Cell Division In Eukaryotic & Prokaryotic Cells

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Notas de aula

The Cell Cycle & Interphase

The cell cycle is the regulated sequence of events between one cell division and the next.
It has three main phases: interphase, nuclear division (mitosis) and cell division (cytokinesis).
Transition between phases is triggered by chemical signals called cyclins.
The length of the cell cycle varies with environmental conditions, cell type and organism (e.g. onion root tip cells divide every ~20 hours; human intestine epithelial cells every ~10 hours).
Interphase consists of G1, S and G2; during interphase the cell grows and carries out normal functions, including protein synthesis and DNA replication.
G1: cell grows, makes enzymes and other proteins for growth, and receives a signal to divide.
S phase: DNA replicates; each chromosome then consists of two identical sister chromatids; S phase is relatively short.
G2: further growth, error checking and repair of new DNA, and production of tubulin for the mitotic spindle.

The Stages of Mitosis

Mitosis is nuclear division producing two genetically identical daughter nuclei, each with the same number of chromosomes as the parent.
Mitosis is important for growth of multicellular organisms, replacement and repair of cells, and asexual reproduction.
The four stages of mitosis in order are prophase, metaphase, anaphase, telophase (remember PMAT).
Prophase: chromosomes condense and become visible; each is two sister chromatids joined at a centromere; centrosomes move to opposite poles; spindle fibres form; nuclear envelope breaks down.
Metaphase: centrosomes at opposite poles; spindle fibres fully formed and attached to centromeres; chromosomes align on the metaphase plate (equator).
Anaphase: spindle fibres shorten, pulling chromatids apart; centromeres divide; chromatids (now chromosomes) move to opposite poles.
Telophase: chromosomes arrive at poles and decondense; nuclear envelopes reform; spindle fibres break down.
Cells in different stages can be recognised from photomicrographs: prophase has one group of chromosomes with a breaking-down nuclear envelope; metaphase chromosomes line up along the middle; anaphase chromosomes move away from the middle; telophase has two groups of chromosomes, one at each pole.

Cytokinesis

Cytokinesis occurs after telophase and is not part of mitosis.
It follows reformation of the nuclear envelope at each pole and involves division of the cytoplasm.
It produces two genetically identical daughter cells.
In animal cells, a cleavage furrow forms and the membrane pinches inwards to separate the cells.
In plant cells, a cell plate forms at the metaphase plate and new cell walls are built from it to separate the cells.

Required Practical: Identifying Mitotic Stages

Growth in plants occurs in specific regions called meristems; the root tip meristem (just behind the root cap) is used to study mitosis.
The root tip meristem contains a zone of cell division with cells undergoing mitosis.
Pre-prepared slides can be studied, or temporary slides prepared using the squash technique (root tips are stained and gently squashed to spread cells into a thin sheet).
Method: cut ~1 cm root tips and place in ethanoic alcohol to fix the tissue and stop mitosis; then place in warm (60°C) dilute hydrochloric acid to separate the cells.
Transfer root tip to a slide, add a stain such as acetic orcein (stains chromosomes deep purple), lower a coverslip and press down firmly with a paper towel to spread cells into one layer.
View under an optical microscope; cells undergoing mitosis can be seen, drawn and annotated.
Limitations: preparation can damage cells and alter appearance; squashing or staining can generate artefacts; cell structures are 3D and cut at different planes, causing inconsistencies; optical microscopes have limited magnification.

Investigating Plant Root Tips

The mitotic index is the proportion of cells in a group or tissue sample that are undergoing mitosis.
Formula: mitotic index = number of cells with visible chromosomes ÷ total number of cells; multiply by 100 for a percentage.
Example: 32 cells with visible chromosomes out of 42 total gives a mitotic index of 32 ÷ 42 = 0.76 (2 d.p.).
Example: (14 + 5 + 3 + 6) ÷ (36 + 14 + 5 + 3 + 6) = 28 ÷ 64 = 0.44 (2 d.p.).
Example: 20 cells with visible chromosomes out of 75 total gives 20 ÷ 75 = 0.27 (2 d.p.).
Actual size of root tip cells can be calculated using: actual size = size of image ÷ magnification.
Cell size is typically measured in micrometres (μm) or nanometres (nm); all measurements must be in the same units.
Unit conversions: 1000 nm = 1 μm; 1000 μm = 1 mm; 1000 mm = 1 m. Magnification has no units.

Uncontrolled Cell Division & Cancer

Mitosis is normally a controlled process.
Cancer results from uncontrolled mitosis, forming a tumour (an abnormal mass of cells).
Mutations in genes controlling the cell cycle (e.g. oncogenes, tumour suppressor genes) can lead to loss of control.
These mutations may cause continuous cell division or prevent programmed cell death (apoptosis).
Most cancer treatments aim to slow or stop mitosis in rapidly dividing cells.
Examples: methotrexate inhibits DNA nucleotide synthesis; taxol prevents disassembly of spindle fibres (freezing mitosis).

Binary Fission

Cell division in prokaryotes is called binary fission.
It is simpler than mitosis because prokaryotes have no nucleus, chromosomes, spindle fibres or membrane-bound organelles.
Prokaryotes only need to replicate a single, circular DNA molecule and plasmids (small, circular DNA molecules).
Process: circular DNA replicates; plasmids replicate; cytoplasm divides roughly equally; each daughter cell receives one copy of circular DNA and a variable number of plasmids.
Each daughter cell is genetically identical; mechanisms ensure all daughter cells inherit a copy of the circular DNA and some plasmids.
If a daughter cell does not receive the circular DNA molecule or at least one plasmid, it dies.
Binary fission can be rapid (e.g. every 20 minutes under ideal conditions), allowing bacteria to colonise new environments, outcompete other microbes and accumulate mutations faster (contributing to antibiotic resistance).

Viral Particle Replication

Viruses are acellular infectious particles; being non-living, they do not undergo cell division.
Structure: a nucleic acid core (DNA or RNA, single- or double-stranded), a protein coat called a capsid, and sometimes an outer envelope (usually from host cell membrane phospholipids).
Viruses are non-living and parasitic – they can only replicate inside host cells.
Replication: attachment proteins bind to complementary receptors on the host cell surface; viral DNA or RNA is injected into the host cell.
The host cell uses its own enzymes and ribosomes to synthesise viral proteins and nucleic acids; new viral particles are assembled.
Viruses are released by cell lysis (bursting) or budding (taking host membrane to form a viral envelope).
Virus release damages or destroys host cells, causing disease.
Different viruses have different attachment proteins and can only bind to specific host cell types with complementary receptors; some infect prokaryotes, others eukaryotic animal or plant cells.

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Questões de prática

Prévia grátis — 8 de 57 perguntas. Cadastre-se para ver todas.

1.Which of the following is the correct order of the stages of mitosis?
Easy
- AProphase → Metaphase → Anaphase → Telophase
- BMetaphase → Prophase → Anaphase → Telophase
- CProphase → Anaphase → Metaphase → Telophase
- DTelophase → Anaphase → Metaphase → Prophase
2.During which stage of the cell cycle does DNA replication occur?
Easy
- AG1 phase
- BS phase
- CG2 phase
- DM phase
3.Cytokinesis is a stage of mitosis.
Easy
True or false?
4.Which of the following correctly describes the behaviour of chromosomes during metaphase?
Medium
- AChromosomes align along the equator of the cell
- BChromatids separate and move to opposite poles
- CChromosomes condense and become visible
- DNuclear envelope reforms around each set of chromosomes
5.Which of the following statements about binary fission is correct?
Medium
- AIt involves the formation of a mitotic spindle
- BIt produces two genetically identical daughter cells
- CIt requires the breakdown of a nuclear envelope
- DIt results in four daughter cells
6.Which of the following is a correct difference between cytokinesis in animal cells and plant cells?
Medium
- AAnimal cells form a cell plate; plant cells form a cleavage furrow
- BAnimal cells form a cleavage furrow; plant cells form a cell plate
- CBoth animal and plant cells form a cell plate
- DBoth animal and plant cells form a cleavage furrow
7.Which of the following is the main event of G1 phase of interphase?
Medium
- ADNA replication
- BCell growth and protein synthesis
- CChromosome alignment
- DCytokinesis
8.Which of the following statements about the mitotic index is correct?
Medium
- AIt is the proportion of cells in a sample that are undergoing mitosis
- BIt is the number of cells in a sample that are in interphase
- CIt is the total number of cells in a sample
- DIt is the number of cells that have completed mitosis

Mais perguntas

9.Which of the following correctly describes the role of cyclins in the cell cycle?
Medium
- AThey are enzymes that replicate DNA
- BThey are chemical signals that trigger the transition between phases
- CThey are structural proteins that form the spindle fibres
- DThey are checkpoints that prevent the cell cycle from proceeding
10.Which of the following events occur during prophase of mitosis? (select all that apply)
Medium
- AChromosomes condense and become visible when stained
- BThe nuclear envelope breaks down
- CSpindle fibres form from the centrosomes
- DSister chromatids are pulled apart towards opposite poles
- EChromosomes align along the equator of the cell
11.Which of the following statements about the cell cycle are correct? (select all that apply)
Medium
- AThe cell cycle is the regulated sequence of events between one cell division and the next.
- BInterphase consists of G1, S and G2 phases.
- CCyclins are chemical signals that trigger transition between phases.
- DDNA replication occurs during G2 phase.
- EThe length of the cell cycle is fixed and identical for all cell types.
12.Match each stage of mitosis with the correct description of the chromosomes' behaviour.
Medium
- Prophase
- Metaphase
- Anaphase
- Telophase
- Chromosomes condense and become visible; nuclear envelope breaks down
- Chromosomes line up along the equator of the cell
- Centromeres divide and chromatids move to opposite poles
- Chromosomes arrive at poles and begin to decondense; nuclear envelopes reform
13.Place the following stages of mitosis in the correct chronological order.
Medium
- Prophase
- Metaphase
- Anaphase
- Telophase
14.Which of the following are functions of mitosis? (select all that apply)
Medium
- AGrowth of multicellular organisms
- BReplacement and repair of damaged tissues
- CAsexual reproduction in unicellular organisms
- DProduction of gametes with half the chromosome number
- EFormation of genetically identical daughter cells
15.Which of the following statements about binary fission are correct? (select all that apply)
Medium
- AIt produces two genetically identical daughter cells.
- BIt involves the replication of a single circular DNA molecule and plasmids.
- CIt requires spindle fibres and a nuclear envelope.
- DThe cytoplasm divides roughly equally between daughter cells.
- EIt is a form of mitosis.
16.Match each cell division process with the correct description.
Medium
- Mitosis
- Binary fission
- Viral replication
- Produces two genetically identical daughter cells; involves spindle fibres and nuclear envelope breakdown
- Produces two genetically identical daughter cells; involves replication of circular DNA and plasmids
- Requires a host cell; involves attachment, injection of nucleic acid, synthesis of viral components, and release
17.Which of the following are differences between cytokinesis in animal cells and plant cells? (select all that apply)
Medium
- AAnimal cells form a cleavage furrow; plant cells form a cell plate.
- BAnimal cells pinch inwards; plant cells build new cell walls.
- CPlant cells form a cleavage furrow; animal cells form a cell plate.
- DAnimal cells divide by binary fission; plant cells divide by mitosis.
- ECytokinesis occurs after telophase in both cell types.
18.Place the following events of binary fission in the correct order.
Medium
- Circular DNA molecule is replicated
- Plasmids replicate
- Cytoplasm divides roughly equally
- Two genetically identical daughter cells are produced
19.Which of the following statements about cancer are correct? (select all that apply)
Hard
- ACancer results from uncontrolled mitosis.
- BMutations in genes controlling the cell cycle can lead to cancer.
- CCancer cells always undergo programmed cell death (apoptosis).
- DTumours are abnormal masses of cells.
- ECancer treatments often aim to slow or stop mitosis in rapidly dividing cells.
20.Which of the following are features of viral replication? (select all that apply)
Medium
- AAttachment proteins bind to complementary receptors on the host cell.
- BViral DNA or RNA is injected into the host cell.
- CThe host cell uses its own enzymes and ribosomes to synthesise viral components.
- DViruses undergo binary fission.
- ENew viral particles are released by cell lysis or budding.
21.Which of the following features are present in meiosis but not in mitosis? (select all that apply)
Hard
- AHomologous chromosomes associate in pairs
- BCrossing over occurs
- CTwo offspring cells produced
- DInitial duplication of parent cell's DNA content
- EFour daughter cells produced
22.Which of the following statements about the G1/S checkpoint are correct? (select all that apply)
Medium
- AIt prevents the cell cycle from proceeding if certain conditions are not met.
- BIt ensures DNA is replicated before the cell divides.
- CIt checks for cell size, nutrients, and DNA damage.
- DIt occurs during mitosis.
- EIt triggers the transition from G1 to S phase.
23.Which of the following correctly describe the role of cyclins in the cell cycle? (select all that apply)
Medium
- AThey are chemical signals that trigger transition between phases.
- BThey are enzymes that replicate DNA.
- CThey control the progression of the cell cycle.
- DThey are structural proteins of the spindle.
- ETheir levels fluctuate during the cell cycle.
24.Which of the following are correct about the mitotic index? (select all that apply)
Hard
- AIt is the proportion of cells undergoing mitosis.
- BIt is calculated as number of cells with visible chromosomes divided by total number of cells.
- CIt can be expressed as a percentage.
- DIt is always greater than 1.
- EIt can be used to identify cancerous tissue.
25.Which of the following are correct about the structure of viruses? (select all that apply)
Medium
- AThey have a nucleic acid core that can be DNA or RNA.
- BThey have a protein coat called a capsid.
- CSome have an outer envelope derived from host cell membrane.
- DThey contain ribosomes for protein synthesis.
- EThey are acellular.
26.Which of the following are correct about cancer treatments? (select all that apply)
Hard
- AMethotrexate inhibits DNA nucleotide synthesis.
- BTaxol prevents disassembly of spindle fibres.
- CThey aim to slow or stop mitosis in rapidly dividing cells.
- DThey specifically target cancer cells without affecting normal cells.
- EThey can cause side effects due to effects on normal dividing cells.
27.Which of the following correctly describe the events of telophase? (select all that apply)
Medium
- AChromosomes arrive at opposite poles and decondense.
- BNuclear envelopes reform around each set of chromosomes.
- CSpindle fibres break down.
- DChromosomes align at the equator.
- ECytokinesis occurs.
28.Which of the following statements about the G2 phase are correct? (select all that apply)
Medium
- AThe cell continues to grow.
- BNew DNA is checked for errors.
- CTubulin protein is produced for microtubules.
- DDNA replication occurs.
- EThe cell prepares for mitosis.
29.Which of the following are correct about the use of root tips in studying mitosis? (select all that apply)
Hard
- ARoot tips contain meristems where cells are actively dividing.
- BThe root tip is stained to make chromosomes visible.
- CThe tissue is squashed to spread cells into a single layer.
- DHydrochloric acid is used to stain the chromosomes.
- ECells are viewed under an optical microscope.
30.Which of the following statements about viral replication are correct? (select all that apply)
Hard
- AViruses attach to host cells via complementary receptors.
- BViral nucleic acid is injected into the host cell.
- CHost cell enzymes and ribosomes synthesise viral components.
- DNew viral particles are released by cell lysis or budding.
- EViruses divide by binary fission.
31.Which of the following are correct about the cell cycle? (select all that apply)
Medium
- AThe cell cycle is a regulated sequence of events.
- BThe length of the cell cycle is variable.
- CCyclins trigger transitions between phases.
- DInterphase is the shortest phase of the cell cycle.
- EMitosis is part of the cell cycle.
32.Which of the following correctly describe the behaviour of chromosomes during mitosis? (select all that apply)
Hard
- AIn prophase, chromosomes condense and become visible.
- BIn metaphase, chromosomes align at the equator.
- CIn anaphase, sister chromatids separate and move to opposite poles.
- DIn telophase, chromosomes decondense and nuclear envelopes reform.
- EIn prophase, chromosomes align at the equator.
33.Which of the following statements about cytokinesis are correct? (select all that apply)
Medium
- AIt occurs after telophase.
- BIt divides the cytoplasm.
- CIt produces two genetically identical daughter cells.
- DIt is a stage of mitosis.
- EIn plant cells, a cell plate forms.
34.Which of the following are correct about the importance of mitosis? (select all that apply)
Hard
- AIt allows growth of multicellular organisms.
- BIt replaces damaged or dead cells.
- CIt produces gametes with half the chromosome number.
- DIt enables asexual reproduction in some organisms.
- EIt produces genetically identical daughter cells.
35.Which of the following statements about the G1 phase are correct? (select all that apply)
Medium
- AThe cell grows and synthesises proteins.
- BThe cell receives a signal to divide.
- CDNA replication occurs.
- DThe cell prepares for S phase.
- EThe cell divides.
36.Which of the following are correct about the S phase? (select all that apply)
Hard
- ADNA replication occurs.
- BEach chromosome consists of two identical sister chromatids after S phase.
- CIt is relatively short.
- DIt is part of interphase.
- EIt occurs after mitosis.
37.A student views a root tip squash under an optical microscope. The image of one cell measures 40 mm across. The actual width of the cell is 50 μm. What is the magnification of the image?
Medium
- A×800
- B×0.8
- C×1250
- D×80
38.A tissue sample has a mitotic index of 0.85. Which of the following is the most likely explanation for this value?
Hard
- AThe tissue contains a high proportion of actively dividing cells, which may indicate a tumour.
- BThe tissue is healthy because most cells are resting in interphase.
- CThe tissue has a low rate of mitosis because few cells have visible chromosomes.
- DThe tissue has completed mitosis and is now undergoing cytokinesis.
39.A drug prevents the disassembly of spindle fibres during mitosis. Which stage of mitosis will be directly affected by this drug?
Medium
- AAnaphase
- BProphase
- CMetaphase
- DTelophase
40.In a root tip squash, cells in prophase can be distinguished from cells in telophase because prophase cells have two groups of chromosomes, one at each pole.
Easy
True or false?
41.Name the phase of the cell cycle in which DNA replication occurs.
Easy
42.Complete the sentence about the cell cycle.
Medium
The cell cycle consists of interphase, ____ and ____.
43.A human cell takes 12 hours to complete one cell cycle. Starting from a single cell, calculate how many cells will be present after 4 days if the cell cycle proceeds at a constant rate. Give your answer as a whole number.
Medium
44.A root tip sample contains 64 cells in total. Of these, 14 are in prophase, 5 in metaphase, 3 in anaphase and 6 in telophase. Calculate the mitotic index for this tissue. Give your answer to 2 decimal places.
Medium
45.A student prepared a sample of cells and counted 42 cells in total, 32 of which had visible chromosomes. Calculate the mitotic index for this sample. Give your answer to 2 decimal places.
Medium
46.A micrograph of an onion root tip contains 20 cells with visible chromosomes and 55 cells without visible chromosomes. Calculate the mitotic index for this tissue. Give your answer to 2 decimal places.
Medium
47.Complete the following paragraph about the cell cycle using the terms provided.
Medium
The cell cycle consists of interphase, mitosis and ____. During interphase, the cell grows and replicates its DNA during the ____ phase. The transition from one phase to another is triggered by chemical signals called ____.
48.Name the phase of the cell cycle during which the cell continues to grow and the newly synthesised DNA is checked for errors.
Medium
49.Describe the events that occur during anaphase of mitosis.
Hard
50.Compare cytokinesis in animal cells and plant cells.
Hard
51.Explain the potential significance of an abnormally high mitotic index in a tissue sample.
Hard
52.State and explain two functions of mitosis.
Hard
53.Describe what chromosomes are and what chromatids are.
Medium
54.A human cell takes 12 hours to complete one cell cycle. Starting from a single cell, calculate how many cells will be present after 4 days if the cell cycle proceeds at a constant rate. Give your answer as a whole number.
Medium
- A230 cells
- B282 cells
- C308 cells
- D256 cells
55.A root tip sample contains 64 cells in total. Of these, 14 are in prophase, 5 in metaphase, 3 in anaphase and 6 in telophase. Calculate the mitotic index for this tissue. Give your answer to 2 decimal places.
Medium
- A1.44
- B2.44
- C-0.56
- D0.44
56.A student prepared a sample of cells and counted 42 cells in total, 32 of which had visible chromosomes. Calculate the mitotic index for this sample. Give your answer to 2 decimal places.
Medium
- A2.76
- B0.76
- C-0.24
- D1.76
57.A micrograph of an onion root tip contains 20 cells with visible chromosomes and 55 cells without visible chromosomes. Calculate the mitotic index for this tissue. Give your answer to 2 decimal places.
Medium
- A2.27
- B-0.73
- C0.27
- D1.27

Resumos de revisão

## The Cell Cycle & Interphase - The cell cycle is the regulated sequence of events between one cell division and the next. - Three phases: **interphase**, **nuclear division (mitosis)**, **cell division (cytokinesis)**. - Transitions triggered by chemical signals called **cyclins**. - Length varies with environmental conditions, cell type, organism (e.g. onion root tip ~20 h; human intestine epithelium ~10 h). - **Interphase** = G1, S, G2: - **G1**: cell grows, makes enzymes/proteins for growth; receives signal to divide. - **S**: DNA replicates; each chromosome becomes two identical sister chromatids (short phase). - **G2**: further growth, error checking/repair of new DNA, production of tubulin for spindle. ## The Stages of Mitosis Mitosis = nuclear division producing **two genetically identical daughter nuclei**, each identical to the parent. Functions: growth, replacement & repair, asexual reproduction. - **Prophase**: chromosomes condense (visible when stained); each = 2 sister chromatids joined at a centromere; centrosomes move to opposite poles; spindle fibres form; nuclear envelope breaks down. - **Metaphase**: spindle fully formed, attached to centromeres; chromosomes align on the metaphase plate (equator). - **Anaphase**: spindle fibres shorten, centromeres divide, sister chromatids separate and move to opposite poles. - **Telophase**: chromosomes arrive at poles and decondense; nuclear envelopes reform; spindle breaks down. - Acronym **PMAT** (Preparing, Middle, Away/apart, Two). ## Cytokinesis - Occurs **after telophase** and is **not part of mitosis**; divides the cytoplasm into two genetically identical daughter cells. - **Animal cells**: cleavage furrow forms; membrane pinches inwards. - **Plant cells**: cell plate forms at the metaphase plate; new cell walls built from it. ## Required Practical: Identifying Mitotic Stages - Growth in plants occurs in **meristems**; root tip meristem is just behind the root cap. - **Squash technique**: stain root tips and gently squash to spread cells into a thin sheet. - Method: cut ~1 cm root tip; fix in ethanoic alcohol; warm (60 °C) dilute HCl separates cells; add stain (e.g. acetic orcein, stains chromosomes deep purple); coverslip pressed down with paper towel. - Limitations: preparation can damage cells/alter appearance, producing **artefacts**; 3D structures cut at different planes look inconsistent on 2D slides; optical microscopes have limited magnification. ## Investigating Plant Root Tips - **Mitotic index** = proportion of cells undergoing mitosis: - mitotic index = number of cells with visible chromosomes ÷ total number of cells - ×100 for a percentage. - **actual size = size of image ÷ magnification**; magnification has no units. - Unit conversions: 1000 nm = 1 μm; 1000 μm = 1 mm; 1000 mm = 1 m. ## Uncontrolled Cell Division & Cancer - Cancer = uncontrolled mitosis forming a **tumour** (abnormal mass of cells). - Caused by mutations in genes controlling the cell cycle (e.g. oncogenes, tumour suppressor genes) → continuous division and/or prevented apoptosis. - Treatments slow/stop mitosis in rapidly dividing cells: **methotrexate** inhibits DNA nucleotide synthesis; **taxol** prevents disassembly of spindle fibres. ## Binary Fission - Prokaryotic cell division; simpler than mitosis (no nucleus, chromosomes, spindle fibres or membrane-bound organelles). - Replicates a single circular DNA molecule and plasmids. - Steps: circular DNA replicates → plasmids replicate → cytoplasm divides roughly equally → each daughter cell genetically identical, receiving one copy of circular DNA and a variable number of plasmids. - A daughter cell without the circular DNA or at least one plasmid dies. ## Viral Particle Replication - Viruses are acellular, non-living infectious particles; they do not undergo cell division. - Structure: nucleic acid core (DNA or RNA, single/double-stranded), protein coat (**capsid**), sometimes an **envelope** from host membrane phospholipids. - Replication (only inside host cells): attachment proteins bind complementary receptors → viral DNA/RNA injected → host enzymes/ribosomes synthesise viral proteins and nucleic acids → new particles assembled → released by **cell lysis** or **budding**. - Release damages/destroys host cells, causing disease.

Cell cycle: The regulated sequence of events that occurs between one cell division and the next.
Interphase: The stage of the cell cycle consisting of G1, S and G2, during which the cell increases in size and carries out normal cellular functions, e.g. synthesising proteins and replicating DNA ready for mitosis.
G1 phase: Part of interphase where cells make enzymes and other proteins required for growth; at some point a signal is received telling the cell to divide again.
S phase: Part of interphase where the DNA in the nucleus replicates, after which each chromosome consists of two identical sister chromatids; relatively short.
G2 phase: Part of interphase where the cell continues to grow, new DNA is checked and errors repaired, and other preparations for cell division are made, e.g. production of tubulin protein.
Cyclins: Chemical signals that trigger the transition from one phase of the cell cycle to another.
Mitosis: The process of nuclear division producing two genetically identical daughter nuclei, each genetically identical to the parent nucleus.
Prophase: Stage of mitosis where chromosomes condense (visible when stained), each chromosome is two sister chromatids joined at a centromere, centrosomes move to opposite poles, spindle fibres form, and the nuclear envelope breaks down.
Metaphase: Stage of mitosis where centrosomes are at opposite poles, spindle fibres are fully formed and attached to centromeres, and chromosomes align on the metaphase plate (equator of the cell).
Anaphase: Stage of mitosis where spindle fibres shorten, centromeres divide, separating sister chromatids, and chromatids (now chromosomes) move to opposite poles.
Telophase: Stage of mitosis where chromosomes arrive at opposite poles and begin to decondense, nuclear envelopes begin to reform, and spindle fibres break down.
Cytokinesis: Division of the cytoplasm after telophase, producing two genetically identical daughter cells; not a part of mitosis.
Cleavage furrow: Structure that forms in animal cells during cytokinesis; the membrane pinches inwards to separate cells.
Cell plate: Structure that forms at the metaphase plate in plant cells during cytokinesis; new cell walls are built from it to separate cells.
Meristem: Specific region of growth in plants; the root tip meristem can be used to study mitosis and is found just behind the protective root cap.
Squash technique: Method where root tips are stained and then gently squashed, spreading the cells out into a thin sheet and allowing individual cells undergoing mitosis to be clearly seen.
Artefacts: Structures generated during slide preparation (e.g. squashing or staining) that can damage cells and alter their appearance.
Mitotic index: The proportion of cells (in a group of cells or a sample of tissue) that are undergoing mitosis; calculated as number of cells with visible chromosomes ÷ total number of cells.
Tumour: An abnormal mass of cells formed by uncontrolled mitosis.
Apoptosis: Programmed cell death; mutations in genes controlling the cell cycle may prevent it.
Binary fission: Cell division in prokaryotes; simpler than mitosis as cells have no nucleus, chromosomes, spindle fibres, or membrane-bound organelles.
Plasmids: Small, circular DNA molecules replicated during binary fission.
Capsid: The protein coat of a virus.
Envelope: Outer layer of some viruses, formed usually from the membrane-phospholipids of a cell they were made in.

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