3.2.10 - Cells divide by binary fission and mitosis.

What are the three stages of cell division?

Interphase, nuclear division (mitosis/meiosis), cell division ( cytokinesis) .

What triggers the movement from one phase to another?

A chemical signal called cyclins.

What are the three phases in interphase?

G1, S, G2

What happens during G1?

During G1 the cell receives a signal telling the cell to divide again. The cell grows by producing proteins and organelles.

What happens during the S phase?

The DNA is replicated. This phase is relatively short.

What happens during the G2 phase?

During the G2 phase, the cell continues to grow and the new DNA that has been synthesised is checked

What is mitosis?

Cell division that generates new cells for growth and repair. The division of one cell into two genetically identical daughter cells

What are the uses of mitosis?

Growth of new organisms, replacement and repair of cells, asexual reproduction. (Differentiations)

What are the 4 stages of mitosis?

prophase, metaphase, anaphase, telophase

What happens in prophase?

In prophase the chromosomes condense and now are visible when stained. The chromosomes consist of two identical sister chromatids. The centrosomes move towards opposite poles and spindle fibres begin to emerge. The nuclear envelope breaks down.

What happens in metaphase?

Metaphase: Centrosomes reach opposite poles, spindle fibres continue to extend from centrosomes. The chromosomes line up at the equator and the spindle fibres reach the chromosomes and attach to the centromeres.

What is anaphase?

The sister chromatids separate at the centromere. The spindle fibres begin to contract to shorten and the chromosomes are pulled to opposite poles.

What happens in telophase?

Chromosomes arrive at opposite poles and begin to decondense. The nuclear membranes begin to reform around each set of chromosomes and the spindle fibres break down.

What happens in cytokinesis?

Cytokensis is the stage where the cytoplasm divides to form two genetically identical cells. It is the physical separation of the parent cell into two genetically identical daughter cells.

What is the difference between cytokinesis in animals and cytokinesis in plants?

In animal cells, cytokinesis happens by the furrowing of the cytoplasm. In plant cells cytokinesis is initiated with the formation of a cell plate in the middle of the cell.

How do you identify the different stages of mitosis through a microscope?

Through a microscope in prophase the chromosomes are visible and the nuclear envelope breaks down. In metaphase chromosomes are lined up along the middle of the cell. In anaphase the chromosomes are moving away from the middle of the cell. In telophase, chromosomes are in the opposite poles of the cell, the chromosomes begin to decondense and the nuclear envelope reforms.

What is used to investigate mitosis?

Meristems are used when investigating mitosis as these regions are where growth in plants occur.

What is the mitotic index used for?

To calculate the proportion of cells undergoing mitosis

What is the formula for the mitotic index?

number of cells with visible chromosomes/number of cells observed

Describe the process of binary fission.

In binary fission, a single circular DNA molecule and any plasmids present undergoe DNA replication. The parent cell divides into two cells with the cytoplasm roughly halved between the two cells. The two daughter cells each contain a single copy of the circular DNA molecule and a variable number of plasmids.

What are the measures in place to make sure all daughter cells inherit a copy of the DNA?

If a daughter cell doesn't receive the single circular DNA molecule or atleast one copy of plasmid they die.

Can viruses undergo cell division?

No

How do viruses divide?

Viruses can only reproduce by infecting living cells. They replicate by injecting their nucleic acid into a host cell. This is done by the virus using attachment proteins on its surface to bind to the host cell, then injecting its DNA/RNA into the host cell. The host cell then uses its nucleic acid and protien building machinery to produce more viral particles.

How is the virus released?

The viral particles are released either by the host cell bursting open or by budding. The exiting of viruses damaged the host cell, which causes disease.