Cell division Flashcards
What is a Cell cycle?
A series of precisely timed and carefully regulated stages of growth, DNA replication and division.
What are the two major phases in the cell cycle (mitosis)?
Interphase and the Mitotic Phase
How is the cell cycle regulated at each stage?
G1- checks for size, nutrients, DNA damage and growth factors
G2- Checked to make sure replication if fully complete for all cells
M- Sister chromatids are checked to confirm that they are attached to the suitable spindles.
What processes take place in the stage of Interphase?
The cell prepares to divide.
DNA is replicated by semi- conservative replication.
There is now two copies of every chromosome.
The organelles are also replicated.
More ATP is produced to be used in cell division.
What processes take place in the stage of Prophase?
The nuclear envelope and the nucleolus break down.
Chromosomes are left floating in the cytoplasm.
The chromosomes coil more tightly and become shorter and fatter.
They can be seen under a light microscope.
Small protein bundles called centrioles move to opposite poles of the cell.
Microtubules form the mitotic spindle between the centrioles.
What processes take place in the stage of Metaphase?
The chromosomes line up along the mid-line of the cell.
In metaphase, the chromosomes are maximally condensed.
They are attached to the spindle by the centromere.
What processes take place in the stage of Anaphase?
The chromosomes break into two chromatids.
The sister chromatids separate at the centromere.
The spindles contract and pull the chromatids to each pole of the cell.
What processes take place in the stage of Telophase?
The chromatids reach the opposite poles and begin to decondense (unravel), becoming chromosomes again.
Nuclear envelopes form around the chromosomes so there are now two nuclei.
The cytoplasm splits and two daughter cells are formed. The daughter cells are identical to the original cell and to each other.
The cell cycle starts again.
What is the Centromere?
The central region of a chromosome to which the microtubules of the spindle attach
What are Chromatids?
The two thread-like strands into which a chromosome divides longitudinally during cell division. Each contains a double helix of DNA.
What is Cytokinesis?
The division of the cytoplasm at the end of mitosis, bringing about the separation into two daughter cells.
What are Centriole?
They are a pair of small cylindrical organelles located near the nucleus and involved in the development of spindle fibres in cell division.
What is mitosis essential?
- Asexual reproduction by single celled organisms
- Reproduces cells that are identical in form and function
- Replace lost cells that have been damaged
How do single celled organisms introduce variation?
Mitosis introduces no genetic variation into populations so bacteria rely on alternative methods, such as horizontal gene transfer of plasmids for variation.
What is the order for the stages of meiosis?
- Interphase and prophase 1
2, Metaphase 1 - Anaphase 1 + Telophase 1
- Cytokinesis
- Prophase 2 + Metaphase 2
- Anaphase 2
- Telophase + Cytokinesis
What is the role of meiosis
Sexual Reproduction
Genetic Variation
Random fertilisation
Gamete Production
How does genetic variation occur in meisosis
Crossing over
Independent assortment
What is Crossing over?
exchange of genetic material between non sister chromatids of homologous chromosomes during meiosis 1
What is Independent assortment?
The chromosomes in a homologous pair are separated in meiosis I in a random formation to produce two genetically different daughter cells. The combination of chromosomes in the two daughter cells is random.
The process of separating chromosomes into random combinations is called independent assortment.
Independent assortment increases genetic variation.
How can a chromosome/ cell go through variation
Crossing over,
Independent assortment,
Fertilization
How many steps in meiosis?
8
Do both mitosis and meiosis go through cytokinesis
Yes
Does mitosis cross over?
No
Describe the functions and importance of mitosis with examples
Daughter cells are exact copies which means they have the same number as parent cell, meaning they are gentically stable.
It is for growth and repir, like replacing missing tissue, or wounds like skin healing, red blood cells are replaced by mitosis,
cancer is a form of mitosis which is going through uncontrolled division.
