Cell Cycle Lecture Overview

Question-and-answer flashcards covering DNA organization, phases of the cell cycle, mitosis, checkpoints, regulatory molecules, and cancer biology, based on the provided lecture notes.

What are the three primary purposes of cell division in multicellular organisms?

Reproduction of cells, organismal growth, and tissue repair.

Define the cell cycle.

The life of a cell from its formation until it divides into two daughter cells.

How is DNA packaged prior to cell division?

DNA wraps around histone proteins to form nucleosomes; nucleosome strings coil into chromatin, which further condenses into visible chromosomes.

What is chromatin?

A DNA–protein complex (DNA plus histones) that is loosely packed when the cell is not dividing and condenses into chromosomes after DNA replication.

What are sister chromatids?

Identical copies of a chromosome joined together after DNA replication.

Name and define the region where sister chromatids are most tightly attached.

Centromere – the constricted region holding sister chromatids together.

What is a kinetochore?

A protein structure on the centromere that attaches each chromatid to spindle microtubules.

Define a genome.

All of a cell’s genetic information (its entire DNA content).

Contrast prokaryotic and eukaryotic genomes in terms of chromosome shape and number.

Prokaryotes usually have one circular DNA molecule; eukaryotes have one or more linear chromosomes, each species-specific in number.

How many chromosomes do humans, chimps, and elephants have?

Humans 46, chimps 48, elephants 56.

Differentiate somatic cells and gametes by ploidy and division process.

Somatic cells are diploid (2n) and divide by mitosis; gametes are haploid (n) and are produced by meiosis.

What chromosome numbers characterize human somatic cells and gametes?

Somatic cells: 46 (2n); gametes: 23 (n).

List the major phases of the cell cycle in order.

G1 → S → G2 → Mitosis → Cytokinesis.

During which phase does DNA replication occur?

S phase (Synthesis).

Which portion of the cell cycle occupies ~90 % of a cell’s life?

Interphase (G1, S, and G2 combined).

What is the end result of mitosis and cytokinesis?

Two genetically identical diploid daughter cells.

Name the five stages of mitosis in order.

Prophase, Prometaphase, Metaphase, Anaphase, Telophase (followed by Cytokinesis).

State two key events of prophase.

Chromatin condenses into chromosomes; nucleoli disappear; mitotic spindle begins to form; centrosomes move apart (any two).

What critical event defines prometaphase?

Nuclear envelope fragments, allowing spindle microtubules to attach to kinetochores.

Where do chromosomes align during metaphase?

Along the metaphase plate (cell equator).

What triggers chromatid separation in anaphase?

Shortening of kinetochore microtubules pulls sister chromatids toward opposite poles.

Describe cytokinesis in animal cells.

A contractile ring of actin forms a cleavage furrow that pinches the cell into two.

Describe cytokinesis in plant cells.

Golgi-derived vesicles coalesce at the center to form a cell plate that develops into a new cell wall.

How many chromatids does a human cell have during metaphase?

92 chromatids (46 chromosomes, each with two chromatids).

What is the most important cell-cycle checkpoint and why?

The G1 checkpoint; it decides whether the cell proceeds through the entire cycle or enters the non-dividing G0 state.

What happens when a cell receives a "stop" signal at the G1 checkpoint?

It exits the cell cycle and enters G0, a quiescent non-dividing state.

What is checked at the G2 checkpoint?

Completion of DNA replication and absence of DNA damage before entering mitosis.

Which checkpoint ensures all chromosomes are attached to spindle microtubules?

The M (spindle) checkpoint at metaphase.

Define apoptosis.

Programmed cell death, a controlled process for eliminating damaged or unnecessary cells.

What two classes of molecules make up the internal cell-cycle control system?

Cyclins (regulatory proteins) and cyclin-dependent kinases (CDKs).

Why are CDKs only active at specific times?

They require binding to their specific cyclin, whose concentration fluctuates during the cell cycle.

Explain contact (density) inhibition.

Cells stop dividing when they sense contact with neighboring cells via surface receptors, halting the cell cycle in G1.

What is anchorage dependence?

The requirement for cells to be attached to a substrate (other cells or extracellular matrix) in order to divide.

List three ways cancer cells differ from normal cells regarding the cell cycle.

They ignore checkpoints, divide indefinitely (immortal), and evade apoptosis even with DNA errors.

Distinguish benign and malignant tumors.

Benign tumors remain at their original site; malignant tumors invade surrounding tissue and can metastasize.

What is metastasis?

The spread of cancer cells from a primary tumor to distant body sites, forming secondary tumors.

Name two lifestyle choices that reduce cancer risk.

Not smoking, healthy diet/hydration, using SPF sun protection, regular screenings (any two).

A drug prevents shortening of microtubules. Which mitotic event is most directly affected?

Movement of chromosomes during anaphase.

Eukaryotic chromatin consists of which two primary components?

DNA and proteins (histones).

If a sperm cell contains 12 chromosomes, how many chromosomes are in that species’ somatic cells?

24 chromosomes (diploid number is double the haploid number).

A daughter cell ends up with 51 chromosomes after mitosis. Predict one cause.

A spindle checkpoint failure leading to improper chromosome segregation (nondisjunction) during anaphase.

Which two phases of the cell cycle are most affected by Vinblastine, a drug that blocks microtubule assembly?

Metaphase (spindle formation/attachment) and Anaphase (chromosome separation).

Which checkpoint arrests the cycle when Vinblastine disrupts spindle formation?

The M (spindle) checkpoint at metaphase.