Mitosis + Cell Cycle Flashcards
Mitosis
Mitosis is division of a cell that results in each of the daughter cells having an identical copy of the DNA of the parent cell.
Except in the rare event of a mutation, the genetic make-up of the two daughter nuclei is also identical to that of the parent nucleus..
there is a part before division called interphase. It is a period of, the replication of DNA. The two copies of DNA after replication remain joined at a place called the centromere.
prophase animal
In prophase, the chromosomes first become visible, initially as long thin threads, which later shorten and thicken. Animal cells contain two cylindrical organelles called centrioles, each of which moves to opposite ends of the cell. From each of the centrioles, spindle fibres develop, which span the cell from pole to pole.
these spindle fibres are called the spindle apparatus.
Prophase - plant cell
plant cells lack centrioles but do develop a spindle apparatus, centrioles not essential to spindle fibre formation. The nucleolus disappears and the nuclear envelope breaks down, leaving the chromosomes free in the cytoplasm of the cell. These chromosomes are drawn towards the equator of the cell by the spindle fibres attached to the centromere.
Metaphase
By metaphase the chromosomes are seen to be made up of two chromatids. Each chromatid is an identical copy of DNA from the parent cell. The chromatids are joined by the centromere
this centromere has some microtubules from the poles attached to it, and the chromosomes are pulled along the spindle apparatus and arrange themselves across the equator of the cell.
Anaphase
In anaphase, the centromeres divide into two and the spindle fibres pull the individual chromatids making up the chromosome apart.
The chromatids move rapidly to their respective, opposite poles of the cell.we now call them chromosomes.
The energy for the process is provided by mitochondria, which gather around the spindle fibres.
If cells are treated with chemicals that destroy the spindle, the chromosomes remain at the equator unable to reach the poles
Telophase and cytokinesis
In this stage the chromosomes reach their respective poles and become longer and thinner, Enally disappearing altogether leaving only widely spread chromatin. The spindle fibres disintegrate and the nuclear envelope and nucleous re-form. Finally the cytoplasm divides in a process called cytokinesis.
Binary fission
The circular DNA molecule replicates and both copies attach to the cell membrane.
• The plasmids also replicate.
• The cell membrane begins to grow between the two DNA molecules 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,
Replication of virus
, they cannot undergo cell division. Instead they replicate by attaching to their host cell with the attachment proteins on their surface. They then inject their nucleic acid into the host cell. The genetic information on the nucleic acid then provides the ‘instructions’ for host cell’s metabolic processes to start producing the viral components which are then assembled into new viruses.
Cancer and the control of mitosis
Cancer is a disease caused by a growth disorder of cells it is the result of damage to the genes that regulate mitosis and the cell cycle. This leads to uncontrolled growth and division of cells. As a consequence, a group of abnormal cells, called a tumour, develops and constantly expands in size.
Tumours can develop in any organ of the body, but are most commonly found in the lungs , prostate and breast a tumour only becomes cancerous if it changes from benign to malignant
Rate of mitosis
The rate of mitosis can be affected by the environment of the cell and by growth factors. It is also controlled by two types of gene. A mutation to one of these genes results in uncontrolled mitosis.
The mutant cells so formed are usually structurally and functionally different from normal cells. Most die. However, any that survive are capable of dividing to form clones of themselves and forming tumours.
Malignant tumours grow rapidly, are less compact and are more likely to be life-threatening, while benign ones grow more slowly, are more compact and are less likely to be life-threatening.
Treatment of cancer
The treatment of cancer often involves killing dividing cells by blocking a part of the cell cycle.. (chemotherapy) usually disrupt the cell cycle by:
• preventing DNA from replicating
• inhibiting the metaphase stage of mitosis by interfering with spindle formation.
The problem with such drugs is that they also disrupt the cell cycle of normal cells. However, the drugs are more effective against rapidly dividing cells.. Those normal body cells, such as hair-producing cells, that divide rapidly are also vulnerable to damage. This explains the hair loss frequently seen in patients undergoing cancer treatment.
