cell cycle and mitosis

• checkpoints


  -occur at key points during cell cycle to ensure cycle is working correctly and is okay to move onto the next stage
• mitosis


  division of nucleus
• Gap 1 (G1)

  -synthesis of new organelles and proteins

  -increase in cell volume

  -respiration- energy required

  -organelles replicated
• Interphase


  -all cell activities as it prepares for cell division

  -non-visible chromosomes
• synthesis


  cell's DNA is copied
• Gap 2

  -volume of cell increases

  -proteins needed for mitosis are synthesised
• cytokinesis


  -division of the organelles, cytoplasm and membranes to form new cells
• checkpoint- mitosis


  -checkpoint chemical triggers condensation of chromatin

  -metaphase checkpoint ensures cell is ready to complete mitosis
• G1 checkpoint

  -ensures chemicals needed for DNA replication are present and DNA is undamaged

  -tumour suppressor gene helps control G1 phase
• S (ynthesis) checkpoint


  -once cell enters synthesis it is committed to completing the cell cycle

  -genes active in all cell types are copied first (known as housekeeping genes)

  -genes usually inactive in specific cell types are copied last
• G2/M checkpoint


  -ensures DNA has been replicated before entering mitosis

  -chemicals ensure cell is ready to start mitosis by stimulating chemicals involved in chromosome condensation and spindle formation
• prokaryotic cells and cell cycle


  -takes a different amount of time- different number of chromosomes, no membrane bound organelles and respire in mesosomes
• hayflick constant


  number of times a cell can divide before it dies
• if cell division gets out of control tumours can form and spread. benign- non-cancerous and malignant- cancerous
• mitosis


  -growth of organisms, asexual reproduction and repair of old or damaged tissues
• homologous chromosomes

  -matching pairs- same genes in same positions
• chromatin


  histone proteins wrap around DNA. called super coiling/ condensing
• chromatid


  -arms of a replicated chromosome. one arm is identical to the other and are called sister chromatids. one was copied from the other in synthesis in the interphase
• centromere


  -area of chromosome where 2 sister chromatids are joined together
• chromosomes


  -linear DNA molecule wrapped around histone proteins found in nucleus
• chromatins


  -DNA is condensed so it can be moved around the cell without damaging the DNA
• prophase


  -supercoiling to form sister chromatids

  -nuclear envelope breaks down

  -centriole divides in 2 and moves to opposite ends of the cell

  -spindle fibres form between the 2 centrioles from a cytoskeleton protein called tubulin

  -chromosomes become visible
• metaphase


  -chromosomes moved to equator- centre of spindle fibres

  -chromosomes attach to spindle fibres by their centromeres
• anaphase


  -centromere splits and chromatids separate

  -spindle pulls sister chromatids to opposite poles of the cell involving the cytoskeleton
• telophase


  -chromatids reach poles of the cell

  -new nuclear envelope forms around each set

  -spindle breaks down

  -chromosomes uncoil and become invisible again
• animal


  -uses centrioles to create spindle fibres

  -all body cells

  -cytokinesis- out to middle- pinches in
• plant


  -cytoplasm to create spindle fibres

  -meristems and buds

  -cytokinesis- middle- out