Sunday, 29 June 2014

How scientists are creating synthetic life from scratch

How scientists are creating synthetic life from scratch 

By Susannah Locke

Over the past decade, the ease of sequencing and creating DNA has improved so much that the possibilities of genetic engineering have expanded tremendously.
Researchers can now go way beyond the slight tinkering they've been done in the past — like adding or deactivating a single gene. Instead, some scientists are now focusing on broadly creating and re-engineering living things wholesale to improve our environment, our energy, and our health
Welcome to the strange new world of synthetic biology, in which living things are a tool to be manipulated for practical ends. It's a world in which, someday, organisms designed from scratch could convert waste into fuel or enter people's bodies to kill cancer.
Some scientists see synthetic biology as the best bet to tackle some of the world's most pressing problems — like the ever-increasing demand for food and energy. But the prospect of possible mishaps, not to mention concerns about tinkering with life to begin with, are certainly there, too. Here's a primer on synthetic biology.

What is synthetic biology, anyway?

The term "synthetic biology" generally refers to the engineering of new biological tools for practical purposes. If that sounds a lot like the existing practice of genetic engineering — well, that makes sense, because it is.
Many scientists simply refer to synthetic biology as "genetic engineering on steroids" (to quote Jim Collins, a pioneer in the field). But there's not always a clear line at which ho-hum genetic engineering flips over into synthetic biology territory.
In general, if you're genetically engineering foods like corn and soy by adding or modifying a single gene, that's not synthetic biology. But if you're adding in a whole suite of genes or creating an entirely new genetic code that doesn't exist anywhere in nature, then you're definitely entering synthetic biology territory.
Synthetic biologists use a variety of approaches, some of which can overlap:
1) Removing inefficiencies in cells

Some researchers are trying to remove inefficiencies from cells that are a byproduct of the haphazard nature of evolution. For example, if you're engineering bacteria to produce biofuels, you want the process to be as efficient as possible. Researchers also use this kind of approach to find the limits of life — how simple or how different can something be and still be alive?
2) Combining genetic sequences in extreme ways

Some researchers want to combine many genes from various organisms to make new tools. For example, some who are interested in having algae make fuel think that combining DNA across many algae strains will be the key that has eluded them so far.
3) Designing new "living machines"

 Others are trying to design living machines by reprogramming DNA into logical circuits to make them function like miniature computers. For example, researchers have gotten cells to do arithmetic and show their answers by lighting up in a certain color.

What could we do with synthetic biology?

Green fuels is one area where synthetic biology could have a major impact. AFP/Getty Images
Like any new technology, it's difficult to tell exactly where synthetic biology will have its biggest impact. But there are a few big areas of interest, which right now are in medicine, energy, food, and environmental remediation.
1) Medicine

Synthetic biology might one day let scientists program cells to precisely detect and kill cancer cells. Or perhaps program cells to self-assemble into spare organs for transplants. Some scientists are already using partially synthetic organisms to manufacture drugs that are otherwise impractical to make.
2) Food and fragrances

 In theory, new techniques could allow researchers to design yeast to make the perfect beer or wine. Or create food in the lab more efficiently than growing it on land. "We can design better and healthier proteins than we get from nature," biologist and entrepreneur Craig Venter told the New York Times.
Already, synthetic biology companies are selling orange and grapefruit flavorings produced by yeast. And the company Evolva makes yeast-generated artificial vanilla flavoring and is working on better tasting sugar substitutes.
3) Energy and environment 

Another possibility is that synthetic biologists could program cells to produce usable fuel. For example, Exxon Mobile has a partnership with Synthetic Genomics (co-founded by Craig Venter) to research fuel from algae. Ideally, helpful organisms would eat things we don't need, like non-edible plant matter. Even more ideally, they'd eat the extra carbon dioxide in the atmosphere that's warming the planet. Or toxic waste or oil from oil spills.
4) The weird stuff

How about some microbes that live on your skin to prevent you from getting oily and smelly? How about some other ones that secrete the perfume of your choice? How about some that quickly break down cholesterol so it won't clog people's arteries?

What have scientists done with synthetic biology so far?

Yeast growing on a petri dish. Yeast is a major player in synthetic biology these days. Rising Damp/Flickr
We're not yet at the point of designer cells that kill cancer or turn plastic waste into fuel. But scientistshave done a few exciting things already:
1) A more efficient process for making anti-malarial drugs 

Artemisinin is one of the most effective drugs to treat malaria. But for a long time, it had to be derived from the sweet wormwood plant Artemisia annua — a slow and expensive process.
That changed in 2013, when pharmaceutical firm Sanofi used synthetic biology to produce artemisinin at an industrial scale. The company did this by taking the plant's genes for making artemisinic acid and putting them in yeast, allowing them to produce the drug more quickly and efficiently. The effort is widely cited as the first large-scale drug project to use synthetic biology and as a major achievement for the field.
2) Creating bacteria from scratch

In 2010, researchers at the J. Craig Venter Institute published the results of a 15-year, $40 million project to make the first synthetic cell. How did they do it? They took the genomic code from one bacterial species, made it in a lab from scratch, and then put it into an entirely different species — that lived.
The genome they made also included some deleted genes and new sequences that acted as watermarks. And, all in all, the scientists created the first life-form living on completely synthetic genetic material. They called it the first synthetic cell. (However, they didn't say that they created life itself from scratch. Had they put the DNA into an already-dead cell, nothing would have happened.)
This work didn't create bacteria that was useful for any particular purpose, but it was an important proof of principle that a cell can survive on lab-made DNA.
3) Creating yeast from scratch

In 2014, a team of researchers from many institutions including Johns Hopkins University revealed that they had synthesized an entire yeast chromosome from scratch. And the chromosome functioned when put back into a yeast cell. This was an especially impressive feat because yeast's genetic material is more complex than bacteria's.
The scientists called the DNA they made a "designer chromosome" because they deleted any sequences that they found unnecessary and added in elements that will allow future researchers to easily delete any gene they want. The goal is to rewrite the entire yeast genome in five years. So far, they've done about 3 percent of it, by length. Only 15 more chromosomes to go.

So how do you design an organism from scratch?

The main tool here is the computer. Researchers work with the code of existing organisms' genetic material as essentially a text file, tweaking it, deleting parts, adding parts, adding parts from other organisms, whatever they want.

Then they need to take that information and turn it into physical DNA. So they use a DNA synthesis machine that creates actual DNA from the necessary molecules. DNA that has been made by a machine is considered "synthetic DNA."
The researchers have to get that DNA into the organism of choice, and the techniques here can vary depending on the type of cell. Shorter chunks of DNA are easier to work with than longer chunks, which is why you see many small DNA pieces in the graphic below (from Nature News).
Designing the first fully synthetic yeast chromosome. Nature News

How do scientists program cells to act like a computer?

This is an approach that has garnered a lot of interest. It's essentially designing genes to function in logical circuits, sort of like computers. It has attracted work from many academic groups and startups. And even high school students are now participating in the yearly synthetic bio iGEM competition, which included 245 teams in 2013.
Here's the idea. Genes can be thought of like an input/output system that already does some simple logic. The inputs are molecules that interact with genes to help turn them on or off. The outputs are what the gene makes after it's turned on — usually a protein of some sort. For example, the gene for the enzyme that digests lactose naturally turns on whenever there's lactose around, but not glucose.
Scientists have come up with clever ways to manipulate, combine, and tweak these stretches of DNA to do some pretty interesting things.
In 2012, Swiss researchers showed that they could get mammalian cells to do math. They created genes that only turn on if two particular inputs are there at the same time — so that the genes essentially compute an "AND" function. And they made others that compute other functions. By combining basic logical functions — "AND," "OR," "NOT," and combinations of them — they got cells to do binary addition and subtraction like computers do and then show the right answer by glowing red or green. Others have done projects that also involved memory.
In another example (pictured), a team from the University of California at San Francisco created a plate ofE. coli bacteria that can sense and then trace out an edge of a picture. It's a demonstration of simple logic that could someday get built up into far more complex code. The logic they programmed is as follows: (1) If you sense light, make a certain cell signaling molecule. (2) If you're sensing the signaling molecule (meaning you're near a cell that's in the light) and are not yourself sensing light, then manufacture a dark pigment.
These E. coli have been engineered so that they can find and trace an edge by producing a dark pigment. Popular Science
Researchers have also made DNA elements that are toggle switches that can be turned on or off, ones that reduce noise in response to negative feedback, and ones that create an oscillating signal, among others.
There are now thousands of such interchangeable building blocks held in various databases, such as the public one run by the BioBricks Foundation. The idea is to use these tools to engineer living machines that can perform a variety of tasks.

What about changing the molecules of DNA itself?

Researchers are changing the molecules that make up DNA. UIG via Getty Images
Normally, the cellular factories that construct proteins from DNA instructions are doing so from a limited number of types of parts. There are only 20 standard amino acids — the building blocks that make up the estimated 19,629 human proteins.

But what if an engineer wants to use a lab-made amino acid, a new widget that's never been seen in nature?
First, they'd have to mess with DNA. The DNA that codes for proteins is read three letters at a time, and all of DNA's four letters (A, C, T, G) already have a hard translation for what amino acids they code for. And all of the combinations are already taken.
So, in order to use new amino acids, some engineers want to expand the DNA alphabet with even more letters. This is tricky because it requires retrofitting artificial DNA letters onto eons-old cellular machinery.
In May, 2014, researchers published in Nature that after screening some 300 possible new DNA letters, they found ones that E. coli bacteria would accept. They called these new letters X and Y. The bacteria were able to use their existing machinery to copy DNA containing X and Y for 24 generations (about 15 hours). But researchers have only shown that the cells could copy the DNA, not actually use it. Next up, they'll need to demonstrate that they can get cells to read these new letters to actually make proteins.
Other groups have been focusing on the chemical backbone that holds DNA together. They've created DNA with several other backbones, called XNAs, and have shown that they can get cells to accept and copy them. One possibility is to use such techniques to make DNA that's hardier and more resistant to degradation.

What are the major challenges in synthetic biology?

1) Designer cells can evolve — in unpredictable ways 

As helpful as evolution has been for actual life in the real world, life's ever-changing nature is annoying if you're trying to engineer life to become a predictable tool.
Here's why: cells acquire random mutations in their DNA. And some cells will produce more offspring than others or completely die off. The result is that every new generation is slightly different than the one before. That can be an annoyance if, say, you are trying to design cells to perform a specific task in a pharmaceutical factory.
2) Cells are very messy 

Another challenge is that cells are far more disorganized than a circuit board or computer program. The elements of a circuit board can be lined up in a precise order so that the output of one element can be funneled straight into the input of the next.
But a cell is an altogether messier situation. The molecules in a cell, including those that people are using as inputs and outputs, are generally lumped together in the same space and — literally — jiggling around randomly. So there's a way higher chance of something cross-reacting, and that can cause problems.
3) Mammals' cells are difficult 

A third challenge is that cells from more complex creatures, like mammals, tend to be far more difficult to engineer than, say, bacteria.
Mammals' cells, for example, usually have two copies of each gene in a cell, whereas bacteria generally have one. Also, the processes that regulate what genes get used are more multilayered and complicated. And inserting and deleting genes in mammals' cells is also far more difficult. (Although in the past few years, a new gene editing system called CRISPR has made deleting genes easier.)

How would I know if my food contains synthetic biology products?

You generally wouldn't know. There's no federal law that requires ingredients from synthetic biology to be labeled. This is the case in the US for all genetically engineered foods, including GMO corn and soy and products made from them.
Several ingredients produced by synthetic organisms (but not actually containing these organisms) are on the market in soaps, cosmetics, and foods. You can read a good review of what's going on with these ingredients and (non-)transparency about them in this New York Times story here.

Isn't there a risk that these artificial cells could escape into the wild?

That's one concern, although researchers aren't usually in the habit of simply sending these organisms to the dump without precautions.
There are generally rules in place for them to kill any lab organisms before disposal, generally in a high-temperature, high-pressure oven called an autoclave. (Even a dead lab mouse that hasn't been genetically altered gets autoclaved first, too.)
In some cases, researchers have made organisms that can only survive in the lab — by, for example, tweaking them to need a nutrient that doesn't exist in the wild. It's also possible that scientists could program a kill switch that would turn on at a certain point. (So, for instance, a cell designed to kill cancer could be programmed to self-destruct after it's done its job.)

Is this going to be one more technology that only the rich will get to use while the rest of the world suffers?

Well, only time will tell. Legally, it's possible to patent most of the things that these people are doing. But it's not necessarily the case that that's how synthetic biology will play out. Many people support an open source model, where all information is free for everyone to use.
In a recent piece in Nature, writer Bryn Nelson describes this debate as a clash between engineers and computer scientists, who tend to favor the open source model, and biotech people, who often argue that patents provide economic incentives for innovation.
So far, synthetic biology has been using both. For example, the people uploading genetic sequences into the BioBricks catalog must affirm that they won't claim the sequences as their own intellectual property. But most companies making commercial products, like drugs and food ingredients, are working under the patent system.
More on synthetic biology:
  • Profile of and a Q&A with Craig Venter, the biggest name in synthetic bio
  • Profile of Jim Collins, synthetic biology pioneer
  • The New Yorker wrote a big piece on synthetic biology in 2009. Old, but still good.
  • The debate over unlabeled synthetic biology products on the market

Source: Vox

Saturday, 21 June 2014

10 Sci-Fi Technologies Moving Us Closer To Immortality

10 Sci-Fi Technologies Moving Us Closer To Immortality


The average life expectancy is constantly rising as we improve our knowledge of medicine and the human body. We have eradicated diseases, discovered powerful treatments, and figured out how to fix ailments which would have once killed us. Now we’re accelerating even more rapidly in the practice of keeping Human alive, jolting toward something close to immortality with technologies that sound like they’ve been ripped straight from the realm of science fiction.

10Blood Factories

1- blood
Blood is so critical to our survival that it’s become the go-to metaphor for people to describe a necessity. Farmers, workers,religion, love, family—they’ve all been described as the “lifeblood” of nations. Excessive blood loss will quickly end a life, so blood transfusions are a vital medical tool. There are two major issues with blood transfusions, though. The first is that the blood has to be donated from other people, which can lead to shortages. The second is that everybody has a different blood type, and transfusing the wrong blood type will lead to an immune system attack and a variety ofawful complications.
Science has managed to address both these issues by manufacturing red blood cells from the universal O- type (which can be given to anybody without immune issues). This is the first time that blood like this has been created in a lab, and it could lead to the end of blood donations and the beginning of industrial blood production.

9Growing Body Parts

2- body parts
There are some common sci-fi tropes that are at least somewhat plausible. When we see interstellar travel, alien life, or food reduced to pills, we can imagine the potential they have to be a part of human life. But some things are a little more far-fetched, like culturing body parts in labs. Like most things, though, the truth is crazier than fiction, since scientists are doing exactly that. The lab-grown organs don’t just look anatomically correct, they work correctly as well. What have we made so far? Vaginas and nostrils, both of which have been safely transplanted into humans with no adverse side effects.
For the first time ever, females who were born without a vagina—or whose vagina was incomplete—received vaginas grown in a laboratory. The women were tracked for eight years before the scientists were satisfied with the results. During that time, the women and their new organs functioned completely normally without adverse side effects. Patients who had lost part of their noses to skin cancer also had new noses grown from their skin cells.

8Reversing Paralysis

3- spine
Injuries to the spinal cord are among the most devastating afflictions suffered by humanity. The spinal cord carries information to every part of the body, so injuries to this area often lead to the awful condition of paralysis. In the past, there was little which could be done for the victims of such injuries. They were left to live out their lives with limited mobility and, often, a great deal of pain.
As the result of groundbreaking research into the role of electrical impulses on the nervous tissue in the spine, modern scientists have now been able to return voluntary movement to people who were supposed to be paralyzed for life. In the exciting experiment, the patients involved were able to move previously paralyzed body parts after electric pulses were applied to their spinal cords. When combined with traditional physical therapy, the improvement became even greater, giving hope to hundreds of thousands worldwide who hope to one day walk, run, and move again.

7Reversing The Aging Process

4- antiaging
Following in the footsteps of their contemporaries in the skin care and bogus superfood industries, a group of scientists have discovered a chemical in the blood of young people that could have a significant impact on the debilitating effects of old age. This wasn’t some one-off, nutjob study, either—three separate groups all came to the same conclusions in experiments with mice. In the research, transfusions of young blood reversed age-related deterioration of memory, learning, brain function, muscle strength, and stamina. Maybe Elizabeth Bathory wasn’t so crazy after all.
Two of the groups even claimed to have identified the single chemical which was responsible for this age-reversing effect. Since the studies were done on mice, it still remains to be seen whether it will also work for people, but the researches are confident that it could. Clinical trials are expected to begin in a few years, potentially paving the way for a genuine anti-aging injection.

6Next-Gen Medication Monitoring

5- monitoring
No matter how far we come as a people, the incredible forgetfulness and laziness of humanity will always prevail. Medication is an extremely important part of many people’s health and forgetting to take it can be dangerous, even deadly. In a development which some will see as incredible and others will see as a frightening step too far, an electronic system which will monitor your medication is now available. Tiny sensors and a skin patch will keep tabs on you, making sure you never miss another pill.
If constant monitoring isn’t your style, they have more advantages. The system can also track the body’s response to said medication, giving you and your physician details on how your body is reacting, so if anything goes wrong you’ll be able to rectify it immediately.

5Giving A Bit of Heart

6- heart
The heart and its health are key to a long, rich life. The biggest cause of death in the United States isn’t AIDS or any kind of cancer, it’s heart disease. Heart disease kills approximately one million Americans each year, equating to about one person passing away every 33 seconds. It is also a huge killer across the rest of the world. It’s the number one cause of death in Australia, claiming a life every 12 minutes, as well as in the UK, where it is responsible for a quarter of the deaths each year.
However, scientists recently managed to transplant a genetically modified pig heart into a baboon and have it function perfectly for over a year. This research gives the medical world hope that one day animals will be able to provide an endless supply of animal hearts (and other organs) to transplant into humans, greatly increasing life expectancy.

4Reducing Disabilities Caused By Stroke

7- stroke
Strokes are terrifying and often deadly. In cases where they don’t kill, strokes can leave the afflicted unable to perform basic tasks, greatly impacting their quality of life. Independence and autonomy are almost completely taken away, and sufferers are unable to control their body as they once could. Previously, there were very few treatment options for these people. But now, scientists have used a revolutionary new procedure to treat these horrific disabilities, giving hope to all of those affected—not to mention their friends and families.
By injecting stem cells into the brains of patients, researchers have managed to restore the ability to move their limbs and perform tasks that were previously impossible. The people involved see this as a very encouraging sign for stroke victims, who number close to a million per year in the US alone.

3Printing New Hearts

8- printed heart
We’ve already gone over the monumental impact that heart disease has on the lives of humanity, as well as the importance of organ transplants to keep people alive. Well, with the increasingly innovative advent of 3–D printing, there are some in the field who believe that within only 10 years they’ll be able to print an entire “bioficial” heart. A group at the University of Louisiana has already taken huge steps toward fulfilling this prediction.
By utilizing fat cells and collagen, the team has managed to print working components of the human heart. They use the analogy of an airplane—a complex machine assembled in parts before being combined—to explain why they can’t just print an entire heart and why it instead must be done part by part. But with the ability to print the parts, 10 years seems a very reasonable time frame to expect the sum of these parts to be complete.

2Bionic Arms

9- bionic
Ever since the first cyborgs appeared in science fiction, scientists have been searching for a way to create bionic body parts. Doing so would immeasurably improve the lives of people with amputated limbs, and every bit of research gets us closer to understanding the intricate communication system between our brains and our muscles. And it looks like that all that effort is finally coming to fruition. The brain impulse-controlled prosthetic dubbed the DEKA arm is no ordinary attachment—it’s a genuine super gadget.
Invented by the same man who invented the Segway, the arm can perform such fine, delicate tasks as zipping up a coat, holding an egg without busting it, or unlocking a door using a key—tasks that even people with fully intact arms seem to struggle with sometimes. The bionic arm is also very adaptable, making it an option for people who were amputated at the shoulder, at the mid-lower arm, or the mid-upper arm. Unfortunately, those amputated at the hand or wrist won’t have the Skywalker arm available to them, at least for now.

1Suspended Animation

10- cryogenic
This one is so stereo typically sci-fi that the researchers involved don’t like to call it suspended animation. One of the leading surgeons at the hospital where it’s being developed prefers to call it “emergency preservation and resuscitation,” even though he admits that they are suspending life. Basically, the patient’s blood is replaced by a very cold saline solution which creates a kind of induced hypothermia, slowing all cellular activity to a near halt. In other words, it’s like flipping the slow-motion switch on the shutdown of the body’s vital systems, giving surgeons more time to fix the problem. According to the man who invented the technique, Peter Rhee, the patients aren’t necessarily alive during the procedure, but they’re not dead either.
In 2000, Rhee demonstrated this technique on pigs and it worked. The pigs suffered massive hemorrhages before they were suspended, then they were treated and “brought back to life.” In most cases, their hearts started again on their own with no loss of cognitive or physical function. Now, Rhee and his team just have to wait for the right human candidate. “After we did those experiments, the definition of dead changed,” says Rhee.


Sunday, 8 June 2014

Researchers created highly complex detailed 3D model of an Neural Synapse ( Video)

A team of researchers in Germany has created a very highly detailed 3D computer model of an individual rat synapse depicting the distribution of approximately 30,000 proteins involved in the process of sending a message from one neuron to another. The below video has cover detail view of the process that take place during information transfer at Synapse

Our brains are full of trillions of synapses, each with the capability of converting an electrical signal into a chemical one and back again.

"That's Really incredible"

In their paper published in the journal "Science" the team describes how they combined several imaging techniques to create the model, and what it is able to display.

In simple terms, Neuron transmit messages between one another via synapses—parts of neurons dedicated to converting electrical signals to  and vice versa. 

Synapses are miniscule – nerve terminals are about one thousandth of a millimetre in diameter, and the space between them (cleft) and the membrane they contact a mere 20-40 millionths of a millimetre wide – and are densely packed in the grey matter of the brain tissue, making them notoriously difficult to study. 

Inside the nerve terminal, neurotransmitter molecules are stored in tiny spheres called synaptic vesicles, which are "docked" in an "active zone" (depicted as red color in the video) just beneath the cell membrane. When a nervous impulse arrives at the terminal, it causes a few of the vesicles to fuse with the membrane and release their contents. Later on, the spent vesicles are recycled – they are pulled back out of the membrane, re-filled with neurotransmitter molecules, and eventually re-used.

At any given terminal, vesicle fusion can occur hundreds of times per second, as trains of impulses arrive one after the other. The whole process of vesicle docking, fusion and recycling is therefore tightly regulated, to ensure that there is a ready supply of vesicles that can fuse in quick succession and maintain the rapid bursts of neuronal activity.

“Our model shows that the proteins involved in neurotransmitter release can be enormously abundant, with up to 27,000 copies per synapse,” says Silvio Rizzoli, senior author of the study, “whereas proteins involved in recycling are present in only 1,000-4,000 copies.” The high number of vesicle-release proteins isn’t entirely surprising, because nerve terminals are thought to contain hundreds of vesicles docked at release sites."

Below Image show various protein that are depicted in the video i.e at the terminal end of the neuron in enlarged & distinct form 

For instance, that green guy, parvalbumin,  in certain neurons that protein seems to trigger high-frequency brain waves that have been linked to cognition. And that red SNAP-25 has been linked to ADHD, and the yellow VDAC has been proposed as a good target for chemotherapy drugs.

To create the model, the Researchers isolated rat brain  and used mass spectrometry, electron microscopy, super-resolution fluorescence microscopy and antibody staining to get different looks at the sending synapse. 

In so doing they were able to determine the number of 62 different proteins involved in the recycling process and where they belong in the synapse. That allowed them to build a model able to depict how the synapse actually looks during each stage of the process—a feat that will undoubtedly help many other Neuro-scientists as they seek to better understand how the brain is able to do all the things it does & various Brain Disorder

(Video credit: Wilhelm et al. 2014, Science)

 Explore further: Brain noise found to nurture synapses

More information: Composition of isolated synaptic boutons reveals the amounts of vesicle trafficking proteins, Science 30 May 2014: Vol. 344 no. 6187 pp. 1023-1028,DOI: 10.1126/science.1252884
Synaptic vesicle recycling has long served as a model for the general mechanisms of cellular trafficking. We used an integrative approach, combining quantitative immunoblotting and mass spectrometry to determine protein numbers; electron microscopy to measure organelle numbers, sizes, and positions; and super-resolution fluorescence microscopy to localize the proteins. Using these data, we generated a three-dimensional model of an "average" synapse, displaying 300,000 proteins in atomic detail. The copy numbers of proteins involved in the same step of synaptic vesicle recycling correlated closely. In contrast, copy numbers varied over more than three orders of magnitude between steps, from about 150 copies for the endosomal fusion proteins to more than 20,000 for the exocytotic ones.
Source:  1. MedicalXpress
                        2. The Guardian
To Read more : The below link article is really describe in very lucid & awesome manner at Nat-geo

Now THIS Is a Synapse