Cell division, cell diversity and cellular organisation

Cell division, cell diversity and cellular organisation 

Cell cycle

consists of interphase (cell growth + DNA replication) mitosis and cytokinesis (m phase) (cell division) 

It is regulated by checkpoints-

First at the end of G1 where the cell checks that teh chemicals needed for replication are present an dthat there is no damage to the DNA. 

Then at G2 where the cell checks all the DNA has been replicated without damage

Finally at Metaphase where the cell checks all the chromosomes are attached to the spindles

Interphase

split into G1 S and G2.  G1- the cell grows and new oragnelles and proteins are made.              S- cell replicates the DNA.                                                                                                   G2- cell keeps growing and proteins needed for cell division are made.                                         The cell carries on with its normal functions as well, DNA is unravelled and replicated, along with organelles and ATP content is increased.

Mitosis

As mitosis begins thge chromosomes are made of 2 strands joined by a centromere. Each strand is called a chromatid and teh 2 strands in a chromosome are called sister chromatids.

 prophase

Chromosomes condense. Centrioles start moving to opposite ends of cell forming a network of spindles. The nuclear envelope breaks down.

  metaphase

Chromosomes line up along middle of cell and attach to spindles.

  anaphase

centromeres divide, spindles contract pulling each chromatid, centromere first, to opposite ends of the cell.

  telophase

chromatids reach opposite poles. they uncoil and become long and thin (called chromosomes again) nuclear envelope forms around each group of chromosomes.

Cytokinesis 

The cytoplasm divides, a cleavage furrow forms to divide cell membrane. There are now two daughter cells genetically identical to origanl cell and ecah other. Cytokinesis starts in anaphase and ends in telophase. It is a separate process to mitosis. 

Mitosis is essential for life cycles, it is used for growth, tissue repair and asexual repoduction in plants and fungi. 

Meiosis

Normal body cells have the diploid number of chromosomes (2n) so each cell has 2 of each chromosome. Pairs of these chromosomes are homologous chromosomes. Gametes have the haploid number (n). This is so at fertilisation a haploid…