Cell Biology Final Exam

Front 1

The signal molecule acetylcholine has different effects on different cell types in a animal and binds to different receptor molecules on different cell types

Back 1

True: Acetylcholine binds to similar receptor proteins on heart muscles cells and salivary gland cells, but it evokes different responses in each cell type

Front 2

After acetylcholine is secreted from cells, it si long-lived, because it has to reach target cells all over the body

Back 2

False: Acetylcholine is a nuero transmitter, and belongs to neuronal signaling which is a very fast pace, even though they are like the endocrine cell that deliver messages across long distances:a message is not broadcast widely but is delivered quickly and specifucally to individual target calls through private lines (along the axon)

Front 3

IP3 is produced directly by cleavage of an inositol phospholipid without incorporation of an additional phosphate group.

Back 3

True: When phospholipase C chops the sugar-phosphate head off the inositol phospholipid, it generates two small messenger molecules inositol 1,4,5-triphosphate (IP3) and diacylglycerol (DAG)

Front 4

Calmodulin regulates the intracellular Ca2+ concentration

Back 4

Calmodulin senses but does not regulate intracellular Ca2+ levels.

Front 5

Different Signals originating form the plasma membrane can be integrated by cross talk btw different signaling pathways inside th cell.

Back 5

True: See Figure 16-38. The diagram sketches the pathways from G-protein-linked receptors via adenylyl cyclase and via phospholipase C and via Ras. The protein Kinases in these pathways phosphorylae many proteins, including proteins belonging to the other pathways. The resulting dense network of regulatory interconnecting is symbolized by the red arrows radiating from each kinase yellow; some kinases phosphorylate some of the same target proteins

Front 6

ras is an oncogene

Back 6

False: ras is a proto-oncogene. It becomes and oncogene, ie promotes the development of cancer, if it harbors mutations that keep it in an active state all the time.

Front 7

Tyrosine phosphorylation serves to build binding sites for other proteins to bind to receptor tyrosine kinases.

Back 7

True: The newly phosphorylated tyrosines serve as binding sites for a whole zoo of intracellular signaling proteins-perhaps as many as 10 or 20 different molecules-which themsleves can become activated upon binding. While it lasts, this protein complex transmits it signal along several routes simultaneously to many destinations inside the cell, thus activating and coordinating the numerous biochemical changes that are required to trigger a complex response, such as cell proliferation.

Front 8

Compare and contrast signaling by neurons, which secrete neurotransmitters at synapse, to signaling carried out by endocrine cells, which secrete hormones into the blood

Back 8

Both types of signaling can occur over long-range: neurons can send action potentials along very long axons (think of the axons in the neck of a giraffe, for example), hormones are passed through the bloodstream throughout the organism. Because neurons secrete large amounts of neurotransmitters at a synapse, a small, well-defined space btw two cells, the concentrations of signal molecules are high; neurotransmitter receptors need only to bind to neurotransmitters with only low affinity.Hormones, in contrast, are vastly diluted in the bloodstream, where they circulate at often minuscule concentrations; hormone receptors, therefore, generally bind their hormone with extremely high affinities

Front 9

Discuss the relative advantages of the two mechanisms.

Back 9

Whereas neuronal signaling is a private affair, one neuron talking to a select group of target cells through specific synaptic connections, hormonal signaling is a public announcement, with target cells sensing the hormone levels in the blood. Neuronal signaling is very fast, limited only by the spped of propagation on the action potential and the workings of the synapse, whereas hormonal signaling is slower, limited by the blood flow and diffusion over larger distances.

Front 10

Both the GTP-bound alpha subunits and nucleotides-free betagamma complexes- but not GDP-bound, fully assembled G proteins-activate other molecules downstream of G-protein-linked receptors

Back 10

True: Nucleotide-free betagamma complexes can activate ion channels, and GTP-bound alpha subunits can activate enzymes. The GDP-bound form of trimeric G proteins is the inactive state.

Front 11

What are the similarities and differences btw the reactions that lead to the activation of G proteins and the reactions that lead to the activation of Ras?

Back 11

Activation in both cases depends on the proteins that catalyze GDP-GTP exchange on the G protein or Ras protein. Whereas activated G-protein-linked receptors perform this function directly for G proteins, enzymes-linked receptors assemble multiple adaptor proteins into a signal complex when the receptors are activated by phosphorylation, and one of these adaptors recruits a Ras-activating protein that fulfills this function for Ras.

Front 12

Kinesin moves endoplasmic-recticulum membranes along microtubules so that the network of ER tubule becomes stretched throughout the cell.

Back 12

True: A continual outward movement of ER is required; on the absence of microtubules, the ER collapses toward the center of the cell.

Front 13

Without actin, cells can form a functional mitotic spindle and pull their chromosomes apart but cannot divide.

Back 13

True: Actin is needed to make the contractile ring that causes the physical cleavage btw the two daughter cells, whereas the mitotic spindle that partitions the chromosomes is composed of microtubules.

Front 14

Lamellipodia and filopodia are feelers that a cell extends to find anchor points on the substratum that it will then crawl over.

Back 14

Both extensions are associated with transmembrane proteins that protrude from the plasma membrane and enable the cell to form new anchor points on the substratum

Front 15

GTP hydrolyzed by tubulin to cause the bending of flagella

Back 15

False: To cause bending, ATP is hydrolyzed by the dynein motor proteins that are attached to the outer microtubules in the flagella

Front 16

Cells having an intermediate-filament network that cannot be depolymerized would die.

Back 16

False: Cells could not divide without rearranging their intermediate filaments, but many terminally differentiated and long lived cells, such as nerve cells, have stable intermediate filaments that are not known to depolymerize.

Front 17

The plus ends of microtubules grow faster b/c they have a larger GTP cap.

Back 17

False: The rate of growth is independent of the size of the GTP cap. The plus and minus ends have different growth rates b/c they have physically distinct binding sites for the incoming tubulin subunits; the rate of addition of tubulin subunits differs a the two ends.

Front 18

The transverse tubules in muscle cells are an extension of the plasma membrane, with which they are continuous, and likewise, the sarcoplasmic reticulum is an extension of the endoplasmic reticulum

Back 18

True: Both are nice examples of how the same membrane can have regions that are highly specialized for a particular function.

Front 19

Activation of myosin movement on the actin filament is triggered by phosphorylation of troponin in some situations and by Ca2+ binding to troponin in others

Back 19

False: Myosin movement is activated by phosphorylation of myosin, or by calcium binding to troponin.

Front 20

Why do eukaryotic cells, and especially animal cells, have such large and complex cytoskeletons? List the differences btw animal cells and bacteria that depend on the eukaryotic cytoskeleton.

Back 20

look up answer in the textbook for Chapter 17-13, page A:47

Front 21

There are not known motor proteins that move on intermediate filaments. Suggest and explanation for this.

Back 21

Intermediate filaments have no polarity; their ends are chemically indistinguishable. It would therefore be difficult to envision how a hypothetical motor protein that bound to the middle of the filament could sense a defined direction. Such a motor protein would be equally likely to attach to the filament facing one end or the other.

Front 22

Which of the following changes takes place when a skeletal muscle contracts?

a. z discs move farther apart
b. actin filaments contract
c. myosin filaments contract
d. sarcomers becoem shorter

Back 22

d. sacromeres become shorter

Front 23

In his highly classified research laboratory Dr. Lawrnece M. is charged with the task of developing a strain of dog-sized rats to be deployed behind enemy lines. In your opinion, which of the following strategies should Dr. M. pursue to increase the size of rats?

Back 23

See answer in book for Chapter 18-11, page A:48