The human body consists of billions of small cells, all of which originate from and are copies of one single cell: the cell that is a result of a sperm cell fusing with an egg cell - the actual conception. This single cell divides again and again, and so do the new cells in a continuous process the rest of your life to renew the cells of the body.
As the cell division progresses, the fetus takes form with a heart, brain, bones, skin, muscles, limbs etc. Every new cell functions as a little factory that works hard around the clock to carry out specifically assigned functions. Some cells undertake the pumping function of the heart, while others - the brain cells - enable us to think, etc.
Every single cell has a nucleus. This is the "command center" that also stores our genetic coding.
A sperm cell differs entirely from the other cells in the body. It is smaller, it is equipped with a tail, and it is detached and able to move. Also, in contrast to all other cells in the body, sperm cells only contain very little cytoplasm. This is where enzymes are produced, such as those enzymes that are responsible for repairing the genetic coding (DNA).
The lack of cytoplasm means that a sperm cell is unable to repair damaged DNA. Therefore, it is vital to support the body with e.g. selenium that is an important constituent of the repair mechanisms responsible for undertaking repair of DNA, proteins, and lipids.
New research demonstrates that about 50% of infertile men have poor protection of sperm cell DNA. This is the underlying cause of a phenomenon known as "DNA fragmentation". This does not affect the sperm cell's ability to swim (motility). However, the sperm cell that reaches the egg first may not be of "top-notch" quality. In other words, the sperm cell may very well be able to fertilize the egg, but the DNA is damaged the egg may not develop normally and could easily be rejected.
We humans consists of billions of cells, all of which are based on the same basic principles. On the outside is a cell membrane.
Behind the membrane are numerous organelles taht ensure the existence of the cell. Also we find a nucleus that contains our genetic coding (DNA). The DNA contains all information about how each individual is constructed.