2.2 mitosis & cell cycle

Define mitosis in terms of DNA outcome in the daughter cells.

Mitosis is the stage of the cell cycle where a eukaryotic cell divides to produce two daughter cells, each receiving identical copies of the DNA made during DNA replication.

During which part of the cell cycle does DNA replication occur?

Interphase.

How are chromosomes arranged in metaphase?

Chromosomes line up along the equator (metaphase plate) with spindle fibres attached to the centromeres.

In which mitosis stage would you expect to see condensed chromosomes aligned across the centre of the cell?

Metaphase.

What is the role of spindle fibres during mitosis?

Spindle fibres attach to centromeres and shorten to separate sister chromatids, pulling them to opposite poles.

What does it mean to say mitosis is a controlled process?

The rate and timing of cell division are regulated cells do not divide continuously without control.

What DNA molecules are replicated in prokaryotic binary fission?

The circular DNA and plasmids.

Why don’t viruses undergo cell division?

Viruses are non

Required practical: what is the purpose of staining root tip squashes?

To make chromosomes/nuclei easier to see so stages of mitosis can be identified.

What is meant by the cell cycle in a eukaryotic cell that can divide?

A repeating sequence of events in which a cell grows, replicates its DNA during interphase, and then divides by mitosis (and usually cytokinesis) to form two daughter cells.

What happens to chromosomes in prophase of mitosis?

Chromosomes condense and become visible

each consists of two sister chromatids joined at a centromere.

What is cytokinesis and what is its outcome?

Cytokinesis is division of the cytoplasm

it usually follows mitosis and produces two separate daughter cells.

In which stage would you expect chromosomes to first become clearly visible as distinct structures?

Prophase.

How does mitosis ensure daughter cells are genetically identical (in terms of DNA copies)?

DNA is replicated in interphase to produce identical copies, then mitosis separates sister chromatids so each daughter cell receives one copy of each chromosome.

Name the process by which prokaryotic cells divide.

Binary fission.

What happens to the cytoplasm during binary fission?

The cytoplasm divides to separate the cell into two daughter cells.

Write the formula for mitotic index (as a fraction).

Mitotic index
=
number of cells in mitosis
total number of cells
Mitotic index=
total number of cells
number of cells in mitosis

​

When viewing a root tip squash, why are many cells typically seen in interphase compared with mitosis stages?

Cells spend most of the cell cycle in interphase (including DNA replication), so a snapshot shows more cells in interphase than in mitosis.

In a multicellular organism, do all cells retain the ability to divide? Explain.

No. Many cells differentiate and lose the ability to divide, while some eukaryotic cells retain division capacity and therefore pass through a cell cycle.

What is the appearance/behaviour of chromosomes during interphase?

Chromosomes are not visible as separate structures because DNA is decondensed (as chromatin) while DNA replication occurs.

Describe chromosome behaviour during telophase.

Chromatids reach the poles and chromosomes decondense, two nuclei form as nuclear envelopes re-form

In which stage would you expect to see two groups of chromosomes at opposite poles with new nuclei forming?

Telophase (often with cytokinesis beginning or occurring).

State the correct order of the mitosis stages named in the specification.

Interphase, prophase, metaphase, anaphase, telophase (then cytokinesis).

How are many cancer treatments linked to the cell cycle?

They aim to control or reduce the rate of cell division (by targeting rapidly dividing cells).

How do plasmids distribute to daughter cells in binary fission?

Each daughter cell receives a variable number of plasmid copies (not necessarily equal).

Required practical: what tissue is used to observe stages of mitosis in plant cells?

Cells from plant root tips.

What is the mitotic index and what does it measure?

The proportion of cells in mitosis at a given time it indicates how actively tissue is dividing

What key event defines anaphase?

Sister chromatids separate at the centromeres and are pulled to opposite poles of the cell.

In which mitosis stage would you expect to see chromatids moving apart toward opposite ends of the cell?

Anaphase.

Why must spindle fibres attach to centromeres for correct separation of chromatids?

Attachment at the centromere allows each sister chromatid to be pulled to opposite poles, ensuring each daughter cell receives an identical set of DNA.

What can uncontrolled cell division lead to?

The formation of tumours and cancers.

What is the genetic outcome of binary fission for circular DNA?

Two daughter cells are produced, each with a single copy of the circular DNA.

After a virus injects its nucleic acid into a host cell, how are new virus particles produced?

The infected host cell replicates the virus particles using the injected viral nucleic acid.

Required practical: what instrument is used to identify mitosis stages in the stained squashes?

An optical microscope.