The Cell Cycle

The life of the Cell:

Just like an organism the cells also have a life cycle. Each cell is made to be a copy of its parent cell. The cells then live, reproduce and then die.

The Cell Cycle:

This term refers to the stages of a cells life:

 A new cell is created. The cell lives and has a specialized  function. The cell reproduces another cell. The cell dies.

Chromosome:

They are structures found within the cells nucleus in eukaryotic cells.They contain the cells DNA (genetic information)They are made of DNA and proteinProkaryotic cells have DNA also but they may not have a nucleus. When this happens the DNA clumps together and floats in the cytoplasm.

Making More prokaryotic cells:

Prokaryotic cells are single cell organisms such as bacteria and fungus.They can have either DNA or RNA (ribonucleic acid)These cells divide through a process known as Binary Fission.

This picture shows how binary fission works for bacteria.

1. The parent cell begins the process of cell division. During this process the inner layer of the cell membrane begins to fold inwards.

2. The cell membrane continues the process of folding inwards till the inner membrane is completely divided. During this process, the cell also divides its DNA. Each new cell will receive an exact copy of the parent cell DNA.

3. Once the inner cell membrane has completely divided, the outer cell membrane begins the process of dividing. At the end of this step there will be two completely new cells. Each new cell will have an exact copy of the DNA of the parent cell.

Eukaryotic cells and their DNA

These are multicellular organisms.Each type of organism will have different number of chromosomes.All of their chromosomes come in pairs.The pairs of chromosomes are usually identical pairs, with similar sequence of genes and structures, known a homologous chromosomes.

Human body cells have 46 chromosomes and 23 homologous pairs.

Eukaryotic cell cycle:

Has three main stages.Stage I is called interphaseDuring interphase, the cell grows and copies its organelles and chromosomes. The two copies of a duplicated chromosome are known as chromatids.Chromatids held together in a region known as the centromere.The joined chromatids then twist and coil and twist into the shape of an X.

During Stage II the chromatids separate during a process known as mitosis.

During Stage III the cell splits into two cells which are identical to each other and to the original parent cell.This Stage is called Cytokinesis.

Mitosis: This process happens in every cell of your body except the cells of the reproductive system.

Interphase: Before mitosis begins the chromosomes are copied. Each chromosome is then two chromatids.

Mitosis Phase 1 (Prophase):

This is the first step of mitosis. During this step the nuclear membrane disappears and the chromosomes clump and coil together as rodlike structures.

Mitosis Phase 2 (Metaphase)

During this phase the chromosomes line up along the middle of the cell and begin to pair up so they can create homologous pairs.

Mitosis Phase 3 (Anaphase):

The chromatids separate at the centromere and move to opposite sides of the cell.

Mitosis Phase 4 (Telophase):

A nuclear membrane forms around each set of chromosomes and the chromosomes unwind. Mitosis is now complete.

Cytokinesis:

After the mitosis is complete two new cells have formed. In organisms that do not have a cell wall the cell membrane simply pinches to separate the two new cells.

In the cells that have a cell wall a cell plate is formed between the two new cells.