Mitotic Cell Cycle Flashcards
Characteristics of chromosomes
Cell nucleus’s contain thread like structures called chromosomes
Each species have a different amount of chromosomes (46 in humans)
Chromosomes become viable during cell division
Structure of chromosomes
Made up of two identical structures called chromatids
Each chromatid contains identical copies of DNA
Chromatids joined at a region called the centromere, its position is characteristic of a particular chromosome
Each chromatid contains one DNA molecule which is composed of a series of genes
There are no genes in the centromere
The DNA is wrapped around globular molecules called histones
Histones hold the DNA molecule in position and prevent it from becoming tangled
DNA+ histone= chromatin
At the end of the chromatids special DNA called telomeres act as caps to stop DNA loss during DNA replication
What are the three stages of the cell cycle?
Interphase
Mitosis
Cytokinesis
Interphase
This is the non-dividing stage that takes up most of the cycle
Consists of three phases G1, S and G2
G1-first growth stage, protein synthesis occurs. If the cell does not divide again it remains in this stage.
S- when the DNA replicates
G2- Second growth phase, when proteins needed for cell division are synthesised (e.g microtubules, spindle fibres)
Mitosis
The process where the nucleus divides to produce to daughter nuclei that genetically identical to each other and the parents cell
Cytokinesis
The division of the cytoplasm and the formation of the two daughter cells
Animals- constriction of the cytoplasm
Plants-New cell wall forms between the two daughter nuclei
Phases of mitosis
Prophase
Metaphase
Anaphase
Telophase
Prophase
Chromosomes confidence and become visible as two chromatids
Centrosomes replicate and the chromatids move apart
Spindle forms between two centrosomes
Nuclear membrane breaks down and nucleoli disappear
Metaphase
Centrosomes reach the poles and the spindle is fully formed
Chromosomes line up along the equator of the spindle, attached by the centrosomes
Anaphase
Spindle fibres shorten and pull chromatids apart at the centromeres
Centromeres move to opposite ends of the cell
Soon as the separate, chromatids become chromosomes
Telophase
New spindle breaks down
New nuclear envelope forms around each set of chromosomes
New nucleoli form
Cytoplasm constricts and cytokinesis begins
What is the significance of mitosis?
Mitosis creates daughter cells are genetically identical to the parent cells, important for:
Growth
Repair and replacement of tissues
Asexual reproduction
Use of telomeres
Protects the end of a chromosome from deterioration
DNA replication the enzyme that performs it cannot continue to the end of the DNA molecule- meaning a loss of DNA each time it is replicated
Telomeres act as barriers and are used up instead meaning no genes are lost
Some cells in the body continually divide- secrets and enzyme called telomerase which rebuilds telomeres
Loss of telomeres is associated with ageing cells, they can only divide 50 to 70 times before that cell becomes inactive and dies- loss of these cells is one of the factors responsible for the way that the body ages
What is a stem cell?
A cell that retains the ability to divide many times by mitosis while remaining undifferentiated, but following this can differentiate into specialised cells such as muscle or nerve cells
Two types of stem cells
Embryotic stem cells- found in the early stage of development of the embryo (called blastocyst)
Adult stem cells- found in various tissues and adults such as the bone marrow skin and lining of the intestine
