cell cycle & chromosomes

• Cell cycle stages


  1. Growth and DNA replication

  2. Mitosis

  3. Cell division
• Human body cells have 46 CHROMOSOMES, which exists as 23 PAIRS, where each pair is inherited from each parent.

  • Sex Cells (GAMETES) have HALF the number of chromosomes (23), and when a sperm cell fertilises an egg cell, the two halves join to form a full set of 46 Chromosomes.

  
• Eukaryotic cells such as animals, have two copies of each chromosome which we call a pair.

  • One of these copies is from their mother and the other copy is from their father.

  
• The cell cycle

  The cell grows and chromosomes duplicate.

  Then one set of chromosomes is pulled to each end of cell by cell fibres.

  Two nuclei forms from that.

  Cytoplasm & membrane divides (Cytokinesis) to form two identical cells.
• 35 %

  
• Describe what's happening in the photo.

  cytoplasm and cell membrane dividing to form two identical daughter cells.

  
• Multicellular organisms require a continuous supply of new cells. The cell cycle makes new cells for:

  • growth (we need more cells as we grow)
  • development (we need new cell types as we develop new tissues)
  • repairing damaged tissues (we need to replace the cells we lose each day)
  • asexual reproduction
• The CELL CYCLE:


  A series of events that cells go through to grow and DIVIDE.

  • The result of the formation of 2 cells that are IDENTICAL to the original cell, which was known as DAUGHTER CELLS.

  
• Other species have different numbers of chromosomes and this is one of the reasons that animals of different species, can’t reproduce to have fertile offspring.
• 1. Cellular Growth


  The cell gets larger and produces more sub-cellular structures, such as mitochondria and ribosomes.

  
• 2. DNA replication:


  As the cell continues to repair for division:

  • it duplicates each of the 46 chromosomes. 
  • The duplicate stays attached to the original chromosome that it was copied from, to form an X shape.
  • The right half is a duplicate of the left half that we started with, so it both has the same DNA.

  Then it Follows with More cell growth.

  
• When cells are not dividing and it’s just going about its normal functions, the DNA in the nucleus exist in the form of LONG STRANDS, spread out.

  
• When cells prepare to divide, the strands of DNA (genetic material) in the nucleus coils into CHROMOSOMES (crude of packets of DNA).

  
• 3. Mitosis:


  Once the cell is ready to divide:

  • The MEMBRANE of the nucleus breaks down.
  • All 46 of the cell’s chromosomes line up along the centre of the cell.
  • Then, cell fibres from either side of the cell attach their half of each chromosome.
  • They break the chromosomes in half into two separate arms.
  • They pull the arms of the chromosomes to opposite sides of the cell.
  • The two sides are “poles”.

  
• Describe how mitosis produces two genetically identical daughter cells:


  When the chromosomes is doubled, it gets pulled apart from cell fibre, then two new nuclei form and each new cell has the same set of genes.

  
•  4. Cell Division (Cytokinesis):

  When all the genetic material has been divided among the two sides of the cell:

  • The cell membrane and cytoplasm split, to form two identical daughter cells.
  • Half of the chromosomes ends up in each of the two cells.
  • New membranes form around each set of chromosomes to form TWO NUCLEI
  • Each cell has the same DNA as each other and the parent cell it started as.

  
• 5. The daughter cells contribute to growth, development, or repair and start the cell cycle again.

  
• CHROMOSOMES:


  Structures within the nucleus of cells containing tightly coiled DNA (genetic material) when the cell prepares to divide.

  • It carries lots of genes.

  
• GENES

  Responsible for various PHYSICAL CHARACTERISTICS like hair colour and eye colour.