Which of the following is a likely explanation of why natural selection favored the evolution of signals for sexual reproduction?
A) Even in the simplest organisms, sexual reproduction required several coordinated responses by cells.
B) Multicellular eukaryotes required signals that were responded to by multiple organ systems.
C) Cells of several kinds of mating types needed to sort themselves to allow self-recognition.
D) Rooted plants required chemical diffusible signals that could travel throughout the organism.
E) Hormones required a mechanism for introducing changes in their target tissues.
Answer: A
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Cell Communication
- Protein phosphorylation is commonly involved with all of the following except
- Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells?
- Apoptosis involves all but which of the following?
- Consider this pathway: epinephrine ? G protein-coupled receptor ? G protein ? adenylyl cyclase ? cAMP. Identify the second messenger.
- Lipid-soluble signaling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because
- The activation of receptor tyrosine kinases is characterized by
- Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?
- Phosphorylation cascades involving a series of protein kinases are useful for cellular signal transduction because
- Humans have receptors for two kinds of beta adrenergic compounds such as catecholamines to control cardiac muscle contractions. Some are beta 1 receptors that promote increased heart rate. Other drugs, called beta blockers, slow heart rate. Smooth muscle cells, however, have beta 2 receptors, which mediate muscle relaxation. Blockers of these effects are sometimes used to treat asthma.
- Affinity chromatography is a method that can be used to purify cell-surface receptors, while they retain their hormone-binding ability. A ligand (hormone) for a receptor of interest is chemically linked to polystyrene beads. A solubilized preparation of membrane proteins is passed over a column containing these beads. Only the receptor binds to the beads.
- A major group of G protein-coupled receptors contains seven transmembrane a helices. The amino end of the protein lies at the exterior of the plasma membrane. Loops of amino acids connect the helices either at the exterior face or on the cytosol face of the membrane. The loop on the cytosolic side between helices 5 and 6 is usually substantially longer than the others.
- In the figure, the dots in the space between the two structures represent which of the following?
- Which of the following types of signaling is represented in the figure?
- The human population's life expectancy has increased significantly but seems to have an upper limit. Which of the following might be described as an ecological consequence of passing that upper limit by regulating cell death?
- Where do apoptotic signals come from?
- In research on aging (both cellular aging and organismal aging), it has been found that aged cells do not progress through the cell cycle as they had previously. Which of the following would provide evidence that this is related to cell signaling?
- In C. elegans, ced-9 prevents apoptosis in a normal cell in which of the following ways?
- Why is apoptosis potentially threatening to the healthy "neighbors" of a dying cell?
- If an adult person has a faulty version of the human analog to ced-4 of the nematode, which of the following is most likely to result?
- Which of the following describes the events of apoptosis?
- Why has C. elegans proven to be a useful model for understanding apoptosis?
- GTPase activity is involved in the regulation of signal transduction because it
- The termination phase of cell signaling requires which of the following?
- What are scaffolding proteins?
- At puberty, an adolescent female body changes in both structure and function of several organ systems, primarily under the influence of changing concentrations of estrogens and other steroid hormones. How can one hormone, such as estrogen, mediate so many effects?