Membranes: The amazing phospholipids

Phospholipids are amazing molecules.  Place them in a watery environment and they self associate into a spherical ball and make membranes. Membranes made of phospholipids  are fluid structures which are sticky  to themselves, so that they make a barrier which typically defines, in part, the outer boundry of a cell and helps hold things in the cell, yet it remains a fluid.  Life would not work without these fluid barriers.  Who would of thought of that?  What a perfect idea for a membrane, a fluid barrier!  We would be very stiff creations indeed if our membranes were not made out of these soapy molecules. 

So we see in membranes the same principle we discussed regarding the idea that all macro-organisms are made of smaller pieces or entities  we call cells, i.e.,  membranes are made of lots of smaller parts (phospholipids). Relatedly, we also see modularity, i.e., the parts are somewhat interchangeable and  pliable.  And this modularity and pliability allows for a lot of things to be stuck in membranes.

But, if phospholipids are sticky (self associate because of hydrophobicity) why don't all cells near one another, stick together and form one big clump....for instance when we bump into each other  why don't we form one big glumpy smear of phospholipid humanity on the earth.   How do pond organisms swim around with these sticky membranes and not get stuck or fuse together?  In fact this is how some viruses work, they invade cells by fusing their outer lipid membrane envelope  with the cell membrane, and they take advantage of this sticky/hydrophobic effect.  Works like a charm.  The virus fuses to the membrane and releases its contents ( at least some viruses work this way, not all do).

So my questions for this blog are;

1 Why and how do phospholipids self associate?
2 What prevents membranes from fusing with all other nearby membranes?
3 Could the self assembly of phospholipids be a posssible explanation for how the first cell membranes evolved?
4 When phospholipids form membranes in a water based environment, do they make membranes  similar to the cell membranes we find in cells today?

globules, cemetery chambers, and noxious seaweed, what is a cell?

Biologist Henri Milne-Edwards and his contemporaries in the 1800s referred to cells as globules.  Many rejected the term “cell” that Robert Hooke used to describe the dead dried plant cells he looked at under the microscope.  He was considered a botanist when he made this declaration, and therefore most likely the animal cell biologists were not sold on the term "cell" being used to describe animal tissues. A cell was a room and the term was used to describe the small above ground cemetery crypts at that time…..so it was not necessarily a term of endearment.  It also implied that  cells were empty, and many early biologists believed they were filled with some kind of “protoplasm.”

After  the term cell became widely accepted many biologists claimed, based on their observations, that all creatures were made of these small compartments called cells.  Additional cell theories implied that cells were derived from cells and their arrangement determined in part the morphology of living things.  Is this true? Is every living creature with the exception of viruses and prions made  of cells?  Maybe not.  There is an asexually reproducing seaweed called Caulerpa taxifolia. It grows so well that it crowds out all other aquatic plants on the ocean floor.  However it appears to be a giant multinucleate single cell. ( so much for my idea that unicellular life does not exist).  What is bizarre is that this single celled creature can form stem-like, root-like and leave-like shapes as a single cell.

In class we will try to define what a cell is, but here is my question for the blog.  From a teleological  perspective, what is the advantage of multicellularity, what is the advantage of making most every macro-creature out of really really small cells?

A tale of two nucleobionts: Holospora obtusa and Holospora undulata

I got really intrigued about the paramecium endonuclear symbionts.  So this will be the subject of our first research challenge in class.  I got really intrigued because these bacteria  (Holospora)  don't just happen to end up in the macro or micronucleus, they possess specific mechanisms to discriminate and enter these nuclei and they also bind to chromatin.  They even dramatically change their morphology to perform this feat.  This is fascinating because I thought that perhaps viruses were the only creatures which possess designs to invade nuclei.  So what could these nucleobionts be doing?  According to a speculative theory developed by my colleague Todd Wood these creatures might be doing something very significant.  But you will have to find his paper to find out more about this (AGEing).  I cannot give away anymore hints now, but stayed tuned to this blog for more hints.

Bioplasten and Henrietta Lacks

In 1890 german biologist Richard Altmann observed mitochondria in cells and named them the “Bioplasten.”  Mitochondria are everyone’s favorite cell organelle.  Unfortunately we never have enough time in class to discuss thoroughly these fascinating cells.  Wait a minute, ….these are cells?  Well I am going to go out on a limb and say that these are obligate endocytobiotic  bacteria.  However this phenomena is not that unusual because more and more endocytobiotic bacteria are being described. 

So I thought we would use this blog to collect information about these interesting creatures.  Lets start with their abundance.  If these are intracellular bacteria then they are perhaps the most numerous bacteria on earth with estimates of  10²⁶.  This may represent a  good portion of all bacteria on earth.  In fact we could estimate that the mitochondria from one person, Henrietta Lacks,  may be one of the most abundant bacteria on earth, with estimates of 10¹⁷.  (Pallen, Trends in Microbiology, 2011)

Who was Henrietta Lacks?

From WikiPedia:

Henrietta Lacks (August 18, 1920 – October 4, 1951) was an African American woman who was the unwitting source of cells from her cancerous tumor, which were cultured by George Otto Gey to create an immortal cell line for medical research. This is now known as the HeLa cell line.

The story of Henrietta Lacks is a fascinating one and was published in a book last year.  Many many researchers have grown her cells and used them in research, thus her mitochondria are very abundant on earth;  some suspended in a timeless state in freezers all over the world.

One scientist suggests that we name the mitochondrian bacteria as Mitochondrian lacksi.

So here is the first set of questions about mitochondria.

1 What are the current theories regarding the origin of mitochondria?

2 What is the structure of the mitochondrial membrane?

3 Mitochondria provide several functions in cells, what are they?

4 What bacteria do mitochondria resemble the most?

5 Do all cells have mitochondria?

6 Why do mitochondria have DNA? 

social networking bacteria, cellulosaic structures, and greenbeard genes

I was surprised this past week when after writing the “unicellular” blog to find a paper titled “social interactions in a unicellular world. “ Fascinating.  The authors seem to struggle in a way with the concept, because it appears that many “social” interactions among microbes appear to be beneficial and not necessarily competitive.  They even mentioned that Darwin struggled with the concept that living creatures can benefit another creature, without receiving a benefit in return.

One example they used was the cooperation among “unicellular”  DIctyostelium discoideum an amoeba which assembles multicellular structures via cooperation.  The structure they form is a fruiting body which culminates in a spore forming tip. So in the soil this microbe can be very happy living as a disorganized mob, but when it comes time to start a colony somewhere in the beyond, they get organized and form a fruiting body. The authors note that when they get together to organize a multicellular fruiting body, 20% of the cells lyse (kill themselves) to form a cellulosaic structure ( I like that word cellulosaic for some reason).  The cellulosaic structure is apparently a dead stalk which supports the fruiting body.  So how do we explain this apparent act of selfless behavior in this slime mold?  Can slime molds really exhibit  selfless behavior?  Do we really care?  I find it fascinating that biologists are interested in this.  It appears to me that the ideas which embody evolution drive them to see these ideas of selfless or selfish behavior in living organism.  Why are biologists interested in these concepts?

The authors also discuss the discovery of genes which are thought to be responsible for co-operation; these genes are called "greenbeard genes."  They mention the discovery  of the greenbeard gene Flo-1 in yeast which codes for a protein which makes yeast work together.

Questions:

1 Find out more about DIctyostelium discoideum.  What role does it play in nature? 

2 What advantages are there to living as an organism which can experience both a closely nit multicellular stage and a loosely nit unicellular-like stage? i.e.  what could organisms  accomplish living in this way?

3 Why are biologists interested in the concepts of selfless behavior or selfish behavior as demonstrated at the cellular level?

4 How does the Flo-1 gene promote yeast communities?

Unicellular life does not exist…..or how to live in a macronucleus!

In my first blog I mentioned that I do not believe that unicellular life exists.  Well that is one of those statements that is subject to a lot of interpretation.  Let me explain.  First, single cells do exist, and some appear to lead independent lives, for instance creatures we call microbes like bacteria or paramecium.   So what then does the term unicellular mean? It is a term used to distinguish free living independent cells from those which live in tissues, or the multicellular condition.  Cells which live in this multicellular state live in close contact with other cells.  But I would argue that all cells live in close contact with other cells.

So how likely is it that you are going to find microbes living alone, in a true unicellular state.  Take a pinch of soil; you will find thousands of creatures living there, many interacting with each other.  Consider an amoeba or paramecium or other pond organism.  How many of these creatures do you know who live in their own private pond!  How many signs do you see posted around ponds or puddles that say…”get your own pond you scum-bag”, signed Peter Paramecium.

But really, lets get down to the nitty gritty, could you not isolate a single bacterium and give it a nice petri dish with lots of nutrients in the corner of your room? But wait a minute, about every 30 minutes, this guy will generate his own friends, within a few hours a full grown microbial party will be in force. I am wondering just how easy it is to isolate a single living bacterium.  How would you do it?  I challenge the microbiology students every year and tell them I will give them an A in the lab course if they can isolate and stain a single bacterium on a single microscope slide.  What would you have to do to accomplish this task? ( I might give some credit just for a protocol for how you would do this).

Lets face it.  Life is multicellular at every level.  But wait.  What about those pond organisms? they seem independent.  More and more studies are showing that most of these critters carry bacteria around.  There is even one strain that lives with a bacterium in its macronucleus.  Why in the world would you want to carry a bacterium in your macronucleus?   I have asked a lot of people, and no one has given me a satisfactory answer.  I have gotten some weird looks ….as if the person is thinking, what the heck is a macronucleus and why do I care?  

A lot of single celled pond organisms eat bacteria or algae. But there is one pond organism Paramecium bursarium which eats algae and bacteria but also knows how to ingest some algae and not digest them; instead it keeps them as energy harvesting slaves! Whoa!  How does it know to eat some critters and digest them and eat other critters an not digest them?  Remember this is a small creature with no brain and no nervous system.

So to review, my three main questions for the blog today are:

1 What is a macronucleus and why would you want to live there? cheap rent? cozy?

2 How would you isolate a single bacterial cell on a microscope slide?

3 How can Paramecium eat algae but not digest it?

4 What is significant about the concept that all living creatures are multicellular?

Next blog….more weird cells..

cellular angst

This is my first blog in this series.  This blog is primarily intended for my cell biology and microbiology students at The Master's College.  My background is in cellular immunology/microbiology and I have been teaching at the undergraduate level for 20 years.  However I am by no means an expert in this field....there is just too much to know and a lot of things yet to discover about these smallest pieces of life.

I intend on blogging at least once a week to share insights from our classroom lectures and discussions. 

Please feel free to contact me at jfrancis@masters.edu.

So what are cells and what is the advantage to having every living thing made of cells?  How do we define what a cell is anyway?  The traditional way to define them is to distinguish them from viruses.  Viruses are typically smaller than cells and do not have a lot of things which cells have.   Recently some very large viruses with membranes and cellular biochemistry have been discovered.  One of these is the Mimi virus... a pretty big virus. It is bigger than some bacteria.  It has metablic pathways to make amino acids and nucleotides.  So is this is virus or a cell? http://www.microbiologybytes.com/virology/Mimivirus.html



Then there is the issue of unicellular life.  I have a sneaky suspicion that unicellular life does not really exist.  Curiosity peaked.  Stay tuned.

Students please feel free to answer my questions with a reply.