Every cellular organism uses the process of cellular division and yes you’ve guessed it, it’s very important. The two ways that cells can reproduce are mitosis or meiosis.
By mitosis a cell splits to create two identical copies of the original cell. In meiosis cells split to form four new cells with half the usual number of chromosomes, to produce gametes for sexual reproduction.
So let’s take a look at mitosis. Mitosis occurs wherever more cells are needed. It produces two new cells that are identical to each other, and to the parent cell. The process of growth and division is called the cell cycle.
The cycle starts as the number of organelles – the different parts of the cell – increases. This is to ensure that each of the two new cells receives copies of all the organelles.
There are four stages to mitosis: prophase, metaphase, anaphase and telophase.
As you’d expect in each stage something different happens to prepare the cell to duplicate.
Chromosomes condense during prophase. They get shorter and fatter. This means we are able to see the chromosomes under a microscope.
In metaphase the chromosomes line up in the cell. The chromosomes then get pulled apart in anaphase.
Telophase is the stage where the chromatids reach the poles of the cell having been pulled apart at the equator.
During mitosis two cells are produced, unlike meiosis which produces four at the end of the process.
If an error occurs in the DNA, this is known as a mutation, though never quite as exciting as the mutations we see in X-Men.
The enzymes that synthesise new DNA molecules check for these errors to minimise the rate of mutations.
DNA helicase is the enzyme that breaks the bonds which is holding the two DNA strands together.
During DNA replication DNA polymerase is the enzyme which joins nucleotides together to form a new strand.
This is a condensation reaction. Hydrogen bonds must be broken to allow the DNA strands to separate.
After the DNA strands have separated during replication nucleotides are attracted to each strand to form a new strand of DNA.
This all means that after replication each new DNA molecule contains one new and one old strand.
The method of DNA being able to replicate itself is called semi-conservative. This is because half of the original DNA is conserved in each new molecule of DNA. Basically, the molecule is semi-old, semi-new.
Semi-conservative replication occurs during a process called interphase. Interphase refers to all stages of the cell cycle other than mitosis. During interphase, cellular organelles double in number, the DNA replicates and protein synthesis occurs.
Replication occurs during the synthesis (S) stage. This is so that the cell is ready to divide by mitosis at the end of interphase.
Interphase is made of up three stages: G1, S and G2.
During G1 organelles are made, this happens straight after mitosis. Some people like to call this the start of the cycle, but because it’s a cycle – there is no beginning, middle or end, its cyclical!
In the G2 phase, it prepares the cell for division by storing energy and making the necessary proteins for division allowing the cell to grow.
It is interphase that takes up the majority of the cell cycle, as mitosis is relatively short in comparison.
Finally, it’s worth noting that humans are unable to reproduce asexually using mitosis – obviously.
Meiosis on the other hand is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four gamete cells. This process is required to produce egg and sperm cells for sexual reproduction.