Chapter 11 (Notes) Flashcards Preview

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Flashcards in Chapter 11 (Notes) Deck (97):
1

Cell-to-cell communication is essential for both

multicellular and unicellular organisms

2

Biologists have discovered some universal mechanisms of

cellular regulation

3

Cells most often communicate with each other via

chemical signals.

For example, the fight-or-flight response is triggered by a signaling molecule called epinephrine

4

External signals are converted to

responses within the cell

5

Microbes provide a glimpse of the role of

cell signaling in the evolution of life

6

A signal transduction pathway is a

series of steps by which a signal on a cell's surface is converted into a specific cellular response

7

Signal transduction pathways convert signals on a cell's surface into

cellular responses

8

Pathway similarities suggest that

ancestral signaling molecules evolved in prokaryotes and were modified later in eukaryotes

9

Cells in a multicellular organisms communicate by

chemical messengers

10

Animal and plant cells have cell junctions that

directly connect the cytoplasm of adjacent cells

11

In local signaling, animal cells may communicate by

direct contact, or cell-cell recognition

12

In many other cases, animal cells communicate using

local regulators, messenger molecules that travel only short distances

13

paracrine signaling-

(local regulator)

grown factors from one cell stimulate numerous neighboring cells

14

synaptic signaling-

(local regulator)

neurotransmitters

15

In long-distance signaling, plants and animals use

chemicals called hormones

16

Endocrine signaling-

(long-distance signaling. hormones)

hormones are released into the circulatory system to reach distance regions of the body

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The ability of a cell to respond to a signal depends on whether or not it has a

receptor specific to that signal

18

Earl W. Sutherland discovered how the hormone

epinephrine acts on cells

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Sutherland suggested that cells receiving signals went through three processess:

Reception
Transduction
Response

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Reception: a signaling molecules binds to a

receptor protein, causing it to change shape

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The binding between a signal molecule (ligand) and receptor is

highly specific

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Ligand-

a molecule that specifically binds to a larger molecule

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A shape change in a receptor is often the

initial transduction of the signal

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Most signal receptors are

plasma membrane proteins

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Most water-soluble signal molecules bind to

specific sites on receptor proteins that span the plasma membrane

26

There are three main types of membrane receptors

1. G protein-coupled receptors
2. Receptor tyrosine kinases
3. Ion channel receptors

Also have intracellular receptors

27

G protein-coupled receptors (GPCRs) are

the largest family of cell-surface receptors

28

A G protein-coupled receptor (GPCR) is a

plasma membrane receptor that works with the help of a G protein

29

The G protein acts as an

on/off switch: If GDP is bound to the G protein, the G protein is inactive

30

Receptor tyrosine kinases (RTKs) are

membrane receptors that attach phosphates to tyrosines

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A kinase is an

enzyme that catalyzes the transfer of phosphate groups

32

A receptor tyrosine kinase can trigger

multiple signal transduction pathways at once

33

Abnormal functioning of receptor tyrosine kinases (RTKs) is associated with

many types of cancers

34

A ligand-gated ion channel receptor acts as a

gate when the receptor changes shape

35

When a signal molecule binds as a ligand to the receptor, the

gate allows specific ions, such as NA+ or CA^2+, through a channel in the receptor

36

Important in the nervous system

-neurotransmitter release

37

Intracellular receptor proteins are found in the

cytosol or nucleus of target cells

38

Small or hydrophobic chemical messengers can

readily cross the membrane and activate receptors

39

Examples of hydrophobic messengers are

the steroid and thyroid hormones of animals

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An activated hormone-receptor complex can act as a

transcription factor, turning on specific genes

41

Transduction:

cascades of molecular interactions relay signals from receptors to target molecules in the cell

42

Signal transduction usually involves

multiple steps

43

Multistep pathways can amplify

a signal: A few molecules can produce a large cellular response

44

Multistep pathways provide more opportunities for

coordination and regulation of cellular response

45

(Signal transduction pathways)

The molecules that relay a signal from receptor to

response are mostly proteins

46

(Signal transduction pathways)

Like falling dominoes, the receptor activates another protein, which

activates another, and so on, until the protein producing the response is activated

47

(Signal transduction pathways)

At each step, the signal is transduced into a different form, usually a

shape change in a protein
-usually phosphorylation

48

((Protein phosphorylation and dephosphorylation))

In many pathways, the signal is transmitted by

a cascade of protein phosphorylations

49

((Protein phosphorylation and dephosphorylation))

Protein kinases transfer phosphates from

ATP to protein, a process called phosphorylation

50

Protein phosphatases remove the phosphates from

proteins, a process called dephosphorylation

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((Protein phosphorylation and dephosphorylation))

This phosphorylation and dephosphorylation system acts as a

molecular switch, turning activities on and off or up or down, as required

52

Small molecules and ions as

second messengers

53

The extracellular signal molecule (ligand) that binds to the receptor is a

pathway's "first messenger"

54

Second messengers are

small, nonprotein, water-soluble molecules or ions that spread throughout a cell by diffusion

55

Second messengers participate in pathways initiated by

GPCRs and RTKs

56

Cyclic AMP and calcium ions are

common second messengers

57

Cyclic AMP (cAMP) is one of the

most widely used second messengers

58

Adenylyl cyclase, an enzyme in the plasma membrane, converts

ATP to cAMP in response to an extracellular signal

59

Many signal molecules trigger formation of

cAMP

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Other components of cAMP pathways are

G proteins, G protein-coupled receptors, and protein kinases

61

cAMP usually activates

protein kinase A, which phosphorylates various other proteins

62

Further regulation of cell metabolism is provided by G-protein systems that inhibit

adenylyl cyclase

63

Calcium ions (Ca^2+) act as a

second messenger in many pathways

64

Calcium is an important second messenger because

cells can regulate its concentration

65

A signal relayed by a signal transduction pathway may trigger an increase in

calcium in the cytosol

66

Pathways leading to the release of calcium involved

inositol triphosphate (IP3) and diaclyglycerol (DAG) as additional second messengers

67

Response:

Cell signaling leads to regulation of transcription or cytoplasmic activities

68

The cell's responses to an extracellular signal is sometimes called the

"output response"

69

Ultimately, a signal transduction pathway leads to a

regulation of one or more cellular activities

70

The response may occur in the

cytoplasm or in the nucleus

71

Many signaling pathways regulate the synthesis of

enzymes or other proteins, usually by turning genes on or off in the nucleus

72

The final activated molecule in the signaling pathway may function as

a transcription factor

73

Other pathways regulate the activity of

enzymes rather than their synthesis

74

There are four aspects of fine-tuning to consider

1. Amplification of the signal (and thus the response)
2. Specificity of the response
3. Overall efficiency of response, enhanced by scaffolding proteins
4. Termination of the signal

75

Enzyme cascades amplify the

cell's response

76

(((signal amplification)))

At each step, the number of activated products is much greater than in the

preceding step

77

Amplification stems from the fact that these proteins persist in the active form long enough to

process numerous molecules of substrate before they become inactive again

78

Few numbers of signal can affect

hundreds of millions of end molecules

79

Different kinds of cells have

different collections of proteins

80

These different proteins allow cells to

detect and respond to different signals.

-A liver cell in the presence of epinephrine breaks down glycogen
-A heart cell in the presence of epinephrine contracts

81

Even the same signal can have different effects in cells with

different proteins and pathways

82

Pathway branching and "cross-talk" further help

coordinate incoming signals

83

Scaffolding proteins are

large relay proteins to which other relay proteins are attached

84

Scaffolding proteins can

increase the signal transduction efficiency by grouping together different proteins involved in the same pathway

85

In some cases, scaffolding proteins may also help

activate some of the relay proteins

86

Inactivation mechanisms are an

essential aspect of cell signaling

87

If ligand concentration falls,

fewer receptors will be bound

88

Unbound receptors revert to an

inactive state
-signal molecules are reversible (on/off)
-allows the cell to be ready for any new signals

89

Apoptosis integrates

multiple cell-signaling pathways

90

Apoptosis is

programmed or controlled cell suicide

91

Components of the cell are

chopped up and packaged into vesicles that are digested by scavenger cells

92

The cell shrinks and becomes

lobed (blebbing)

93

Apoptosis prevents enzymes from

leaking out of a dying cell and damaging neighboring cells

94

Caspases are the main

proteases (enzymes that cut up proteins) that carry out apoptosis

95

Apoptosis can be triggered by

-an extracellular death-signaling ligand
-DNA damage in the nucleus
-protein misfolding in the endoplasmic reticulum

96

Apoptosis evolved early in animal evolution and is essential for

the development and maintenance of all animals

97

Apoptosis may be involved in some

diseases (for example, parkinson's and alzheimer's); interference with apoptosis may contribute to some cancers