Mitosis

• Mitosis is the process of cell division, in which the cell divides into two, and then into two again and again. Cell division in other terms is the division of the cell to make two genetically identical copies of the previous cell (two daughter cells).

• During Mitosis, the chromosomes aren’t split- the chromosome amount stays exactly the same in the previous cell, and the cell which was made from the previous cell will have the exact same amount of chromosomes as the previous cell.

• Cell division has three main stages.

• Stage one (Cell Division)- Replication of DNA to form two copies of each chromosome and synthesis of new subcellular structures.

• Stage 2- Mitosis- nucleus is divided.

• Stage 3- cell divides into two.

• Each cell in the whole body has 46 chromosomes (diploid nucleus), except from sperm cells and egg cells which have 23 chromosomes each, (In other terms, a haploid nucleus).

• The cell cycle can take less than 24 hrs or more than 7 years depending on the cells involved. As well as this, when you get old Mitosis slows down.

Cell Cycle

• The cell cycle contains 6 main steps= Interphase (in between), prophase (prepare), metaphase (middle), amaphase (apart), telophase (two) and finally cytokinesis (division).

• During Interphase, new sub-cellular structures are made like mitochondria to prepare for mitosis (which is the stages of prophase, metaphase, amaphase, telophase and cytokinesis)

• Prophase is when the DNA unwinds and condenses into chromosomes and the nucleus breaks down. Spindle fibres become visible. The membrane around the nucleus disappears also.

• Metaphase is when the spindle fibres attach to the chromosomes at the centrometre (a constricted region of a chromosome). The chromosomes then line up along the equator/centre of the cell.

• Amaphase is when the spindle fibres shorten and pull the chromosomes apart to the two poles.

• Telophase is when a nuclear membrane forms around each set of chromosomes, separating them to form two new nuclei.

• Finally, cytokinesis is when the cytoplasm splits to create two separate genetically identical diploid cells.

Stem Cells

• Stem cells come in two types- embryonic stem cells and adult stem cells. Embryonic stem cells are able to differentiate a lot more easily into different cells whereas adult stem cells are only able to fix damaged or dead cells. Adult stem cells have a very short range such as red blood cells and skeletal tissue.

• Differentiation happens at a young age, and so all specialised cells are made at the early stages of life.

• Plant cells are able to differentiate throughout their lives, and undifferentiated cells are made at the active zones of the stems called meristems (the tip of the shoot where cell division takes place).

• Plants keep growing at their growing points, mainly growing during elongation, and many plant cells can retain the ability to redifferentiate into any cell type. This is why any cutting of a plant can be used to make a new plant of the same kind.

• Cloning is when offspring is identical genetically. From a tiny piece of leaf tissue, huge numbers of identical plant clones can be produced.

• Stem cells are undifferentiated cells and can differentiate into any cells depending on whether it is an embryonic stem cell (large range) or an adult stem cell (short range).

• Embryonic stem cells are pluripotent. This means it is able to develop into many different types of cells.

• Adult stem cells are found only in certain places in the body within differentiated tissues for example bone marrow. They can only become a limited range of cell and they usually replace old or damaged tissue. Most cells in the body aren’t stem cells.

• Stem cells can divide and differentiate through mitosis.

• Stem cells can cure illnesses such as cancer, leukaemia, Huntingdon’s and Parkinson’s disease.

• Adult stem cells can be taken from bone marrow, the brain and other places in the body whereas embryonic stem cells can be collected from leftover embryos not implanted after IVF treatments. Since these are embryonic stem cells, they can differentiate into any specialised cell in the body.

• Rejection can often happen in treatments to cure leukaemia as rejection can occur when trying to give the patient white blood cells, and the white blood cells could attack the cells of either the patient or the cells that were implanted.

• Differentiation in animal cells can either be that the stem cells replicate themselves, or they differentiate into a different kind of cell.

• In therapeutic cloning, an embryo could’ve been made to have the same genetic material as the patient. This means that if the stem cell was to clone, the clones would have the same genetic material as the patient and therefore won’t be rejected.

• If stem cells are used in the lab, they are at risk of being contaminated with viruses which could be passed onto the patient who takes them.

Meristems

• In plants, the stem cells are found in the meristems, and these can differentiate into any plant cell.

• These stem cells can be used to make identical copies of the plant quickly and cheaply.

• This method can be used to grow out plants which are at risk of being extinct.

Embryonic stem cell research

• Embryos are made from mitosis when the egg cell becomes a zygote (fertilised egg cell) and divides to make the embryo.

• Some people have negative opinions against embryonic stem cell research as it requires “killing” the embryo to research.

Binary Fission

1. Replication of DNA: The process begins with the replication of the bacterial chromosome, which is a single circular DNA molecule. This replication starts at the origin of replication and proceeds bidirectionally along the chromosome.

2. Cell Growth: As the DNA replicates, the bacterial cell grows in size to accommodate the increased amount of genetic material.

3. Formation of Septum: The bacterial cell contains a structure called the septum, which begins to form across the center of the cell. This septum is made of cell wall material and divides the cell into two compartments.

4. Completion of Septum: The septum continues to grow inward, eventually pinching the cell into two separate daughter cells. Each daughter cell contains a copy of the original bacterial chromosome.

5. Cell Separation: Once the septum is complete, the two daughter cells separate from each other. This separation is facilitated by the action of proteins and enzymes that degrade the cell wall at the site of division.

6. Cellular Reorganization: Following division, each daughter cell undergoes cellular reorganization to establish its own independent cellular machinery, including the synthesis of cell wall components, proteins, and other essential molecules.

7. Maturation of Daughter Cells: The two daughter cells mature into fully functional bacterial cells capable of carrying out all necessary cellular processes.

Terms

• Differentiate- to change from undifferentiated to differentiated.

• Meristems- the tissue at the tip of the plant where cell division takes place.

• Zygote- fertilised egg cell.

• Elongate- to make something longer.

• Growth in plants only occur in certain tissues.

• Many plants continue growing throughout their life.

• Most cell growth occurs by cell elongation not cell division (plants).

• Redifferentiate- to differentiate again

• Clone- to make a genetically identical copy.