what happens in interphase
the cell prepares to divide, the cells dna unravelled and replicated to double the genetic content. the organelles are also replicated. the atp content is also increased (atp provides the energy needed for cell division)
prophase
- chromosomes get shorter and fatter
- centrioles move to opposite ends of the cell making spindle fibres
- nuclear envelope breaks down (so chromosomes are in the cytoplasm)
metaphase
- the chromosomes line up in the middle of the cell
- attached to the spindle fibres by their centromere
anaphase
- the centromeres divide, seperating the chromosomes into sister chromatids
- the spindle fibres pull the chromatids to the opposite sides of the cell
telophase
- the chromatides become long and thin again (they can be called chromosomes again)
- nuclear envelope forms around each group of chromosomes (two nuclei)
cytokinesis
- the cytoplasm divides
- two new identical daughter cells
adaptation of the sperm cell
- flagellum = for mobility needs to swim to the fallopian tube for fertilisation
- acrosome (at the head) = dygestive hydrolytic enzymes to penetrate the zona pellucida
- lots of mitochondria = necessary for the mobility of the sperm
- constant haploid = to restore the diploid after fertilisation
produced in large quantities = to increase probability of one sperm penetrating the cell.
adaptation of the egg cell
- zona pellucida = jelly coating which surround the cell, to prevent other cells form penetrating the cell
- cytoplasm = contains proteins and lipid to help develop the embryo.
fertilisation
- the sperm reaches the egg cell
- acrosome reaction is then triggered by the chemicals surrounding the egg cell
- the acrosome begins to swell and fuses with the cell surface membrane of the sperm cell
- releasing digestive ions (acrosin) digesting the follicle cells, zona pellucida and the fuses with the membrane of the egg cell.
- the nucleus of the sperm cell is then released into the egg cell - which activates the cortical reaction
- the cortical granuels then move to the surface of the egg membrane,
- they then release their lysosome by exocytosis to hardern the egg cell
- the nuclei of the egg and sperm fuse.
differential gene expression
a transcription factor (chemical stimulus) such as a hormone will switch on the genes needed to transcribe the
the genes are then activated and transcription occurs on the activated genes producing mRNA
then this mRNA will then be translated at teh ribsomes
producing a protein and this is specialised through differentiation and the comes permenantly modified.
