When Flip-flopping is good....
When Flip-flopping is good....
Unlike many times in politics, flip-flopping is good for the cell. The integrity of the heterogeneous nature of the membrane bilayer (i.e. the fluid-mosaic model) must be preserved at all times in order for the cell to remain viable; however, the amphipathic nature of the phospholipid membrane poses a challenge when the need for molecules are needed to traverse the membrane from one sheath to the other. It would take eons of time for a moiety with a hydrophilic "head" group to wiggle through the hydrophobic interior and emerge on the other side.
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The cell utilizes three different enzymes to catalyze the diffusion of lipids from one leaflet of the membrane to the other leaflet. These three enzymes--flippase, floppase, and scramblase--can be seen in the figure to the right.
Flippase and floppase couple the energy-releasing hydrolysis of ATP with the otherwise thermodynamically unfavorable movement of lipids. Flippases specifically move phosphotidylethanolamine (PE) and phosphotidylserine (PS) from the outer leaflet to the inner leaflet. One reason that this is important is that the presence of PS on the outer leaflet is a signal of cellular distress normally and results in apoptosis. Floppases move phospholipids from the inner leaflet to the exposed outer leaflet. [I personally remembered the difference with the mnemonic device of FlIppases move the lipids Into the Inside layer whereas FlOppases move the lipids to the Outside layer.] Finally scramblases maintain the equilibrium of the lipids by moving them in either direction.
For the classroom lecture videos pertaining to this topic, see Chapter 11 (Membranes).
As a side note of interest, one group of Biochem students composed their extra credit video on this topic.
Haha First I would just like to say, if we ever become famous because of this post we will put you in our Grammy speech.Secondly, I think this is perhaps one of the coolest topics in Biochemistry. I had no idea there were means of transversing the membrane that quickly. While ATP helps with Flippase and Floppase, scramblase doesn't need the extra energy to keep equilibrium. Again, these methods of keeping the body in equilibrium just astound me. The design needed for the body to function properly just lends to the intelligence of the designer.
ReplyDeleteFlipppase, floppase, and scramblase? They really put some thought into naming these proteins. It is like naming the gluteus maximus the “sit-upon”. I personally love cellular and molecular biology. The cell is like a tiny factory, producing things and moving things around in little packages. Everything is so intricate, even the lipid bilayer is extremely detailed.
ReplyDeleteMariah mentioned intelligent design and that is exactly all I see when I read about this. This would be a great argument to have in Faith Integration. “What came first, the flippase or the floppase according to evolution?” All of the cell’s proteins and organelles need to be at the right place all at the same time for the cell to function properly.
After watching all of these extra credit videos, I think we should start a band haha:D
The actions of flippase, floppase, and scramblase are a fascinating aspect of membrane dynamics. This is a very interesting biological phenomenon that occurs quite rapidly within the phospholipid bilayer. Without the use of flippase, floppase, and scramblase, transitions between the inner and outer leaflets would take days to accomplish. However, with the help of these enzymes, these transitions occur billions of times every second! They also provide some forms of protection for the cell. When phosphotidylserine (PS) is present in biologically relevant amounts in the outer membrane, macrophages are stimulated to induce cellular apoptosis. Flippase prevents apoptotic activity by moving PS from the outer to the inner leaflet. This is crucial for cellular vitality. Do these enzymes have any effect on methylation or sumoylation? Also, what kinds of metabolic problems are caused by increased/unbalanced levels of flippase and floppase? I'd be very interested to find research on this topic and whether or not it affects arachidonic acid production (and subsequent conversion to proinflammatory molecules). Research in this area could be extremely relevant for neurodegenerative disorders, such as Alzheimer's disease and Parkinson's.
ReplyDeleteI enjoyed the drama of the video and the use of the word “translocated”-that really gave it some flare. I'm interested to see more biochem video productions.
I agree with Mariah and Heather, this flipping and flopping is so detailed and orderly that it reflects the brilliant mind of our Creator. I am always fascinated by all the cellular activity that occurs in our bodies and how intricate these system really are. All the minute details of our complex cells and organ systems depend upon one another and they could not exist or function successfully even if just one piece was missing. This irreducible complexity always intrigues me and proves that evolution could not have taken place since these systems needed to be established at the same time in order to work properly. Great video by the way Michael!
ReplyDelete"AND THE GRAMMY GOES TO..." I think 2015 is the year this video will go viral. :D Anyways, this topic was super interesting. Flippase and floppase are also protecting the cell such as keeping out certain receptors that could activate apoptosis within the cell. Scramblase is also interesting because it can do both flippase and floppase's job without ATP, which could replace the other two but doesn't. Another great way of showing God's is an amazing Creator.
ReplyDeleteI think flippase and floppase was a really interesting topic to learn about in biochemistry. Remembering that fl-I-phase moved things to the inner leaflet because it had an "I" in it and fl-o-ppase moved things to the outer leaflet because it had an "o" in it was really helpful for the test! I think that the phenomenon of cells being able to utilize these enzyme to move things from the inner leaflet to the putter leaflet and vice versa is amazing.
ReplyDeleteOh and I will never hear that Beyoncé song the same again thanks to Michael and Mariah :)
This is such an interesting topic. As mankind learns more and more about the molecular interactions of our planet, we are constantly finding immensely complex systems and processes that are clearly highly organized. Even the most "primitive" organisms display immense order, rather than chaos. It is a wonder that there are still those who postulate that this could all arise from chance. To believe that order could come from chaos in a biological sense is purely ludicrous; even now we see everything moving from order to disorder. It reminds me of a quote from the Roman historian Cicero, who claimed that the constant order in the cosmos speaks of a divine intelligence, later going on to call it God.
ReplyDeleteOn an entirely different subject, I often find scientists' humor amusing. Even in the names I find myself chuckling: flippase, floppase, and scramblase. All three terms, in combination, form a decent definition for the word "politician." These three enzymes could also refer to a lazy Saturday: flip-flops and scrambled eggs . . . Okay, yes, that's a bit of a stretch.
When we first discussed this in biochemistry 1, it was definitely my favorite group of enzyme names. They are named for what they do in a sense, but I figure that the scientist who named these enzymes had a sense of humor.
ReplyDeleteDespite their “funny” names, which are actually more memorable than anything, these enzymes have such a valuable role in the cell. As you already mentioned, they maintain equilibrium in the phospholipid bilayer, and this plays a role in regulating apoptosis. In unhealthy cells, this signals for the body to carefully remove the cell. In healthy cells, this signal is not present, keeping the healthy cells alive and the unhealthy cells to a minimum.
Additionally, this phospholipid bilayer equilibrium (scramblase does this specifically) is essential for maintaining proper transport across the cell membrane, so the selectively permeable barrier stays selective. For example, flippase plays a role in the transport of the lipid-soluble vitamin A, which allows it to carry out its role in vision (1). I cannot even begin to imagine all of the roles and functions these silly little enzymes have, but I can guarantee they are numerous!
1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3222080/
I have had the opportunity to cover these enzymes superficially during cell and molec, and I am looking forward to learning more about them during biochem. Each if these seem extremely convenient and beneficial to the cell, allowing it to configure itself to best fit its needs in a given environment. They definitely represent efficiency, which is a common characteristic within the many processes of the body. This is also a representation of just one instance where such detail was taken into consideration during the formation of the body -- so complex and intricate. When David thanked the Lord for making us complex, he really was not playing!
ReplyDeleteFirst, I am really sad that we will no longer be making extra credit music video because that video with Mariah and Michael had me feeling some type of way.
ReplyDeleteSecond, I remember learning about flippases, floppases, and scrambles in cell and molecular biology and the whole process fascinated me. Intricate details like these always leave me in awe of our Creator. I look forward to learning more about processes like these in my future studies.
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ReplyDeleteI find this piece quite interesting and informative as it helped clarify one aspect of transbilayer lipid motion that has remained less clear to me in the past, i.e. the difference between flip-flop, or transbilayer motion, and lipid scrambling in bilayers. The difference is both conceptual and mechanistic. Conceptually, transbilayer lipid motion refers to the diffusion of single molecules, while lipid scrambling involves necessarily a population of lipid molecules.
ReplyDeleteMechanistically, a single molecule may diffuse to the opposite bilayer spontaneously, because of thermal motion. This may be a relatively frequent event, as with diacylglycerol, or a rare one, as with phospholipids.
Transmembrane motion of a single lipid molecule may be enzyme-catalyzed. Lipid scrambling however is somewhat of a precipitous event, which requires the building-up of a certain amount of energy to occur.
Ill be honest, when I first read the title of this blog post I assumed that it was going to be discussing the benefit of wearing flip flops. I thought that it was going to discuss how they might improve your posture or blood flow. To my surprise it was discussing the cell and the movement of particles in to and out of the phospholipid bilayer. The most fascinating portion of this article is the fact that without these mechanisms the cell would literally explode because of the markers on the surface. However, because of their ability to move substances across the membrane, the markers that would typically induce apoptosis are moved within the cell and not detected. It never ceases to amaze me the intricacies of the cell, all the way down to pathways in the membrane that allow movement into and out of.
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