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.

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.

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.

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.

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?

sperm cell

source of photo: http://aycu31.webshots.com/image/44110/2002564320883082356_rs.jpg
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 http://hypertextbook.com/facts/2000/EugeneKogan.shtml, the average speed of a sperm is "1–4 millimeters per minute".

egg cell

source of picture:http://encarta.msn.com/media_461516399/egg_cell.html
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.