Studied by 4 people
How do cells interact with each other
By sending and recieving signals. The signals can be sent using a chemical substance. The signals are produced in one cell and bind to receptors in another cell.
What are Receptors
They are proteins, with a site to which the signalling chemicals can bind. Binding cause changes in the receptor, which stimulate a response to the signal by the target cell.
What is a ligand
A molecule that binds selectively to a specific site on another molecule. For chemical signalling
What is the ligand-binding site
The site on the receptorto which the signalling chemical binds. This is similar to enzyme-substrate specifity, BUT IT IS NOT THE SAME. those are for calalysing and this is for CHEMICAL SIGNALING. -ish
A quorum
a fixed number of individuals needed for a meeting to go ahead.
What is quorum sensing?
It is a method developed to assess wether a popuation is large enough for group activities. It is based on intercellular communication. A switch in activity or behaivior is trigerred when the population density rises above a certain threshold.
How is group activities achieved in quorum sensing ?
Signalling molecules are secreted at a low rate by all cells in the population. These molecules diffuse freely between cells and bind to receptors in each cell. When there has been sufficient binding of the signalling molecules to receptors in a cell, gene expression is changed. This causes a switch in activities.
How do cells sense that there has been a quorum?
As population density rises, all cells recieve more of the signalling chemical from other cells. Above a certain density, every cell in the population recieves enough to causee the change in gene expression and the resulting switch in activity.
What is quorum sensing an example of
Interdependence. It is only effective if more than one cel participates.
Bioluminescence as an example for quorum sensing
Vibrio fischeri is a marine bacterium where bioluminesence. The cell’s produces and secrete a type of signalling molecule known as autoinducer. The autoindcer can diffusee between cells. It binds to a receptor protein in the cytoplasm, known as LuxR. When binding occurs, the LuxR binds to the DNA of the cell where it induces te transcription of genes. Expression of these genes results in production of the enzymes luciferase. Light will be induced when there is a high concentration of those enzymes produced.
What are hormones
They are signalling chemicals produced in small amounts by a group of specialized cells in the body and transported by the bloodstream.
What are glands?
oragans that are specialized for secretion
Where are most glands secreted
blood capilaries and gland tissues
Endocrine glands
Glands that secretes hormones. These glands have a duct leading out of the organ to transport the secretion.
What do hormones effect
Hormones are transported through the bloodstreams to all parts of the body, but only effect target cells that has receptors for the hormone.
How do hormones effect target cells
The hormone regulates the activities of the targetcells by promoting or inhibiting specific processes.
Examples of hormones
Insulin, thyroxin, and testosterone
What are neurotransmitters
They are chemicals that transmits signals across synapses.
What is a synapse
It is a junction between two neurons in the nervous system.
the presynaptic neuron secretes it
The postsynaptic neuron recieves it
When is the neurotransmitter secreted
It is secreted when a nerve impulse reaches the end of the presynaptic neuron
How do neurotransmitter tranmits signals across
It diffuses across the gap between the two neurons and then binds to receptors in the plasma membrane of the postsynaptic neuron. This binding influeneces wherter a nerve impulse is initiated in the postsynaptic neuron.
Exitatory neurotransmitters
Stimulates nerve impulses
Inhinbitory neurotransmitters
Inhibits nerve impulses
What is the gap between two neurons at a synapse
Between 20-40 nm (nanometres)
why is there rapid removal of neurotransmitter from the synaptic gap
To ensure it only affects one specific postsynaptic neuron; it does not usually diffuse out of the synapse to have more widespread effects.
Examples of neurotransmitters
Acetylcholine, norepinphrine, and dopamine
What are cytokines
They are small proteins that acts as a signalling chemicals. They ca be secreted by a wide range of cells
Cytokine secretion
The same cytokine may be secreted by different cell types and one cell type may be secrete several different cytokines
What do cytokines act on
They act on either on the cell that produced them or on a nearby cell.
How do cytokines affect target cells
They cannot enter cells, therfore they bind to a receptor in the plasma membrane of the target cell. The binding causes a cascades of signalling inside the cell. This causes change sin gene expressions and thus in cell activity.
What roles to cytokines play ?
They play roles in inflammation and in other responses of the immune systems. As well as control of cell growth and proliferation and in the development of embryos.
Examples of cytokines
Erythopoietin (EPO), interferon, and interleukin
What are calcium ions used for
They are used for cell signalling in both muscle fibres and neurons.
What does calcium ions do in muscle fibres
calcium ions are pumped into a specialized form of endoplasmic reticulum called the sacroplasmic reticulum generating a high concentration
When the muscle fibre recieves a nervous impulse, calcium channels open in the membrane of the sacroplasmic reticulum and all the ions can diffuse out
They bind to proteins that block muscle contractions, causing the proteins to change poition
This allows muscle contraction to occur
If the muscle fibre doenst recieve more nerve impulses, these changes are reversed and the calcium pumped bck into the sacroplasmic reticulum.
What does ccalcium ions do in neurons
The arrival of a nerve impulse at a presynaptic membrane causes calcium channels to open, allowing inward diffusion. Inside the presynaptic neron Ca2+ ions cause secretion of nerotransmitters into the presynaptic gap by exocytosis. The calcium ions are rapidly pumped back out into the synaptic cleft.
A signalling chemical must :
have a distinctive shape and chemical properties so the receptor can distinguish between it and other chemicals
be small and soluble enough to be transported
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