mitosis

definition

eukaryotic cell divides to produce two daughter cells,each with the identical copies of DNA produced by the parent cell during DNA replication

stages of mitosis

interphase

prophase

metaphase

anaphase

telophase

cytokinesis

INTERPHASE

Gap 0 - resting phase, for cells not dividing 

Gap 1 - cell grows, new organelles, proteins and mRNA made 

Synthesis - DNA replication, 2N → 4N for mitosis 

Gap 2 - cell grows, new organelles, proteins and mRNA made 

CHECKPOINTS

G1 - checks cell is big enough and proteins are made, if fail goes into G0

S - checks if DNA has been replicated 

G2 - checks if it’s big enough to enter mitosis and if replication was correct

PROPHASE

• Chromosomes condense, becoming short and fat

• Become visible under microscopes 

• X-shaped chromosomes, joined by centromere, sister chromatids are identical

• Centrioles (bundles of protein) move to poles of cell 

• Network of spindle fibres form across the cell

• Nuclear envelope starts to break down to release chromosomes into cytoplasm 

METAPHASE

• Chromosomes line up along the centre/equator of the cell 

• Attached to the mitotic spindle by their centromeres 

• Arranged sideways and neatly 

ANAPHASE

• Spindle fibres contract 

• Pulling the sister chromatids away from each other, towards the poles 

• Centromeres are pulled first causing them to look v-shaped 

• 2 separate groups of chromatids 

TELOPHASE

• Chromatids each the poles  

• Uncoil and become long and thin again

• New nuclear envelope form around the two new full sets of chromosomes 

• Forms two new nuclei, daughter nuclei 

• Genetically identical 

CYTOKINESIS

• When the cell physically separates/divides and the cytoplasm splits 

• Contractile ring forms at the centre 

• Makes an indentation called a cleavage furrow 

• Pinches in and the cell divides into 2 identical daughter cells 

• Starts in telophase 

uncontrolled mitosis

When there is a mutation in a gene that controls cell division, cells grow out of control, forming a tumour. A mutation is a change in the base sequence of DNA.

Malignant tumour

grows rapidly and can invade healthy neighbouring tissues

Benign tumour

grows slowly and does not spread

cancer treatment

CHEMOTHERAPY 

Prevents synthesis of enzymes that are needed for DNA replication in gap phase 1, meaning the cell cannot enter the synthesis phase, disrupting the cell cycle and causing the cell to kill itself. 

binary fission

1. Circular DNA and plasmids replicate  (once for circular, more for plasmids). 

2. Cell gets bigger and DNA loops move to  opposite poles of the cell. 

3. Cytoplasm begins to divide and new cell  walls begin to form 

4. Cytoplasm fully splits and 2 daughter cells  are made, each with one identical loop of 

circular DNA and with variable plasmids. 

VIRAL REPLICATION

1. Attach to host cell using their attachment proteins which bind to  complementary receptor proteins  on the surface membrane on the host cell.

2. Genetic material from virus is released into the host cell.

3. Use host cell’s ‘machinery’ like enzymes and ribosomes to replicate the genetic material and  proteins

4. Viral components assemble inside host cell  Replicated viruses released from the host cell 

Different viruses have different attachment proteins so attach to different receptors so therefore can only infect one kind of cell.