Mod 5 Flashcards
(237 cards)
1
Q
What happens when a toxicant interacts with a specific target in the body?
A
It may result in a direct perturbation of cellular function, which may lead to reversible or irreversible cellular injury, manifesting as a toxic response
2
Q
What is the second step of a toxic response?
A
Cellular dysfunction, where the interaction between the toxicant and its target(s) triggers perturbations in cell function and/or structure, leading to cellular dysfunction and injury.
2
Q
What is the first step in a toxic response?
A
Interaction between the toxicant and its target(s), where the toxicant is delivered to and interacts with an endogenous target.
3
Q
What is the third step of a toxic response?
A
Inappropriate repair or adaptation, where repair mechanisms are initiated but may fail if the damage exceeds repair capacity, resulting in toxicity.
4
Q
What occurs during the “Inappropriate Repair/Adaptation” stage?
A
Repair mechanisms are activated at molecular, cellular, and tissue levels. If these mechanisms are overwhelmed, or repair is dysfunctional, toxicity occurs.
5
Q
What can contribute to or exacerbate a toxic response beyond cellular injury alone?
A
Inappropriate or dysfunctional repair or adaptation in response to the cellular injury can exacerbate the toxic response.
6
Q
What are the three steps of a toxic response?
A
1) Interaction between toxicant and target,
2) Cellular dysfunction,
3) Inappropriate repair/adaptation.
7
Q
What are the two possible types of interactions between a toxicant and its target?
A
1) Direct interaction with a target molecule
2) Alteration of the biological environment.
8
Q
What causes toxicity in most circumstances following exposure to a toxicant?
A
Direct interaction of the toxicant with an endogenous molecule that acts as a target.
9
Q
What factors influence the direct interaction between a toxicant and its target?
A
The chemistry of the toxicant and the characteristics of the biological target.
10
Q
How does the alteration of the biological environment contribute to toxicity?
A
It triggers perturbations in cell function or structure, directly or indirectly leading to cellular dysfunction and injury.
11
Q
What process typically increases the likelihood of a toxicant directly interacting with its target?
A
Bioactivation (“toxication”) increases the likelihood of direct interaction between a toxicant and its target.
12
Q
How does toxication contribute to increased reactivity of toxicants?
A
Toxication can result in increased reactivity of xenobiotics with endogenous molecules through chemical changes or the production of reactive molecules or fragments.
13
Q
What are two ways increased reactivity of a toxicant can result?
A
1) A chemical change in the toxicant itself
2) The production of reactive molecules or molecular fragments
14
Q
What happens to a xenobiotic during toxication in terms of its chemical properties?
A
Toxication can produce either an electrophile or a nucleophile, increasing the toxicant’s reactivity by affecting its ability to gain or lose an electron pair.
15
Q
What are electrophiles, and how are they formed?
A
Electrophiles are “electron-loving” compounds with an electron-deficient atom. They are often formed by an oxidation reaction, such as the insertion of an oxygen atom, which increases their reactivity with negatively charged nucleophiles.
16
Q
What is the significance of many ultimate carcinogens being electrophiles?
A
Many ultimate carcinogens are electrophiles and react with nucleophilic DNA, leading to the formation of bulky DNA adducts that can cause DNA mutations.
17
Q
What are nucleophiles, and how do they function in chemical reactions?
A
Nucleophiles are “nucleus-loving” compounds that are electron-rich, possessing an electron pair that they can donate to an electrophile in a chemical reaction.
18
Q
How does the nucleophile glutathione protect cells?
A
Glutathione, a cytoprotective endogenous nucleophile, binds to electrophilic toxicants, reducing their toxicity by neutralizing their reactivity.
19
Q
Are nucleophiles commonly formed through toxication?
A
No, while many toxicants are nucleophiles initially, toxication rarely results in the formation of nucleophiles endogenously.
20
Q
What are free radicals, and why are they reactive?
A
Free radicals are molecules or molecular fragments that contain one or more unpaired electrons, making them highly reactive.
21
Q
How are free radicals typically produced during toxication reactions?
A
Free radicals are often produced through enzymatic reactions that result in an unpaired electron on a xenobiotic, which is transferred to smaller molecules like oxygen or nitrogen, forming reactive oxygen species (ROS) or reactive nitrogen species (RNS).
22
Q
What are some examples of reactive oxygen species (ROS)?
A
Examples of ROS include:
- Superoxide anion radical (O₂⁻)
- Hydroxyl radical (HO⁻)
- Hydrogen peroxide (H₂O₂)
- Carbonate anion radical (CO₃⁻)
23
Q
What are some examples of reactive nitrogen species (RNS)?
A
Examples of RNS include:
- Peroxynitrite (ONOO⁻)
- Nitrogen dioxide (NO₂)
24
What is a superoxide, and why is it important?
A superoxide is the anionic form of O₂, produced from the one-electron reduction of dioxygen (oxygen gas). It is a free radical due to its unpaired electron and plays a significant role in biological systems.
25
What are three ways free radicals can be formed in the presence of a toxicant?
1) Accepting an electron, 2) Gaining an electron, and 3) Redox cycling.
26
How are free radicals formed by accepting an electron?
Free radicals can be formed when a toxicant accepts an electron from cofactors like NADPH through a reaction catalyzed by enzymes such as reductases.
27
How are free radicals formed by gaining an electron?
Electrons can be lost from certain xenobiotics and transferred to another endogenous molecule in a reaction catalyzed by enzymes like peroxidases, leading to the formation of free radicals.
28
What is redox cycling, and how does it contribute to the formation of free radicals?
Redox cycling occurs when unpaired electrons from a xenobiotic are transferred to oxygen, returning the xenobiotic to its original state. This process can repeat, producing more free radicals.
29
In which types of toxicities are ROS and RNS implicated?
ROS and RNS are implicated in the toxicity of carcinogens, teratogens, and neurotoxicants.
30
How can reactive species like ROS and RNS be measured directly?
They can be measured directly using substrates that react with ROS or RNS to produce a fluorescent or colored product.
31
How can reactive species be measured indirectly through reaction products?
By measuring the products formed from their reaction with macromolecules, such as lipid peroxidation, oxidative DNA damage, or reduced glutathione depletion.
32
How can enzyme activity be used to measure reactive species indirectly?
The activity of endogenous detoxifying enzymes like catalase or superoxide dismutase can be measured to indicate cellular stress caused by free radicals.
33
How can you determine if ROS levels are increased following exposure to a toxicant, other than measuring ROS directly or indirectly?
You could pre-expose cells to an antioxidant or transfect them with a plasmid that over-expresses a ROS detoxifying enzyme.
Then, compare cell death between pretreated/transfected cells and normal cells.
If the pretreated/transfected cells show reduced cell death, it suggests that increased ROS production is contributing to toxicity.
34
Why are electrophiles and free radicals considered the most damaging metabolites of xenobiotics?
They are highly reactive and tend to interact with critical cellular biomolecules due to their chemical properties.
For example, toxic reactions with DNA often involve:
- Alkylation of DNA (a nucleophile) by an electrophile.
- Reaction of a C-H bond in DNA with a free radical.
35
Is toxication necessary for a toxicant to be an electrophile or to produce free radicals?
No, toxication is not necessary. Some toxicants can be electrophiles or produce free radicals in their parent form. However, the reactivity associated with these traits increases the likelihood of the toxicant interacting with a target, leading to toxic effects.
36
Which of the following can interact with the target molecule or alter the biological environment:
a) Reactive molecule (e.g. ROS/RNS)
b) Toxicant
c) Toxicant metabolite (e.g. electrophile)
ALL OF THE ABOVE
37
What is a target molecule in the context of toxicology, and which types are more likely to be targeted by toxicants?
A target molecule is any endogenous molecule that can be affected by a toxicant. However, certain endogenous molecules, such as DNA and proteins, are more likely to be targets compared to others like cofactors.
38
Why is proximity an important factor in determining the target of a xenobiotic?
Proximity is crucial because a molecule is often a target simply due to its exposure to the toxicant and its biochemical compatibility. Targets are typically located at the site of absorption or metabolism. If a reactive metabolite is produced in a specific location, nearby cells or tissues are more likely to be affected.
If the target is not in close proximity, the toxicant may travel through the body until it finds a suitable target, with its reactivity influencing how far or long it circulates before interacting.
39
Define Ultimate Toxicant:
The chemical that reacts with an endogenous molecule or alters the biological environment resulting in toxicity.
40
Why is it important to consider that a toxicant may have multiple target molecules?
Many xenobiotics, especially those that produce free radicals, can interact with multiple targets within the body.
For ex, While a carcinogen may react with DNA, it can also interact with other cellular structures or proteins that may not contribute to its toxic effects.
Some interactions may have little physiological consequence, meaning they do not affect the overall toxicity of the chemical.
41
What types of interactions can occur between a toxicant and its target molecule?
There are five different types of direct interactions that can occur between a toxicant and its target molecule(s):
1. Non-covalent binding
2. Covalent binding
3. Hydrogen Abstraction
4. Electron transfer
5. Enzymatic reactions
The specific reactions depend on the chemistry of both the toxicant and the biological target, influencing how they interact and the resulting effects.
42
What is the difference between a non-covalent and covalent bond?
Covalent bonds involve the sharing of electrons between two molecules, while non-covalent bonds do not share electrons. Instead, non-covalent bonds are based on electrostatic interactions between molecules.
Examples of covalent bonds include sigma and pi bonds, whereas examples of non-covalent bonds include hydrogen bonds and Van der Waals forces.
43
What are non-covalent bonds, and why are they significant in biological interactions?
Non-covalent bonds include apolar interactions, hydrogen bonds, and ionic bonds. These interactions are generally reversible due to their comparatively low bonding energy.
They play a crucial role in cellular structures, interacting with components such as membrane receptors, intracellular receptors, ion channels, and certain enzymes.
44
What is covalent binding, and how does it differ from non-covalent binding in biological contexts?
Covalent binding is typically classified as irreversible, leading to permanent changes in cellular structures.
This type of binding often occurs when electrophilic compounds interact with nucleophilic macromolecules, such as proteins and nucleic acids (e.g., DNA), resulting in lasting modifications.
45
What is hydrogen abstraction, and how does it affect cellular structures in the context of toxicants?
Hydrogen abstraction is the process by which a toxicant removes a hydrogen atom from an endogenous molecule. This reaction can produce free radicals, which are highly reactive and can further interact with other cellular structures, potentially leading to covalent binding and additional cellular damage.
46
What is electron transfer in the context of xenobiotics, and what are the processes of oxidation and reduction?
Electron transfer refers to the exchange of electrons between xenobiotics and endogenous molecules, which can result in harmful by-products.
In oxidation, a reductant loses electrons (oxidation number increases), while in reduction, an oxidant gains electrons (oxidation number decreases).
47
What is an enzymatic reaction in the context of toxins, and how does it affect endogenous biomolecules?
An enzymatic reaction involves a toxicant, which acts as an enzyme, altering endogenous biomolecules and resulting in negative effects.
Toxins are toxicants produced by living organisms; while all toxins are toxicants, not all toxicants are toxins.
48
Which of these interactions would be considered the most harmful type of interaction?
1. Non-Covalent Binding
2. Covalent Binding
3. Electron Transfer
4. Hydrogen Abstraction
2. covalent binding because it is irreversible
49
What are the potential outcomes of interactions between toxicants and target molecules?
Interactions can result in:
1. Target Molecule Dysfunction: Impaired function of the target molecule.
2. Target Molecule Destruction: Structural damage leading to loss of function.
3. Neoantigen Formation: Creation of new antigens that may trigger immune responses.
50
What are the two common ways through which a toxicant can cause dysfunction of target molecules?
Activation: Toxicants can activate target molecules, mimicking endogenous ligands, leading to structural changes and potentially activating signal transduction pathways.
Inhibition: Toxicants commonly inhibit target molecule function, blocking signal transduction pathways and impairing cellular maintenance by disrupting energy and metabolic homeostasis.
51
How do some toxicants activate target molecules?
They mimic the role of an endogenous ligand, leading to structural or conformational changes in the target molecule.
52
What can result from the activation of a target molecule by a toxicant?
The activation can potentially lead to the activation of a signal transduction pathway.
It can lead to unintended cellular responses, altering normal biological processes and potentially causing toxicity.
53
What is a more common effect of toxicants on target molecules?
Inhibition of the target molecule's function.
This results in blocked signal transduction pathways and impaired cellular maintenance through altered energy and metabolic homeostasis.
It can disrupt normal signaling pathways and lead to problems with energy production and metabolism in the cell.
54
What are the two key ways in which a toxicant may cause destruction to a target molecule?
Cross-linking/fragmentation and degradation.
55
How does cross-linking affect target molecules when they interact with a toxicant?
Cross-linking can result in the formation of bonds between different molecules, leading to the destruction of the target.
56
What is fragmentation in the context of toxicant interactions with target molecules?
Fragmentation refers to the breaking apart of a target molecule, resulting in its destruction following interaction with a toxicant.
57
What happens to target molecules that are susceptible to spontaneous degradation after exposure to a toxicant?
They may undergo breakdown processes that lead to their destruction.
58
Can both cross-linking and degradation lead to the same outcome regarding target molecules?
Yes, both can result in the destruction of the target molecule, impacting cellular integrity and function.
59
What is neoantigen formation in the context of toxicants?
It refers to the process where a toxicant binds to an endogenous protein, potentially eliciting an allergic immune response.
60
What type of bond typically forms between a toxicant and a protein during neoantigen formation?
A covalent bond.
61
How can some toxicants become reactive with endogenous proteins?
Some toxicants may bind spontaneously to proteins, while others require biotransformation to become reactive.
62
What is a potential undesired effect of neoantigen formation?
The elicitation of an allergic reaction.
63
Can neoantigen formation occur without prior biotransformation of the toxicant?
Yes, some toxicants can bind spontaneously to proteins without needing biotransformation.
64
What are two ways a toxicant can alter a biological or cellular microenvironment?
1. pH alteration
2. Lipid alteration
65
What is one way a toxicant can alter the cellular microenvironment?
By altering the pH of intracellular or extracellular fluid through changing the concentration of hydrogen ions.
66
How does pH alteration by a toxicant affect cellular functions?
It impacts numerous cellular functions and activities because the structure and function of macromolecules are largely pH-dependent.
67
How do toxicants that alter lipid properties affect cells?
They can disrupt solute and ion gradients across membranes, impacting cellular function and homeostasis.
By altering the physicochemical properties of lipids, which disrupts membrane structure and integrity.
68
What two general roles can the function of a target molecule be divided into?
Regulatory role and maintenance role.
69
In a neuron, what is the regulatory role of macromolecules?
They contribute to neuron-specific signaling and carry out functions like conducting electrical impulses in a stimulus-dependent manner.
70
What is the maintenance role of macromolecules in cells?
They maintain an appropriate cellular and extracellular environment to ensure effective cellular function.
71
Why is the function of the target molecule critical in determining toxicity?
The specific roles and functions of macromolecules within the cell determine how a toxicant interacts and the resulting primary toxicity observed,
72
Give an example of a maintenance function in neurons.
Proteins involved in oxidative phosphorylation that help maintain cellular energy levels.
73
What types of macromolecules contribute to the regulatory role in neurons?
Molecules, proteins, and enzymes that carry out neuron-specific functions.
74
Why is the function of the target critical in determining the primary toxicity observed?
Because different macromolecules have varying functions that can be affected by toxicants, leading to dysregulation or dysfunction.
75
What is cellular dysregulation?
It refers to the disruption of a target that has a regulatory role due to the interaction with a toxicant.
76
What is disrupted cellular maintenance?
It results from a toxicant affecting a target that has a maintenance role, leading to an inability to maintain cellular and extracellular environments.
77
How can the interaction of a toxicant with target molecules lead to different types of toxicity?
Depending on whether the toxicant interacts with regulatory or maintenance targets, the resulting toxicity can manifest in various ways.
Understanding this distinction helps in predicting the type of toxicity that may arise from toxicant exposure based on the specific function of the affected target.
78
What are the three mechanisms of cellular dysregulation that a toxicant can interfere with?
Gene expression, protein expression, and specialized functions of cells.
79
What experimental approach can you use to determine if interaction with a toxicant results in altered gene expression?
Expose cells or an organism to a toxicant and a vehicle control, then extract RNA and measure transcript levels of mRNA using techniques such as qRT-PCR for specific genes, or microarray/next-generation sequencing for large-scale changes in gene expression.
80
What structural components of a gene can be targeted by toxicants to disrupt gene expression?
Toxicants can target exons, regulatory regions (such as promoter regions), and transcription factors, affecting transcription processes.
81
How can a toxicant interact with the exon of a gene?
A toxicant may directly bind to or interact with DNA in the exon, interfering with RNA polymerase's ability to transcribe the gene.
82
What effect does a toxicant have on the regulatory binding region of a gene?
A toxicant may bind to or interact with DNA in the regulatory region, hindering transcription factors' ability to initiate transcription.
83
How can toxicants interfere with transcription factors?
Toxicants may directly bind to or interact with transcription factors, impairing their ability to interact with the regulatory region of a gene.
84
What are exons and introns in the context of gene expression?
Exons are coding segments of DNA that produce gene products, while introns are non-coding segments that are spliced out after transcription.
85
What are promoter regions?
Regions of a gene that a transcription factor binds, initiating transcription
86
What is a transcription factor?
A transcription factor is a protein that binds to specific DNA sequences to regulate gene transcription. They can act as activators or repressors, influencing gene expression by forming a transcription complex with other proteins and are essential for processes like development and response to environmental signals.
87
What role do co-activators and co-repressors play in gene expression regulation?
Co-activators and co-repressors are proteins that interact with transcription factors to enhance or inhibit the transcription of specific genes, influencing gene expression.
88
What is ligand activation in the context of gene expression regulation?
Ligand activation refers to the process where a ligand binds to a transcription factor, leading to its activation and promoting the transcription of target genes.
89
How can toxicants affect gene expression regulation?
Toxicants can disrupt the interactions between transcription factors, co-activators, or co-repressors and DNA, as well as interfere with ligand activation and upstream signaling cascades, ultimately impacting gene expression.
90
What does it mean for a transcription factor to be ligand-activated?
A ligand-activated transcription factor requires a ligand to bind to it, which allows the transcription factor to bind to regulatory sequences and initiate transcription.
91
How can a toxicant act as a ligand in gene expression regulation?
A toxicant can act as a ligand by binding to a transcription factor, inappropriately activating it, and initiating DNA transcription.
92
In what way can a toxicant interfere with ligand-activated transcription factors?
A toxicant can interfere with the ligand itself, preventing it from binding to the transcription factor, which inhibits transcription.
93
What are two ways that toxicants can disrupt the ligand-dependent mechanism of the transcription factor?
It can either:
- act as a ligand by binding to a transcription factor, inappropriately activating it, and initiating DNA transcription.
- interfere with the ligand itself, preventing it from binding to the transcription factor, which inhibits transcription.
94
What are signaling cascades in the context of gene expression?
Signaling cascades are chains of protein-protein interactions that lead to the activation or inactivation of a transcription factor, often initiated by extracellular signaling molecules.
95
How can toxicants affect signaling cascades?
Toxicants can interrupt signaling cascades at any point, which can prevent the activation of transcription factors and lead to decreased gene expression.
96
What is the consequence of breaking a signaling cascade?
If a signaling cascade is broken, the end result, such as the activation of a transcription factor, is unlikely to occur as intended, leading to altered cellular activity.
97
Provide three specific ways exposure to a toxicant might alter signal transduction:
Affecting Protein Phosphorylation: Toxicants can interfere with the enzymes responsible for adding or removing phosphate groups (kinases and phosphatases) from proteins, disrupting the phosphorylation state of key signaling proteins. This can alter their activity and affect downstream signaling pathways.
Disrupting or Changing Protein-Protein Interactions: Toxicants can bind to proteins involved in signal transduction, preventing them from interacting properly with other proteins. This disruption can impede the formation of signaling complexes that are essential for the transmission of signals within the cell.
Altering Synthesis/Degradation of Signaling Proteins: Toxicants may influence the expression levels of signaling proteins by affecting their synthesis (transcription and translation) or degradation (proteolysis). This can lead to an imbalance in the concentrations of signaling molecules, altering the signaling pathways they are involved in.
98
What are the three main epigenetic processes that can be affected by toxicant exposure?
Histone modifications, DNA methylation, and microRNA regulation.
99
What are the two most well-characterized epigenetic modifications of histones?
Methylation and acetylation.
100
How do histone modifications affect gene expression?
Depending on the type of modification and the specific histone involved, these modifications can lead to either upregulation or downregulation of gene expression.
101
What is the general effect of histone acetylation on transcription?
Acetylation is generally associated with increased transcription.
102
How can methylation of histones influence gene expression?
Methylation can either upregulate or downregulate gene expression, depending on which residue of the histone is methylated.
103
What factors can toxicants affect regarding histone modifications?
Toxicants can affect the availability of acetyl or methyl donors,
or interfere with the activity of enzymes that catalyze these modifications.
104
What are histones?
Histones are a family of basic proteins that associate tightly with DNA in the chromosomes of eukaryotic cells and help condense DNA.
105
How can levels of acetylated or methylated histones be measured?
Levels can be measured using antibody-based assays such as western blots or ELISAs.
106
What enzymes are responsible for histone modifications?
Histone deacetyltransferases (HDACs) and histone acetyltransferases (HATs).
107
How can the activity of histone-modifying enzymes be assessed?
The activity can be measured using specified assays designed for those enzymes.
108
What is DNA methylation?
DNA methylation is the addition of methyl groups to DNA nucleotides, which is a type of epigenetic modification.
109
What are CpG islands?
CpG islands are clusters of nucleotides rich in cytosine and guanine that influence gene expression.
110
How does hypermethylation affect gene expression?
Hypermethylation of DNA is associated with a decrease in gene expression, as it can prevent transcription factors from binding to the promoter region.
111
What is the effect of hypomethylation on gene expression?
Hypomethylation is associated with an increase in gene expression.
112
How can toxicant exposure affect DNA methylation?
Toxicant exposure can decrease the availability of methyl donors or interfere with the enzymes responsible for methylating or demethylating DNA.
113
Are the effects of methylation at sites other than CpG islands well understood?
No, the role of methylation at sites other than CpG islands in regulating gene expression is less understood.
114
What type of assay is most straightforward for measuring global DNA methylation?
ELISA-based assays
115
What does an ELISA assay measure in the context of DNA methylation?
ELISA assays measure 5-methylcytosine (5-mC), which are methyl groups covalently bound to cytosines in DNA at the 5-carbon location.
116
How do ELISA assays work for measuring DNA methylation?
ELISA assays use an antibody that binds to methyl groups on DNA, allowing for the detection of methylated cytosines.
117
What is methylation-specific PCR?
Methylation-specific PCR is an assay designed to measure promoter methylation for specific genes by using primers for methylated and unmethylated DNA.
In methylation-specific PCR, primers designed for methylated and unmethylated DNA are run separately for each sample, and the relative levels are compared.
118
What is the primary function of microRNA (miRNA) in gene expression?
miRNA influences gene expression by targeting mRNA for degradation following transcription.
119
How are miRNA genes transcribed?
Similar to mRNA, miRNA are transcribed from genes.
120
How can toxicant exposure affect miRNA?
Toxicant exposure may affect the expression of genes that code for miRNA, potentially altering their levels.
121
What happens if a toxicant increases the transcription of a particular miRNA gene?
An increase in that miRNA will lead to a decrease in the gene expression of the target gene that the miRNA is targeting.
122
What is the relationship between miRNA and mRNA?
miRNA binds to mRNA to promote its degradation, thereby regulating gene expression.
123
How can miRNA levels be measured?
miRNA levels can be measured using qRT-PCR, next-generation sequencing, or other similar technologies.
124
What does qRT-PCR stand for?
Quantitative Reverse Transcription Polymerase Chain Reaction.
125
How does qRT-PCR indicate the quantity of miRNA?
The quantity of miRNA transcripts doubles with each cycle, and samples that reach the threshold earlier in the exponential phase correspond to a greater quantity of the miRNA.
126
In a qRT-PCR experiment, what does a stronger signal indicate?
A stronger signal indicates that the sample has a greater quantity of the miRNA being measured.
127
If Sample 1 in a qRT-PCR assay has more copies of the miRNA of interest than Samples 2 and 3, what can be inferred?
Sample 1 has a higher expression level of that specific miRNA compared to Samples 2 and 3.
128
Briefly describe qRTPCR and PCR.
in PCR and qRTPCR, the quantity of mRNA transcripts duplicate with each cycle.
Samples that show a stronger signal, reaching the threshold and the exponential phase in an earlier cycle, correspond to a sample that has a greater quantity of the mRNA that you are measuring.
129
What is the first step you should take to determine the cause of reduced insulin receptor (INSR) gene expression after exposing cells to a toxicant?
Investigate the effects of the toxicant on the expression and function of transcription factors that regulate insulin receptor expression.
130
Which assay can be used to measure the effects of a toxicant on transcription factor expression?
Western blotting can be used to measure the effects of the toxicant on transcription factor expression.
131
How can you investigate the effect of a toxicant on DNA binding of transcription factors?
A filter plate assay can be used to investigate the effects of the toxicant on DNA binding.
132
What method can be used to measure the activity of a transcription factor after transfecting cells with a reporter plasmid?
The activity of a transcription factor can be measured through reporter assays following transfection.
133
If there are no changes in transcription factor expression, DNA binding, or activity, what hypothesis could explain the decreased gene expression?
It could be hypothesized that the toxicant exposure has increased the expression of one or more miRNAs that regulate INSR transcripts, leading to increased degradation of INSR mRNA.
134
Why might a toxicant disrupt protein expression even if it does not affect gene expression?
A toxicant may affect the stability of a protein, alter its forward trafficking and maturation, or change its localization within the cell, affecting the amount of protein available at any given time.
135
What is the typical relationship between gene expression and protein expression?
In many cases, a disruption in gene expression results in a disruption in protein expression, as many genes code for proteins.
136
Can a toxicant exposure affect protein expression without altering gene expression?
Yes, a toxicant can affect protein expression without impacting gene expression.
137
How can a toxicant affect protein stability?
A toxicant may increase or decrease the degradation of a protein, impacting the amount of protein that is expressed at any given time.
138
What processes can toxicants alter that affect protein expression?
Toxicants can alter protein forward trafficking and maturation, as well as the expression of proteins at their functional locations within the cell.
139
What does "forward trafficking and maturation" refer to in protein expression?
It refers to the process of proteins being altered by post-translational modifications and moved within the cell until they are fully matured and ready to function properly.
140
Why might there not always be a correlation between gene and protein expression for the same gene?
Because disruptions in protein expression can occur independently of gene expression, such as through changes in protein stability or localization within the cell.
141
What are chaperone proteins?
Proteins that assist the covalent folding or unfolding and the assembly or disassembly of other macromolecular structures.
142
What does the term "ongoing cellular activity" refer to?
It refers to the specific cellular activities of various cell types and encompasses their normal functions.
143
How can toxicant exposure affect cellular activity?
Toxicant exposure may disrupt the normal activity of a cell, which can occur alongside or as a result of altered gene and/or protein expression.
144
What is a common mechanism by which toxicants interfere with cellular activity?
Many toxicants interfere with cellular activity by affecting signaling cascades that regulate specific functions or processes within the cell.
145
How do different cell types exhibit variations in their functions?
Different cell types have distinct cellular functions; for example, the normal activity of neurons differs significantly from that of white blood cells.
146
Why might a particular cell type be more susceptible to certain toxicants?
The unique cellular processes that ensure the intended functions of different cell types can make them particularly vulnerable to specific toxicants.
147
How can chemicals affect neurotransmitter concentration in neurons?
Chemicals can interfere with neurotransmitter synthesis, storage, release, or synaptic removal, impacting the concentration of neurotransmitters in the synaptic cleft.
148
What are the two ways toxicants can affect neurotransmitter receptors?
Toxicants can mimic neurotransmitters, acting as agonists or activators, or they can block the receptors, acting as inhibitors or antagonists.
149
What role do ion channels play in neuronal function?
Ion channels control the membrane potential along the axon by opening and closing in response to signals, allowing ions to move in and out of the neuron.
150
How can toxicants interfere with intracellular signal transduction in neurons?
Toxicants can directly activate or inactivate axonal ion channels, disrupting the propagation of the membrane potential.
151
What is the process of signal termination in neurons, and how can toxicants disrupt it?
Signal termination involves restoring the membrane potential through ion movement. Toxicants can inhibit transporters responsible for this movement, preventing signal termination.
152
How might a toxicant interfere with adrenergic receptors in smooth muscle?
A toxicant could block or inhibit adrenergic receptors, which are responsible for stimulating smooth muscle contraction, thus reducing the muscle's ability to contract.
153
What role does calcium play in smooth muscle contraction?
Calcium influx into smooth muscle cells is crucial for contraction, as it triggers the contraction process by interacting with contractile proteins.
154
How could a toxicant disrupt the signaling cascade that leads to calcium influx in smooth muscle?
A toxicant could interfere with the signaling pathways (such as G-protein coupled receptor pathways) that initiate calcium influx, thereby preventing muscle contraction.
155
What specific calcium channels could a toxicant target to affect smooth muscle contraction?
A toxicant could block or impair calcium channels (like L-type calcium channels) responsible for allowing calcium to enter smooth muscle cells, inhibiting contraction.
156
How could a hypothetical toxicant interfere with the ability of a smooth muscle to contract?
Varying mechanisms are involved in the control of smooth muscle contraction, and therefore toxicants could interfere with any number of steps in this process. Some possibilities are:
1. Interference with adrenergic receptors that stimulate smooth muscle contraction
2. Interference with the signalling cascade that is initiated that results in an influx of calcium into the smooth muscle cell
3. Interference with the calcium channels responsible for the influx of calcium into the cell
157
What is one of the key functions that cells must perform to maintain their intracellular environments?
Cells must synthesize various endogenous molecules to support their functions.
158
What are three important functions that cells must do to maintain their intracellular environments?
1. Synthesize endogenous molecules
2. Assemble macromolecular complexes and organelles
3. Produce energy.
159
Why is assembling macromolecular complexes, membranes, and organelles important for cells?
Assembling these components is essential for maintaining cellular structure and facilitating specialized cellular functions.
160
What role does energy production play in cellular maintenance?
Energy production is critical for ensuring that all cellular processes, including synthesis and assembly, can occur efficiently.
161
Name the three primary changes that toxicants can cause, contributing to cell death.
Depletion of ATP, rise in intracellular Ca²⁺ concentration, and excessive production of reactive species.
162
Which processes are driven by ATP? Select all that apply.
1. Muscle Contraction
2. Cytoskeleton Polymerization
3. Cellular Motility
4. Cell Division
5. Vesicle Transport
6. Ion Transport via Transporter proteins
7. Cellular morphology maintenance
ALL
163
What is the primary process through which ATP is synthesized in the cell?
ATP is primarily synthesized via oxidative phosphorylation in the mitochondria.
164
How can a toxicant inhibit hydrogen delivery to the electron transport chain (ETC)?
A toxicant can interfere with the delivery of hydrogen ions, preventing them from being pumped into the mitochondrial matrix via ATP synthase.
165
What effect does the inhibition of ETC complexes have on ATP production?
Inhibiting ETC complexes disrupts electron delivery and hydrogen ion transport, impairing the function of oxidative phosphorylation and ATP synthesis.
166
How can toxicants "steal" electrons from the electron transport chain?
Toxicants can take electrons from NADH, which donates electrons to the ETC, leading to a lack of electrons necessary for the chain's function.
167
Why is oxygen essential for the electron transport chain?
Oxygen acts as the final electron acceptor in the ETC; without it, the reaction to form water and continue ATP production cannot occur.
168
What is the consequence of inhibiting ADP phosphorylation by toxicants?
Inhibiting this reaction prevents the conversion of ADP into ATP, halting the production of the final product of the ETC.
169
What impact can toxicants have on mitochondrial integrity?
Toxicants can damage the structural integrity of mitochondria, impairing their ability to perform oxidative phosphorylation.
170
How do toxicants interfere with ATP production via oxidative phosphorylation in mitochondria?
Toxicants can deplete ATP by:
(1) inhibiting hydrogen delivery to the electron transport chain (ETC), preventing hydrogen ion pumping;
(2) inhibiting ETC complexes, disrupting electron and hydrogen transport;
(3) stealing electrons from NADH, halting ETC function;
(4) blocking oxygen delivery, preventing the formation of water;
(5) inhibiting ADP phosphorylation, stopping ATP formation;
(6) damaging mitochondrial structure, impairing overall oxidative phosphorylation.
171
What is the role of calcium in cellular processes, and how can toxicants affect it?
Calcium is crucial for various cellular processes, including:
- muscle contraction,
- vesicular release of neurotransmitters, - and acting as a cofactor for enzymes.
Intracellular calcium levels are tightly regulated, and toxicants that disrupt these levels can significantly impact cell function.
172
How does a sustained increase in intracellular calcium affect mitochondrial membrane potential?
A sustained increase in intracellular calcium can affect the membrane potential of the mitochondria, which is crucial for driving oxidative phosphorylation due to the positive charge of calcium ions.
This change in electric potential can disrupt oxidative phosphorylation, the process by which ATP is produced, compromising cellular energy production.
173
How does high intracellular calcium affect actin filaments?
High intracellular calcium levels can lead to the dissociation of actin filaments from their anchoring proteins.
This weakening of the cytoskeletal structure makes the cell membrane more vulnerable to rupture, potentially resulting in cell lysis and loss of function.
174
What is the impact of elevated intracellular calcium on hydrolytic enzymes?
Elevated intracellular calcium activates hydrolytic enzymes that break down key biomolecules, including proteins, lipids, and nucleic acids.
This activation can lead to widespread cellular degradation, damaging essential cellular structures and contributing to cell death.
175
How is intracellular calcium typically regulated within cells?
Cells maintain intracellular calcium levels by actively pumping calcium out of the cytoplasm and sequestering it within the endoplasmic reticulum and mitochondria.
This regulation is essential to prevent calcium overload, which can disrupt normal cellular functions.
176
How does excessive production of ROS and RNS affect cellular maintenance and function?
The overproduction of ROS and RNS can interfere with critical cellular processes, including oxidative phosphorylation, leading to decreased energy production and increased oxidative stress, which can further damage cellular structures.
177
In what way does oxidative stress influence the production of ROS within the cell?
Under normal conditions, oxidative phosphorylation generates ROS. However, when oxidative stress disrupts this process, it can cause a feedback loop that amplifies ROS production, worsening cellular damage and dysfunction.
178
How can increased intracellular calcium levels contribute to the production of reactive species?
Elevated intracellular calcium levels increase the energy demands on the cell. This heightened energy requirement can enhance the production of ROS and RNS, compounding the effects of oxidative stress and cellular damage.
179
What are the potential consequences of excessive ROS and RNS production on cellular components?
xcessive ROS and RNS can lead to oxidative damage to proteins, lipids, and nucleic acids, impairing cellular function, promoting inflammation, and potentially resulting in cell death.
180
How do alterations in ATP production influence intracellular calcium (Ca²⁺) levels?
Decreased ATP production can impair the mechanisms that actively pump calcium out of the cell, leading to increased intracellular calcium levels. This disruption can further exacerbate cellular dysfunction.
181
What role does calcium (Ca²⁺) play in the production of reactive oxygen species (ROS)?
Elevated intracellular calcium levels can increase the energy demands of the cell, leading to greater oxidative stress and enhancing ROS production, which can damage cellular components.
182
How do changes in ROS production impact ATP synthesis?
Increased ROS can impair mitochondrial function and oxidative phosphorylation, leading to decreased ATP synthesis. This creates a cycle where low ATP further affects calcium regulation, worsening oxidative stress.
183
What happens when compensatory mechanisms in a cell are overwhelmed by changes in ATP, Ca²⁺, and ROS?
When compensatory mechanisms can no longer control substantial changes in ATP, calcium, and ROS levels, it leads to a cascade of cellular dysfunction that can result in cell death.
184
What are some ways exposure to a toxicant can cause cell death by affecting ATP, intracellular calcium, and ROS/RNS levels?
Exposure to a toxicant can lead to cell death through various mechanisms, including:
1. Mitochondrial Damage: Impairs ATP production, leading to increased intracellular calcium and ROS levels.
2. Direct Damage to the Plasma Membrane: Causes uncontrolled calcium influx, activating hydrolytic enzymes and resulting in cellular degradation.
3. Direct Damage to the Lysosomal Membrane: Releases hydrolytic enzymes into the cytoplasm, degrading cellular components and increasing oxidative stress.
4. Toxicants Targeting the Cytoskeleton: Disrupt cellular structure and transport, impairing ATP production and calcium regulation, leading to stress and cell death.
5. Disruption of Protein Synthesis: Reduces essential proteins for ATP production and calcium handling, causing decreased ATP, altered calcium signaling, and increased oxidative stress.
185
What are the two most common types of cell death, and what are the primary differences between them?
The two most common types of cell death are:
Apoptosis:
- Description: A form of programmed cell death.
- Characteristics: Involves distinct morphological changes (such as cell shrinkage, chromatin condensation, and membrane blebbing) and specific biochemical pathways.
- Function: Typically a regulated process that removes unwanted or damaged cells without causing inflammation.
Necrosis:
- Description: Refers to the death of most or all cells in an organ or tissue.
- Causes: Often results from disease, injury, or lack of blood flow (ischemia).
- Characteristics: Generally leads to cell swelling, rupture, and an inflammatory response, affecting surrounding tissues.
186
What are the key characteristics and differences between apoptosis and necrosis?
Apoptosis:
Description: An energy-dependent process of programmed cell death.
Key Features:
- Involves activation of enzymes (e.g., caspases) for controlled cell death.
- Can be initiated through intrinsic or extrinsic pathways.
- Mitochondria may contribute to the process.
- Results in distinct morphological changes, such as cell shrinkage and membrane blebbing.
Necrosis:
Description: A form of catastrophic cellular injury.
Key Features:
- Characterized by injury to the plasma membrane.
- Cellular contents are released into the extracellular space, causing inflammation.
- Initially thought to be passive and uncontrolled, but now recognized as a regulated process with specific signaling pathways and biochemical processes.
187
Why is it important to know the type of cell death caused by a chemical or toxicant?
The consequence that the type of cell death has on the surrounding tissue is different between the two types of cell death, so the extent of tissue damage between the two can be vastly different. Additionally, knowing the mechanism of cell death can help us understand what protective measures can be taken to avoid toxic responses
188
How can cell death be measured when evaluating the effects of a toxicant?
Cell death can be measured using various assays, including cell viability assays. Key points include:
Purpose: These assays determine whether exposure to a toxicant causes cells to become non-viable or dead.
Metabolic Activity Measurement: Many viability assays measure the metabolic activity of the cell, in which a reagent that is a substrate for an enzyme involved in general cellular metabolism is converted by that enzyme to a colorimetric or fluorescent product that can be measured using a spectrophotometer.
Example - MTT Assay:
In the MTT assay, viable cells convert the reagent to a purple product.
The intensity of the purple color is proportional to the number of living cells; darker color indicates higher cell viability.
189
What assays are needed to distinguish between apoptosis and necrosis?
Assays that allow visualization of morphological characteristics of cell death under a microscope are needed to differentiate between apoptosis and necrosis.
190
What are some key morphological characteristics of apoptosis?
Cell Shrinkage: Apoptotic cells typically shrink in size.
Minimal Effect on Neighbouring Cells: Apoptosis has little impact on adjacent cells and usually does not trigger an inflammatory response.
191
What are some key morphological characteristics of necrosis?
Cellular Swelling: Necrotic cells tend to swell.
Loss of Membrane Integrity: The plasma membrane is compromised, leading to the release of cellular contents.
Presence of Necrotic Cells: There may be a string of necrotic cells visible within the tissue.
Inflammatory Response: Necrosis is likely to elicit an inflammatory response in the surrounding tissue.
192
Why can determining the type of cell death be challenging in practice?
Determining the type of cell death can be difficult because dead cells may be rapidly removed by immune cells, making it harder to observe the morphological characteristics directly.
193
How does DNA disintegration differ between apoptosis and necrosis?
In apoptosis, DNA fragmentation occurs, resulting in distinct bands when analyzed on an agarose gel. In contrast, necrosis leads to DNA degradation, which appears as a smear on the gel.
194
What assay can be used to visualize DNA fragmentation associated with apoptosis?
The TUNEL assay (TdT dUTP Nick-End Labelling) can be used to label fragmented DNA and detect levels of apoptotic cells colorimetrically or fluorometrically.
195
What is the visual result of running DNA from apoptotic cells on an agarose gel?
Distinct bands representing fragmented DNA can be visualized on the agarose gel.
196
What is the visual result of running DNA from necrotic cells on an agarose gel?
A smear is observed on the agarose gel, indicating DNA degradation.
197
What does the presence of distinct bands in DNA analysis indicate?
The presence of distinct bands typically indicates apoptosis, where DNA is fragmented into specific sizes.
198
What enzymes are activated during apoptosis that can be measured to determine cell death?
Caspases are the enzymes activated during apoptosis, playing a key role in the apoptotic process.
199
Which antibody-based assays can be used to measure levels of caspases associated with apoptosis?
Western blotting and ELISAs (Enzyme-Linked Immunosorbent Assays) can be used to measure caspase levels.
200
Why is it important to distinguish the type of cell death in research?
Distinguishing the type of cell death can provide insights into the underlying mechanisms and potential protective measures against toxic responses.
201
What is a recommended approach if distinguishing the type of cell death is necessary for a research project?
Conduct a literature search to identify the best assay for your specific research question regarding cell death.
202
What is one key characteristic of apoptosis that can be measured?
The activation of caspases, which can be detected using specific assays.
203
Why are apoptosis and necrosis considered overly simplistic descriptions of cell death?
They do not account for the variability and additional forms of cell death that can occur due to toxicant exposure.
204
What is an additional form of cell death that can be initiated by toxicant exposure?
Autophagy.
205
How is autophagy characterized in the context of cell death?
It involves the sequestration of large areas of cytoplasm and contents into vacuoles, which then fuse with lysosomes for degradation.
206
Does autophagy always lead to cell death?
No, autophagy is often associated with promoting cellular survival rather than death.
207
How can the morphology of autophagy differ from that of apoptosis and necrosis?
Autophagy involves distinct morphological changes related to the formation of vacuoles, whereas apoptosis and necrosis have their own specific cellular characteristics.
208
What are some additional types of cell death that may be encountered in research?
Necroptosis, entosis, and cell-type specific forms of cell death.
Necroptosis is a type of cell death that includes features of both apoptosis and necrosis.
Entosis is a form of cellular cannibalism where one cell engulfs its living neighboring cell, which is then degraded.
209
What are the key distinctions between cellular processes affected by toxicants?
Cellular Regulation: Processes that interfere with specific functions of different cell types.
Cellular Maintenance: Processes required by most cell types to maintain function.
210
What are potential outcomes of cellular damage due to toxicant exposure?
Repair: The cell may repair damage sufficiently to prevent death.
Adaptation: The cell may adapt to function in altered ways despite toxicant presence.
211
What are the risks associated with cellular repair and adaptation?
While repair and adaptation can be beneficial, they may also be erroneous or inappropriate, contributing to toxic responses.
212
What are the potential responses of cells or tissues to damage caused by toxicants?
Inappropriate Repair: Endogenous mechanisms may attempt to repair damage, but this process can be flawed or insufficient.
Adaptation: Cells or tissues may alter their functions to cope with the toxicant, potentially leading to changes that are not beneficial.
Combined Responses: Both repair mechanisms and adaptive changes can occur simultaneously in response to the same toxicant.
213
What happens if damage does not initiate repair or adaptation?
The damage itself can lead to toxicity without any compensatory mechanisms being activated.
214
What are the three levels of repair mechanisms discussed in the context of cellular health and survival?
The three levels of repair mechanisms are:
Molecular Repair
Cellular Repair
Tissue Repair
215
Why do repair mechanisms exist in cells?
Repair mechanisms exist to promote cell health and survival in response to damage caused by normal biochemical, cellular, and tissue processes, as well as toxicant insults.
216
What are the primary mechanisms of molecular repair in response to damage caused by toxicants?
Molecular repair mechanisms aim to fix DNA, lipids, and proteins, primarily through:
- Reversal of Damage: Enzymatic reactions that restore the damaged molecule to its original state.
- Degradation: Breaking down the damaged molecule when reversal is not possible.
Different types of DNA repair processes address specific types of mutations associated with DNA damage, which can be influenced by the developmental stage and cell cycle stage of the cell.
217
What are potential target molecules of toxicants that could affect the DNA repair process and initiate carcinogenesis?
Potential target molecules include the DNA repair machinery composed of numerous interacting proteins, which are upregulated in response to DNA damage. This upregulation can occur through:
- Increased transcription of DNA repair genes.
- Epigenetic regulation (e.g., DNA methylation, histone acetylation).
- Activation of transcription factors that encode DNA repair genes.
These mechanisms are critical in the response to DNA damage often resulting from toxicant exposure.
218
What are the primary mechanisms of cellular repair at the cellular level in response to toxicant exposure?
At the cellular level, repair mechanisms include:
- Autophagy: A process that removes damaged organelles from the cell.
- Specialized Structures Repair: Certain cell types, such as neurons, can regenerate larger structures like axons following damage. This regeneration is supported by macrophages and Schwann cells.
These processes help maintain cellular function and promote recovery from toxic insults.
219
How do tissues repair themselves after damage, and what are the differences in repair capability among various tissue types?
Tissues primarily repair themselves through a combined process of:
- Removal of Damaged Cells: Damaged cells undergo apoptosis.
- Regeneration of Healthy Cells: Proliferation of healthy cells occurs, leveraging the regenerative capacity of tissues.
Tissues such as bone marrow, respiratory and gastrointestinal epithelial layers, and the epidermis can effectively regenerate. However, tissues like female germ cells, card`iac muscle, and neural tissue are less capable of proliferation, leading to overall tissue loss when apoptosis occurs. Additionally, tissue injury activates resident macrophages and endothelial cells, contributing to inflammation and further consequences of tissue damage.
220
Which tissue types are less capable of proliferating and what happens when apoptosis occurs in these tissues?
Tissues such as female germ cells, cardiac muscle, and neural tissue are less capable of proliferation; apoptosis in these tissues leads to general tissue loss.
221
What additional processes occur alongside tissue injury during repair?
Tissue injury is often accompanied by the activation of resident macrophages and endothelial cells, which can lead to inflammation.
222
What is a potential negative outcome of DNA repair mechanisms?
DNA repair mechanisms can lead to disrepair, where erroneous repairs result in new mutations, potentially initiating carcinogenesis.
223
At what levels can disrepair occur as a result of toxicant exposure?
Disrepair can occur at the molecular, cellular, or tissue level.
224
What factors can lead to the failure of repair mechanisms?
Repair mechanisms can fail if the extent of the damage overwhelms them or if a toxicant damages the repair mechanisms themselves.
225
How can the repair process itself contribute to toxicity?
The repair process can contribute to toxicity if it is uncontrolled, such as causing an excessive inflammatory response or leading to fibrosis.
226
What is fibrosis?
Fibrosis is the excessive deposition of the extracellular matrix (ECM), which can occur if the increase in ECM production following tissue injury is not halted.
227
What is the purpose of adaptive mechanisms in response to toxicant exposure?
Adaptive mechanisms result in physiological changes to maintain normal cellular functioning or to alter functioning to tolerate the toxicant.
228
How can exposure to a toxicant lead to physiological dependence?
Adaptive mechanisms that arise from toxicant exposure can contribute to physiological dependence on the substance by altering normal cellular functions.
229
What are 6 mechanisms that allow an organism to adapt to exposure to a toxicant?
1. Reduction in delivery of the toxicant to the target.
2. Increased ability for repair at the molecular, cellular, or tissue level.
3. Decreased susceptibility of the target to the toxicant.
4. Compensatory mechanisms to counteract toxicant-induced dysfunction.
5. Reduction in bioactivation of the toxicant.
6. Increased detoxification reactions to eliminate or neutralize the toxicant.
230
How does increased repair capacity contribute to adaptation to toxicants?
An increased ability for molecular, cellular, or tissue repair helps the organism cope with and recover from the damage caused by toxicants.
231
What does decreased susceptibility of the target mean in the context of toxicant exposure?
It refers to the mechanisms that reduce the target's vulnerability to the harmful effects of a toxicant.
232
What role do compensatory mechanisms play in adaptation to toxicants?
Compensatory mechanisms help counteract dysfunction induced by toxicants, allowing cells and tissues to maintain functionality.
233
How can reducing bioactivation be an adaptive response to toxicant exposure?
Reduction in bioactivation minimizes the conversion of a toxicant into its active, harmful form, thereby decreasing its potential effects.
234
What is the significance of increased detoxification reactions in adaptation?
Enhanced detoxification reactions allow the organism to more effectively eliminate or neutralize toxic substances, aiding in recovery and adaptation.
235
Why might a reduction in bioactivation contribute to toxicity?
Reduction in bioactivation can lead to down-regulation of enzymes at the gene expression level, specifically affecting the transcription of genes encoding these enzymes.
This down-regulation can decrease the production of active metabolites, but it may also inadvertently lower the transcription of detoxifying enzymes and transporters necessary for the elimination of toxicants.
Thus, while the immediate effect is reduced bioactivation, the broader impact may hinder the body’s ability to detoxify harmful substances, contributing to toxicity.
236
What is a response element?
Short sequences of DNA within a gene promoter region that are able to bind specific transcription factors and regulate transcription of genes
