BIO U1 AOS1 SAC 1B

• describe the purpose of binary fission


  to grow larger or replace old, worn-out cells with new ones. It is the primary method of reproduction of prokaryotic organisms
• steps of binary fission

  1. DNA replication starts at the origin of replication

  2. cell elongates and DNA migrates to opposite ends

  3. Cell undergoes cytokinesis to form two new cell by pinching inwards and forming a septum

  4. New cell wall and membrane form to producee two daughter cells
• what is the result of binary fission

  two identical daughter cells (cells with the same number and type of chromosomes)
• What happens at the G1 checkpoint?

  cells grow in size by producing proteins and cytoplasmic organelles
• What happens in the S phase?

  genetic material of a cell is doubled before it enters mitosis, allowing there to be enough DNA to be split into daughter cells
• what happens at the G2 checkpoint?

  • checks for errors
  • cell grows in size as molecules are produced in preparation for mitosis
  • makes proteins and organelles
• what happens in prophase?(PECS)

  PROPHASE

  envelope (nuclear) breaks down

  Chromatin condenses into chromosomes

  spindle form
• what happens in metaphase?(MEMS)

  Mitotic spindle is fully developed

  Equator of cell has chromosomes positioned

  Microtubules bind to sister chromatids

  Spindle extend at centrioles
• what happens in anaphase?(ASS)

  Anaphase

  Sister chromatids separate, centromeres divide

  Spindles shorten, pulling chromosomes in half towards each pole of the cell
• what happens in telophase?(NUTS)

  Nuclear envelope reforms

  Uncoiling of chromosomes

  telophase

  Spindle disappears
• what happens in cytokinesis?

  Physical separation of 2 daughter cells

  Ensures nuclear and cytoplasmic contents are accurately partitioned between two new cells
• why is mitosis important?


  plays a part in development of embryos and important for the growth and development of our bodies - produces new cells and replaces old, lost or damaged cells.

  Responsible for the development of the zygote into an adult.
• describe the outcome of mitosis

  The outcome of mitosis is 2 genetically identical daughter cells that both form from a single parent cell
• chromosome


  A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.
• chromatid


  one half of a duplicated chromosome
• what is the purpose of the checkpoints in the cell cycle?

  Cell cycle checkpoints are surveillance mechanisms that monitor the order, integrity, and fidelity of the major events of the cell cycle. These include growth to the appropriate cell size, the replication and integrity of the chromosomes, and their accurate segregation at mitosis.
• what is cytokinesis in plant cells?


  involves forming and inserting a new cell wall that separates daughter nuclei after mitosis. .
• what is cytokinesis in animal cells?


  partition the contents of a single cell into two. In animal cells, cytokinesis occurs through cortical remodelling orchestrated by the anaphase spindle.
• what is apoptosis?


  A type of cell death in which a series of molecular steps in a cell lead to its death. This is one method the body uses to get rid of unneeded or abnormal cells.
• steps of apoptosis

  1. Cell shrinking

  2. Membrane blebbing [pinching off]

  3. Cell fragmented into apoptotic bodies

  4. apoptotic bodies form

  5. macrophages phagocytose apoptotic bodies
• when will apoptosis occur?

  - in early development to eliminate unwanted cells

  - defence mechanism such as in immune reactions

  - when cells are damaged by disease
• why does apoptosis occur?

  it occurs when the cell is unhealthy or its DNA is damaged and it cannot go through division

  Apoptosis also plays a role in preventing cancer
• what is the role of caspases in apoptosis?

  They are enzymes that carry out the controlled destruction of the cell's components during apoptosis.
• what can happen when the cell cycle is disrupted?

  - Can lead to diseases such as cancer. When the cell cycle proceeds without control, cells can divide without order and accumulate genetic errors that can lead to a cancerous tumour.

  - loss of genetic information during cell division, or to mitotic catastrophe, a form of cell death that arises from mitosis
• what can cause disruptions in the cell cycle?

  Mutation can possibly disrupt the cell cycle. The mutation of the cell can affect the cell in many ways. The mutation may cause inhibition or massive cell division. It can disrupt the natural cell division, which can eventually cause cancer.
• how can cancer be formed?

  Physical mutagens - UV radiation

  Chemical mutagens - heavy metals, chemicals in pollution and cigarette smoke

  Biological mutagens - viruses

  When cells grow old or become damaged, they die, and new cells take their place. Sometimes this orderly process breaks down, and abnormal or damaged cells grow and multiply when they shouldn't. These cells may form tumours, which are lumps of tissue. Tumors can be cancerous or not cancerous (benign).
• what can happen when DNA is damaged?

  can cause genetic alterations - mutations can lead to the development of cancer
• 5 types of stem cells

  totipotent, pluripotent, multipotent, unipotent, oligopotent
• example of a totipotent stem cell

  fertilized egg/zygote
• example of a pluripotent stem cell


  • embryonic stem cells
  • cell of blastocyst 5-14 days
• example of a multipotent stem cell

  foetal tissue
• function of a totipotent stem cell

  can differentiate into all possible cell types
• function of a pluripotent stem cell


  can differentiate into multiple cell types
• function of a multipotent stem cell

  cell that can differentiate into a closely related family of cells
• example of a unipotent stem cell

  cardiomyocytes
• example of an oligopotent stem cell

  lymphoid stem cell
• function of a unipotent stem cell


  cell in an adult organism that isn't matured yet but has differentiated - can progress into only one cell type
• function of an oligopotent stem cell


  similar to multipotent cells but become less able to differentiate
• what is a blastocyst


  a cluster of dividing cells made by a fertilized egg. It's the early stage of an embryo
• what will a blastocyst become

  The inner group of cells will become the embryo. The outer group will become the cells that nourish and protect it.