C2.1 Chemical Signalling (HL) (to check) Flashcards
What is chemical signalling?
A process by which cells, tissues, and organisms communicate using signalling molecules.
What are the two types of cell-to-cell interactions in chemical signalling?
- Direct interactions
- Indirect interactions
What are ligands?
Signalling molecules that include hormones, neurotransmitters, cytokines, and growth factors.
What is the process called when ligands cause a cascade of biochemical reactions?
Ligand binding.
What role do receptors play in chemical signalling?
Receptors exhibit specificity to ligands due to the structure of their binding sites.
What are the main functions of chemical signalling in humans?
- Maintaining homeostasis
- Development
- Immune response
- Neural function
- Metabolic regulation
What is the first stage of chemical signalling?
Synthesis and release of a ligand from a signalling cell.
Fill in the blank: Ligands travel through the bloodstream or by diffusion through the extracellular fluid to reach the _______.
[target cells]
What happens during receptor binding in chemical signalling?
Signalling molecules bind to specific receptors on the target cell.
What initiates the cascade of biochemical reactions in signal transduction?
Conformational change in the receptor caused by ligand binding.
What are some specific cellular responses that can result from activated signalling pathways?
- Changes in gene expression
- Activation or inhibition of enzymes
- Alteration of ion channel activity
- Modulation of cellular metabolism
What is the final stage of chemical signalling?
Signal termination.
True or False: The signalling molecule is always retained in the extracellular space until the signal transduction process ends.
False.
What is quorum sensing in bacteria?
A process where bacteria communicate to coordinate group behaviour in response to cell density.
What are autoinducers?
Small signalling molecules released by bacteria that diffuse and accumulate in their environment.
What types of autoinducers do Gram-positive and Gram-negative bacteria use?
- Gram-positive: processed oligopeptides
- Gram-negative: acylated homoserine lactones (acyl-HSLs)
How does Vibrio fischeri utilize quorum sensing?
Releases N-acyl homoserine lactone to bind to regulators and induce the lux operon.
What is the function of the lux operon in Vibrio fischeri?
Regulates luminescence by encoding regulatory and luminescent proteins.
What chemical reaction produces light in bioluminescence?
The oxidation of luciferin by luciferase.
Fill in the blank: Quorum quenching methods can be used in the treatment of bacterial infections without the use of _______.
[antibiotics]
What potential applications does targeting quorum sensing have in the food industry?
Addressing food spoilage and biofilm formation.
What is the significance of careful examination of names and labels in knowledge acquisition?
To avoid oversimplification and misconceptions.
How can labels hinder knowledge acquisition?
By introducing biases and prejudices, limiting comprehensive understanding.
What is the effect of touching the nettle plant?
A stinging pain is felt due to a nerve signal traveling from the hand to the brain
What are chemical substances used for in the animal kingdom?
They act as signalling molecules to trigger different signalling pathways by activating different receptors
What is the role of signalling chemicals in organisms?
They help organisms to react to changing environments and allow fine-tuning of responses
What hormone is produced by the pancreas in response to high blood glucose levels?
Insulin
What hormone is produced by the pancreas in response to low blood glucose levels?
Glucagon
What are hormones?
Chemicals secreted by endocrine glands into the extracellular fluid that act on target organs/tissues
What is the function of hormones?
They regulate the metabolic function of other cells and have prolonged effects
What are neurotransmitters?
Chemical substances that carry signals from one neuron to another or from a neuron to a target cell
How are neurotransmitters released?
They are released into the synaptic cleft as a result of an action potential
What are cytokines?
Small proteins important in cell signalling related to immune response
Which cells primarily secrete cytokines?
White blood cells such as macrophages and lymphocytes
What role do calcium ions play in cellular signalling?
They can act as ligands and move in and out of the cell, activating proteins
What are the three main types of hormones?
Amines, peptide hormones, and steroids
What are amine hormones derived from?
Amino acids, specifically tyrosine and tryptophan
Give an example of an amine hormone.
Epinephrine (adrenaline)
What are peptide hormones?
Hormones in the form of polypeptide chains or small proteins
What is an example of a peptide hormone?
Insulin
What are steroid hormones derived from?
Cholesterol
What is the dual function of epinephrine?
It acts as both a hormone and a neurotransmitter
How do hormones induce cellular changes?
By binding to receptors and inducing changes in plasma membrane permeability, activating protein synthesis, and altering gene expression
What are the two ways hormones can act?
Activate second messengers or activate genes
What types of substances can serve as neurotransmitters?
Amino acids, peptides, amines, and nitrous oxide
Give an example of an amino acid neurotransmitter.
GABA (Gamma-aminobutyric acid)
What is the mechanism of action of neurotransmitters?
They are released into the synaptic cleft and bind to receptors on target cells
How do cytokines affect target cells?
They bind to specific receptors and trigger signal transduction pathways that alter gene expression
What can calcium ions trigger in cellular processes?
Muscle contraction, nerve impulses, and fertilisation
What are the four types of signalling based on distance?
- Autocrine signalling
- Paracrine signalling
- Endocrine signalling
- Juxtacrine signalling
What is autocrine signalling?
Signalling where cells secrete molecules that act on themselves
What is paracrine signalling?
Signalling where molecules travel a short distance to nearby target cells
What is endocrine signalling?
Signalling where hormones travel long distances via the bloodstream to target cells
What is juxtacrine signalling?
Signalling that occurs when two cells are in physical contact
What are cell-surface receptors?
Receptors present on the cell membrane that transmit signals from outside to inside the cell
What are intracellular receptors?
Receptors located inside the cell that bind to lipid-derived signalling molecules
What are the three domains of a typical cell-surface receptor?
- Extracellular ligand-binding domain
- Transmembrane hydrophobic domain
- Intracellular domain
What do intracellular receptors do upon ligand binding?
They form a hormone-receptor complex that can move to the nucleus to affect gene expression
What are Type I intracellular receptors?
Cytoplasmic receptors that translocate to the nucleus upon ligand binding
What are Type II intracellular receptors?
Nuclear receptors directly involved in gene transcription
What happens when a ligand binds to a cell-surface receptor?
An intracellular signal is generated which may get amplified
Name the three categories of cell-surface receptors.
- Enzyme-linked receptors
- G-protein-linked receptors
- Ion channel-linked receptors
What amino acids are typically found in transmembrane receptors?
Hydrophobic amino acids like phenylalanine, leucine, isoleucine, and others
What is the main difference between hydrophobic and hydrophilic signalling molecules?
Hydrophobic signalling molecules can diffuse across the cell membrane, while hydrophilic ones cannot
What is the first step in the signal transduction process?
Receptor activation
Receptors get activated when specific ligands bind to them.
What does signal amplification refer to in the context of signal transduction?
A process where a small signal triggers a larger response through activation of downstream messengers/effectors
Hormones or neurotransmitters can activate protein kinases, amplifying the signal.
What is a common second messenger in signal transduction?
Cyclic AMP (cAMP)
cAMP plays a crucial role in relaying signals inside cells.
What is the function of protein kinases in signal transduction?
To phosphorylate proteins by adding a phosphate group
Protein kinases remain inactive until activated by second messengers like cAMP.
What are the potential outcomes of changes in gene expression or cellular function during signal transduction?
Altering gene expression, opening/closing ion channels, activating enzymes
These changes ultimately lead to a modification in cellular behavior.
How is the signal terminated in signal transduction?
By degradation, diffusion, reuptake, inactivation of receptors, or feedback inhibition
For example, acetylcholinesterase degrades acetylcholine to terminate its action.
What are the three types of neurotransmitters based on their effects?
- Excitatory neurotransmitters
- Inhibitory neurotransmitters
- Modulatory neurotransmitters
Examples of excitatory neurotransmitters include glutamate; inhibitory neurotransmitters include GABA.
What is the role of acetylcholine at the neuromuscular junction?
Regulates muscle contractions and other functions like heartbeat and blood pressure
Acetylcholine is the primary neurotransmitter associated with motor neurons.
What happens when an action potential reaches the axon terminal?
It depolarizes the membrane and opens voltage-gated Na+ channels
This depolarization is crucial for neurotransmitter release.
What are G proteins and their function in signal transduction?
Molecular switches that undergo conformational changes when GPCRs bind to ligands
They facilitate GDP/GTP exchange within the cell.
How many subunits do G proteins consist of?
Three subunits: ɑ, β, and γ
Inactive G proteins have the ɑ subunit bound to GDP.
What is the structure of a typical G protein-coupled receptor (GPCR)?
Has seven transmembrane ɑ helices
GPCRs are the largest class of membrane receptors found in eukaryotes.
Fill in the blank: The binding of a ligand to a receptor induces a _______ change.
conformational
This change activates the receptor’s intracellular domain.
True or False: The ultimate response of the cell to a signal is independent of the type of receptor involved.
False
The response depends on the type of receptor, nature of the signal, and downstream effectors.
What is epinephrine also known as?
Adrenaline
What hormone is secreted by the adrenal glands in response to stress or danger?
Epinephrine
What are the two major outcomes of protein kinase A activation by epinephrine?
- Inhibition of glycogen synthesis
- Initiation of glycogen breakdown
What does cAMP stand for?
Cyclic AMP
What role does cAMP play in the cell?
Acts as a second messenger
What is the function of adenylate cyclase in the presence of epinephrine?
Converts ATP to cAMP
What type of receptors are involved in the mechanism of action of epinephrine?
G protein-coupled receptors (GPCRs)
What happens to GDP when epinephrine binds to its receptor?
GDP is replaced by GTP
What is the effect of protein kinase A activation in the liver?
Activates phosphorylase, breaking down glycogen to glucose
What are tyrosine kinase receptors involved in?
Cell growth, differentiation, and proliferation
What is the role of insulin in glucose homeostasis?
Increases glucose uptake and reduces glucose synthesis in the liver
What is the structure of the insulin receptor?
A dimer consisting of alpha(ɑ) and beta(β) subunits
What process does tyrosine kinase undergo upon insulin binding?
Autophosphorylation
What does the activation of IRS proteins lead to?
Activation of downstream signalling pathways
What is GLUT-4?
A glucose receptor embedded in the cell membrane
What type of receptors do steroid hormones bind to?
Intracellular (nuclear) receptors
What happens when oestradiol binds to its receptor?
Dimerisation of the receptor-hormone complex
What does oestradiol enhance in the hypothalamus?
Secretion of gonadotropin-releasing hormone (GnRH)
What are the two hormones released by the anterior pituitary gland due to GnRH?
- Follicle-stimulating hormone (FSH)
- Luteinising hormone (LH)
What is the main role of progesterone in the reproductive system?
Maintaining the menstrual cycle
What effect does progesterone have on endometrial cells?
Causes differentiation and prepares for possible implantation
What happens to progesterone levels if pregnancy does not occur?
Progesterone levels decline, leading to shedding of the endometrial lining
What is the tendency of all systems in nature?
To attain balance
This concept is often referred to as homeostasis in biological systems.
How does a thermoregulated waterbath maintain equilibrium?
The thermostat cuts off heating when the set temperature is reached and switches on when the temperature drops below the set point
What role do feedback loops play in living organisms?
They connect output signals back to their inputs to maintain a balanced internal environment
What are the two critical components of feedback mechanisms in regulating signalling pathways?
- Positive feedback
- Negative feedback
What is homeostasis?
The maintenance of a stable internal environment in living organisms
What is the significance of chemical signalling in microorganisms?
It regulates growth and mediates communication with the environment
What does ‘drug resistance’ mean in the context of pathogenic microorganisms?
Some microorganisms undergo random mutations that allow survival in the presence of drugs
Why is drug resistance considered a serious threat?
It poses risks to both immunosuppressed and immunocompetent individuals
What is the effect of positive feedback mechanisms in cell signalling?
They result in amplification of cell signals
Give an example of a process governed by positive feedback mechanisms.
Blood clotting, where activated platelets release chemicals to activate nearby platelets
What is the role of negative feedback in cell signalling pathways?
It inhibits upstream activation, dampening the amplification of signals
How does insulin function in regulating blood glucose levels?
Insulin is secreted when blood glucose rises, promoting glucose uptake, and its release is inhibited when glucose levels fall
What do positive and negative feedback loops form the foundation of?
The cellular signalling pathway
What happens to reactions in the signalling process based on the type of signal they receive?
They are constantly turned on or off
