Human Biology (Mitosis & Interphase) Flashcards
What is the Cell Cycle and what are the phases and subphases?
The cell cycle is the events that take place from one cell division to the next. The phases involved include:
- Interphase:
- G1-Phase
- S-Phase
- G2-Phase
- M-Phase (Mitosis)
What is Mitosis?
When a cell reproduces each new cell must contain the same genetic information as the parent cell. This is achieved by division of the nucleus, known as mitosis.
What does Mitosis ensure for daughter cells in relation to their parents?
Mitosis ensures that each body cell receives the exact same hereditary material (DNA) as that possessed by its parent cell.
What are the 4 phases of Mitosis? Is the process continuous or in a chronological order?
- Prophase
- Metaphase
- Anaphase
- Telophase
However, the process is continuous; it does not occur in steps.
Describe Interphase
Interphase is the period between nuclear divisions. The cell goes through the G1, S and G2 phases of the cell cycle. In the S phase, the DNA molecules in the nucleus form exact copies of themselves. Therefore in the period between one cell division and the next, the quantity of DNA in the nucleus doubles.
Describe the beginning of the 1st phase of Mitosis
Prophase
- Two pairs of centrioles become visible.
- Centrioles move to opposite ends (or poles) of the cell and microtubules begin to radiate from them.
- Nucleolus disappears and the nuclear membrane begins to break down.
- The chromatin threads of DNA become tightly coiled and can be seen as chromosomes.
During Prophase why is it efficient to coil up the chromatin?
Coiling the long, delicate DNA molecules makes it easier to distribute the DNA to the daughter cells.
What is the centrepoint of a chromosome called?
Each chromosome consists of two chromatids, which are joined at a point called the centromere.
When is the DNA Replicated?
Tightly coiled DNA molecules for daughter cells are produced from DNA replication during the S-phase of interphase from a parent cell.
Describe the end of the 1st phase of Mitosis
** Prophase**
- By the end of prophase, the radiating microtubules from the centrioles, join to form a framework of fibres called a spindle.
- The nuclear membrane has now completely disappeared.
- chromatid pairs migrate towards the centre (equator) of the cell.
Describe the 2nd phase of Mitosis
Metaphase
- The chromatid pairs line up on the equator of the spindle.
- The centromere of each pair of chromatids is attached to a spindle fibre.
Describe the 3rd phase of Mitosis
** Anaphase **
- Each pair of chromatids separates at the centromere.
- As the chromatids have become independent of each other, they are now each called chromosomes.
- The new chromosomes are then pulled away from one another towards opposite poles of the cell.
- The centromeres are still attached to the spindle fibres, and it seems that the spindle fibres pull the chromosomes apart in some way.
Describe the 4th phase of Mitosis
** Telophase **
- During telophase, the two sets of chromosomes form tight groups at each pole of the cell.
- A nuclear membrane forms around each group, and a nucleolus appears in each new nucleus.
- The spindle fibres disappear
- The chromosomes gradually uncoil to become chromatin threads once more.
Describe Cytokinesis
- The cytoplasm usually begins to divide
- A furrow develops in the cytoplasm between the two nuclei
- The furrow gradually deepens until it cuts the cytoplasm into two parts, each with its own nucleus.
Summarise the end products of Mitosis and Cytokinesis
- Result in the formation of two daughter cells, which are now in interphase.
- Each daughter cell has exactly the same number and type of chromosomes as the parent cell
- The genetic information is therefore passed from parent cell to daughter cells and without change.
