all cells arise from other cells

• in diploid cells there is a long chromosome and a short one
• mitosis is used for growth, repair and a sexual reproduction
• mitosis is part of the cell cycle
• the cell cycle consists of interphase (G1, S and G2) and mitotic phase (M)
• S phase is where DNA replication occurs
• interphase is when DNA replicates and proteins are synthesised
• interphase (S phase)

  • energy stores increase
  • cell grows in size
  • organelles replicate
  • DNA is copied
• Mitotic phase (M)

  • nucleus divides by mitosis
  • cell divides by cytokinesis
• During interphase the chromosomes are not visible but chromatin is visible

  • the chromosomes are loose and open so the DNA is open for transcription and replication
• chromosomes are a single long molecule of DNA
• chromosomes are replicated during interphase
• 2 sister chromatids are attached at the centromere
• AFTER interphase the nucleus divides into 2 by mitosis
• mitosis the cell cycle starts and end here
• gap phase 1

  • cell grows and new organelles and proteins are made
• during synthesis

  • cell replicates it’s dna ready for division by mitosis
• gap phase 2

  • cell keeps growing and proteins needed for cell division are made
• during interphase the cell carries our normal functions but also prepares to divide, the cells DNA is unravelled and replicated to double its genetic content. the organelles are also replicated so it has spare ones and it’s ATP content is increases ( because ATP provides the energy needed for cell division )
• the structure of a chromosome

  • during interphase an identical copy of each chromosome is made and joined by a centromere
• interphase (not mitosis, cell replication)

  prophase

  metaphase

  anaphase

  telophase
• PROPHASE

  • the chromosomes condense getting shorter and fatter
  • centrioles move to the opposite side of the cell
  • forming the network fibre of spindles
  • the nuclear envelope starts to break down
• METAPHASE

  • chromosomes line up along the middle of the cell
  • become attached to the spindle by the centromere
• ANAPHASE

  • the centromeres divide, separating each pair of sister chromatids
  • spindles contract pulling chromatids to opposite poles of the spindle
• tumours are diseases caused by a growth disorder of cells

  rapid and uncontrolled growth and division of cells
• benign tumour: generally don’t spread and are surrounded by a membrane
• malignant tumour: can spread through bloodstream and lymphatic systems to form secondary tumours in other parts of the body
• many cancers are result of a mutation of genes that regulate mitosis
• chemotherapy

  G1- some drugs prevent the synthesis of enzymes needed for DNA replication

  so the cell is unable to enter the Synthesis phase and kills itself
• Chemotherpay

  S phase- radiation and some drugs damage DNA,

  at several parts in the cell cycle the dna is checked for damage if the severe damage is detected the cell will kill itself so prevent further tumour growth
• apoptosis is controlled cell death
• if a dose of a cancer drugs is increased at the wrong time it would kill even more healthy cells each time and the numbers would decline rapidly after a few treatments
• mitosis index should not be represented as a percentage
• if the dose of the cancer drug was given more frequently the healthy body cells would not have enough time to increase their numbers again in between treatments and the numbers of healthy cells would decline rapidly after a few treatments and kill the patients
• cells from the root tip are used for the practical because the cells in mitosis are there
• the root is squashed and not anything else because the tissue remains unfolded and with good seperation of the chromosomes
• mitotic index is the proportion of cells undergoing mitosis
• cancer cells go through the cell cycle more rapidly as many of the molecular brakes that control cell growth are broken
• a higher number of cells in mitosis than normal shoe the cycle is running faster than it should
• the microscope image and mitotic index can be used to diagnose abnormal growth, help suggest treatments, assess the efficacy of the drugs