Cell Division

• Define the Cell Cycle:

  the regulated cycle of division with intermediate growth periods. It includes the interphase, mitosis, and cytokinesis.
• Define Mitosis:

  A process of cell division that produces two genetically identical diploid daughter cells for asexual reproduction
• State all the checkpoints of the Interphase:

  • G1
  • S
  • G2
• During interphase, the cell may enter a G0 phase, where the cell may undergo apoptosis, differentiation, or may enter senescence
• Define Apoptosis:

  An active programmed cell death to get rid of unneeded or abnormal cells
• In the interphase, there are two main checkpoints, G1/ S phase which are also called the restriction points
• Outline the purpose of the checkpoints in interphase:

  • to prevent uncontrolled division that would lead to tumours and cancer
  • to detect and repair damage to DNA
  • to ensure the cell cycle cannot be reversed
  • to ensure the DNA is only duplicated once during each cell cycle
• The hayflick limit in embryonic cells:

  52
• Define the Hayflick Limit:

  The number of times a cell divides before it dies
• The division phase, mitosis, of each cancerous cell takes the same length of time as in non-cancerous cells
• Define Senescence:

  The process of aging in which the cell's ability to divide is lost so it eventually dies
• Define Cytokinesis:

  The cytoplasmic division at the end of mitosis which produces two daughter cells
• Define the Interphase:

  The longest part of the cell cycle where the cell is growing and synthesising biomolecules to prepare for mitosis.
• Define Meiosis:

  A process of two cell divisions that produces four genetically different haploid daughter cells to produce gametes for sexual reproduction
• What's the first checkpoint of the interphase?

  Growth 1 ( G1 )
• What's the last checkpoint of the interphase?

  Growth 2 ( G2 )
• Viruses do NOT undergo cell division as they are non-living
• Prokaryotic cells divide by binary fission
• What's the G0 phase?

  A resting phase where the cell leaves the cycle when DNA is damaged, it is triggered during early G1 at the restriction point by a checkpoint chemical
• Give two examples of the types of cell that stays in the G0 phase for a very long time or indefinitely.

  neurons and mature cardiac muscle cells
• What's the G1 checkpoint in the interphase?

  The first checkpoint in the cell cycle which occurs just before the end

  of the G1 phase. When it detects no damage to DNA, it commits the cell to division under favourable conditions.
• Define and outline the G1 phase.

  The first growth phase in the interphase which ensures that the cell is ready to enter the S phase

  • Organelle replication
  • Increases in size
  • Biosynthesis; Protein synthesis, including making enzymes and transcription of genes to make RNA
  • Respiration
  • The p53 tumour suppressor gene helps control this phase
  • the G1 checkpoint detects if there is any damage to DNA
• Define and outline the S phase:

  The second phase in the interphase where DNA replication occurs

  • The cell cycle will complete once it enters this phase
  • All chromosomes are replicated, each one consist of a pair of identical sister chromatids
  • It is a quick phase to reduce the chances of spontaneous mutations due to the exposed DNA base pairs
  • housekeeping genes are replicated first
• Define Housekeeping genes:

  Genes that are expressed in all cells and carry out cellular maintenance
• What is the G1 phase?

  The first growth phase in the interphase which ensures that the cell is ready to enter the S phase
• What is the S phase?

  The second phase in the interphase where DNA replication occurs
• Define and outline the G2 phase.

  The second growth phase of the interphase where the cell continues to increase in size and biosynthesis

  • energy stores increase
  • newly replicated DNA is checked for copying errors
  • special chemicals ensure the cell is ready for mitosis
• What is the G2 phase?

  The second growth phase of the interphase where the cell continues to increase in size and biosynthesis
• What is the G2 checkpoint in the interphase?

  The second checkpoint in the cell cycle which occurs at the end of

  G2 phase. It checks that the DNA was replicated correctly during the S phase before the cell enters mitosis.
• Name the four stages of Mitosis:

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Describe the prophase in mitosis:

  • the nuclear envelope breaks down
  • chromosomes condense - short, thick, visible
  • centrioles divide and move to opposite ends of the cell to form spindle fibres
• Describe in metaphase in mitosis:

  • Spindle fibres attach to the centromeres of chromosomes
  • Sister Chromatids align at the centre of the cell
• Plant cells form spindle fibres for mitosis without centrioles
• Describe the anaphase in mitosis:

  • Spindle fibres shorten and contract- motor proteins walk along the tubulin threads
  • Sister chromatids are pulled to opposite ends of the cell
  • this causes the centromere to split
  • this stage requires ATP via respiration in the mitochondria
• Describe the telophase in mitosis:

  • chromatids uncoils- long, thin, invisible
  • spindle fibres breaks down
  • Nuclear envelope forms around the separated sets of chromosomes
  • the cell now contains two genetically identical daughter cells
• Describe Cytokinesis:

  • occurs after mitosis

  In animals:

  • the cytoskeleton pulls the cell membrane inwards
  • a cleavage furrow forms in the middle of the cell
  • the cytoplasm divides
  • produces two genetically identical diploid daughter cells

  In plants:

  • vesicles fuse with the cell membrane
  • produces two genetically identical diploid daughter cells
  • the cell wall forms
• Describe cytokinesis in animals:

  occurs after mitosis

  • the cytoskeleton pulls the cell membrane inwards
  • a cleavage furrow forms in the middle of the cell
  • the cytoplasm divides
  • produces two genetically identical diploid daughter cells
• Describe cyokinesis in plants:

  occurs after mitosis

  • vesicles fuse with the cell membrane
  • produces two genetically identical diploid daughter cells
  • the cell wall forms
•   What stage of mitosis is this?

  Prophase

  
• What stage of mitosis is this?

  Anaphase