Let’s talk about human sperm. In this blog post I want to share my love for spermatozoa with you by pointing out some interesting facts about them. Maybe by the end of this blog post you will also be in love with these magnificent wonders of nature that are spermatozoa. One of the reasons why I am always so fascinated by these cells is that from a biological standpoint, they are quite special and very different from any other cells in the body.
For example, their genetic material is packed with protamines instead of histones. Typically, the DNA in the nucleus of a cell is arranged with proteins called histones forming what is known as chromatin. In sperm, however, histones are replaced during spermatogenesis by protamines, another kind of proteins. These allow sperm to have a highly compact arrangement of DNA which is more stable. Keep in mind that these cells have not only an important luggage to carry but they also need to travel very long distances to deliver the package.
The anatomy of sperm also differs greatly from the typical cell structure that you may be familiar with of a cell membrane containing cytoplasm, all the organelles and the cell nucleus. In the case of sperm, you can identify three main parts: the sperm head, the midpiece and the tail. The head is compartmentalized, with a vesicle in the anterior region called the acrosome which contains enzymes that will help fertilize the egg. Then the postacrosomal region of the head consists of the highly compact genetic material described above.
On the midpiece you find the mitochondria. Mitochondria are known as the powerhouse of the cell, because they are responsible for the production of ATP (i.e. adenosine triphosphate) which is the currency of chemical energy. Of course, sperm need lots of energy. So, these organelles will play an important role in any sperm activity requiring energy, such as motility, acrosome reaction and fertilisation.
Another difference is that spermatozoa, unlike other cells, lack cytoplasm. It is removed during spermatogenesis. Again, sperm need to be able to carry what is strictly necessary for their purpose, so not only do they have a highly dense packaging of DNA as mentioned before, but they will also get rid of most cytoplasm, thus reducing to a minimum size. In fact, sperm are considerably small – head is approx. 5μm long, especially if you compare it with the oocyte which will be around 130 μm diameter. These two cells, the male and female gametes, are the smallest and largest cell in the body, respectively. I think this is also quite interesting!
Back to sperm. Another reason why I never stop to feel amazed whenever I see sperm in the microscope is that they are life itself as they represent half the potential of a human being. You see, sperm are haploid since they are a gamete, meaning they carry half the genetic material needed to make a human being. The other half is of course carried by the oocyte. The other cells in the organism are diploid, carrying full genetic material of 46 chromosomes. So, sperm contains one half (23 chromosomes) which will add to the oocyte’s 23 to make the two sets of 23, that is a total of 46. From these 23 pairs, 22 pairs of chromosomes are known as autosomes and the last pair are the sex chromosomes, which make the baby either XX or XY. Because the female cells are XX, the oocyte will always have an X as the sex chromosome. And because male is XY, sperm will either carry an X sex chromosome or a Y sex chromosome. This is the reason why the sperm will determine the sex of the baby.
just a few interesting facts about sperm, and I hope that you could find new
insights here. Please do leave your comments and thoughts below. And if you have any questions or would like
to learn more, feel free to ask.
Sanchez (Dr. rer. nat.) is a passionate biologist, born and raised in
Maracaibo, Venezuela, where she started her career in the field of Assisted
Reproductive Technologies (ART) with special clinical focus on Andrology. In
2010 she was one out of only three professionals chosen from her home country
to be awarded a scholarship by the German Service of Academic Exchange (DAAD)
to pursue a PhD. She has been based in Germany ever since, where she received a
doctoral degree with magna cum laude honor. She further developed in academia
with her doctoral and postdoctoral research in sperm biology, sperm DNA analysis
and Raman microspectroscopy. During this time, she also took on the role of
junior deputy in the special interest group of Andrology from the ESHRE
(European Society of Human Reproduction and Embryology). Most recently,
Victoria worked in the laser technology industry used in the IVF (in vitro
fertilisation) lab. Her specialty was embryo biopsy, and this took her around
the world teaching embryologists about this technology and its applications.
You can follow Victoria on social media @drvictoriasanchez and find out more at