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Biology 2311-- Fall 2022 > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

Why are receptors important in interacting with the environment?

A

Receptors are needed to sense environmental conditions and create a pathway for the appropriate cellialar response

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2
Q

What is quorum sensing?

A

Single-celled organisms communicate with eachother in response to changes in population density. Bacteria release signalling molecules that become more concentrated as the concentration of cells increase, and each cell responds to adapt to the changing environment.

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3
Q

How do yeast mate?

A

One cell secretes a hormone recognized by a cell of a different sex

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4
Q

Give examples of cellular signalling in bacteria

A

Cellular slime molds spend most of their time as single-celled amoeba, but become multicellular in order to reproduce. They sometimes gather together in response to chemical signals released by all cells in an area, forming a fruiting body

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5
Q

What is a fruiting body?

A

A multicellular organism formed by dictyostelium amoebas that produce spores that divide to form new populations of cells. They are formed by a form of quorum sensing.

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6
Q

True or false: most of the basic molecular mechanisms used in cell signalling in multicellular organisms evolved in single celled organisms millions of years ago

A

True

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7
Q

True or false: the signalling molecules and pathways are all extremely different across different organisms

A

False (cyclic AMP is produced both in animals and in the dictyostelium amoeba, for example)

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8
Q

What are the three steps of cellular signalling?

A

Reception, transduction, and response

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9
Q

Cellular reception

A

In reception, a signalling molecule binds to a receptor, and this changes its conformation. Cells have many receptors specific to a molecule or type of molecule, and different cell types express different receptors, which allows selectivity in signal response.

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10
Q

T or F: receptors are insoluble and are always in the membrane

A

False, receptors can be dissolved in the cytosol

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11
Q

What type of molecule most often binds to a receptor on a cell’s plasma membrane?

A

Polar, hydrophilic signalling molecules with binding sites facing the outside of the cell

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12
Q

What kind of molecules can bind to receptors inside the cell?

A

Nonpolar, hydrophobic ones since they can just diffuse through the membrane

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13
Q

What is transduction?

A

The process of converting a signal into the form necessary to cause a cellular response. This involves all of the interactions and modifications in a signalling pathway up until initiation of the cellular response. It is usually the most complex part.

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14
Q

How are signal transductions stopped?

A

These pathways contain off switches that inactivate the pathway once the signalling molecule is no longer present.

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15
Q

What is the cellular response?

A

Occurs after the transduction step. They are tailored to the specific needs of a cell and different cells can exhibit different responses, even in signalling pathways that employ the same receptors and pathways.

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16
Q

What does the specificity of a cellular response depend on?

A

The proteins and RNA molecules expressed in the cell, and the way those molecules are regulated by signal transduction mechanisms.

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17
Q

What is a protein that many transduction steps include, and why?

A

Protein kinases- they transfer a phosphate from an ATP onto an amino acid on a target protein, which changes the conformation of the protein and activates or inactivates them.

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18
Q

What are serine and threonine kinases?

A

Protein kinases that phosphorylate the amino acids serine and threonine

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19
Q

What are histidine, tyrosine, and aspartate kinases?

A

Protein kinases that phosphorylate histidine, tyrosine, and aspartate

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20
Q

How does a protein kinase know which amino acid to phosphorylate?

A

The active site recognizes a specific sequence of amino acids that includes the specific amino acid to be phosphorylated, and only proteins containing that sequence will be target proteins

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21
Q

Can protein kinases phosphorylate other protein kinases?

A

Yes, this is called a phosphorylation kinase, and the last kinase in the series phosphorylates other target proteins, producing the cellular response

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22
Q

Describe the role that epinephrine plays in breaking down polymers

A

Epinephrine binds to cell-surface receptor proteins, then allows a G protein to bind to the activated receptor and be activated. The activation of the G protein initiates a series of molecular interactions in the cell that eventually activate glycogen phosphorylase, which cleaves glucose monomers off of glycogen polymers.

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23
Q

Describe Sutherland’s experiment

A
  1. Homogenize liver tissue, which has supernatant containing inactive glycogen phosphorylace
  2. centrifuge, producing a supernatant containing cytoplasm
  3. centrifuge again, so supernatant contains glycogen phosphorylase
  4. resuspend the cell membranes and debrise, and add epinephrine, atp, and mg
  5. epinephrine binds and elicits a response and a second messenger
  6. combining the inactive glycogen phosphorylase and the active second messenger creates active glycogen phosphorylase
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24
Q

What was the conclusion of Sutherland’s experiment?

A

Response to the hormone epinephrine does not involve epinephrine directly; rather, it requires the first messenger, epinephrine, to activate a second messenger

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25
Q

What are some examples of cellular responses in single-celled organisms?

A

Changes in cellular metabolism in response to nutrient availability and changes in environmental variables such as temperature and pH

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26
Q

Examples of cellular responses in multicellular organisms

A

Cellular metabolism, transport mechanisms, electrical properties of neurons and muscles, changes in shape, migration

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27
Q

Communication by direct contact

A

Adjacent cells communicate with eachother when a membrane protein of one cell binds to a membrane protein in the other cell, which activates one or both proteins, which then activates a transduction pathway in one or both cells. Animals form tissues by binding to other cells of the same type- they recognize eachother using direct contact communication, and responses reinforce this communication (this is called cell-cell communication)

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28
Q

How do animal cells do direct contact?

A

Via gap junctions- electrical and metabolic activities between cells in a tissue, including electrical signals in cardiac and neuronal cells

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29
Q

How do plants do direct contact?

A

Through plasmodesmata- plant hormones regulating growth use this

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30
Q

Communication by local signalling

A

One cell releases a signalling molecule that diffuses through the extracellular fluid and causes a response in nearby target cells. Since the cell signalling is local, the molecule is a local regulator and the process is paracrine signalling

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31
Q

Where does paracrine signalling take place?

A

Chemical synapses (gaps separating plasma membrane of two cells, ensuring that only one adjacent cell is affected). Neurons use this. Muscle cells also use this.

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32
Q

Autocrine regulation

A

The local regulator acts on the same cell that produces it- a form of local signalling

33
Q

Long-distance signalling

A

Cells excrete a hormone which produces a response in target cells that may be far from the hormone-excreting cell- hormones are found in animals and plants.

34
Q

How does long distance signalling take place in animals and in plants?

A

Hormone enters circulatory system and travels elsewhere; in plants, they may move through cells, ECF, or through gaseous diffusion

35
Q

Examples of hydrophilic signalling molecules

A

Amino acids and molecules synthesized by modification of amino acids, peptides, and nucleotides

36
Q

The surface receptors that recognize and bind extracellular signalling molecules are all _______-

A

Transmembrane proteins

37
Q

How do membrane receptors work?

A

The signalling molecule changes the conformation of the cytoplasmic face of the receptor, which activates the receptor and allows molecules inside the cell to bind to the receptor. They thus communicate the cell through the cell membrane to the interior

38
Q

True or false: enzymes may be activated by surface receptors, acting as a proxy within the cell

A

True- the extracellular molecule is the first messenger, and the intracellular molecule is the second messenger

39
Q

What are the two components of a signalling pathway in bacteria?

A
  1. A surface receptor protein that functions as a kinase enzyme
  2. An intracellular response regulator that regulates the expression of certain genes
40
Q

What are transcription factors?

A

Proteins that bind to specific DNA sequences and help activate or inactivate them. Transcription factors themselves can be regulated and response regulators like the ones in bacterial 2 component systems are an example

41
Q

Describe the bacterial two-component system

A

A sensor kinase is activated, and a phosphate is transferred from ATP to this receptor kinase, and then again to the response regulator. The phosphorylated response regulator binds to control sequences of genes in the nucleus, leading to activation or inactivation. Environmental factors can contribute to this pathway since some sensor kinases bind nitrates,, O2, or phosphate ions, and the genes regulated formulate the response. This system is involved in quorum sensing

42
Q

What type of kinase is used in bacterial two-component systems?

A

The inner-facing part of a receptor molecule is a histidine/aspartate kinase

43
Q

What are GPCR’s?

A

They respond to a signal by activating an inner membrane protein called a G protein, which binds GDP and GTP

44
Q

Monomeric G proteins

A

consist of a single polypeptide chain

45
Q

trimeric g proteins

A

have 3 polypeptide chains- alpha, beta, gamma, and the alpha binds the gdp

46
Q

where are gpcr’s found?

A

Prokaryotes and eukaryotes including animals, plants, and fungi. researchers have identified thousands of different gpcrs in mammals

47
Q

structure of gpcrs

A

a single polypeptide chain by 7 alpha helical segments that zigzag back and forth 7 times

48
Q

T or F: gpccrs are the target for most drugs and mutations result in many diseases including hyperthyroidism, retinitis pigmentosa, fertility disorders, short statude, diabetes, and precocious puberty

A

T

49
Q

Describe the GPCR pathway

A

GPCR activated by a signal, allowing a g protein to bind and change conformation. change in conformation allows the g protein to bind a gtp to replace the gdp, which activates the g protein and allows it to bind to a plasma membrane associated effector protein. in trimeric g proteins, the alpha subunit breaks off

50
Q

summarize the g protein pathway

A

1st messenger, receptor, g protein, effector, second messenger, protein kinase, target protein

51
Q

describe the camp pathway

A

reception occurs, the activated g protein activates the effector, adenylyl cyclase, which converts atp into camp. camp is the second messenger. it then activates protein kinases

52
Q

where is the camp second messenger pathway found?

A

animals, fungi, plants, other eukaryotes

53
Q

does glucagon trigger a camp pathway?

A

yes, camp triggers protein kinase a, then initiates a phosphorylation cascade in which phosphorylase kinase activates glycogen phosphorylase, which then breaks monomers off of the ends of glycogen polymers

54
Q

Describe how RTKs work

A

they phosphorylate tyrosines. the activated kinase enzyme phosphorylates target proteins and other proteins are activated by binding to the autophosphorylated sites on the rtk

55
Q

action of an rtk

A
  1. signalling molecules bind and the monomers move together to form a dimer
  2. activation of protein kinases and autophosphorylation of the receptor allows the kinase monomers to phosphorylate eachother
  3. the signalling protein binds to an activates site and this triggers a transduction pathway leading to a cellular respons
56
Q

Are RTKs found in plants or fungi?

A

No, so thought to evolve before evolution of animals

57
Q

What is special about RTKs?

A

Each RTK mediates a unique signalling pathway.

58
Q

RTK pahway example

A

RTKs bind insulin, which triggers several cellular responses, including glucose uptake, the rates of metabolic reactions, and cell growth+division. defects lead to diabetes since receptors do not respond to the signal to add glucose receptorsRTKs also bind epidermal growth factor, platelet derived growth factor, and nerve growth factor

59
Q

Ligant-gated ion channels

A

receptor changes conformation by opening or closing an ion channel, changing flow of ions. involved in synaptic signalling, including the acetylcholine neurotransmitter, which diffuses to a receptor and causes the ion channel to open, allowing sodium to flow into the neuron, creating a new electrical signal

60
Q

nicotinic cholinergic receptor

A

activated by nicotine and is a receptor for acetylcholine, produces pleasurable sensations associated with nicotine

61
Q

What is special about hydrophobic signals?

A

they can enter anywhere in a cell so receptors can be close to their targeting area- for example, receptors can also act as a transcription factor

62
Q

does quorum sensing use hydrophobic molecules?

A

in some cases, yes

63
Q

steroid hormones

A

combine with hydrophilic carrier proteins, forming a complex that comes into contact with the cell then releases steroid directly into the cell, where it binds to its internal receptor. slightly different structure of steroids allows different receptors to recognize it.

64
Q

two major domains of steroid hormone receptors

A
  1. hormone binding domain- recognizes and binds a specific steroid hormone
  2. dna binding domain- binds specifically with dna sequences in targer genes - changes conformation when binding a steroid hormone, which activates it and allows it to bind to dna
65
Q

nitric oxide pathway

A

no diffuses across plasma membrane and is synthesized by arginine. it diffuses from site of synthesis into nearby cells (paracrine) and only acts locally. it is synthesized in neurons, liver cells, immune cells, and endothelial cells

66
Q

no in endothelial cells

A

released from endothelial cells in response to acetylcholine, causes underlying smooth muscle to dilate, so it has an important role in controlling blood flow through tissues and maintaining blood pressure in arteries. it also regulates muscle contractions in the intestinal tract

67
Q

no pathway

A

no binds to and activates guanylyl cyclase, which catalyzes cgmp synthesis, which then binds to and regulates specific proteins. cgmp can regulate protein kinase g, which phosphorylates serine and threonine.

68
Q

what is cgmp broken down by?

A

A phosphodiesterase- viagra inhibits this diesterase, rpolonging cgmp

69
Q

signal amplification

A

occurs when a protein performs its funcction repeatedly, producing many of the next step (enzymes catalyze over and over)- protein kinases can phosphorylate hundreds of target proteins

70
Q

what increases signal amplification?

A

longer and more complex pathway- gpcr can activate 50-100 g proteins, which activate one adenylyl cyclase, which activates 100+ camp, which produces one kinase A, which phosphorylates phosphorylase kinase, which targets glycogen phosphorylase, which releases glugose monomers, so millions of glucose molecules can be released from a single liver cell

71
Q

off switches

A

without off switches, pathway would continue forever

72
Q

first off switch in a pathway

A

elimination of signalling molecule- broekn down or excreted by kidneys or taken up by cells.

73
Q

other off switches

A

gtp to dgp conversion- gtps have gtpase activity so can inactivate themselves and proteins can speed up this conversion.

second messengers can be eliminated/converted by enzymes

protein phosphatase enzymes counter kinase enxyme activity. as long as kinase remains active, phosphatases are outweighted, but if kinase is inactive, phosphatases take over

74
Q

simpler signal transduction pathways produce faster/slower responses and longer/shorter lasting responses

A

faster, shorter

75
Q

divergence

A

one step triggers two different pathways- ip3 and dag or when a protein kinase phosphorylates 2+ target proteins- if they are kinases, they may each activate a different phosphorylation cascade

76
Q

convergence

A

two molecules produce same response- glugagon and epinephrine that both activate adenylyl cyclase. other mechanisms increase ca2+ in the cell and camp and ip3/dag both activate kinases that close k+ proteins in neurons to activate them

77
Q

crosstalk

A

pathways modulate eachother

78
Q

what influences crosstalk?

A

more comlex and longer pathways

Biology 2311-- Fall 2022 (12 decks)

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