B/B UWorld 1

Keratins are a large family of intermediate filament proteins. Scientists studying the effect of keratins in the liver generated model organisms deficient in keratins. These organisms may display abnormal hepatocyte phenotypes because keratin deficiency may reduce the: A. ability of cells to undergo cytokinesis. B. intracellular transport of substances. C. capacity of cells to resist mechanical forces. D. number of cilia on the cell surface.

AAV2 entry into cells could best be blocked by a drug that inhibits which of the following mechanisms? A. Fusion of viral and cell membranes upon receptor binding B. Formation of membrane extensions that engulf external particles C. Inward budding of the cell in response to receptor binding D. Constitutive invagination of the cell membrane to take up extracellular liquid

True or false: non phospholipid components cannot migrate laterally through the cell membrane.

True or false: transmembrane proteins can only interact with the outer leaflet of the cell membrane

In quiescent cells, early endosomes containing AAV2 would most likely move toward: A. mitochondria. B. centrioles. C. cilia. D. kinetochores.

Based on Figure 1, HMGN2 is most likely to interact with histone complexes that are rich in: A. aspartate and glutamate. B. aspartate and arginine. C. lysine and glutamate. D. lysine and arginine.

A recent study of a model organism found that a specific HMG protein localized mainly to the ends of chromosomes. Given this result, the site of localization for this HMG protein would correspond to regions in humans that: A. contain multiple copies of different DNA sequences. B. contain heterochromatin similar to that found in centromeres. C. are subsequently lengthened with each round of cell division. D. are actively replicated by the enzyme DNA polymerase in all cells.

A single-stranded DNA oligonucleotide composed of which of the following would move most slowly down an alkaline agarose gel during electrophoresis? A. Deoxyadenosine monophosphate B. Deoxythymidine monophosphate C. Deoxycytidine monophosphate D. Deoxyguanosine monophosphate

A physician finds that a patient experiences excessive bleeding after sustaining a cut on the arm. The excessive bleeding is LEAST likely to be caused by: A. reduced liver function. B. high numbers of macrophages near the cut. C. reduced production of platelets. D. high levels of serum antibodies against clotting factors.

What is complex II known as in the ETC? A. α-Ketoglutarate dehydrogenase B. Succinate dehydrogenase C. Malate dehydrogenase D. Pyruvate dehydrogenase

Palomino (golden brown) horses are bred for their coat coloration. A breeder will achieve 100% Palomino offspring by crossing a chestnut (dark brown) horse with a cremello (cream) horse. However, if a breeder crosses two Palomino horses, only 50% of the offspring will be Palomino, while 25% will be chestnut and 25% will be cremello. Genetic inheritance of coat color in these horses is best described as: A. codominance. B. complete dominance. C. variable expressivity. D. incomplete dominance.

A typical plasma membrane protein with a pI value of 8.0 is trafficked to an endolysosome prior to its degradation. How will the membrane protein’s net charge change as the endolysosome acidifies from pH 7.4 to pH 5? The protein’s charge changes from: A. positive to negative. B. positive to more positive. C. negative to positive. D. negative to more negative.

Which of the following does NOT explain why the proteome pI distribution is bimodal? A. Proteins are typically most active when pH exactly equals pI, so a bimodal distribution allows a different population of proteins to activate upon pH disturbance. B. Proteins are electrically neutral and therefore more prone to aggregation when pH = pI, resulting in an underrepresentation of pI values of 7.4. C. Most proteins are more soluble if their pI is either above or below, but not equal to, the surrounding pH. D. The pKa distribution of the amino acid side chains is bimodal, leading to a bimodal distribution of pI values in the proteins they compose.

The compound 5,10-methylene tetrahydrofolate (5,10mTHF) is derived from folic acid (vitamin B9) and is required in the active site of the enzyme thymidylate synthase for thymine nucleotide synthesis. Therefore, 5,10mTHF is most likely: A. a transcription factor. B. an inhibitor. C. an allosteric activator. D. a coenzyme.

The reduced virulence of lac+S. typhimurium has been correlated with an inability to generate the torque that turns the flagellum. Which structure in the flagellum is most likely being affected by lac genes? A. Hook B. Filament C. Basal body D. Cell membrane

Which process occurs when reverse transcriptase converts mRNA into cDNA, which is then amplified in cycles to yield thousands of copies?

Which type of neuroglia forms myelin sheaths around axons to reduce ion leakage, decrease capacitance, and increase action potential propagation speed along the axon?

Heterochromatin is tightly wound DNA characterized by ___ levels of histone acetylation and ___ levels of DNA methylation

Euchromatin is marked by ___levels of histone acetylation and ___ levels of DNA methylation

Euchromatin is __ accessible to DNA transcription because it’s loosely packed, while heterochromatin is ___ accessible to DNA transcription because it’s tightly packed

In adults, which of the following cell types would be LEAST active in healthy long bones? A. Osteoblasts B. Osteoclasts C. Bone marrow cells D. Chondrocytes

Which cell in the bones are responsible for hematopoiesis (blood cell production) in adults and remain active throughout life?

When the pH is lower than the pI, the protein ___ protons and becomes ___ charged. When pH is greater than the pI, the protein ___ protons and becomes ___ charged.

Which phase of an action potential occurs when the cell’s membrane potential becomes less negative?