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Human Reproduction

DNA is a long molecule, which stays in the nucleus of the cell where it is “written” all the information needed for the cell to work well. If it is a cardiac cell, DNA will give instructions so it works as a cardiac cell; if it is a brain cell, the instruction is to work as a brain cell. 

 The DNA molecule is similar to a stair: there are two banisters and some steps linking the banisters. The steps are the variable part of the DNA, represented by the letters A, T, G and C – which are the organic compounds adenine, thymine, cytosine, and guanine, respectively. These letters are in a sequence that only a cell can read and each sequence is named gene. 

For a proper reading, the cell sends a copy of the gene outside the nucleus under the shape of RNA. 

In the cytoplasm there are elements (ribosomes) capable of reading the RNA and when it happens, we say that the gene is expressing, because the gene expresses its information by the RNA. Many genes can be read at the same time. From this set of information that the reading offers, various characteristics are set, as the shape of the face, the size of the body, the color of the eyes, etc. These characteristics are known as phenotype.  

Because of its great length, the DNA has to roll up until it gets very “tight” to fit in the cell, forming a structure named chromosome. Every species of living beings has a number of chromosomes, the human species possesses 46. Half of the chromosome is taken after the mother, 23, and the other half after the father. 

In the reproductive organs of the woman (ovarian) and the men (testicles) there are cells specialized in generating gametes (cells that possess 23 chromosomes): egg and sperm. The process by which a cell with 46 chromosomes produces other cells with 23 chromosomes is called meiosis.

When the egg and the sperm meet within the uterus, they form the zygote (with 46 chromosomes), it is our first cell. Once generated, the zygote starts to multiply, forming identical cells. For a cell to produce two, it has first of all to duplicate all the structures existing inside the cell, including the DNA. Replication is the name of the process in which DNA duplicates, mitosis though is the name given to the whole cell duplication.  

After the whole process, the cells start forming different types of organs: muscles, bones, intestine, liver, etc. When this organism is complete, after developing and growing, it is birth time. 

Generally, during our lifetime, if some damage destroys a cell, it is replaced from the cells existing by mitosis. For example: if a kidney cell is ruined, a cell from this organ, identical to the one lost, multiplies and generates an identical cell. This is a coordinated and synchronized process, if this harmony is somehow threatened, the diseases may occur.  


 

DNA molecule duplication 

 

 

Cell division (meiosis and mitosis)

 

 


Process from the ovulation until the embryo implantation  in the uterus 

 

Text: Daniel Dentillo (post-doctorate at the Department of Gynecology and Obstetrics - FMRP/USP)

 

Comments  

 
0 # Human Reproductioninternational 2015-09-13 18:10
Your way of telling all in this piece of writing is in fact fastidious,
every one be able to without difficulty understand it, Thanks a lot.
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0 # Human Reproductionmore info 2015-09-14 09:42
I could not refrain from commenting. Perfectly written!
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0 # Human ReproductionMargherita 2017-07-16 11:43
Thanks, it's quite informative
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