In the Mammalian Eye, the Lens Is Composed of a Large

question 193

Multiple Choice

In the mammalian eye, the lens is composed of a large number of cells called lens cells.Only lens cells along the edges are close to a blood supply where they exchange nutrients and waste molecules.Lens cells in the middle of the lens are connected via gap junctions.Cataracts appear as a cloudiness that develops in the lenses of the eye, often with age.Biologists have suspected that cataracts result from a disruption in intercellular communication between lens cells through gap junctions.Which type of investigation would best provide more information about whether gap junctions are involved in cataract formation?

• A) Measure cAMP levels inside lens cells that have developed cataracts, and compare them to controls without cataracts.
• B) Break open lens cells that have developed cataracts, isolate the cytoplasmic fraction, and test it for elevated nitric oxide levels.
• C) Quantitatively compare mRNA transcripts in lens cells that have been affected by cataracts, and compare them to unaffected controls.
• D) Count the gap junctions in lens cells, and compare to the number of gap junctions found in other cells, such as heart cells.
• E) Engineer mice to carry a mutation that knocks out connexin protein, and test to see whether these mice develop cataracts at a younger age than control mice.

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Definitions:

Adjusting Entries

Journal entries made at the end of an accounting period to allocate income and expenses to the period in which they actually occurred.

Prepaid Insurance

The portion of an insurance premium that has been paid in advance and is recognized as an asset until it is used.

Accrued Salaries

Salaries that have been incurred but not yet paid, representing an expense for the company and a liability until the payment is made.

Periodic Inventory System

An inventory accounting system where inventory levels and cost of goods sold are determined at the end of an accounting period through physical counts.