Egg Sperm and Mitochondria

The Human body is made up from millions and millions of tiny parts called CELLS.

Cell Simplified Structure

This is a very simplified diagram of a typical cell.

The cell is surrounded by a CELL MEMBRANE.

Each cell has one NUCLEUS.  This is where a lot of the inherited information for the cell is stored.  A chemical called DNA stores information on how to make chemicals called PROTEINS and other information the cell needs to do its job.  Because it is stored inside the Nucleus of the Cell, scientists sometimes call this DNA the NUCLEAR DNA.  That is just to make it clear this DNA is different to the stuff stored inside Mitochondria, called the MITOCHONDRIAL DNA.

The cell has thousands of MITOCHONDRIA (pronounced MITE-OH-KON-DREE-AH).  One of these is called a MITOCHONDRION (pronounced MITE-OH-KON-DREE-ON).  Each mitochondrion has  its own DNA – lots of copies of the same DNA structure.  The MITOCHONDRIA release most of the energy the cell needs from carbohydrates such as Glucose, and produce the cell’s fuel called ATP.

Every person starts off as one cell, the fertilized human egg cell.

This is created by one Sperm Cell from the father delivering its DNA to one unfertilized Egg from the mother.

The fertilized egg cell starts dividing to form two cells, then four cells and so on.

A simplified diagram of a Human Egg Cell .  Doctors sometimes call this an Ovum from the Latin word for Egg.



Diagram of Human Egg Cell

The Nucleus has half the amount of DNA in a body cell – one of each pair of the Mother’s Chromosomes.

There are thousands of Mitochondria inside the Cell.

The Egg cell is protected by a coat of jelly.

The Sperm Cell looks quite different.  Like the Egg Cell, each Sperm Cell only has half the amount of DNA of a normal body cell.  It has one  from each pair of the Father’s Chromosomes.

Diagram of Human Sperm Cell

Each Sperm Cell has a lot of Mitochondria, but these are not packed into the Head, they are attached to the Tail.  the Mitochondria are there to provide fuel for the Tail so it can  move and propel the Sperm toward an Egg.

When a Sperm Cell joins with an Egg Cell, this is called Fertilization.

The Head of the Sperm Cell delivers its DNA into the Egg Cell. The Nuclear DNA from the Father joins with the Nuclear DNA from the Mother .  This means that the Fertilized Egg has 46 Nuclear Chromosomes, made up of 23 Pairs.  Each pair of Nuclear Chromosomes has one from the Father and one from the Mother.

The Father’s Mitochondria have done their job, giving the Tail of the Sperm enough fuel to swim. They are not passed into the Fertilized Egg.

This diagram of Fertilization is not to scale – in reality Sperm are tiny compared to the size of the Egg Cell.


Diagram of Human Fertilizationi


This page was last updated on August 20 2015



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