Monday, November 26, 2012

making heads or tails of phospholipids

Cells are, in some ways, measurable units of life. Life started out as single, functioning, living, cells. In school, they teach you to associate cells with fancy words like “endoplasmic reticulum,” “organelle,” and “Golgi apparatus.” Look past those biology tests from high school, and you can appreciate what a cell is on a deeper level. It is a division from the environment. Outside of the cell is non-living space, and inside of the cell is life. The structures that are ticking within the cell must be housed, separate from the watery dead-space around them. That housing must also provide a means of transport for waste and nutrients to leave and enter the cell, as we know a living system is not a closed system. How does the membrane of a cell work?
Figure 1: A single phospholipid

The membrane of a cell is made up of a phospholipid bilayer. When you break those terms down, you can see it has something to do with phosphorous, lipids, and two layers. Phospholipids are two-part molecules- on one end, a phosphate group- called the head; on the other, two dangly chains of fatty acids- the tail (Fig. 1).

The phosphate head is polar, while the fat chains are non-polar. Polar simply means that the charges within the molecules are more clumped than evenly distributed. Polar molecules are attracted to other polar molecules, like, oh say, water. As a result, the phosphate heads love to snuggle up next to water, and always try to acclimate so that they are in contact with it. As for those fat chains, well, they’re lipids. And we all know that lipids (oils, fats, wax) repel water. Slap some fancy terminology in there, and we have a molecule with one hydrophilic (water-loving) end and one hydrophobic (water-fearing) end.

Figure 2: Phospholipid bilayer that forms a cell membrane
The end result of all this is that phospholipids tend to form sheets, where the hydrophobic fatty acids are sandwiched in between the protective phosphate heads, which are exposed to the aqueous environments inside and outside of the cell. These sheets form the shell of a sphere, and are the cell membrane (Fig. 2).

Now, let’s apply this setup to reality. The phospholipids are not cemented in place, and in fact shuffle amongst each other like tightly-packed floating ducks in a bath tub. This non-static membrane system is described by the fluid mosaic model.  That basically says that cell membranes are fluid (non-static) and mosaic in nature (made up of sub-units). Ah lah, a membrane that is made up of subunits that float and shift to form an ever-changing cell surface. 

I like this cell membrane business because it shows how a bunch of non-living molecules like phosphates and fatty acids can work together to form a system that is living. Because of the fluid mosaic model and it’s important duty of dividing non-life from life, the spectrum of “living” spans from an itty bitty amoeba to a T-rex. As complex as we are as vertebrate organisms, it’s important to remember that we are complexities made up of even more complexities. Complexities like phospholipids, that are flashes of our humble beginnings as single cells- a collection of working parts, housed together.

Monday, November 12, 2012

big gurl hongry

Here in Alaska, the temperatures have dropped a good bit recently. We went from having highs in the 60’s to highs in the 20’s. Considering I’ve only ever lived in Texas, Louisiana, and Alabama and used to shiver at 60°, I’d say I’ve adapted very well. I have noticed an unexpected side effect however: increased grocery bill. I mean, like double. But what’s an endotherm to do?

I’m sure you’ve heard the terms “warm-blooded” and “cold-blooded.” Those are silly. Let’s use “endotherm” and “ectotherm.”  They describe an animal’s strategy to temperature regulation. You see, all animals have an optimal temperature at which their metabolic processes occur most efficiently. So life has developed ectothermy and endothermy as ways to maximize the bang for your buck. Or, energy for your food, as it were.

And herein lies a common misconception. Heat is not the end-goal of metabolism; you do not eat food for the purpose of heating your body. You- and all animals- eat food to power your systems, like the muscle fibers that contract to make your heart beat, or the network of brain cells that allow you to form thoughts. True, heat determines the efficiency of these functions, but does not directly power them.

As an endotherm, your body produces heat from the inside. Humans have evolved to produce- and dissipate- enough calories of heat to keep our bodies at a steady 98.6°. Each and every one of your living cells contributes a bit of by-product heat in the midst of its own chemical reactions to maintain this temperature.

Ectothermic animals absorb heat from their environment- not as a means of energy acquisition- but simply as a means of heat acquisition. They also dissipate heat to the environment- think of a snake hiding under leaves trying to escape the hot sun. Here, it is easier to see that heat ≠ energy when it comes to metabolism. It’s all about keeping the body at its optimum temperature- and for ectotherms, that temperature is usually significantly lower than that of endotherms- hence the warm/cold blooded silliness (but, the temperature of the blood of the animal doesn't determine nor describe how it temperature regulates- ectothermic and endothermic do. They win).

To me, the really interesting difference between endothermy and ectothermy is how they keep temperatures regulated: endothermy by physiology, ectothermy by behavior. Endotherms’ (mammals and birds) steady metabolic reactions take care of the temperature regulation for them. Ectotherms (reptiles, amphibians, fish, etc.) must actively scuttle between shade and sunny spots to either absorb heat or dissipate it, always trying for that sweet spot.
Hot breath from a dinosaur? Could it be?

You know that scene in Jurassic Park where the brother and sister are hiding in the kitchen and the velociraptor peers in through the kitchen window and fogs it up with its hot breath? Well, seeing as we know reptiles are ectotherms- what do you think of that? Have we caught good ole Spielberg in a blunder?

Of course we haven’t; he’s Steven Spielberg. Once an exothermic species reaches a certain size, heat from metabolism is actually unable to escape from the large body. The density and size of the body keeps internal heat from dissipating to the environment, in effect, making the animal endothermic. This is called gigantothermy- and all large dinosaurs are thought to have been gigantotherms. So indeed, a velociraptor would probably fog the window up with its breath before it ate your ass.

Now, I must go consume the family-sized portion of red beans and rice I made for supper. It’s frickin cold here, folks. Girl’s gotta supply her chemical pathways with carbohydrates and protein so they can release heat to keep her little body warm. Don’t judge.

Thursday, November 8, 2012

a delicious anomoly

Somebody's lame (but oh-so-comfy) shoes and socks

What is your reproductive strategy? Are you the jerk with the popped collar who hits on every girl ever, knowing that with an increased sample size comes increased odds of taking one home? Maybe you’re the sassy lady who dresses to the nines to increase visibility of your secondary sexual characteristics (sexual traits other than the obvious one- like boobs). Maybe you have good intentions to be attractive but find yourself wearing “active casual shoes” with striped socks and high-water jeans to work and wonder what happened to your self respect.

Well, let me just go ahead and answer the question for you. You, PUNY HUMAN, have an iteroparous reproductive strategy.

Iteroparity and semelparity are the two main approaches life can take to reproduction. Semelparous organisms are usually short-lived and “put all their eggs in one basket,” if you will. They pool all their bodily resources into a single reproductive event and then die. Think about those clouds of gnats that buzz around in your yard during the summer. Those little gnats are just a few days old and are already having a giant orgy. After their thousands of eggs are fertilized and laid, the bugs’ tiny bodies are so exhausted and depleted that they die. Then just days later, their offspring emerge and the cycle starts again. This is semelparity.

Iteroparity (latin for “to beget repetitively”) is characterized by multiple reproductive events before death- ones that usually occur over a much longer time span. Almost all vertebrates are iterparous and invest only part of their physical resources towards gravidity, allowing them to live past each reproductive event and have future ones. Subsequently, iteroparous organisms have longer lifespans and experience more growth.

Of course, each strategy has its pros and cons. Semelparous events are usually so large that a single gnat will have more offspring in a single event than you, as an iterparious critter, ever will. Iterparous organisms generally live longer, experience more parental care, and grow larger; therefore they have increased fitness and odds of surviving the elements (gnat vs. human in high winds or something of the like).

I’ve been living in Alaska for a few months now and have become well acquainted with one of the foremost exceptions to the semelparity/iteroparity trends. The Pacific Salmon is a relatively large vertebrate with a fascinating reproductive cycle. First off, a little salmonlet hatches in a freshwater stream. The newborns hang around in their stream anywhere from a few months to a few years, depending on the species. During this time, 90% of them will die. When they have grown into little silver fishies, they swim down the streams and into the salty ocean, where they will spend up to five years swimming around and eating. During this time, they grow in size and sequester the nutrients that the ocean has to offer. After five or so years, it is time to do the hanky panky.

These incredible fish find their way back to the same spot on the shore from which they emerged as little tiny salmon years ago, with their destination being the original stream in which they were hatched. There, females lay eggs and males fertilize them and are responsible for defending the nests. Their bodies, ravaged from the long journey from the ocean and reproduction are physiologically spent. At this point, the fish begin to die.

When this sexy journey begins, the physiology of the fish changes into reproductive mode. This means they completely quit eating, and their bodies begin to consume reserves and tissue for energy. Some species undergo a color change- males becoming bright red to attract the lay-des, and their mouths changing so dramatically as to become hooked with a ferocious set of teeth. Aside from their bodies being energetically depleted, this new morphology is completely unsuitable for life in back the ocean. Any way you slice it, it is the end of the road for these fish.

Top: Sockeye salmon before reproductive journey
Bottom: Sockeye salmon during reproductive jounrey
And there you have it- a single reproductive event before death. Semelparity. But in a vertebrate that devotes five years and hundreds of miles to becoming a 4 pound hunk of impressive fish! It is an anomaly. But it is a successful enough strategy to cause the yearly Pacific Salmon runs to be stable, repetitive, and critical cornerstones of coastal ecosystems of the great Northwest.

It seems as though the odds are stacked against these guys. They must overcome so many treacherous obstacles- not being eaten as an egg and surviving larval-hood, dodging the hungry predators of their natal streams, enduring 5 years in the perilous ocean, and then making the arduous journey back (without being caught by a bear or fly fisherman). But nonetheless, it works. Millions of years of natural selection and random chance have whittled what we see as statistically unlikely into a highly refined, highly adapted system.

AND, they taste really good. Especially when fresh. And with butter.

Wednesday, November 7, 2012

nature's russian nesting dolls

Geoff Grammer, evolutionary baggage reader and master of science geekery, requested I write a little something up about reoccurring patterns in nature, and more specifically, fractals. But the two topics are so interesting that I think we should cover just one per post. Fractals, you’re up.

Fractals are physical phenomena where patterns occur infinitesimally within themselves. You could say they are the Russian nesting dolls of natural design. The same design occurs over and over within itself; the catch being that it does not lose detail with magnification level. For example, the crystalline structures of snow flakesare just the same when looking at the flake with your naked eye as it is when you put it under a microscope. Ice crystals, lightening bolts, sea shells, fiddleheads, animal coloration patterns, blood vessels, and various vegetables are a few well-known instances of fractal development. You could generalize and say that things that “branch” have a tendency to exhibit fractals. Let’s begin our tour-de-fractals.

Lichtenberg figures are the nifty designs that electricity produces when traveling through an insulator. They show the branching paths that electricity wants to take when it travels. Often times, lightening-strike survivors have Lichtenberg figure burns on their skin. They represent electricity's tendency towards entropy- little fingers desperately stretching in all directions seeking a medium by which to travel.

Man struck by lightening marked by Lichtenberg figure
A full head of Romanesco broccoli

Romanesco broccoli is what we call an approximate fractal, since the pattern does not exactly occur infinitesimally- but pretty darn close. Once it reaches a very tiny size, the pattern ceases. But for some magnification levels, each little bud looks like an entire head of broccoli. And each bud on that bud looks like an entire head of broccoli. And each bud on that bud on that bud... okay I'll stop. Same deal with the fronds of a fern.

Ice crystals are fractal in nature. They are always hexagonal and symmetrical- but no two are exactly the same. When a snow flake lands on you, you can see with your naked eye that it is snow-flakey looking (hexagonal and symmetrical). Take it apart, and you will see that it is really a clump of ice crystals, each of which is snow-flakey. As the frozen water masses fall through different temperatures and humidity, ice crystals form on the ice crystals. It is this stage of formation that creates the details that make each snowflake unique. In the pictures below, you can see the "pieces" of a snowflake and how they come together to make more intricate, larger versions of themselves.


When people see the detail and "perfectness" of such things, they often say "how could that just happen? There's got to be something bigger." And I agree- there is something bigger. It's the definition of "something bigger" that varies from person to person. But really, does that definition matter that much? I think we can all agree on the impressiveness of nature when viewed through a microscope.