Cell division

Students will learn which are the processes linked to cell division (development, growth, tissue repair);

Why do we need cellular division?

Mitosis is the process through which cells can make copies of themselves.  Why do they do that?

For several reasons:

1. When multicellular organisms (either plants or animals) want to GROW

2. When multicellular organisms need to REPLACE cells that have been damaged 

3. When an unicellular organism wants to REPRODUCE (ASEXUAL REPRODUCTION)

To do this a cell has to:

a. make copies of its DNA

b. divide DNA in a correct way so that each DAUGHTER cell has the same DNA as the original MOTHER cell

So, when a human cell divides, MOTHER and DAUGHTER cell has the same number of chromosomes, which is 46. They are both diploid cells because each cell has the same information two times! This means that between point a and point b we will have a cell with 4-time the same information!

 

Why do we need mitosis? TEST

  • When we grow it is because cells are becoming bigger
  • When we grow it is because cells are dividing
  • If we cut ourselves, our skin cells can replace damaged cells with mitosis
  • Asexual reproduction does not need mitosis
  • a human diploid cell has 23 chromosomes
  • after mitosis we have two different cells with different genetic information

Students will be able to link different mitosis phases to their pictures

What happens during mitosis?

 

Mitosis stages at the microscope

Which of this picture represents Prophase?

Mitosis stages at the microscope

Which of this picture represents Anaphase?

Mitosis stages at the microscope

Which of this picture represents Metaphase?

Students will be able to recognize cellular cycle phases

What is the cell cycle?

Mitosis is only a part of a process called cell cycle which regulates cellular division. Cells do not keep on dividing unless it is not needed. 

The cell cycle phases are:

  G0 cell rests and does not divide
Interphase G1 cell grows 
  S cell duplicates DNA
  G2 cell saves energy and grows
Mitosis (or Meiosis) M cell divides 

 

Watch this video

When cell cycle is not working some problems could occur: when cell cycle is out of control a cell keeps dividing and cancer is developed.

Cell cycle TEST

  • DNA is copied ..
    in phase S
  • Cell grows...
    in G1 and G2 phases

Students will be able to describe what is a stem cell and they will be able to give opinions on the issues around using embryonic stem cells in medical research

What is a stem cell

In our organism there are different kinds of cells. They share some common features (such as nucleus, DNA, mitochondria...) but they are specialised in relation to what is their duty. A skin cell will be very different from a liver cell. Have a look:

This is an epidermal layer with skin cells These are hepatocytes (liver cells) These are blood cells: red cells and leukocytes

However, it is true that each single cell of our organism has developed from a first single cell, the zygote. So, how have cells become different?

The differentiation process is possibile because we have STEM CELLS. 

First of all, a stem cell is undifferentiated.

Secondly, it can develop into different types of cells depending on the instruction that it receives. 

Last but not least, a stem cell can always divide and multiply:for the whole life of the organism it belongs to. Most of the cells of our body loose this ability when they "grow up" and differentiate.

On the contrary, in plants this ability is mostly maintained.

We have two groups of stem cells: embryonic stem cells and adult stem cells.

The most powerful ones are embryonic stem cells. They can differentiate in every type of cell of the organism and of course they are found in embryos. 

Adult stem cells are less powerful and they can just turn into few types of cell. We can find adult stem cells in several district of our "grown up" organism, such as bone marrow and skin, so they are more attainable than embryonic stem cells but less versatile. Adult stem cells are used to replace damage cells in our body.

 

Stem cells and research

Due to their ability of multiplication and differentiation, scientists have always been interested in stem cells. We could use stem cells to replace cells or organs that are not working anymore because of illnesses, such as Alzheimer's disease and diabetes.

It is true that adult stem cells are quite easy to reach but this is not true for embryonic cells. Embryonic cells would be more powerful to cure diseases but there are many people that think that it is not ethic to use them since each embryo is a potential human life. On the other hand, we have to remember that we do not know yet how stem cells "choose" what to become and a lot of research is needed.

Nowadays, some adult stem cells therapy are available and scientists are looking for more.

Which of the following are features of stem cells?

  • They can always divide
  • They cannot divide
  • They can turn into different type of cell
  • They can be found only in plants

Which of these features belong to embryonic stem cells?

  • They are the most powerful stem cells
  • They can turn into only a little group of cell
  • They are found in embryos
  • They are found in adult organisms

Which of these features belong to adult stem cells?

  • They can be found in bone marrow
  • They are more powerful than embryonic stem cells
  • They are found in embryos
  • They can turn into every type of cell

What do you think about using embryonic stem cells in research?

Stem cells statement

  • there are some therapies that are based on embryonic stem cells
  • An adult stem cell can turn into few type of cell
  • Research is important to understand how we could use stem cells to cure diseases
  • The more a cell is specialised, the more it can divide