What are the phases of the cell cycle?
G1→S→G2→M→Cytokenesis
G1→S→G2 is interphase
What happens in interphase of the cell cycle?
- the longest stage and we call the genetic info chromatids - we can’t see chromosomes
- when organelles double, the cells grown and then DNA replicates
G1→growth
S→DNA synthesis
G2→growth and preparation for mitosis
What is mitosis?
when a parent cell divides to produce 2 genetically identical diploid cells - 1 round of division
What is mitosis needed for?
growth of multicellular organisms and repairing damaged tissues
What is the structure of chromosomes during mitosis?
as mitosis begins the chromosomes are made of strands (chromatids) that are connected by a centromere - two strands on the same chromosome are called sister chromatids→each chromosome already made a copy of itself in interphase
What happens in prophase of mitosis?
- chromosomes become visible as they condense (become shorter + thicker)
- centrioles mover to opposite poles and spindle fibres develop from each centriole and span from pole to pole
- nuclear envelope breaks down and chromosomes lie free in the cytoplasm
What happens in metaphase?
- chromosomes align along the equator of the cell and the spindle fibres released from the poles now attach to the centromere
- chromosomes visible as 2 sister chromatids attached via centromere
What happens in anaphase?
- the centromere divide into 2 and the spindle fibres pull the chromatids causing them to move to opposite poles as the spindle fibres contract
- chromatids now referred to as chromosomes
- requires energy in the form of ATP which is provided by respiration in the mitochondria
What happens in telophase?
- the chromosomes reach their respective poles and become longer and thinner
- the spindle fibres disintegrate
- nuclear envelope and nucleolus reform
- cytokinesis → cytoplasm divides to create 2 new genetically identical cells
How can mitosis lead to cancer?
- mitosis and the cell cycle are controlled by genes
- if there is a mutation in a gene that controls cell division the cell keeps on dividing which forms a tumour (cancer is a tumour that invades surrounding tissue)
What treatments are there for cancer related to mitosis?
some treatments are designed to control the rate of cell division in tumour cells by disrupting the cell cycle which kills the tumour cells
- this can also kill normal body cells dividing but is more likely to kill tumour cells as they divide more frequently
How do you calculate mitotic index?
the number of cells in mitosis/the total number of cells x 100
How do prokaryotic cells divide?
Binary fission:
1.) circular DNA replicates and both copies attach to the cell membrane and plasmids replicate
2.) cell membrane begins to grow between 2 DNA molecule, dividing cytoplasm into 2
3.) new cell wall forms between the 2 molecules of DNA, dividing original cell into 2 identical daughter cells each with single copy of circular DNA and variable number of plasmid copies
How do viruses replicate?
- attach to their host cell with attachment proteins on their surface and inject their nucleic acid into their host cells
- the genetic info the nucleic acid provides the instructions for the host cells metabolic processes to start producing the viral components needed to make a new virus
