Wednesday, December 31, 2008

Stem cells

It’s New Year’s eve in a few hours. When I thought about which cell reminds me of New Year, stem cells immediately came to mind. Stem cells remind me of new beginnings, new possibilities, new hope. New Year is always exciting for me, so are stem cells.

Of course there are two kinds of stem cells: embryonic and adult. Embryonic stem cells have the potential to be anything, even a whole new organism (especially for some animals or plants). Adult stem cells on the other hand can only give rise to a specific cell line. So we have stem cells for skin or for intestine or for blood.

Using embryonic stem cells for research is of course controversial because of the source and the way the cells are prepared. Technical and moral issues are involved here. Use of adult stem cells is not as controversial and this is where most of researches are now focused.

Actually use of adult stem cells has been going on for a long period of time. Bone marrow transplant for example uses the stem cells in the bone marrow as source of new cells to replace damaged or abnormal blood cells of the recipient.

More recently, there is a buzz about stem cell therapy. Some have advertised stem cell therapy as a kind of rejuvenating intervention for people who want to stay young and look young.  Others have used stem cell therapy for curing certain illnesses especially cancer. I just hope that those who undergo this kind of therapy will first weigh all the possible consequences of this kind of therapy. As I already mentioned at the start, there are two kinds of stem cells - embryonic and adult with their corresponding characteristics. This kind of therapy must only be done by highly qualified physicians. Some unscrupulous people are also using stem cells that are not human. So we have to be very careful about this new therapy.

Tuesday, December 30, 2008

Major biomolecules of cells

Every cell needs 4 major molecules, little bits of odds and ends, and plenty of water. These major biomolecules are: carbohydrates, lipids, proteins and nucleic acids.

Carbohydrates are used mainly as energy source for cells. However, some carbohydrates are also used as structural components. Cell walls for example consist of carbohydrates. Some components of the cell membrane as well as the extracellular matrix are also carbohydrates.

Lipids on the other hand make up the basic component of the cell membrane. They are also the major backbone of steroid hormones as well as the main form of stored energy.

Proteins meanwhile have both structural as well as functional roles in the cell. Structurally, they are major components of the cell membrane. Functionally, they act as enzymes, hormones, carrier molecules, antibodies, and several other roles.

Nucleic acids are of course the carriers of hereditary information of cells.

Monday, December 29, 2008

cell design 101.6, fat cell

Do you know that fat and thin people have actually the same number of fat cells? Yes, we have. The only difference is in the amount of fat stored inside the cells. So if somebody is fat, their fat cells appear bigger because of the greater amount of fat stored inside.

We also have two kinds of fat cells: those that store fat as a single large fat droplet and those that store fat as several small droplets. The first cells are called unilocular fat cells and the latter are called multilocular fat cells. The unilocular cells form what we call as white adipose tissue while the multilocular ones are what forms the brown adipose tissue. We have more white than brown adipose tissue.

Sunday, December 28, 2008

not all bacteria are bad

I always see or hear in advertisements that we should get rid of the bacteria in our surroundings thus we need to use a certain brand of alcohol or some antiseptic. However, this idea is rather misleading. It gives the impression that all bacteria are bad. But such is not the case, there are also good bacteria.

Just think for example of the bacteria that degrade the substances in the soil. If these bacteria are not there then we would have been buried by now in all the garbage that we produce. Or think of the bacteria that help us in digestion of food or help process the undigested material in our large intestine. We will have all kinds of digestive disorders if these bacteria are not there.

We have several other examples of good bacteria like the nitrogen-fixing ones or the oil removing ones. However, I think the above examples are sufficient enough to make us rethink about getting rid of all bacteria.

Saturday, December 27, 2008

spermless development?

I have been sitting here in front of my computer thinking of something to write about cells. Somehow, after writing about the egg cell and the sperm cell, I cannot think of anything else to talk about. Of course there is still so much more to discover about cells. I have not even talked about the energy-generating centers in cells yet – meaning the mitochondria and chloroplasts. However, I don’t feel like starting their stories today. Not just yet anyway. So what cell story should I tell today?

Okay, here’s one – do you know that egg cells can start the first stages of development even without the sperm cells? Yes they can!

The first stage of development after fertilization is what is called as cleavage. This simply involves the rapid cell division of the fertilized egg. Experiments have shown than even a pin-prick can trigger this initial stage. However, after dividing several times, the egg cell will stop dividing and will not proceed to the next stage of development which is called gastrulation.

So later stages of development need the combined information coming from both the egg cell and sperm cell but the initial stage of development does not need the information from the sperm cell. Isn’t this amazing?

Friday, December 26, 2008

sperm cell

source of photo:
Since I talked about the egg cell yesterday, I thought I might as well talk about the sperm cell today.

If you look at the picture, you will notice the big difference between the size of the sperm and the egg. What is shown in the picture is only a small segment of the egg cell. A sperm cell is only about 25 micrometers or less in diameter while the egg cell is about 200 micrometers or even more in some animals.

A sperm cell contains only the nucleus which occupies the "head" part of the sperm, plus several mitochondria in the "neck" part. The rest of the sperm consists of the flagellum.

According to, the average speed of a sperm is "1–4 millimeters per minute".

Thursday, December 25, 2008

egg cell

source of picture:
To me, the egg cell is always a special cell. It is as if it carries all the future of a new organism in itself.

The egg cell is the biggest cell in the body. It can even be seen without the aid of a microscope. It contains so much yolk especially in those animals that develop outside of the female’s body. The sperm cell only contributes its nucleus during fertilization, but the egg cell contributes not only its nucleus but also its cytoplasm and everything in it including the organelles.

During the early stages of development after fertilization, the yolk in the egg cell’s cytoplasm is actually the only source of nutrition for the growing embryo.

By the way, since the mitochondria of a developing embryo only comes from the egg cell, one line of research has tried to follow our supposed to be "Eve" by following the mitochondrial DNA or "mitochondrial Eve" through the ages.

Wednesday, December 24, 2008

taking a break

It's Christmas eve here tonight. I'm taking a break from this blog today.
Have a Merry Christmas!

Tuesday, December 23, 2008

Season's greetings

Instead of writing some cell story, I just want to greet everyone a very Merry Christmas!

Monday, December 22, 2008

why cells are small

Sorry I could not find the table I was talking about last time. However, I found the following notes (which can be converted to a table, but I don't have time, sorry) in my notebook:
In a cell, equilibrium through diffusion is attained within 0.00000456 seconds if the distance from the boundary is 0.1 of a micrometer. If the distance is 1 micrometer, then equilibrium is attained within 0.000456 seconds and if the distance is 10 micrometer, then equilibrium is attained within 0.0456 seconds. If however the distance from the boundary is 1 mm, then equilibrium is attained only after 7.6 minutes while if it is 1 cm, then it would take 12.75 hours for equilibrium to be attained.

If we examine the figures above therefore, it is obvious why cells have to be small, that is, they are in micrometers. A red blood cell for example is about 7 micrometers. Just imagine what will happen if a cell is in centimeters, it would take several hours (half a day, actually!) for substances to move from the cell membrane to the cytoplasm. That is not compatible with life at all! And if the cell is as big as a basketball, can you imagine how long equilibrium by diffusion would take? - months maybe or would it be years? Oh no!

Sunday, December 21, 2008

why are cells small?

Why are cells small indeed? Well, it's really the physical and chemical laws that limit cell size. Substances need to move to and from cells and also within cells. If cells become big, it will take a long time for substances to move from one part of the cell to another and this will not be compatible with life. I have an actual table showing how far substances can move if the distance between the cell membrane and the cytoplasm is in nanometers or in millimeters. However, I cannot find the table right now. I promise I will post it sometime soon. As soon as I find it that is.

Suffice it to say for the moment that one should never expect to find a single cell that is as big as a basketball.

Saturday, December 20, 2008

what can In give you this Christmas

The song “What can I give you this Christmas” keeps ringing in my brain as I think about what story to write about cells today. So what can I give you this Christmas? Well, maybe I can share with you how I got fascinated with cells. It all started when I took up Cytology in the undergrad.

As you know, Cytology is the study of cells. It was the first time the course was offered as an elective so our teacher was so excited about it. Her excitement was contagious such that we the students also got excited at learning more about cells. Even if we only had our compound microscope then, our teacher had so many electron micrographs of various cells and their components. I would pour over these micrographs and marvel at the orderliness of everything in the cell.

Later, when I was in graduate school, I took up Cell Biology and this got me even more interested in cells. Eventually, when I started teaching, I taught Cell and Molecular Biology and I was hooked for good. I would read anything and everything about cells and excitedly shared everything I learned with my students. Now I’m extending this love of cells in this blog.

Friday, December 19, 2008

Cilia and flagella

Some cells have cilia or flagella on their cell surface. What are these structures for? Well, whenever these structures are present one can be sure that there is movement going on.

Cells lining our respiratory tract for example use their cilia to move mucus and trapped particles towards the mouth. Movement is usually towards one direction, so in a sense the cilia act somewhat like escalators that move people or things upwards or downwards.

We are familiar of course with the flagellum of sperm cells. This propels the sperm as it moves along the reproductive tract of females.

Structurally, both cilia and flagella consist of microtubules that are arranged in a specific manner together with associated proteins dynein and kinesin. They only differ in length and number as well as in the kind of movement. Cilia are shorter and more numerous than flagella. Ciliary motion is also more like the power stroke in swimming while flagellar movement is a wavelike motion.

By the way, ciliated unicellular organisms like the Paramecium use their cilia not only for moving about but also for moving food towards their oral groove or "mouth".

Thursday, December 18, 2008

Intermediate filaments

I have talked before about the microtubule and microfilament components of the cytoskeleton. Now let’s turn our attention to the third component, the intermediate filaments.

Intermediate filaments unlike the microtubules and microfilaments are not always present in all cells. When present however, they can indicate the cellular origin of tumors. Why? How?

Well, there is a specific intermediate filament associated with specific cells and tissues. For example: cytokeratin is specific for epithelial tissue, desmin is found only in muscle cells, vimentin is found only in cells derived from mesenchyme, neurofilament is specific for neurons and glial fibrillary acidic protein or GFAP is specific for glial cells except microglia.

By the way, Alzheimer’s is associated with extensive tangles of neurofilament.

Wednesday, December 17, 2008

Complementarity between structure and function, part II – the squamous cell

Have you ever seen a squamous cell? You have? Good, because it is my topic for today. I thought I will take a break from looking for something Christmassy to looking at complementarity between structure and function once again. As I mentioned before, this complementarity is a recurring theme in biology so I’m sure we will not ran out of examples. So today is the turn of squamous cells.

Squamous cell is a term given to describe a cell that is thin and flat when viewed from the side and is tile-like (the old-style, honeycomb-like tile) when viewed from the top. This cell never occurs alone but is found in the body as a single layer of cells or as multiple layers of cells.

If occurring as only a single layer of cells, their main function is for rapid exchange of materials. Thus they can be found lining the alveolar sacs of our lungs and the inner lining of blood vessels. When arranged as multiple layers of cells however, they assume a protective function. In this case, we can therefore expect to find them on the surface of our skin, the exposed portions of our digestive tubes, the exposed portions of our reproductive system and any other exposed parts of our body.

Since these layers of cells are always exposed to all kinds of wear and tear, they are thus prone to infections and even cancer. I’m sure you have heard of squamous cell carcinoma or cancer of squamous cells.

Tuesday, December 16, 2008

the megakaryocyte story (a gift of self)

I got this picture from: Thank you. Sorry, no time to ask permission.

What else can cells tell me about Christmas?

Yah, what else? Hmm...this is getting harder everyday. In trying to think of which cell story reminds me about Christmas, I form a mental picture of cells and their parts. There is a kind of slide show in my mind and I let it ran, then pause for a while, turn around the cell and proceed once more. Now my slide show stopped on... the megakaryocyte.

The megakaryocyte, what kind of cell is it? Well, if you examine the name, “mega” means big and “karyocyte” means a mature cell. So it’s a big, mature cell. Just how big? – about 10 – 15 times bigger than our red blood cells. That’s big! It’s only found in the bone marrow. So if you examine a bone marrow smear under the microscope, it’s the biggest cell around and you can’t miss it, as shown in the picture.

So, what is so special about megakaryocytes and what is Christmassy about it?
Well, megakaryocytes give rise to our platelets by fragmentation of its cytoplasm. Yes, you read that right... its cytoplasm fragments to give rise to platelets, around 2000 – 5000 of them. Imagine that, being fragmented to give rise to little buggers! That is true giving of self, isn’t it?

What remains of the megakaryocyte after this is simply the nucleus with a teeny weeny bit of cell membrane. This then leaves the bone marrow and migrates to the lungs where it is “eaten up” by lung macrophages. I don’t know why it goes to the lungs to die (macrophages are everywhere anyway), but that is how the megakaryocyte story ends.

Monday, December 15, 2008

Glial cells

Very few people have heard about glial cells. They do not have the same “superstar” status as the nerve cells or neurons. However, glial cells are just as important as neurons in the function of the nervous system. In fact they outnumber the neurons by a ratio of about 10 (glial cells) to 1 (neuron), maybe even more in some parts of the brain.

So what are glial cells? Well, they are known as the supporting cells of the nervous system. They provide support to both the cell body and the cell processes of the nerve cells. However, they do much more than just provide support: they also provide nutrition, form myelin sheath, maintain homeostasis, insulate neurons, and modulate nerve impulse transmission. They also guide neurons in making the correct connections during development. Some glial cells even act as scavengers and clean-up crew because they destroy pathogens and remove dead neurons.

There are specialized glial cells for each of those functions. For example, there is a different glial cell that forms the myelin sheath. A different glial cell also provides nutrition and another acts as scavenger. So they come in different names like microglia, oligodendroglia, astroglia, ependyma, and Schwann cell.

Glia is actually Greek for “glue.” So glial cells kind of “glue” together the components of our nervous system.

Sunday, December 14, 2008

cells and the spirit of Christmas

I am in a Christmassy (is there such a word?) mood today. I sat for a while thinking if there is anything in the cell or about cells that is somehow related to Christmas.

Well, what predominates during Christmas is the spirit of giving. So, is such a spirit present at all in cells? I think I can answer “ yes” to that. I think there is so much giving in cells actually. Just take a look at our soldier cells for example – the macrophages and some of the white blood cells, they are called “soldiers of the body” because they do defend us. In the process of defense however, they must "give up their lives".

In my Nov 26 post, “display, tell, and kiss” I mentioned that macrophages act as APCs or antigen presenting cells. Well, these cells once they “kiss” with the T lymphocytes actually die because the T cells (specifically the killer T cells) punch holes in these APCs and literally these cells “spill their blood”. So these cells die in the process but they have done their duty – that of informing the T cells that there is an infectious agent or an abnormal molecule in the body. Imagine that, that is a true spirit of giving, “giving up one’s life” in the line of duty.
If that does not show the spirit of Christmas, I don’t know what does.

Have a happy Christmas!

Saturday, December 13, 2008

Upstream ...downstream

We usually encounter the terms “upstream” and “downstream” when researchers talk about cell processes. What do they mean by that?

Well, we are familiar with the flow of information in cells or what is usually referred to as the “central dogma” of molecular biology, right? That is, – DNA ---> RNA ---> proteins. Well, upstream means the replication of DNA and the formation of RNA or transcription, while downstream is the formation of proteins or translation. So when the write-up says that the problem appears to be upstream, then it means that something is wrong with either the replication or the transcription process. A downstream problem on the other hand means something wrong with the translation process.

Friday, December 12, 2008

When a cell divides, it multiplies

When a cell divides, it actually multiplies. Huh? This may not be possible mathematically but it possible biologically. Yes, that is how we get to have many cells, by division.

We all started as one fertilized egg cell. The cell then divided and divided until there are hundreds of millions of cells (refer to Nov 10 post, “cells touch”). See, by division a single cell has multiplied into millions of cells. Imagine that! This cell division is called mitosis.

Through mitosis, new cells are formed to replace dying, dead, or old worn out cells. Through mitosis, new cells are also formed to repair wounds or to even grow new parts. Unfortunately, as a cell becomes more specialized, it loses its ability to divide. Thus, nerve cells which are highly specialized cannot be replaced once they die because there no new source of cells. Other cells however are rather “enterprising”. When they divide, only some of the cells become specialized, the others remain unspecialized and they can keep on dividing and dividing so there is a constant source of new cells. These unspecialized cells are called stem cells.

Skin cells have their own stem cells, so do our intestinal cells and blood cells. Thus we have new skin every month and new intestinal cells every week. Sperm cells also have their own stem cells but egg cells do not have any (alas!).

Thursday, December 11, 2008

A cell with multiple nuclei

If the mature red blood cell has no nucleus, the opposite is true for the mature skeletal muscle cell - it has several nuclei per cell. How did this happen?

Well, the myoblasts or young muscle cells start out as uninucleated cells. Sometime during their development however, these cells fused with each other and become surrounded by connective tissue. The fused cells then elongate and develop into what is now called muscle fiber or the mature muscle cell. Thus, a single muscle fiber is equivalent to one muscle cell with multiple nuclei.

Muscle fibers are also bundled together by connective tissue and form what we recognize as our muscles. So our triceps or biceps and other muscles actually consist of bundles of muscle fibers.

Wednesday, December 10, 2008

Why our red blood cell has no nucleus

Our red blood cell actually has a nucleus when it starts to develop (while still an erythroblast, see Dec 8 post). However, it extrudes or throws out its nucleus as it matures. Why? Well, to have more space for carrying oxygen which is its main function.

While still developing, our red blood cell actually starts as a big cell with a big nucleus. It also divides several times to produce more of its kind. At the same time, it synthesizes hemoglobin, the molecule that actually carries oxygen. Later, it becomes smaller and smaller and the nucleus becomes more clumped until it (the nucleus) no longer can participate in cell division. When that happens, the cell then extrudes the nucleus. By this time it has produced all the hemoglobin it needs to carry the maximum amount of oxygen.

Since the mature red blood cell has no nucleus, it can no longer make new proteins. Thus, it can survive for only about 120 days. However, we should not worry that we will run out of red blood cells. Our bone marrow continuously produces red blood cells at a rate of about 2 million per second. These are then released into the bloodstream in a regulated manner or as needed by our body.

If you look at the picture of our red blood cells, they look like a doughnuts. What appears like the “hole” is where the nucleus used to be.

Tuesday, December 9, 2008

Barr body

Do you know that the discovery of the Barr body was actually through serendipity? Yes, it was. Murray Llewellyn Barr was actually working on the effects of fatigue on the nerve cells of cats. However, he did not find any changes in the nerve cells of fatigued animals. Instead, he noticed a mass of chromatin material on the nuclear membrane of some nerve cells but not all cells. When he crossed checked the sources of those cells, he discovered that they actually all came from female cats. When he examined cells coming from other mammals including human, the same chromatin mass was also observed only in females. He later discovered that this mass of chromatin material is actually a sex chromatin.

This sex chromatin is now referred to as the “Barr body”. It represents an inactivated X chromosome. It is now known that in mammalian and human females, one of the X chromosomes becomes inactivated during development and it appears as a dark mass (Barr body) near the nuclear membrane of their cells. So a female with XX sex chromosome will always show one Barr body, while a male who has XY sex chromosome should have no Barr body on his cells.

The number of Barr bodies observed in cells is always a good indicator of the number of X chromosomes in an individual. Individuals with multiple X chromosomes will have all the X chromosome inactivated (will appear as Barr bodies) except one. Thus, as mentioned earlier, females with normal number of sex chromosomes will always show one Barr body. Some females however have XXX sex chromosomes. Their cells will thus show 2 Barr bodies. Males showing a Barr body in their cells therefore have XXY sex chromosome.

The discovery of the Barr body thus launched a new era of research on genetic disorders.

Monday, December 8, 2008

"blast" means young

Have you ever noticed that all young cells are called ___blast? Osteoblast for example is a young bone cell while chondroblast is a young cartilage cell. Erythroblast is a young red blood cell while a neuroblast is a young nerve cell. A young muscle cell is called a myoblast and a young while blood cell is a leucoblast... and so on and so forth.... So, if somebody calls you “blasted thing”, it means you are young. Take it as a compliment and say “thank you”. Ha ha ha.... Sorry, I got a weird sense of humor today...

By the way, when a cell is old it’s called _____cyte. So we have osteocyte, chondrocyte, erythrocyte…etc.

Sunday, December 7, 2008

one more from Lewis Thomas

I mentioned in one of my earlier post (Nov 1) that my favorite part of the cell is the cell membrane. Well, I was happy to rediscover this paragraph while I was rereading Lewis Thomas' "Lives of a Cell" the other day...

"It takes a membrane to make sense out of disorder in biology. You have to be able to catch energy and hold it, storing precisely the needed amount and releasing it in measured shares. A cell does this, and so do the organelles inside. Each assemblage is poised in the flow of solar energy, tapping off energy from metabolic surrogates of the sun. To stay alive, you have to be able to hold out against equilibrium, maintain imbalance, bank against entropy, and you can only transact this business with membranes in our kind of world".

All I can say is "Amen" to this. Lewis Thomas speaks exactly what I think about cell membranes. What do you think?

Complementarity between structure and function at the cellular level

One recurring theme in biology is the complementarity between structure and function. This can be observed starting from the subcellular level up to the organismic level. Since my blog is about cells, I’ll focus first on the cellular level. Then in a future post, I will talk about this on the subcellular level.
Since you have already seen how a nerve cell and an intestinal cell look like (Nov 20and 22), I’ll just focus on these two first.

A nerve cell’s function is communication, so its many processes are arranged in such a way that it can receive as well as send as much information as possible. The dendrites, the receiving ends, are highly branched, while the axon, the sending end, reaches out as far as possible.

An intestinal cell on the other hand is mainly absorptive in its function. Thus the “frills” or microvilli that I mentioned before are designed to increase the absorptive surface of this cell.

We can look other cells in a future post or you can start looking at other cells in your books and try to see if you can determine the function of the cell based on its structure.

Friday, December 5, 2008

"Lives of a Cell"

Today I thought I will diverge from my usual post about some cell lessons. Today I would like to share a favorite quotation from an author who made me think about cells in a different way. I'm talking about Lewis Thomas who wrote "Lives of A Cell" sometime in 1971.

I'm lucky I was able to listen to Lewis Thomas in person when I was studying in the US in 1979 - 1980. He was as fascinating in person as in his book.

The following lines are found in the 1st page of his book.
"I have been trying to think of the earth as a kind of organism, but it is no go, I cannot think of it this way. It is too big, too complex, with too many working parts lacking visible connections... If not like an organism, what is it like, what is it most like? Then, satisfactorily it came to me: it is most like a single cell".
- Lewis Thomas
"Lives of A Cell"

What do you think? Why did Lewis Thomas think of the earth as like a single cell?

Thursday, December 4, 2008

Another correcting misconception day – about cholesterol

“Cholesterol is a steroid that is harmful to the body because it causes heart ailments”. This is a very common misconception found in many biology textbooks. It is always mentioned in relation to the chemicals making up cells.

The correction is: Cholesterol is only harmful if present in large amounts. Cholesterol per se is not harmful. In fact it is needed for synthesis of steroid hormones and for maintaining the fluidity of cell membranes.

We have to be aware that there are two kinds of cholesterol in our body: LDL (low density lipoprotein) cholesterol or the “bad” cholesterol and HDL (high density lipoprotein) or the “good” cholesterol. When too much LDL or “bad” cholesterol circulates in the blood, it can clog arteries and increase our risk of heart attack and stroke. HDL or “good” cholesterol on the other hand helps remove the “bad” cholesterol from our arteries.

We also have to be aware that most (about 75 %) of the cholesterol we have is actually produced naturally by our own liver. Only a small amount (25%) comes from the food that we eat. Unfortunately, many people inherit genes from their parents or even grandparents that cause them to make too much LDL. Inheritance plus the kind of food that we eat can therefore cause high LDLs in our blood and this is the one that triggers ailments of our circulatory system.

If high blood cholesterol runs in our family, therefore, a change in lifestyle (like watching our diet and refraining from smoking) plus some medications will probably be needed.

One more thing, if high blood LDL runs in our family, then it is important to watch the diet even of children because deposit of fatty plaques in the arteries starts even in childhood and slowly builds up as we grow older.

Wednesday, December 3, 2008

Cell design 101.5, skin cell or keratinocyte

Several kinds of cells make up our skin. However, today, I’m just going to talk about the main cell type or the keratinocyte.

Keratinocytes start from the basal layer of our skin’s epidermis. Here, they divide several times to produce more keratinocytes. Several of them are later pushed up slowly to the surface of our skin. As they move up, they lose their ability to divide but become more specialized by accumulating keratin filaments in their cytoplasm. As more keratin accumulate in their cytoplasm, some are also secreted out into the surroundings of the cell and create a barrier. Thus, nutrients can no longer move into the cells, and they die. The topmost cells of our skin are therefore dead keratinocytes. They are later removed from our skin surface and will be replaced by new cells coming from the basal layer of our skin. Keratin plus other molecules joined with them make our skin waterproof.

The whole process of skin renewal takes about 20 – 30 days. That means every 20 -30 days we have new cells on the surface of our skin. If one has the skin disease, psoriasis however, new skin is produced in less than 20 days. Thus, people with psoriasis have portions of “bumpy” skin.

By the way, formation of new keratinocytes by mitosis usually takes place at night while we sleep. This might explain why our skin suffers if have too many late nights.

Tuesday, December 2, 2008


So far I have only mentioned the functions of the microfilaments as part of the cell’s bones and muscles or cytoskeleton. To even up matters, I’ll talk about the microtubules today.

The microtubules consist mainly of the protein tubulin which has 2 phases, the alpha and beta tubulin. These tubulin molecules form a tube like structure that can elongate at one end and shorten at the other. This is a continuously occurring process so the microtubules and also the microfilaments are always in a state of dynamic instability. That means that nothing is permanent with the cell’s cytoskeleton.

Microtubules serve as scaffolding inside cells and act as “tracks” on which cells can move organelles, chromosomes, vesicles and other things inside. In other words, they act like bullet trains inside cells. Microtubules are also responsible for the movement of cilia and flagella. Imagine that, molecules that can act as scaffolding, train, and propeller at the same time! Yessiree, those are your microtubules.

In order to do their function however, microtubule need to associate with proteins like dynein and kinesin. These two serve as motors to power the movement of microtubules. If something goes wrong with these motors, then any of the movements mentioned above will not be possible. Sperm cells for example will be immotile if dynein is absent in their flagellum.

Monday, December 1, 2008


Cytokinesis is another activity that is generated by the cytoskeleton, particularly the microfilament.

After the chromosomes of a cell separate during anaphase, the microfilaments together with their associated protein, myosin, create a contractile ring somewhere near the middle of a cell. This ring tightens like a purse string until finally the cell is divided into two. This division completes the final stage of mitosis wherein two new cells with the same chromosome number are formed.

Separation of chromosomes and cytokinesis have to be properly coordinated so that the chromosome number of each generation of cells remain the same. If the timing of these two processes is off, we can end up with cells that have abnormal chromosome number or cells that can develop into cancerous ones.
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