Cell Cycle & Cell Division

A comprehensive set of flashcards covering key concepts of the cell cycle, mitosis, meiosis, their regulation, and significance.

What two processes make up cell reproduction in organisms?

The division and enlargement (multiplication) of cells.

Define the cell cycle.

The life period of a cell during which it grows, replicates its DNA, and divides into two daughter cells.

During the cell cycle, which process is continuous and which occurs only at a specific stage?

Cytoplasmic growth is continuous, while DNA synthesis occurs only during the S phase.

Approximately how long is a typical human cell cycle, and how long is the yeast cell cycle?

Human: ~24 hours; Yeast: ~90 minutes.

Name the two basic phases of the eukaryotic cell cycle.

Interphase and M phase (mitotic phase).

What percentage of the cell cycle is usually occupied by interphase?

More than 95%.

List the three stages of interphase in order.

G1 phase, S phase, G2 phase.

State three major events that occur in G1 phase.

Continuous cell growth, high metabolic activity, and synthesis of RNA and proteins preparing for DNA replication.

What key event characterizes the S (synthetic) phase?

Replication of DNA, doubling its amount without increasing chromosome number.

Which cytoplasmic structure duplicates during S phase in animal cells?

The centriole (part of the centrosome).

Differentiate between a chromosome and a chromatid.

A chromosome is a DNA molecule containing genetic material; a chromatid is one copy of a newly duplicated chromosome still joined to its sister by a centromere.

What happens during the G2 phase?

Further cell growth, continued RNA and protein synthesis, and preparation for mitosis.

How long does M phase last in a typical human cell cycle?

About one hour.

Name the two main components of M phase.

Karyokinesis (nuclear division) and cytokinesis (cytoplasmic division).

Into what stage do non-dividing cells exit from G1, and what is it called?

They enter the quiescent stage called G0.

What is the primary role of the G1 checkpoint?

To determine whether conditions are favorable for DNA replication and cell division.

What is checked at the G2 checkpoint?

Completion and accuracy of DNA replication; DNA repair enzymes act here before mitosis begins.

What does the M (spindle) checkpoint ensure?

That all chromosomes are properly attached to the spindle before mitosis ends.

Name one possible consequence when cell-cycle checkpoints fail.

Uncontrolled cell growth leading to cancer.

Define karyokinesis and cytokinesis.

Karyokinesis: division of the nucleus; Cytokinesis: division of cytoplasm and organelles.

Haploid vs. diploid: how many chromosome sets do they contain and where are they typically found?

Haploid: one set, found in gametes; Diploid: two sets, found in most body (somatic) cells.

Why is mitosis called equational division?

Because it produces daughter cells with the same chromosome number as the parent cell.

List the four stages of mitotic karyokinesis in order.

Prophase, Metaphase, Anaphase, Telophase.

What major events mark early prophase?

Condensation of chromatin into visible chromosomes and migration of centrosomes to opposite poles.

What cellular structures form the mitotic apparatus?

Two asters and the spindle fibres emanating from the centrosomes.

Which organelles disappear by the end of prophase?

Golgi complexes, endoplasmic reticulum, nucleolus, and nuclear envelope.

What is the metaphase plate?

The plane at the cell equator where chromosomes align during metaphase.

Through what structure do spindle fibres attach to chromosomes?

They attach via kinetochores located at the centromere.

Which stage of mitosis is the shortest and what key event occurs then?

Anaphase; sister chromatids separate and move to opposite poles.

List two hallmark events of telophase.

Re-formation of nuclear envelopes around chromosome sets and uncoiling of chromosomes into chromatin.

Define cytokinesis.

The division of the cytoplasm resulting in two separate daughter cells.

How does cytokinesis occur in animal cells?

By formation and deepening of a cleavage furrow in the plasma membrane.

Describe cytokinesis in plant cells.

Golgi-derived vesicles coalesce at the equator to form a cell plate that extends outward, becoming the middle lamella and separating the daughter cells.

What is a syncytium and give one example.

A multinucleate cell formed when karyokinesis is not followed by cytokinesis; e.g., liquid endosperm in coconut.

How does mitosis help maintain chromosome number in somatic cells?

By producing diploid daughter cells genetically identical to the parent.

Name two roles of mitosis in multicellular organisms besides chromosome maintenance.

Body growth and repair/replacement of damaged cells.

What ratio is restored by mitosis after cell growth?

The nucleo-cytoplasmic ratio.

Define meiosis.

A nuclear division in diploid germ cells that halves the chromosome number to produce haploid gametes.

State two key features that distinguish meiosis from mitosis.

Meiosis has two successive divisions with only one round of DNA replication and includes pairing/recombination of homologous chromosomes.

How many haploid cells are produced from one diploid cell at the end of meiosis II?

Four haploid daughter cells.

List the stages of meiosis I and meiosis II.

Meiosis I: Prophase I, Metaphase I, Anaphase I, Telophase I; Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II.

Name the five sub-stages of Prophase I in order.

Leptotene, Zygotene, Pachytene, Diplotene, Diakinesis.

What occurs during the leptotene stage?

Chromatin condenses into long, slender chromosomes and the nucleus enlarges.

What structure facilitates synapsis in zygotene, and what is the paired chromosome unit called?

The synaptonemal complex; the paired unit is a bivalent (homologous pair).

During which sub-stage does crossing over occur, and what enzyme mediates it?

Pachytene; the enzyme recombinase.

What are chiasmata and when do they first become visible?

X-shaped crossover sites where homologues remain connected; visible during diplotene.

What key changes define diakinesis?

Terminalisation of chiasmata, full chromosome condensation, spindle formation, and disappearance of nucleolus and nuclear envelope.

In metaphase I, how do chromosomes arrange and attach to spindles?

Homologous chromosome pairs align at the equatorial plate; spindle microtubules attach to each homologue.

What separates during anaphase I versus anaphase II?

Anaphase I: homologous chromosomes separate; Anaphase II: sister chromatids separate.

What is interkinesis and does DNA replication occur in it?

A brief interphase between meiosis I and II; no DNA replication occurs.

Why is meiosis II considered similar to mitosis?

Because sister chromatids separate, producing one chromatid per daughter cell, akin to mitotic anaphase.

State two evolutionary advantages of meiosis.

Maintenance of constant chromosome number across generations and introduction of genetic variation through crossing over.

Which meiotic division is termed reductional and why?

Meiosis I, because it reduces the chromosome number from diploid to haploid.

After meiosis, what is the chromosome number in human gametes?

23 chromosomes (haploid).

Which type of cells undergo mitosis and which undergo meiosis?

Somatic cells undergo mitosis; germ cells undergo meiosis.

How can environmental damage lead to cancer via checkpoint failure?

Damage may bypass checkpoints, allowing mutations that cause uncontrolled cell proliferation.

At which checkpoint are unrepaired DNA errors likely to halt the cell cycle before mitosis?

The G2 checkpoint.