All Cells Arise from Other Cells: Mitosis and the Cell Cycle

Comprehensive question-and-answer flashcards covering eukaryotic cell cycles, stages of mitosis, cytokinesis, binary fission, viral replication, cancer treatment mechanisms, and practical skills for calculating the mitotic index.

What does the biological principle of biogenesis state?

All living cells arise from pre-existing cells.

What are the three main stages of the eukaryotic cell cycle?

Interphase, Mitosis (nuclear division), and Cytokinesis (cytoplasmic division).

Approximately what percentage of the cell cycle is occupied by interphase?

Often occupying $90\%$ of the cycle.

What occurs during the G1 phase (First Gap) of interphase?

The cell grows, and organelles (such as mitochondria and ribosomes) replicate.

What occurs during the S phase (Synthesis) of interphase?

DNA replication occurs semi-conservatively,

each chromosome is copied to form two identical sister chromatids

joined at a centromere.

What occurs during the G2 phase (Second Gap) of interphase?

Further growth and error-checking of the replicated DNA.

Why are chromosomes not visible under a light microscope during interphase?

Because the chromatin is not yet condensed.

What is the biological definition of mitosis?

The division of the nucleus into two genetically identical daughter nuclei.

What events occur during prophase of mitosis? 4

Chromosomes condense and become visible,

the nuclear envelope breaks down,

centrioles move to opposite poles of the cell,

and spindle fibres begin to form.

What major events occur during metaphase of mitosis? 2

Chromosomes line up along the equator (middle) of the cell,

spindle fibres attach to the centromere of each chromosome.

What happens during anaphase of mitosis, and where is the required energy sourced? 3

The centromeres divide to separate sister chromatids,

spindle fibres shorten to pull the chromatids (now called chromosomes) to opposite poles.

Energy is provided by mitochondria (ATP).

What structural changes occur in the cell during telophase of mitosis? 3

Chromosomes reach the poles and decondense (become longer and thinner),

the nuclear envelope reforms around each set of chromosomes,

spindle fibres disintegrate.

What is cytokinesis,

Cytokinesis is the division of the cytoplasm to form two separate, genetically identical daughter cells.

What is the genetic and cellular cause of cancer?

Uncontrolled cell division resulting from a mutation in the genes that regulate the cell cycle

How does the cancer drug Cisplatin target the cell cycle?

It prevents DNA replication by inhibiting the S phase.

How do Vinca alkaloids act to disrupt the cell cycle in cancer treatment?

They inhibit spindle formation, stopping the cell in metaphase.

Why do cancer drugs produce side effects such as hair loss or damage to the gut lining?

They do not only kill cancer cells; they affect any rapidly dividing cell.

What are the four sequential steps of binary fission in prokaryotes?

1. The circular DNA molecule replicates once.

2. . The plasmids replicate (can be multiple times).

3. The cell membrane grows between the two DNA molecules and pinches inward, dividing the cytoplasm.

4. A new cell wall forms, producing two daughter cells.

How does the inheritance of circular DNA compare to plasmids in daughter cells following binary fission?

Each daughter cell receives one copy of the circular DNA, but a variable number of copies of plasmids.

What is the formula used to calculate the Mitotic Index in AQA Required Practical 2?

$$\text{Mitotic Index} = \frac{\text{Number of cells with visible chromosomes}}{\text{Total number of cells observed}}$$