had a unique carbohydrate sample that they needed to analyze.

Question:
Based on this evidence, which of the following carbohydrates did the most likely suspect possess?

a. Fructose

b. Maltose

c. Starch

d. Sucrose

Answer 4

d. Sucrose

Question 5

Case:
A research associate wants to radioactively label thymine bases in a sample of DNA, using tritium (H3). The researcher was given this sample by a colleague who designed primers intending to amplify a product of 500 base pairs (bp) by polymerase chain reaction (PCR). This colleague faced significant difficulty amplifying the product, however, and sent the sample for sequencing. The sequencing laboratory reveals that the guanine base content in the sample is 40%.

Question:
Based on the sequencing results, what is the thymine base content of this sample?

a. 10%

b. 40%

c. 60%

d. 80%

Answer 5

a. 10%

If guanine is 40%, cytosine will also be 40% (they pair together). This brings G:C content to 80%.

The remaining 20% will have to be the A:T content. Since A and T pair together and have to be equal in ratio, thymine content can only be 10%.

Question 5

The peptide pictured here is made up of _____ amino acids and _____ peptide bonds.

a. 3; 2

b. 4; 3

c. 4; 4

d. 5; 4

Answer 5

b. 4; 3

A peptide bond exists at every junction between an amino group (shown as N on this diagram) and a carboxyl group (a node with =O on this diagram)

Question 5

What are the main constituents of triglycerides?

a. Glycogen and unsaturated fat

b. Glycerol and fatty acid

c. Ester and unsaturated fat

d. Adipose in animals and vegetable fat in plants

e. Carboxyl group and stearic acid

Answer 5

b. Glycerol and fatty acid

Question 6

Case:
A graduate student received organellar fractions from 4 different sources. The student was asked to extract DNA from each and was surprised to find 1 sample devoid of any genetic material.

Question:
Given that the student was careful and there were no mistakes in the extraction procedure, what source would be devoid of genetic material?

a. Beetle leaf extract

b. Onion peel

c. Red blood cells

d. Semen sample

Answer 6

c. Red blood cells

Question 7

Case:
You have isolated a group of cells containing the Na+/K+ pump in their cell membranes.

Question:
If you added a non-hydrolyzable analog of ATP to the solution outside the cell membrane, what effect would you expect to observe?

a. Cytoplasmic pH would fall due to the increased production of lactic acid.

b. K would accumulate outside the cell, and Na would accumulate inside the cell.

c. Na would accumulate outside the cell and K would accumulate inside the cell.

d. Transport of Na and K would cease because the Na/K pump would be inhibited.

Answer 7

c. Na would accumulate outside the cell and K would accumulate inside the cell.

Question 7

Case:
Two cells in the body are touching, but they are separated by plasma membranes that only allow water to flow between the cells. Cell 1 has an osmolarity of 1.6 osm/L. Cell 2 has an osmolarity of 1.9 osm/L.

Question
What will happen?

a. Solute will flow from cell 1 to cell 2 until equilibrium is reached.

b. Solute will flow from cell 2 to cell 1 until equilibrium is reached.

c. Water will flow from cell 1 to cell 2 until equilibrium is reached.

d. Water will flow from cell 2 to cell 1 until equilibrium is reached.

Answer 7

c. Water will flow from cell 1 to cell 2 until equilibrium is reached.

Question 8

Pinocytosis and phagocytosis are two important forms of endocytosis, in which cells ingest extracellular substances by surrounding and transporting the substances using vesicles. What is the most critical organelle for aiding to digest the ingested substances in vesicles?

a. Lysosome

b. Peroxisome

c. Ribosome

d. Vacuole

Answer 8

a. Lysosome

Question 8

Mature erythrocytes do not perform cellular respiration in the same way as other somatic cells. What metabolic difference exists between erythrocytes and other somatic cells?

a. ATP production is substantially lower in erythrocytes.

b. Cellular respiration produces more water in erythrocytes.

c. Oxygen consumption is elevated in erythrocytes.

d. The Krebs cycle is less efficient in erythrocytes.

Answer 8

a. ATP production is substantially lower in erythrocytes.

Question 9

The enzyme dihydrofolate reductase breaks folic acid into a precursor to thymine. The chemotherapy drug methotrexate binds to the same site on the enzyme as folic acid. What is true about methotrexate?

a. Methotrexate has a similar chemical structure to folic acid.

b. Methotrexate is a non-competitive inhibitor of dihydrofolate reductase.

c. Methotrexate would increase the reaction rate of dihydrofolate reductase.

d. Methotrexate would increase in effectiveness if more folic acid was added.

Answer 9

a. Methotrexate has a similar chemical structure to folic acid.

Question 10

Suppose that the reactant and product in a solution are in balance. Which of the following conditions will occur if an enzyme is poured into the solution?

a. Product is formed

b. Reaction stays at equilibrium

c. New reactant is formed

d. Free energy will adjust

Answer 10

b. Reaction stays at equilibrium

Question 10

Adenosine triphosphate (ATP) is a nucleotide that plays a major role in many bioenergetic reactions by being consumed or produced. What is the accurate relationship between a bioenergetic reaction and ATP?

a. Degradation of glycogen during exercise or fasting generates ATP.

b. Mobilization of triacylglycerols from adipose tissue requires ATP.

c. Movement of protons during oxidative phosphorylation consumes ATP.

d. Synthesis of urea during the urea cycle produces ATP.

Answer 10

b. Mobilization of triacylglycerols from adipose tissue requires ATP.

Question 11

Case:
Kearns-Sayre Syndrome is a rare mitochondrial disorder first discovered as a condition of muscular weakness affecting the eyes and the heart. It affects an average of 2 in 100,000 individuals. It is a maternally inherited condition caused by large deletions (up to 2-10 kilobases) of mitochondrial DNA (mtDNA) that remove ~12 genes crucial for oxidative phosphorylation and ATP generation, resulting in defective mitochondrial output. The eyes and heart are typically affected most due to their high dependence on mitochondria for energy.

At present, there are no disease-modifying therapies available. The condition is generally managed by supportive care and regular cardiological and ophthalmological monitoring. With the advent of Crispr-assisted gene therapy, scientists believe that one day they will be able to find a way to inhibit mutant mtDNA replication and/or promote healthy mtDNA replication instead. Until then, however, KSS patients do not have any reliable treatments at hand.

Question:
Given the above information, what drug could be the most relevant treatment for managing Kearns-Sayre Syndrome?

a. Coenzyme Q10 (CoQ10), a fat-soluble cofactor that mediates electron transfer

b. Complex IV inactivator that prevents electron transfer to oxygen and ATP synthesis

c. Mitochondrially-targeted nanoparticle (MITO-Porter) linked to a topoisomerase inhibitor

d. Superoxide dismutase (SOD), an antioxidant enzyme that quenches reactive oxygen species

Answer 11

a. Coenzyme Q10 (CoQ10), a fat-soluble cofactor that mediates electron transfer

Question 12

Case:
Desulfurobacterium indicum is a bacterium that uses a process similar to eukaryotic cellular respiration. Instead of using oxygen as the final electron acceptor in the electron transport chain, however, this bacterium uses sulfur (S).

Question:
Assuming that sulfur behaves the same way as molecular oxygen (O2) in the electron transport chain, what do you predict as one of the products of the electron transport chain?

a. ATP with sulfur replacing the oxygen

b. CS2

c. H2S

d. NAD+ bonded to S

Answer 12

c. H2S

Question 13

In eukaryotes, a defect in a certain biochemical system leads to an impairment of oxidative phosphorylation. This caused symptoms such as pigmenturia, exercise-induced myalgia, and elevated serum creatine kinase. During glycolysis, this biochemical system failed to translocate which of the following across the mitochondrial membrane?

a. NADH

b. Malate

c. Electrons

d. Aspartate

Answer 13

c. Electrons

Question 13

Suppose someone is deficient in pyruvate dehydrogenase, an enzyme that plays a crucial role in glycolysis. What would you expect to happen to ATP production in the cells of this individual?

a. Stay the same

b. Increase

c. Decrease

d. Stop altogether

Answer 13

c. Decrease

Question 14

Case:
People with pyruvate dehydrogenase complex deficiency (PDCD) have an inherited lack of a key enzyme in cellular respiration. Patients with PDCD are usually placed on a ketogenic diet, which has very low amounts of sugars and other carbohydrates but is high in protein and fat.

Question:
By eating few sugars but more fat, the ketogenic diet prescribed to PDCD patients avoids what stage of cellular respiration?

a. Electron transport chain

b. Glycolysis

c. Krebs cycle (citric acid cycle)

d. Oxidative phosphorylation

Answer 14

b. Glycolysis

Question 15

Case:
At puberty, human growth hormone (HGH or GH) is produced in the pituitary gland and released into the bloodstream. The growth hormone receptor (GHR) is located on the surface of a number of cells throughout the body, including cells in the liver. When bound to HGH, liver GHRs form dimers that are phosphorylated by the protein JAK2. This phosphorylation causes GHR to phosphorylate proteins called STATs. The STATs go to the nucleus, acting as transcription factors and causing proteins to be transcribed. This results in the liver cells producing the hormone IGF-2, which causes bone growth.

Question:
What type of signaling does HGH send to the liver cells?

a. Autocrine

b. Endocrine

c. Juxtacrine

d. Paracrine

Answer 15

b. Endocrine

Question 16

Case:
A molecular biology graduate student is studying a new signaling molecule: annokine. The student discovers that if they add it to cells, those cells start to divide rapidly. When they first treat these cells with a pan-G-protein-coupled receptor (GPCR) inhibitor, however, annokine treatment does not provoke a response from the cells.

Question:
What conclusions can be drawn from this result?

a. Annokine receptor binding leads to an increase in intracellular K+ concentration.

b. The annokine receptor does not rely on any signaling intermediates to activate cell division.

c. GTPase activity is necessary for annokine’s cell division-inducing effect.

d. Annokine is able to passively diffuse through the cell membrane in order to activate nuclear receptors to engage cell division.

e. Annokine induces cellular chemotaxis.

Answer 16

c. GTPase activity is necessary for annokine’s cell division-inducing effect.

Question 16

Testosterone is a male hormone that is considered to be a fat-soluble signaling molecule. Which of the following pieces of information most appropriately explains why testosterone can cross all cell membranes but only selects the target cells?

a. Target cells have the appropriate DNA segments.

b. Target cells have intracellular receptors.

c. Most cells lack the Y chromosome.

d. Target cells possess cytosolic enzymes.

Answer 16

b. Target cells have intracellular receptors.

Question 17

Case:
Chronic myeloid leukemia (CML) is a myeloproliferative disorder that occurs because of a chromosome translocation that results in the formation of BCR-ABL1 gene. This gene encodes the BCR-ABL1 fusion protein, a mutant tyrosine kinase that is constitutively active. Imatinib is a drug used to treat CML and results in long-term control of the disease in most patients.

Question:
What is the most likely mechanism of imatinib?

a. Inhibition of coagulation factors

b. Inhibition of phosphorylation

c. Inhibition of purine synthesis

d. Inhibition of topoisomerase

Answer 17

b. Inhibition of phosphorylation

Question 18

Case:
At puberty, human growth hormone (HGH or GH) is produced in the pituitary gland and released into the bloodstream. The growth hormone receptor (GHR) is located on the surface of several cells throughout the body, including cells in the liver. When bound to HGH, liver GHRs form dimers that are phosphorylated by the protein JAK2. This phosphorylation causes GHR to phosphorylate proteins called STATs. The STATs go to the nucleus, acting as transcription factors and causing proteins to be transcribed. This results in the liver cells producing the hormone IGF-2, which causes bone growth.

Question:
What would happen if the GHR gene were mutated so that the protein was pre-dimerized and always had a phosphate group?

a. IGF-2 would never be produced.

b. IGF-2 would be constantly produced.

c. IGF-2 would only be produced when HGH is present.

d. IGF-2 would only be produced when HGH is absent.

Answer 18

b. IGF-2 would be constantly produced.

Question 19

What quality best describes an allele?

a. Can be expressed as a phenotype

b. Part of a gene that serves as a messenger

c. Controls replication of a gene

d. Primary protein of an embryo

Answer 19

a. Can be expressed as a phenotype

Question 19

Which component of genetic material is the smallest?

a. Allele

b. Chromosome

c. Gene

d. Nucleic acid

Answer 19

d. Nucleic acid

Question 20

DNA is composed of bases that pair together to form a double helix. What type of bond is responsible for holding base pairs together?

a. Covalent

b. Hydrogen

c. Ionic

d. Metallic

Answer 20

b. Hydrogen

Question 21

What nitrogenous base of the DNA is the partner of guanine?

a. Adenine

b. Uracil

c. Guanine

d. Cytosine

Answer 21

d. Cytosine

Question 21

What DNA repair mechanism is most similar to chromosomal crossover in meiosis with respect to replication machinery?

a. Homologous recombination, a double-strand break type repair

b. Pyrimidine dimers, a direct reversal type repair

c. Methylguanine methyltransferase (MGMT), a direct reversal type repair

d. Base excision repair (BET), a single-strand type repair

e. Nucleotide excision repair (NER), a single-strand type repair

Answer 21

a. Homologous recombination, a double-strand break type repair

Question 22

RNA is flexible macromolecule that can adopt a variety of conformations. A graduate student in structural biology lab has successfully purified a ribonucleoprotein complex (RNP). In order for the graduate student to identify the RNP function, they must identify the tertiary structure of the complex. What technique would be best to reveal the structure of the complex?

a. Electron microscope

b. X-ray crystallography

c. Denaturing polyacrylamide gel electrophoresis (PAGE)

d. High-performance liquid chromatography (HPLC)

Answer 22

b. X-ray crystallography

Question 23

Transcription is the process of DNA being copied into RNA. Translation is the process of a ribosome taking the transcribed mRNA and translating it, matching it to form a complementary base sequence molecule known as tRNA. It is then used to code for proteins.

Assuming that the DNA sequence does not include introns, what is the tRNA base sequence that corresponds to the DNA base sequence (AGG)?

a. ATT

b. AGG

c. TCC

d. UCC

e. GUU

Answer 23

b. AGG

Question 24

Case:
Scientists identify a strain of bacteria with an intriguing property: any time the bacterial DNA codes for a leucine amino acid, there is a 55% chance that the resultant proteins will instead contain a serine at that position and only a 45% chance that a leucine will be present.

Question:
What is the best explanation for this phenomenon?

a. The bacteria do not have a leucine tRNA, and so the serine tRNA takes its place during transcription.

b. The bacteria have a mutation in the serine tRNA anticodon, changing its sequence to resemble the leucine anticodon.

c. The ribosomes in this bacteria have a unique structure that does not accommodate the leucine codon well.

d. The mRNA in these bacteria is undergoing alternative splicing 95% of the time, changing the protein coding sequence.

e. There is a defect in the leucine synthesis pathway in these bacteria, resulting in the production of serine rather than leucine.

Answer 24

b. The bacteria have a mutation in the serine tRNA anticodon, changing its sequence to resemble the leucine anticodon.

Question 24

Case:
Frontotemporal dementia is a form of dementia characterized by cognitive decline and changes in personality, behavior, and language. Research has shown that there is a genetic component to this disease. Specifically, the MAPT gene, which encodes for the tau protein, has been implicated. Several mechanisms have been proposed, one of which is an altered ratio of tau isoforms caused by defects in splicing at exon 10 of MAPT.

Question:
Patients with frontotemporal dementia due to this mechanism have a defect in the processing of what type of molecule?

a. Double-stranded DNA

b. Messenger RNA (mRNA)

c. Single-stranded DNA

d. Transfer RNA (tRNA)

Answer 24

b. Messenger RNA (mRNA)

Question 25

The DNA sequence 5’-ATGGTAGC-3’ will pair with which of the following RNA sequences?

a. 5’-AUCCUACG-3’

b. 5’-AUGGAUGC-3’

c. 5’-GCAUCCAU-3’

d. 5’-GCUACCAU-3’

Answer 25

d. 5’-GCUACCAU-3’

Question 25

What pair of regulatory proteins has contrasting functions?

a. Helicase and nuclease

b. Kinase and phosphatase

c. Polymerase and acetylase

d. Translocase and recombinase

Answer 25

b. Kinase and phosphatase

Question 26

Why do different cells in the same organism express different genes?

a. Different gene regulatory proteins are activated.

b. Their genomes are different.

c. They contain different promoter regions.

d. They use different genetic codes.

Answer 26

a. Different gene regulatory proteins are activated.

Question 26

Case:
Eukaryotic proteins are known to be phosphorylated at Ser, Thr, Tyr, or His residues where prokaryotic proteins phosphorylate at 2 additional residues (Arg or Lys).

A student is given a porcine (pig) protein sample that has undergone a point mutation. The mRNA sequence of this protein (given below) contains a substitution at position 20 from adenine to guanine. This porcine protein is phosphorylated at 4 residues that are crucial for its function.

5’- AUG GAC UCU UAC UGC ACC CAC AUU GGU GCC -3’

Question:
Based on the genetic code (refer to the image), what will result upon translation of this sequence?

a. Functional protein with altered amino acid

b. Functional protein with unaltered amino acid

c. Non-functional protein due to an altered amino acid

d. Truncated protein

Answer 26

c. Non-functional protein due to an altered amino acid

Question 27

How do small interfering RNAs (siRNAs) inhibit expression of a target protein?

a. siRNAs directly bind the DNA encoding their target gene.

b. siRNAs directly bind the mRNA of their target gene to induce degradation.

c. siRNAs directly degrade their target protein.

d. siRNAs globally inhibit gene expression.

Answer 27

b. siRNAs directly bind the mRNA of their target gene to induce degradation.

Question 28

Case:
Parkinson’s disease is a neurologic disorder characterized by resting tremor, slow movements, unstable posture, and rigidity. A pathologic finding that characterizes the disease is Lewy bodies, which are abnormal protein aggregates that accumulate in neurons. These abnormal proteins are believed to contribute to the disease process and accumulate due to problems with protein degradation. Pathologic examination of brain tissue often shows immunoreactivity for ubiquitin.

Question:
Dysfunction of what cellular component would most likely explain the aggregation of abnormal proteins seen in Parkinson’s disease?

a. Lysosome

b. Plasma membrane

c. Proteasome

d. Ribosome

Answer 28

c. Proteasome

Question 28

Interest has recently increased in phage therapy to treat bacterial infections. What would be a likely advantage of phage therapy over current treatments?

a. Bacteria cannot evolve resistance to bacteriophages.

b. Bacteriophages can be used to immunize people against bacteria.

c. Bacteriophages turn the innate immune system against the bacteria.

d. Bacteriophages would target specific bacteria better than antibiotics.

Answer 28

d. Bacteriophages would target specific bacteria better than antibiotics.

Question 29

A bacteriophage is a ______ that inserts its ______ into a host ______, resulting in the production of new DNA.

a. Macrophage; antibodies; bacteria

b. Macrophage; nucleus; bacteria

c. Virus; DNA; bacteria

d. Virus; genome; virus

Answer 29

c. Virus; DNA; bacteria

Question 30

Human immunodeficiency virus (HIV) is an RNA virus that must be converted to DNA before entering its host cell. What enzymatic activity is required for this?

a. Acetylation

b. Methylation

c. Phosphorylation

d. Reverse transcription

Answer 30

d. Reverse transcription

Question 31

Case:
Over the course of 1 month, a doctor has 12 patients visit his practice with a previously unknown disease. With the help of a virologist, he discovers that these patients have 2 unique viruses: Virus A and Virus B.

When he extends this research further, he makes a few observations:

• There are many people in the general population who seem to be infected with Virus A but show no symptoms of disease.
• No humans can be found that are only infected with Virus B.
• Infecting mice with Virus A leads to infection, but not disease.
• Infecting mice with Virus B does not lead to infection or disease.
• Infecting mice with both Virus A and Virus B leads to infection with both viruses and disease.

Question:
What can be concluded about Viruses A and B?

a. Virus A is a satellite virus.

b. Virus B is not infectious.

c. Virus B is a virusoid.

d. Virus B is a DNA virus.

e. Virus A is unrelated to the disease the doctor is studying.

Answer 31

c. Virus B is a virusoid.

Question 32

Some animals regulate body temperature through perspiration. What property of water is associated with the ability to decrease body temperature?

a. There is a change in density when water condenses.

b. Water can dissolve molecules in the air.

c. Water can release heat by the formation of hydrogen bonds.

d. Water absorbs heat by breaking hydrogen bonds.

Answer 32

d. Water absorbs heat by breaking hydrogen bonds.

Question 33

What percentage of the cell is water?

a. 20%

b. 55%

c. 70%

d. 65%

Answer 33

c. 70%

Question 34

What event establishes the first step of initiation during protein synthesis?

a. DNA binds to 50s subunit

b. mRNA binds to 30s subunit

c. rRNA binds to 50s subunit

d. tRNA binds to 30s subunit

Answer 34

b. mRNA binds to 30s subunit

Question 35

Ligands are signaling molecules that bind to receptors either on the cell surface or inside the cell. Which of the following statements is true of ligands?

a. Ligands bind to receptors with a high degree of specificity.

b. Ligands permanently bind to corresponding receptor sites, creating a ligand-receptor complex.

c. The higher the concentration of ligands present, the fewer active ligand-receptor complexes.

d. Ligands are primarily hydrophilic.

Answer 35

a. Ligands bind to receptors with a high degree of specificity.

Question 36

Case:
Mutated or overexpressed receptor tyrosine kinases are frequently observed in tumors. For example, the epidermal-growth-factor receptor (EGFR) is overexpressed in some human epithelial cancers, including breast cancer. Because a small portion of the receptors can dimerize and activate the signal transduction pathway even without binding to epidermal growth factors (EGF), overexpression of the receptor increases the likelihood that an activation signal will be improperly sent to the cell, making the cells grow and divide uncontrollably, as observed in most cancers.

Question:
What is the most practical strategy to control this kind of offending signal transduction pathway?

a. Decreasing EGFR

b. Inhibiting EGFR

c. Reducing EGF

d. Replacing EGF

Answer 36

b. Inhibiting EGFR