10. Cell Signaling

Introduction to Cell Signaling

Moss sperm are motile and capable of swimming short distances to fertilize an egg. However, it was unknown until recently how sperm make their way from male to female gametophytes that may be separated by a distance of several centimeters or more.

Beyond the results presented here, what other evidence would be useful when drawing conclusions about the role of springtails in moss reproduction?

 Different types of cells possess different genomes. 

 No. Recall that all cells generally possess the same genome. 

 Different types of cells possess different types of phospholipids in their plasma membranes. 

 No. Although this may be true, the membrane phospholipids do not "receive" the information from a signaling molecule, so this cannot be correct. 

 Different cells have different patterns of carbohydrates on their cell surfaces. 

 No. Although this may be true, membrane carbohydrates do not "receive" the information from a signaling molecule, so this cannot be correct. 

 Nuclear envelope proteins vary from cell type to cell type, and this means that cells respond to signaling molecules differently. 

 Different types of cells possess different proteins. 

Consider how cells that respond to these hormones differ from those that do not.

Different types of cells can respond differently to the same signaling molecule. Which of the following explains this apparent paradox?

 The atomic numbers of the atoms involved 

 No. Atomic number is not as important as how the atoms interact to form a particular shape. 

 No. Valence electrons are important in putting molecules together by way of covalent bonds. Molecular shape is more important in determining how molecules interact. 

 No. Although the type of bonding within the molecule does determine the shape of the molecule, there is a better answer. 

How can biological molecules recognize each other? Think of the interaction between drug molecules and their target receptors on cell surfaces.

Pharmaceutical researchers are often interested in blocking particular receptor proteins on cell surfaces. What chemical property of a molecule would be most important for this type of application?

 comparative studies of mitochondrial DNA 

 No. This would provide genetic evidence of the historical relationships among organisms. 

 No. Cell-signaling pathways are not preserved in the fossil record. 

 the study of protein receptors embedded in the nuclear membrane 

 No. Because receptors for signaling molecules are present in the plasma membrane or in the cytoplasm, studying receptors on the nuclear envelope would not provide any information concerning the evolution of signaling mechanisms. 

 the similarity of cell-signaling mechanisms in organisms that have a very distant common ancestor 

Consider which of the following provides evidence of something being evolutionarily conserved.

Evidence that cell signaling evolved early in the history of life comes from __________.

Active, Passive, and Bulk Cell Transport

The receptor protein binds to the signal if it has a complementary shape.

If the signal is able to bind to the receptor it induces a change in the receptor protein's shape.

The change in the receptor protein's shape results in cellular action.

Which of the following is likely to be a response by a receptor protein to an approaching signal molecule?a) The receptor protein binds to the signal if it has a complementary shape.b) If the signal is able to bind to the receptor it induces a change in the receptor protein's shape.c) The change in the receptor protein's shape results in cellular action.d) All of the above are correct.

Animation: Overview of Cell Signaling

Common cell signaling pathway

 Glucagon breaks down glycogen to glucose in liver cells. 

 No. He found that epinephrine triggers the breakdown of glycogen into glucose. 

 The hormone that breaks down glycogen into glucose enters the liver cell. 

 No. He found that the hormone epinephrine never enters the cell where glycogen is metabolized to glucose. 

 Glucose is produced from glycogen when epinephrine binds to a cytoplasmic protein. 

 No. Glucose was produced only when whole cells with intact plasma membranes were used, which indicated that epinephrine does not interact directly with a cytoplasmic protein. 

 A cytoplasmic receptor triggers the signal transduction pathway that produces glucose from glycogen. 

 The hormone epinephrine binds to a specific receptor on the plasma membrane of the liver cell. 

This discovery led to the search for the second messenger.

What did Sutherland discover about glycogen metabolism in liver cells?

Cellular communication | Cells | MCAT | Khan Academy

The cells of multicellular organisms use a variety of molecules as signals which area) Amino acids and proteins.b) Nucleotides and lipids.c) Dissolved gases like nitric oxide.d) Only a and b.e) a, b, and c.

Are necessary for signals to cross the membrane.

Include the intracellular events caused by a signal binding to a receptor.

Include the extracellular events caused by a signal binding to a receptor.

Carry a signaling molecule to the nucleus of a cell.

Signal transduction pathways:a) Are necessary for signals to cross the membrane.b) Include the intracellular events caused by a signal binding to a receptor.c) Include the extracellular events caused by a signal binding to a receptor.d) Carry a signaling molecule to the nucleus of a cell.

3 Steps of Cell Signaling

Cell Signaling | Cellular Biology | Medicine Student Lecture | V-Learning™ | sqadia.com

How do plant cells talk to each other using systemic signalling?

 Move up a concentration gradient and are nonpolar 

 Move up a concentration gradient and are polar 

 No. Think about the chemical composition of steroid hormones such as testosterone and estrogen. 

 Move down a concentration gradient and are polar 

 Move through a channel, down a gradient, and are nonpolar 

 No. Although this is partly correct, you should think about the definition of simple diffusion 

 None of the listed responses is correct. 

Consider how such a molecule can trigger a specific cellular response.

When steroid hormones enter a cell by simple diffusion, they can be said to do what in terms of concentration?

Principle of Cellular Communication | Overview of Cell Signalling

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of substances on opposite sides of the membrane?
a. intracellular receptor
b. G protein-coupled receptor
c. phosphorylated receptor tyrosine kinase dimer
d. ligand-gated ion channel

The signal enters the cell directly and binds to a receptor inside.

The physical form of the signal changes as it passes from the cell membrane to the intracellular target.

The signal is amplified, such that even one signal molecule evokes a large response.

The signal triggers a sequence of phosphorylation events inside the cell.

What does it mean to say that a signal is transduced?a) The signal enters the cell directly and binds to a receptor inside.b) The physical form of the signal changes as it passes from the cell membrane to the intracellular target.c) The signal is amplified, such that even one signal molecule evokes a large response.d) The signal triggers a sequence of phosphorylation events inside the cell.

Overview of cell signaling

 the GI tract does not have receptor tyrosine kinases 

 No. Epinephrine does not act through receptor tyrosine kinases. 

 in cells of the GI tract epinephrine operates via a cytosolic receptor, whereas in cells of the heart epinephrine acts via a plasma membrane receptor 

 No. Epinephrine works via a plasma membrane receptor regardless of cell type. 

the concentration of Ca2+ is lower in the cytosol of GI-tract cells than in the cytosol of heart cells

 No. Calcium is not a second messenger in epinephrine's signal-transduction pathway. 

 there are differences in the proteins found in the two types of cells 

Consider what makes a GI tract cell different from a heart cell.

Cells of the gastrointestinal (GI) tract and cells of the heart respond differently to epinephrine because __________.

 the signal molecule combined directly with a cytosolic enzyme to form an active quaternary structure 

 No. In cell extract experiments, the signal molecule could not activate the enzyme. 

 the signal molecule worked equally well with intact or disrupted cells 

 No. When the experiment was performed with disrupted cells, no response was observed. 

 the cell-signaling pathway involves two separate steps: transduction and response 

 No. The cell-signaling pathway has three steps: reception, transduction, and response. 

 epinephrine is involved in response to stress 

 No. Though true, this choice does not address the question. 

 the signal molecule did not interact directly with the cytosolic enzyme but required an intact plasma membrane before the enzyme could be activated 

Sutherland discovered that epinephrine acts in a three-step pathway.

Early work on signal transduction and glycogen metabolism by Sutherland indicated that __________.

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