What Is The Molecular Biology Of A Sperm?

Did you know that sperm cells are one of the smallest cells in humans?¹ Despite its size, it holds the genetic information which makes you “you”! It's only a wonder (and science of course) how this little droplet can go on to create a full-fledged human! So, join us to learn the basic understanding of what a sperm is and how it helps in the creation of the little wonder- a baby!

Are you ready to learn about the molecular biology of a sperm? 

Firstly, a sperm is the male reproductive cell produced in the testicles, which fuses  with an egg (female reproductive cell) to produce an embryo (early developmental stage of the baby inside the mother's womb).²

Structure of A Sperm

If you examine a sperm under a microscope, you will notice two different morphological features: the tail and the head. Both of these sections are protected by an outer layer known as the plasma membrane. The tail aids sperm in swimming and burrowing its way through the egg, whereas the head contains nucleus (the primary DNA content).³

The genetic material or DNA found in the nucleus is tightly wrapped, resulting in a smaller volume that is easier to transport.³ 

A sperm is a special cell that is compact and contains every component needed for it to fuse with the egg. However, unlike a normal cell, sperm lacks organelles such as the Golgi apparatus, ribosomes, and so on. Yet, it does have mitochondria to propel the flagella tail.³ 

Head Of The Sperm

An acrosomal vesicle is a pocket-like structure found at the head of a sperm. The acrosomal vesicle contains special enzymes (hydrolytic enzymes) that aid sperm penetration through the outermost layer of an egg. When a sperm touches an egg, the contents of the acrosomal vesicle are released by an acrosomal reaction.³ 

Tail Of The Sperm

A sperm's mobility is provided by its tail, also known as the flagellum. The flagella of certain sperm (including mammals) differs in morphology from the standard 9+2 pattern (an arrangement of cytoskeleton structure wherein 9 fused pairs plus one pair in the middle of microscopic tubes is present) are found in the majority of the axoneme (core of a flagellum). Furthermore, it is surrounded by 9 thick fibres on the outside. The thickened flagellum is useful for bending motions.³

The movement of flagella is driven by the dynein motor proteins (molecules responsible for converting chemical energy into mechanical energy⁴), which uses ATP hydrolysis. The ATP is produced by the mitochondria, present at the front part of the sperm tail.³ 

Now that we have learnt the molecular biology of a sperm in the previous section, in this section let’s discuss how sperm is synthesized.

Synthesis Of The Sperm

In males, sperm production (spermatogenesis) takes place in the testis (two oval-shaped male reproductive organs), which starts in the seminiferous tubules (coiled tubes that produce sperms). And, this process of sperm formation is classified into the following stages:^5,6,3

• Stage 1 (Spermatogonia) - This is an early stage of sperm (spermatozoa) formation in which the spermatogonia are located at the outer edge of the seminiferous tubules. They are about 9 μm in diameter and somewhat oval in shape.^6,3
• Stage 2 (Primary spermatocytes) - In this stage, the spermatogonia further develop to form primary spermatocytes, which are 7 μm in diameter.⁶
• Stage 3 (Secondary spermatocytes) - Two secondary spermatocytes are formed from the primary spermatocytes by meiosis (cell duplication) and are about 6 μm in diameter.^6,3
• Stage 4 (Spermatids) - Lastly, the secondary spermatocytes again undergo meiosis and produce four spermatids, which then form the sperm.³ 

Pathway Of Sperm

The testis' coiled epididymis serves as a storage area for immature sperm cells. Sperm are discharged from the epididymis and transported to the deferent ducts during every ejaculation. From there, it travels through the ureter and reaches the prostate before traveling to the spermatic cord and pelvic cavity (which is located behind the urinary bladder). An ejaculatory duct that connects the vas deferens and seminal vesicle travels through the prostate before connecting to the urethra. Sperms finally come out of the penis during ejaculation due to the rhythmic muscle movements.⁷ 

Fusion Of The Sperm And Egg

When sperm cells are released from the penis, semen acts as a barrier to protect them from the acidic vaginal environment. Once the sperm has entered the uterus and passed through the cervix, it comes into contact with the egg. During the fusion, sperm enters the egg's zona pellucida, or outer membrane. Several processes then take place to create the first cell division to form "zygote" or single-cell embryo. The human embryo then goes through mitosis (further cell divisions) in a period of 7 days. Additionally, the final phase of this cell division produces a "blastocyst," which is an organized mass of cells.⁸

About 5 to 6 days post fertilization, when the embryo reaches the blastocyst stage, it comes from its shell (zona pellucida) and begins the implantation process. Before the 2 week mark (at which a pregnancy can be detected), the blastocyst implants. However, the implantation process is highly dependent on the uterus’ receptivity and the embryo's overall health.⁸ 

Ending Note!

Understanding molecular biology of sperm will help you better comprehend how your body creates life. We are aware that for many people, becoming a father still seems like a far-fetched dream. Nevertheless, one shouldn't lose hope because modern healthcare science and medicine have recently improved the chances for many couples to conceive a child on their own. In addition, it is now much simpler to learn and track one’s reproductive health from the comfort of their homes. You must be wondering how? With the help of LifeCell’s SpermScore semen analysis test kit! Gone are the days when you’d have to visit a clinic just for "sperm health examination," as with our kit, all you need to do is collect your sample at home and ship it back to us. Our test kit examines 11 sperm parameters and 14 sperm health conditions, helping you determine the potential impediments to your overall reproductive wellness.