Concept 11.1: External signals are converted to responses within the cell

Question 1

There are two sexes, or mating types, called

Answer 1

a and α

Question 2

Each type secretes a specific factor that binds only to

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receptors on the other type of cell.

Question 3

When exposed to each other’s mating factors, a pair of cells of opposite type change

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shape, grow toward each other, and fuse (mate).

Question 4

The new a/α cell contains all the genes of both original cells, a combination of

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genetic resources that provides advantages to the cell’s descendants, which arise by subsequent cell divisions.

Question 5

The unique match between mating factor and receptor is key to ensuring mating only among cells of the same species of

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yeast.

Question 6

How does the binding of a mating factor by the yeast cell surface receptor initiate a signal that brings about the cellular response of mating? This occurs in a series of steps called a

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signal transduction pathway.

Question 7

Scientists think that signaling mechanisms first evolved in ancient

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prokaryotes and single-celled eukaryotes like yeasts and then were adopted for new uses by their multicellular descendants.

Question 8

Sensing the concentration of such signaling molecules allows bacteria to monitor their own local cell density, a phenomenon called

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quorum sensing.

Question 9

Quorum sensing allows bacterial populations to coordinate their behaviors in activities that require a given number of

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cells acting synchronously

Question 10

One example is formation of a __________, an aggregation of bacterial cells adhered to a surface.

Answer 10

biofilm

Question 11

is a common bacterial species found on the surface of healthy skin that can turn into a serious pathogen if introduced into tissue through a cut or abrasion.

Answer 11

Staphylococcus aureus (S. aureus)

Question 12

Once inside the body, a population of _______________ that reaches a certain density will start to secrete a toxin, killing body cells and contributing significantly to inflammation and damage

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S. aureus

Question 13

Because about 1 in 100 people carry a strain of S. aureus that is resistant to common antibiotics, a minor infection can turn permanently

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harmful or even deadly.

Question 14

Like bacteria or yeast cells, cells in a multicellular organism usually communicate via signaling

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molecules targeted for cells that may or may not be immediately adjacent.

Question 15

eukaryotic cells may communicate by direct contact, which is one type of

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local signaling

Question 16

Both animals and plants have cell junctions that, where present, directly connect the

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cytoplasms of adjacent cells

Question 17

In these cases, signaling substances dissolved in the cytosol can pass freely between

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neighboring cells.

Question 18

Moreover, animal cells may communicate via direct contact between membrane-bound cell-surface molecules, in a process called

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cell-cell recognition

Question 19

In many other cases of local signaling, signaling molecules are secreted by the

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signaling cell.

Question 20

Some molecules travel only short distances; such local regulators influence cells in the vicinity. This type of local signaling in animals is called

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paracrine signaling

Question 21

One class of local regulators in animals, _______________, are compounds that stimulate nearby target cells to grow and divide

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growth factors

Question 22

Numerous cells can simultaneously receive and respond to the growth factors produced by a single cell in their

Answer 22

vicinity.

Question 23

A more specialized type of local signaling called __________________occurs in the animal nervous system

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synaptic signaling

Question 24

An electrical signal along a nerve cell triggers the secretion of

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neurotransmitter molecules.

Question 25

These molecules act as chemical signals, diffusing across the synapse—the narrow space between the nerve cell and its target cell—triggering a response in the

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target cell.

Question 26

Both animals and plants use molecules called

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hormones for long-distance signaling.

Question 27

In hormonal signaling in animals, also known as _________________________, specialized cells release hormones, which travel via the circulatory system to other parts of the body, where they reach target cells that can recognize and respond to them

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endocrine signaling

Question 28

Plant hormones (often called __________________________) sometimes travel in plant vessels (tubes) but more often reach their targets by moving through cells or by diffusing through the air as a gas

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plant growth regulators

Question 29

The ability of a cell to respond is determined by whether it has a specific receptor molecule that can bind to the

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signaling molecule.

Question 30

Our current understanding of how signaling molecules act via signal transduction pathways had its origins in the pioneering work of

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Earl W. Sutherland, whose research led to a Nobel Prize in 1971.

Question 31

Sutherland and his colleagues at Vanderbilt University were investigating how the animal hormone _____________________________ triggers the “fight-or-flight” response in animals by stimulating the breakdown of the storage polysaccharide glycogen within liver cells and skeletal muscle cells.

Answer 31

epinephrine (also called adrenaline)

Question 32

Glycogen breakdown releases the sugar glucose 1-phosphate, which the cell converts to

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glucose 6-phosphate.

Question 33

The liver or muscle cell can then use this compound, an early intermediate in glycolysis, for

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energy production

Question 34

Alternatively, the compound can be stripped of phosphate and released from the cell into the __________________ , which can fuel cells throughout the body.

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blood as glucose

Question 35

Thus, one effect of epinephrine is the mobilization of fuel reserves, which can be used by the animal to either ________________________________________________, as the impala in Figure 11.1 is clearly doing.

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defend itself (fight) or escape whatever elicited a scare (flight)

Question 36

Sutherland’s research team discovered that epinephrine stimulates glycogen breakdown by somehow activating a

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cytosolic enzyme, glycogen phosphorylase

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However, when epinephrine was added to a cell-free mixture containing the enzyme and its substrate, glycogen,

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no breakdown occurred

Question 38

Glycogen phosphorylase could be activated by epinephrine only when the hormone was added to

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intact cells.

Question 39

This result told Sutherland two things.

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First, epinephrine does not interact directly with the enzyme responsible for glycogen breakdown; an intermediate step or series of steps must be occurring in the cell. Second, an intact, membrane-bound cell must be present for transmission of the signal to take place.

Question 40

Sutherland’s work suggested that the process going on at the receiving end of a cellular communication can be dissected into three stages:

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reception, transduction, and response

Question 41

is the target cell’s detection of a signaling molecule coming from outside the cell

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Reception

Question 42

The binding of the signaling molecule changes the receptor protein in some way, initiating the process of

Answer 42

transduction.

Question 43

The transduction stage converts the signal to a form that can bring about a specific

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cellular response.

Question 44

Transduction sometimes occurs in a single step but more often requires a sequence of changes in a series of different molecules—a

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signal transduction pathway

Question 45

The molecules in the pathway are often called

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relay molecules.

Question 46

In the third stage of cell signaling, the transduced signal finally triggers a specific cellular

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response.

Question 47

The response may be almost any imaginable cellular activity—such as

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catalysis by an enzyme (for example, glycogen phosphorylase), rearrangement of the cytoskeleton, or activation of specific genes in the nucleus.