cell cycle, mitosis, binary fission and cancer

• What happens in interphase?

  • In G1 cell grows, organelles are duplicated, protein synthesis occurs. 
  • In S, DNA replication occurs so each new cell receives identical copy of genetic material.
  • In G2 cell keeps growing, produces proteins and organelles needed for cell division.
• What factors influence the duration of the cell cycle?

  • Cell type - rapidly dividing cell vs slow growing cell
  • The organism - fast growing vs slow growing
  • The conditions
• What is mitosis needed for?

  • Growth - organism gets bigger as more cells are produced
  • Replacing damaged cells 
  • For asexual reproduction
• What happens in prophase?

  • Chromosomes condense and become visible
  • Chromosomes appear as two sister chromatids joined at the centromere.
  • Centrioles move to opposite ends of cell
  • The nucleolus/nuclear envelope breaks down
• What happens in metaphase?

  • Nuclear membrane disappears.
  • Chromosomes line up on the equator.
  • Chromosomes are attached to spindle fibres by the centromere.
• What happens in anaphase?

  • The centromere divides
  • Spindle fibres get shorter and the sister chromatids are pulled to opposite poles of the cell, centromere first. 
  • This stage makes sure that each half of the cell receives one chromatid from each chromosome
• What happens in telophase?

  • The chromatids reach the opposite poles on the spindle. They uncoil and become long and thin. They’re now called chromosomes again. 
  • A nuclear envelope forms around each group of chromosomes, so there are now two nuclei. 
  • Cytokinesis, which starts in anaphase, finishes in telophase.
  • There are now two daughter cells that are genetically identical to the original cell and to each other. 
• What is cytokinesis?

  The cytoplasmic division of a cell at the end of mitosis/meiosis, bringing about the separation into two daughter cells.
• How does cytokinesis differ between plant and animal cells?

  In animal cells:

  • Cell membrane is pulled inwards across centre of cell
  • This separates the cytoplasm into two halves each containing a new nucleus

  In plant cells:

  • Vesicles fuse to extend the cell membranes across the cytoplasm
  • New cell walls develop
• What is mitotic index?

  mitotic index = number of cells with visible chromosomes/total number of cells observed
• What is binary fission?

  Cell division in prokaryotic cells
• What are the stages of binary fission?

  • Circular DNA replicates and both copies attach to the cell membrane
  • Plasmids replicate
  • Cell membrane grows between the two DNA molecule and begins to pinch inward, dividing the cytoplasm into two
  • A new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single copy of circular DNA and variable number of copies of the plasmids
• What are the features of a benign tumour?

  • Do not spread from their original site 
  • Do not cause cancer
  • Grow more slowly and are more compact
  • Can damage the specific organ in which they occur
  • Can cause blockages/obstructions
• What are the features of a malignant tumour?

  • Grow more quickly
  • Can break of and spread via blood and lymphatic system (metastasis) causing secondary tumours
  • Can cause cancer
  • They are most likely life-threatening
• What is cancer?

  Cancers arise due to uncontrolled mitosis.

  Cancerous cells divide repeatedly and uncontrollably, forming a tumour (an irregular mass of cells).

  Cancers start when the genes that control cell division mutate.
• What is a mutation?

  A change in the base sequence in DNA/RNA of any gene is known as a mutation.
• What is an oncogene?

  If the mutated gene is one that causes cancer it is referred to as an oncogene.