Sunday, 13 December 2020

Cell Communication And Signalling

 Do you know how cells communicate with one another. We know lot of about cells, but it actually gets even more complicated than that, because your Cells need to communicate with one another in order to respond to environmental stimuli like potential danger and to elicit certain behavior during various stages in your lifetime so that your body makes the correct changes as you grow.


Cell Communication

There are receptors that sit in the cell membrane and wait for a particular substrate to bind. Many of these receptor substrates are signalling molecules like hormones and neurotransmitters, which upon binding to the receptor set off the process of signal transduction, which can have a variety of results.

Some of this signalling is local, occurring between adjacent cells, but long-distance signalling can also occur, where a message travels all the way across your body to deliver a signal to a particular type of cell.

Three types of cell signalling. Those are Autocrine, Paracrine, and Endocrine.


a) Autocrine signaling


  The prefix auto means "self", so autocrine signalling refers to when the cells secrete signalling molecules which then bind to receptors on that same cell. This will trigger some kind of response from the cell.

b) Paracrine Signalling


The prefix "para" means beside or nearby, so paracrine signalling is a type of local signalling where a compound like a growth factor is secreted by a cell which then interacts with nearby cells. Growth factors are signals that tell a cell to begin dividing which is what allows us to become so much taller during intense periods of growth in childhood.

  Another example of local signalling is called synaptic signalling. This is how messages travel through your nervous system. A nerve cell can be triggered by an electrical signal to release certain molecules called neurotransmitters into the synaptic space, which then interact with the next nerve cell, eliciting another electrical signal which releases neurotransmitters into the next synaptic space, and so forth.
  

A nerve cell can also be attached to a muscle cell which makes it able to trigger muscular contraction. This kind of signalling is used when your hand needs to tell your brain that something it is touching is hot, which will then send another signal back down to your hand to tell it to stop touching it. An incredible amount of chemistry has to happen for all those signals to be transmitted, but lucky for us chemistry happens imperceptibly quickly.


c) Endocrine signalling


the long-distance signalling that happens in our bodies occurs via endocrine signalling. This is when a particular type of compound called a hormone is released by a gland and is then carried through the bloodstream to its destination. This system has a range of functions like maintaining blood pressure, the regulation of development, and more.

Types of signalling molecules
Many of the signalling molecules fall into three structural categories:
• Polypeptides like oxytocin,
• Steroids like cortisol, and
• Amines like epinephrine.

How signalling molecule interact with the body ?

1) Hormon solubility
Polypeptides and amines are water-soluble, whereas steroids are not. But non-polar molecules like steroids are lipid soluble, so this discrepancy will affect the way these molecules are transmitted.
 
Water-soluble hormones can travel through the aqueous bloodstream freely, but they can't pass through the non-polar plasma membrane of a cell so these will typically be recognised by receptors on the surface of the cell, which upon binding will initiate signal transduction. 
  
For example, when an organism finds it self in a particularly stressful situation, like evading a predator, the adrenal glands secrete a hormone called epinephrine. This is more commonly known as adrenaline. When this molecule reaches liver cells it binds to a membrane receptor. This sets off a cascade of events which generates cAMP, which in turn activates an enzyme called protein kinase A.
   This enzyme will inhibit glycogen synthesis and promote glycogen breakdown. This means that the cell will stop storing glucose in the form of glycogen and will instead start breaking up glycogen to make more glucose molecules, which will enter the bloodstream and become available for cellular respiration. Essentially it kicks energy production into overdrive so that the organism can get away from the predator.

  lipid-soluble hormones will have to bind to transport proteins inorder to be soluble in the bloodstream but once they reach a cell they are typically able to pass right through the cell membrane, being non-polar, so the receptors that interact with these types of hormones are usually already inside the cell.
 
For example, in many vertebrates like birds and frogs, estradiol is a hormone that regulates female reproductive function. This can enter aliver cell and bind to a receptor in the cytoplasm. This complex will then undergo a conformational change due to the binding that allows it to enter the nucleus, bind to a specific DNA sequence and transcribe the gene for vitellogenin.Once produced, this protein is then transported to the reproductive system to produce egg yolk.
  Some lipid-soluble hormones pass through both the cell membrane and nuclear membrane to bind to a nuclear receptor. Nuclear receptors are typically transcription factors which once activated, will initiate the expression of a particular gene.

Some hormones elicit multiple responses simultaneously. i.e.
Epinephrin Not only will this promote glycogen breakdown but it also increases blood flow to skeletal muscles and decreases blood flow to the digestive tract.

This is occurs because different cells might contain different enzymes than others and therefore elicit a different cellular response to the same hormone. But also some hormones are able to activate several completely different receptors each with their own unique response to binding.

All hormones are secreted from glands. These are just some of the glands in your body, including the hypothalamus, thyroid, pineal, and pituitary glands.
  Many of these may sound familiar and they have a wide variety of functionality, including the regulation of biological rhythms like your sleep cycle as well as growth, metabolic functions, and social behavior.

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