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Biology HL - IB > Chemical signalling > Flashcards

Chemical signalling Flashcards

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1
Q

What happens when a population rises?

A

As the population rises, all cells receive more of the signaling chemical from other cells.

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2
Q

What happens when a certain density is achieved?

A

Above a certain density, every cell in the population receives enough to cause the change in gene expression and the resulting switch in activity, because they have sensed there in a qurom.

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3
Q

What is quorum sensing an example of?

A

Interaction

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4
Q

Why is quorum sending an example of interaction?

A

Because signaling molecules pass from cell to cell.

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5
Q

What are activities promoted by quorum?

A

The activities promoted by quorum sending are examples of interdependence.

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6
Q

Why are the activities promoted by quorum an example of interdependence?

A

Because they’re only effective if more than one cell participates.

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7
Q

Two examples of interdependence is quorum activities

A

For example, high densities of bacteria on teeth secrete glue-like chemicals onto the tooth surface. Bacteria adhere (stick) to these chemicals in a layer called biofilm, In other bacteria, bioluminescence is only switched on when there is a high population density capable of producing bright light.

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8
Q

What are signaling chemicals in animals?

A

They are very varied chemically

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9
Q

How are signaling chemicals classified?

A

Signaling chemicals in animals are classified according to their function rather than their structure.

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10
Q

What are hormones?

A

Signaling chemicals are produced in small amounts by a group of specialized cells in the body and transported by the bloodstream.

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11
Q

What are the organs that are specialized for secretion called?

A

Glands

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12
Q

What are most hormones secreted in?

A

Into blood capillaries in the gland tissue.

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13
Q

Why are glands that secrete hormones called endocrine glands?

A

Because they internally secrete.

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14
Q

How do exocrine glands transport the secretion?

A

Exocrine glands have a duct leading out of the organs to transport the secretion.

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15
Q

What does the bloodstream do?

A

Transports hormones to all parts of the body.

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16
Q

What is one limit of hormones?

A

They only have effects on target cells which have receptors for the hormone.

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17
Q

What does a hormone do?

A

The hormone regulates the activities of the target cells by promoting or inhibiting specific processes.

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18
Q

What is one advantage of hormones?

A

They can persist in the body for hours after being secreted, so the activities of target cells can be affected for much longer than never impulses.

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19
Q

What is one advantage of hormones being transported in the bloodstream?

A

Transport in the bloodstream means the secreting and target cells can be far apart and one hormone can have very widespread effects.

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20
Q

Three examples of hormones

A

Insulin, thyroxin and testosterone

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21
Q

What are neurotransmitters?

A

Chemicals that transmit signals across synapses.

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22
Q

What is a synapse?

A

A junction between two neurons in the nervous system.

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23
Q

What is the presynaptic neuron?

A

It secretes the neurotransmitter.

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24
Q

What is the postsynaptic neuron?

A

It receives the neurotransmitter.

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25
Q

When is a neurotransmitter secreted?

A

When a nerve impulse reaches the end of the presynaptic neuron.

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26
Q

What does a neurotransmitter do after it has been secreted?

A

It diffuses across the gap between the two neurons and then binds to receptors in the plasma membrane of the postsynaptic neuron.

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27
Q

What does the binding between the neurotransmitter and receptor determine?

A

The binding influences whether a nerve impulse in initiated in the postsynaptic neuron.

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28
Q

What do excitatory neurotransmitters do?

A

They stimulate nerve impulses.

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29
Q

What do inhibitory neurotransmitters do?

A

They sedate nerve impulses.

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30
Q

What is the distance of the gap between two neurons at a synapse?

A

It’s between 20 and 40 nanometers.

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31
Q

What do neurotransmitters do in terms of the gap between the two neurons at a synapse?

A

Neurotransmitters only travel this very short distance.

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32
Q

What is the effect of the gap being so small between the two neurons at a synapse?

A

It allows neurotransmitters to convey their signal far more quickly, than hormones. Neurotransmitters can convey a message in a fraction of a second.

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33
Q

Why do neurotransmitters only persist for a fraction of a second?

A

Neurotransmitters are rapidly broken down in the synaptic gap or reabsorbed into the presynaptic neuron. So, neurotransmitters only persist for a fraction of a second.

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34
Q

What does rapid removal of neurotransmitters ensure for?

A

Rapid removal of neurotransmitters from the synaptic gap ensures it only affects one specific postsynaptic neuron. It does not usually diffuse out of the synapse to have more widespread effects.

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35
Q

Three examples of neurotransmitters

A

Acetylcholine, norepinephrine, and dopamine

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36
Q

What are cytokines secreted by?

A

A wide range of cells.

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37
Q

What are cytokines?

A

Cytokines are small proteins that act as signaling chemicals.

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38
Q

Where can cytokines come from?

A

Different cell types may secrete the same cytokine.

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39
Q

What can one cell type secrete?

A

One cell type may secrete several different cytokines.

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40
Q

What is an advantage of cytokines?

A

They can be secreted by almost all cells in the body.

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41
Q

Do cytokines travel far?

A

Cytokines are not usually transported as far as hormones.

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42
Q

Where do cytokines act?

A

Either on the cell that produced them or on a nearby cell.

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43
Q

What is one limit of cytokines?

A

It cannot enter cells.

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44
Q

How do cytokines adapt from not being able to enter cells?

A

They bind to receptors in the plasma membrane of a target cell.

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45
Q

What does the binding of cytokines and a receptor in the plasma membrane of a target cell cause?

A

It causes cascades of signaling inside the target cell. This leads to changes in gene expression and in cell activity.

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46
Q

What can a cytokine bind to?

A

It can bind to several types of receptors.

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47
Q

What is the effect of cytokine being able to bind to several receptors?

A

It can have multiple effects.

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48
Q

What do cytokineses have?

A

They have cell signaling roles in inflammation and in other responses of the immune system. They also have roles in the control of cell growth and proliferation and in the development of embryos.

49
Q

Three examples of cytokines

A

Erythopoiten (EPO), interon and interleukin.

50
Q

What are calcium ions used for?

A

For cell signaling in both muscle fibers and neurons.

51
Q

In muscle fibres where are calcium ions pumped into?

A

A specialized form of endoplasmic reticulum called the sarcoplasmic reticulum, generating a high concentration.

52
Q

What happens when muscle fibers receive a nerve impulse?

A

When muscle fibers receive a nervous impulse calcium channels open in the membrane of the sarcoplasmic reticulum and the ions can diffuse out. They bind to proteins that block muscle contraction, causing the proteins to change position. This allows muscle contraction to occur.

53
Q

What would happen is muscle fibers didn’t receive more nerve impulses?

A

The changes would be reversed, and the calcium would be pumped back into the sarcoplasmic reticulum.

54
Q

How do calcium channels open?

A

In neurons, when the nerve impulse arrives at a presynaptic membrane.

55
Q

What does the calcium channel opening allow for?

A

Inward diffusion.

56
Q

Inside the presynaptic neuron, what do calcium ions cause?

A

Inside the presynaptic neuron, calcium ions cause the secretion of neurotransmitters into the synaptic gap by exocytosis. The calcium ions are rapidly pumped back out into the synaptic cleft.

57
Q

What have signaling molecules using neurotransmitters and hormones undergone?

A

They have evolved repeatedly.

58
Q

What have chemical substances become?

A

They have become signaling chemicals.

59
Q

What are two requirements for a signaling chemical?

A
  • They must have a distinctive shape and chemical properties so the receptor can distinguish between it and other chemicals.
  • They must be small and soluble enough to be transported.
60
Q

What are the chemical categories of hormones?

A

Amines:
- melatonin
- thyroxine
- epinephrine

Peptides:
- insulin
- glucagon
- ADH

Steroids_
- progesterone
- testosterone

61
Q

What are the chemical categories of neurotransmitters?

A

Amines:
- dopamine
- norepinephrine

Gases:
- nitrous oxide

Amino acids:
- glutamate
- glycine

Esters:
- acetylcholine

62
Q

How far are some signaling molecules transported?

A

A very short distance.

63
Q

Because signaling molecules are only being transported a short distance what does this mean?

A

That they only have localized effects.

64
Q

Example of signaling molecules only being transported a short distance and its effect

A

For example, neurotransmitters are released by presynaptic neurons, and many only have to diffuse 20 nanometers to reach the one postsynaptic neuron that they affect.

65
Q

How far can other signalling molecules travel?

A

Other signaling molecules are transported long distances in the body, from the cells that secrete them to target cells.

66
Q

One example of signaling molecules that travel far

A

Hormones are transported in the blood from the gland that produces them to all parts of the body, and the target cell could be in any part of the body. For example, luteinizing hormone (LH) is secreted by the pituitary gland adjacent to the brain. In males, the target cells of LH are in the testes, and in females, they’re in the ovaries, so the effects of this hormone are very distant from its source.

67
Q

How can signaling molecules be divided into two groups?

A

According to whether they enter the target cell or not.

68
Q

What are receptors called if they do enter the plasma membrane, and where are they located?

A

Receptors for signaling chemicals that do pass through the plasma membrane are located in the cytoplasm or nuclear of the cell. These receptors are intracellular.

69
Q

What are receptors called if they do not enter the plasma membrane, and where are they located?

A

Receptors for chemicals that do not penetrate are located in the plasma membrane of the target cell, with the binding site exposed to the exterior. These receptors extend across the membrane with a region extending into the cytoplasm. These are called transmembrane receptors.

70
Q

What is the location of receptors determined by?

A

The location of receptors is determined by the distribution of hydrophilic and hydrophobic amino acids on the surface of the receptor protein.

71
Q

Why do intracellular receptors remain dissolved in the aqueous fluid of the cytoplasm or nucleus?

A

Intracellular receptors have hydrophilic amino acids so they remain dissolved in the aqueous fluids of the cytoplasm or nucleus.

72
Q

What do transmembrane receptors include in terms of hydrophilic and hydrophobic amino acids?

A

Transmembrane receptors have a band of hydrophobic amino acids on their surface that is attracted to the polar tails of phospholipids in the core of the membrane. On either side of the band, there are hydrophilic amino acids that are in contact with aqueous solutions inside and outside the cell.

73
Q

What is a transduction pathway?

A

The binding of a signaling chemical to a receptor causes a sequence of interactions in the cell, which is a transduction pathway.

74
Q

Why are transduction pathways varied?

A

Because they have evolved repeatedly, they don’t have a common origin.

75
Q

What do signaling chemicals do if they cannot pass through the plasma membrane?

A

Some signaling chemicals such as proteins cannot pass through the plasma membrane, so they bind to receptors in the plasma membrane.

76
Q

What do signaling chemicals do if they can pass through the plasma membrane?

A

Other signaling molecules, like steroids, pass through the membrane and bind to intracellular receptors.

77
Q

One difference between transmembrane and intracellular receptors

A

They use different transduction pathways.

78
Q

What happens when a signaling chemical binds to the outer side of a transmembrane receptor?

A

If it binds to the outer side of a transmembrane it will cause a change in the structure of the receptor. The inner side of the receptor becomes catalytically active and causes the production of a secondary messenger within the cell. This conveys the signal to effectors within the cell that carry out the responses.

79
Q

What happens when a signaling chemical binds to an intermembrane receptor?

A

Binding of signaling chemicals to intracellular receptors results in the formation of an active ligand-receptor complex. In most cases, the complex regulates gene expression by binding to DNA at specific sites, promoting or inhibiting the transcription of particular genes.

80
Q

What do neurotransmitters do?

A

They convey signals between neurons and between neurons and muscles.

81
Q

What are neurotransmitters released and diffused into?

A

Neurotransmitters are released into the synaptic gap and diffuse to the membrane of the postsynaptic neuron or muscle fiber.

82
Q

What happens after the neurotransmitters have been released and have diffused into the membrane of the postsynaptic neuron or muscle fiber

A

Once the neurotransmitters have been released and have diffused into the membrane of the postsynaptic neuron or muscle fiber, they bind to the receptors of these membranes.

83
Q

What does the binding of the neurotransmitter to the receptors in the postsynaptic neuron of muscle fiber cause?

A

The binding causes the membrane channels to open and ions move through these channels by facilitated diffusion, which changes the membrane potential.

84
Q

What is the effect of the change in membrane potential?

A

This change in potential is a signal that stimulates or inhibits either a nerve impulse in a postsynaptic neuron or a contraction in a muscle fiber.

85
Q

Explain the use of acetylcholine and what happens when it binds to its receptor

A

Acetylcholine is used as a neurotransmitter in many synapses, including those between neurons and muscle fiber. When acetylcholine binds to an acetylcholine receptor, the conformation (shape) of the receptor changes. A channel opens, allowing sodium ions to pass into the cell. This leads to a local depolarization that triggers an action potential.

86
Q

What is g-protein coupled receptors (GPCRs)?

A

They’re a large and diverse group of transmembrane receptors.

87
Q

How do GPCRs convey a signal?

A

GPCRs convey signals into cells using a second protein located in the plasma membrane, which is called
g-proteins.

88
Q

How does the g-protein remain in an inactive site?

A

A g-protein has 3 subunits (a, b and y) and these assemble on the receptor. A molecule of GDP (guanosine diphosphate) binds to the a subunit, which keeps the g-protein in an inactive site.

89
Q

What happens when the ligand binds to the receptor?

A

When a ligand binds to the binding site on the receptor, the receptor changes shape. This causes changes in the g-protein, and so the GDP detaches from the subunit.

90
Q

What does GDP detaching allow for?

A

It allows for the GTP (guanosine triphosphate) to bind in its place. The binding of GTP activates the g-protein, which separates the g-protein into its subunits, which causes further changes in the cell, triggering the cell’s response to the signal brought by the ligand.

91
Q

Overview of the 3 steps of how a signal is conveyed within a cell

A

Resting-state - the alpha subunit of the g-protein is inactive because GDP is bound to it.

Binding of ligand - a ligand binds to the receptor, causing conformational changes that cause GDP to detach from the alpha subunit. This allows GTP to find, activating the g-protein.

Active state - the activated g-protein splits into a, b, and y subunits which convey signals to effectors with the cell.

92
Q

What is a, b and y?

A

Alpha, beta, and gamma.

93
Q

Are g-proteins important?

A

A broad range of receptor functions are mediated by
g-protein coupled receptors and their associated g proteins.

94
Q

What are the ligand compounds sensitive to?

A

The ligands that bind to g-protein-coupled receptors are diverse and include light-sensitive compounds, odors, pheromones, hormones, and neurotransmitters.

95
Q

What does epinephrine bind to?

A

A transmembrane receptor in the plasma membrane of target cells.

96
Q

What does the binding of epinephrine to the transmembrane receptor do?

A

This binding changes the shape of the receptor activating g-protein within the membrane. This activates the g-protein, and the activated g-protein activates the enzyme adenylyl cyclase in the membrane and this converts ATP in the cytoplasm into cyclic AMP (cAMP).

97
Q

What is cAMP?

A

cAMP is the secondary messenger.

98
Q

What do secondary messengers do?

A

They start a sequence of responses within the cell, amplifying the signal until a large scale process is triggered. This happens very rapidly.

99
Q

An example of speed that a large-scale process is triggered by secondary messengers

A

liver cells break down glucose and release it into the blood within seconds of receiving an epinephrine signal.

100
Q

What is a kinsase?

A

An enzyme that adds a phosphate group to a specific molecule. This process is phosphorylation.

101
Q

One example of an enzyme that does phosphorylation

A

Tyrosine kinase transfers phosphate from ATP to the amino acid tyrosine in a protein.

102
Q

Explain transmembrane insulin receptors

A

The insulin receptor is a transmembrane protein that is activated by the binding of insulin.

There are two tails of these receptors that extend into the cytoplasm, and these are tyrosine kinase enzymes.

The binding of insulin to these receptors causes structural changes in the receptor, so the two tails connect to form a dimer.

Then each tail phosphorylates the other tail. These changes trigger a biochemical chain of events inside the cell.

Vesicles containing glucose transporters move to the plasma membrane and fuse with it, inserting transporters into the membrane.

These transporters are channel proteins that allow glucose to enter the cell by facilitated diffusion. The glucose can then be used as a substrate in cell respiration.

103
Q

Are steroid hormones hydrophobic or hydrophillic?

A

Hydrophobic, meaning they’re soluble in lipids and able to pass through the cell membrane.

104
Q

What are the next stages after steroids pass through the membrane?

A

Once the steroids are inside the cell, they bond to receptors on the cytoplasm. The hormone-receptor complex enters the nucleus and attaches to the DNA. This activates the production of a particular polypeptide.

105
Q

Example of an intracellular receptor that affects gene expression

A

The androgen receptor binds to testosterone and the resulting complex increases the production of FASD1 gene. This in turn increases the production of important fats in prostate cells.

106
Q

Two hormones involved in reproduction

A

oestradiol and progesterone.

107
Q

Where does oestradiol have effects?

A

It has a broad range of effects in the ovary and uterus.

108
Q

What does oestradiol also do?

A

It also acts on the brain, helping regulate the release of reproductive hormones.

109
Q

What does oestrdiol do within the brain?

A

Within the hypothalamus of the brain, the hormone gonadotopin-releasing hormone (GnRH) is produced and release.

110
Q

Explain how oestradiol works and its effects

A

GnRH triggers the release of the sex hormones LH (luteinizing hormone) and FSH (follicle-stimulating hormone) from the anterior pituitary. Just before or during ovulation, oestradiol has a stimulating effect by binding to a receptor within the cytoplasm of the hypothalamus cell. Once bound, the hormone receptor complex moves to the nucleus where it acts as a transcription factor, enhancing the transcription of GnRH and mRNA.

111
Q

Where is progesterone produced?

A

The ovary.

112
Q

What does progesterone do?

A

Maintains the uterine lining so that it can support a developing foestus.

113
Q

What is progesterone?

A

A steroid that is capable of passing through the plasma membrane of uterine cells and bind to a receptor in the cytoplasm.

114
Q

What does progesterone do after its bind to its receptor in the cytoplasm?

A

A hormone-receptor complex then enters the nucleus where it interacts with DNA as a transcription factor. This affects gene expression.

115
Q

An example of a progesterone

A

One of the genes activated is insulin-like growth factor which contributes to the cellular proliferation necessary for maintaining the lining of the endometrium.

116
Q

What is the result of a posistive feedback process?

A

In a positive feedback process, the end product of a pathway amplifies the starting point so that more product is created.

117
Q

Example of a positive feedback

A

The binding of an inositol triphosphate molecule to another inositol triphosphate receptor causes the partial release of calcium from the ER. This increase in calcium activates the inositol triphosphate receptor on a neighboring calcium channel, causing a further increase in calcium. This process is known as calcium-induced calcium release.

118
Q

What is the result of a negative feedback process?

A

An increase in the end product of a pathway shuts off the start of the pathway. In other words, the end product inhibits its own production.

119
Q

Example of a negative feedback

A

Testerone production if regulated by negative feedback. GnRH released by the hypothalamus acts on the hypothalamus stimulating the release of LH. LH stimulates the release of testosterone from Leydig cells in the testes. Increasing testosterone has two effects:
- signals to the anterior pituitary decrease the release of LH
- signals to the hypothalamus stop the release of GnRH

Biology HL - IB (5 decks)

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