Human immunodeficiency virus (HIV) infects cells that have both CD4 an d CCR5 ce

Question

Human immunodeficiency virus (HIV) infects cells that have both CD4 an d CCR5 cell surface molecules. The viral nucleic and viral sivencapsid, and the protein capsid is itself contained inside an envelope consisting of a One hypothesis for viral entry into cells is that binding of HIV membrane glycoproteins to CD4 and CCR5 initiates fusion of the IHIV membrane with the plasma membrane, releasing the viral capsid into the cytoplasm. An alternative hypothesis is that HIV gains entry into the labeled the meme fusion occurs in the endocytotic vesicle. To test these alternative hypotheses for HIV entry, researchers lipids on the HIV membrane with a red fluorescent dye. Viral envelope 8998 Capsid RNA (two identical strands) Reverse688 transcriptase HIV 20) Using live-cell fluorescence microscopy, researchers observed that a red fluorescent spot moved 20) from the plasma membrane into the interior of target cells when red fluorescent dye-labeled HIV was added to the cells. What is the best conclusion from these observations? A) The hypothesis that HIV enters the cell via fusion with the target cell plasma membrane is proved. B) Neither hypothesis is supported by these results. C) The hypothesis that HIV enters the cell via endocytosis is not supported. D) The hypothesis that HIV enters the cell via fusion with the target cell plasma membrane is not supported. E) The hypothesis that HIV enters the cell via endocytosis is proved. 21) Which of the following factors would tend to increase membrane fluidity? A) a greater proportion of saturated phospholipids B) a greater proportion of relatively large glycolipids compared with lipids having smaller molecular masses C) a relatively high protein content in the membrane D) a lower temperature E) a greater proportion of unsaturated phospholipids 22) For living organisms, which of the following is an important consequence of the first law of 22) thermodynamics? A) Organisms grow by converting energy into organic matter B) The energy content of an organism is constant. C) Life does not obey the first law of thermodynamics. The organism ultimately must obtain all of the necessary energy for life from its environment. D) E) The entropy of an organism decreases with time as the organism grows in complexity.

Explanation / Answer

ques. 20) correct answer is "D"

that is The Hypothesis that HIV enters the cell via fusion with the target cell plasma is not supported.

ques. 21) correct answer is "E"

that is ' a greater portion of unsaturated phospolipids'.

ques. 22) correct answer is 'D'

that is 'The organism ultimately must obtain all of the necessary energy for life from its environment'.

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