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Biology PA-CAT Review > Biology Review > Flashcards

Biology Review Flashcards

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1
Q

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

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2
Q

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 intracellular pH

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3
Q

What makes RNA less stable and more reactive than DNA?

A

RNA contains an extra hydroxyl group

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4
Q

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

Vitreous humor

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5
Q

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.

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

A

Sucrose

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6
Q

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%.

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

A

10%

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7
Q

What are the main constituents of triglycerides?

A

Glycerol and fatty acid

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8
Q

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.

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

A

Red blood cells

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9
Q

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

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

A

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

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10
Q

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.

What will happen?

A

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

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11
Q

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

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12
Q

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

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13
Q

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

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14
Q

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

Reaction stays at equilibrium

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15
Q

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

Mobilization of triacylglycerols from adipose tissue requires ATP

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16
Q

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.

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

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17
Q

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).

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

H2S

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18
Q

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

Electrons

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19
Q

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

Decrease

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20
Q

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.

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

A

Glycolysis

21
Q

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.

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

A

Endocrine

22
Q

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.

What conclusions can be drawn from this result?

A

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

23
Q

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 intracellular receptors

24
Q

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.

What is the most likely mechanism of imatinib?

A

Inhibition of phosphorylation

25
Q

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.

What would happen if the GHR gene was mutated so that the protein always had a phosphate group?

A

IGF-2 would be constantly produced

26
Q

What quality best describes an allele?

A

Can be expressed as a phenotype

27
Q

Which component of genetic material is the smallest?

A

Nucleic acid

28
Q

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

Hydrogen

29
Q

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

A

Cytosine

30
Q

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

31
Q

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

X-ray crystallography

32
Q

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

AGG

33
Q

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.

What is the best explanation for this phenomenon?

A

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

34
Q

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.

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

A

Messenger RNA (mRNA)

35
Q

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

A

5’-GCUACCAU-3’

36
Q

What pair of regulatory proteins has contrasting functions?

A

Kinase and phosphatase

37
Q

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

A

Different gene regulatory proteins are activated

38
Q

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’

Based on the genetic code, what will result upon translation of this sequence?

A

Non-functional protein due to an altered amino acid

39
Q

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

A

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

40
Q

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.

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

A

Proteasome

41
Q

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

A

Bacteriophages would target specific bacteria better than antibiotics

42
Q

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

A

Virus; DNA; bacteria

43
Q

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

Reverse transcription

44
Q

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.

What can be concluded about Viruses A and B?

A

Virus B is a virusoid

45
Q

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

A

Water absorbs heat by breaking hydrogen bonds

46
Q

What percentage of the cell is water?

A

70%

47
Q

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

A

mRNA binds to 30s subunit

48
Q

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

49
Q

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.

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

A

Inhibiting EGFR

Biology PA-CAT Review (1 decks)

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