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What is the purpose of cell signalling?
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What is the purpose of cell signalling?
Cell signalling allows messages to be sent to cells in multicellular organisms, allowing the control and coordination of their bodies and facilitating a response to their environments.
Define the term "transduction" in the context of cell signalling.
Transduction is the process of converting a signal received by a receptor into a signal that can be passed on.
What are some examples of molecules that act as ligands in cell signalling?
Examples of ligands include proteins, amino acids, nucleotides, steroids, and amines.
Describe the basic stages of a cell signalling pathway.
The basic stages are:
a stimulus or signal is received by a receptor
the signal is converted to a signal that can be passed on (transduction)
the signal is transmitted to a target (effector), and an appropriate response is made
True or False?
Ligands are secreted from the target cell and bind to receptors on the sending cell.
False.
Ligands are secreted from the sending cell and bind to receptors on the target cell.
What is the purpose of quorum sensing in bacteria?
Quorum sensing allows bacterial colonies to respond to changes in population size by altering gene expression.
Describe the mechanism of quorum sensing in bacteria.
Ligands released by bacteria bind to receptors on other bacteria, and when a threshold number of receptors are occupied, a change in gene expression and activity is triggered.
What is the benefit of forming a mutualistic relationship with bobtail squid to the Vibrio fischeri bacteria?
The benefit to the Vibrio fischeri bacteria is the provision of amino acids and sugar from the squid's metabolic processes.
What is the benefit of forming a mutualistic relationship with Vibrio fischeri to the bobtail squid?
The benefit to the bobtail squid is increased camouflage, as the Vibrio fischeri bacteria emit light by bioluminescence, lighting up the underside of the squid.
When does Vibrio fischeri produce bioluminescence?
Vibrio fischeri produces bioluminescence only when the bacterial colony is large enough to switch on the synthesis of the enzyme luciferase. This is an example of quorum sensing.
What is the definition of a hormone?
A hormone is a chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target cells or organs.
How do hormones interact with their target cells?
Hormones bind to receptors that are either found on the cell surface membrane or inside the target cells.
What is the difference between hormones and neurotransmitters in terms of their effects?
Hormones have a more distant effect as they travel in the blood to target cells, while neurotransmitters have a localised effect across a very short distance at the synapse.
Give three examples of hormones.
Examples of hormones include:
insulin
glucagon
thyroxine
testosterone
oestrogen
epinephrine (adrenaline)
FSH
LH
ADH
These hormones are named in the IB specification, however, there are many other examples
Define the term "neurotransmitter".
Neurotransmitters are chemicals that transmit signals across the synaptic cleft from the presynaptic neurone to the postsynaptic neurone.
Describe how neurotransmitters work at the synapse.
Neurotransmitters diffuse across the synaptic cleft and bind to receptor molecules on the postsynaptic membrane, causing sodium ion channels to open and generating a nerve impulse due to an influx of sodium ions.
Give an example of a neurotransmitter.
An example of a neurotransmitter is acetylcholine (covered by the IB specification)
There are many other examples of neurotransmitters including:
norepinephrine
dopamine
What is the role of cytokines in cell signalling?
Cytokines are proteins released by cells that interact with receptors on other cells, leading to a cascade of events that impact gene expression and cell activity. Cytokines play an important role in signalling between cells in the immune system.
Describe how calcium ions (Ca2+) are involved in cell signalling.
Calcium ions are involved in many signalling pathways, such as triggering muscle contraction and neurotransmitter release at synapses. They can also act as second messengers inside cells.
What is the defining characteristic of transmembrane receptor proteins?
Transmembrane receptor proteins have an external binding site and an internal region that extends into the cytoplasm, spanning the width of the cell membrane.
Describe the typical structure of transmembrane receptor proteins.
Transmembrane receptor proteins have hydrophilic amino acid regions at either end that contact the aqueous solutions inside and outside the cell, and a hydrophobic amino acid region within the membrane that contacts the phospholipid tails.
Where do ligands bind to transmembrane receptors?
Ligands bind to the external binding site of transmembrane receptors, instead of entering the cell cytoplasm.
What type of ligands can diffuse through the cell membrane and bind to intracellular receptors?
Non-polar, hydrophobic ligands, such as steroid hormones, can diffuse through the phospholipid bilayer and bind to intracellular receptors.
Where are intracellular receptors located?
Intracellular receptors are located in the cytoplasm or on the DNA in the nucleus of the cell.
What happens when a ligand binds to an intracellular receptor?
When a ligand binds to an intracellular receptor, it activates the receptor to initiate a signal transduction pathway that leads to changes in cell activity.
Describe the general process of signal transduction pathways.
Signal transduction pathways involve the binding of a ligand to a receptor, followed by a cascade of events like phosphorylation and the use of second messengers, which ultimately lead to a cellular response.
What are some possible cellular responses to signal transduction pathways?
Possible cellular responses include:
regulation of gene expression
changes in metabolic activity
regulation of enzyme activity
cell death
cytoplasmic rearrangement
regulation of membrane proteins
True or False?
Different ligands and receptors trigger the same signal transduction pathways.
False.
Different ligands and different receptors trigger different signal transduction pathways.
What is the basic difference in the signal transduction pathways for transmembrane vs. intracellular receptors?
For transmembrane receptors, the signal transduction pathway involves phosphorylation events and second messengers, while for intracellular receptors, the ligand-receptor complex is directly activated to initiate the signal transduction pathway.
What is a cholinergic synapse?
A cholinergic synapse is a synapse that uses the neurotransmitter acetylcholine (ACh).
How does acetylcholine (ACh) change the membrane potential of a neurone?
ACh binds to ligand-gated sodium ion channels in the postsynaptic membrane, causing them to open and allowing sodium ions to diffuse into the cell, reversing the charge across the membrane.
What happens to the acetylcholine molecules after they have triggered the change in membrane potential?
The ACh molecules are broken down by the enzyme acetylcholinesterase to prevent continued stimulation, and the products are absorbed back into the presynaptic membrane.
What is a G-protein-coupled receptor (GPCR)?
A GPCR is a transmembrane receptor protein responsible for the activation of an intracellular G-protein, which then initiates changes inside the cell.
Describe the structure and function of G-proteins.
G-proteins bind to either GTP (active) or GDP (inactive), and act as a switch, being activated or deactivated by signals at the membrane surface.
Explain the process of G-protein activation.
A ligand binds to the GPCR, causing a conformational change that activates the attached G-protein, replacing GDP with GTP and causing the G-protein to dissociate into subunits that can interact with other membrane proteins.
True or False?
G protein coupled receptors are found in prokaryotic and eukaryotic cells.
False.
GPCRs are found only in eukaryotic cells, not in prokaryotic cells.
What is a receptor tyrosine kinase (RTK)?
An RTK is a class of transmembrane receptors that become phosphorylated on their intracellular portion after a ligand binds, triggering signal transduction pathways.
How does insulin binding to receptor tyrosine kinase affect glucose uptake in target cells?
Insulin binding to receptor tyrosine kinases triggers the phosphorylation of tyrosine, which stimulates the production of relay proteins that cause glucose transporter vesicles to fuse with the cell membrane, increasing glucose permeability.
True or False?
One receptor tyrosine kinase can only trigger one signal transduction pathway.
False.
One receptor tyrosine kinase can trigger multiple different signal transduction pathways simultaneously.
True or False?
Epinephrine is another name for adrenaline.
True.
Epinephrine is another name for adrenaline.
How does epinephrine affect blood glucose concentration?
Epinephrine can act to increase blood glucose concentration in response to biological stress. This helps to prepare the body for fight or flight.
Define the term "second messenger".
Second messengers are molecules/ions inside cells that relay signals received by cell-surface receptors.
What is the function of adenylyl cyclase?
Active adenylyl cyclase catalyses the conversion of ATP to the second messenger, cyclic AMP (cAMP).
Describe the mechanism by which the effect of adrenaline is amplified in a second messenger response?
The effect of adrenaline is amplified so that each molecule can stimulate many molecules of cAMP, which in turn activate many enzymes.
Explain the origins of the words "adrenaline" and "epinephrine"? (NOS)
Coined by researchers with the following origins:
Adrenaline comes from the Latin translating to 'at kidney' (ad = at and ren =kidney).
Epinephrine comes from ancient Greek translating to 'above kidney' (epi = above and nephros = kidney).
State the meaning of "international cooperation in science". (NOS)
International cooperation in science refers to the work of scientists that does not take place within the confines of a laboratory or a single country, but can have implications for the work of other scientists around the world.
Describe how an intracellular receptor acts as a transcription factor?
Transcription factors are proteins that control the transcription of genes by binding to a specific region of DNA. An activated intracellular receptor binds to a specific region of DNA acting as a transcription factor.
How does oestradiol affect gene expression?
Oestradiol binds to receptors which activate the receptor. The activated receptor then binds to specific DNA sequences initiating transcription. A gene is expressed if it is transcribed and translated, so the binding of oestradiol allows expression of the gene in that cell.
True or False?
Steroid hormones are small, hydrophilic, lipid-based hormones.
False.
Steroid hormones are small, hydrophobic, lipid-based hormones.
What is the role of nuclear pores in the steroid hormone pathway?
Steroid hormones can pass directly into the nucleus through nuclear pores.
Define steroid hormone.
A steroid hormone is a type of lipid-based hormone derived from cholesterol that can pass through cell membranes to regulate gene expression and influence cellular activity.
What is the role of the cofactor in the oestradiol stimulation pathway?
The cofactor enables the ERα oestradiol receptor to bind to the promoter region of the gene, stimulating RNA polymerase binding and gene transcription.
Describe the effects of oestradiol and progesterone.
Oestradiol regulates female sexual characteristics and the menstrual cycle, while progesterone maintains the endometrial lining and prevents further ovulation during pregnancy.
Which gland releases gonadotropin-releasing hormone?
Gonadotropin-releasing hormone is released by the hypothalamus.
Define negative feedback?
Negative feedback is a homeostatic control mechanism that acts to reverse changes and keep physiological factors within normal limits.
What are the steps in a negative feedback control loop?
The steps are:
A receptor detects a stimulus
A coordination system transfers information
An effector carries out a response
What is the outcome of a negative feedback loop?
If there is an increase in the factor, the body responds to make the factor decrease. If there is a decrease, the body responds to make the factor increase.
Provide an example of negative feedback.
If body temperature rises, a negative feedback system will act to lower body temperature, bringing it back to normal.
There are other valid examples.
Define positive feedback?
In positive feedback loops, the original stimulus produces a response that causes the factor to deviate even more from the normal range, enhancing the effect.
Provide an example of positive feedback.
During labour, the stretching of the cervix stimulates the release of oxytocin, which increases uterine contractions, further stretching the cervix.
What is the purpose of positive feedback?
Positive feedback loops are useful to quickly activate a process, such as blood clotting to close up a wound.