Chapter 9: The Cell Cycle & Cellular Division

Comprehensive vocabulary flashcards covering the cell cycle, DNA compaction, mitosis stages, cytokinesis, cell cycle checkpoints, apoptosis, cancer biology, and binary fission from Chapter 9.

Interphase

The period constituting approximately $90\%$ of the cell cycle where the cell performs normal metabolic functions, grows, and replicates its DNA in preparation for division.

$G_1$ Stage (First Gap / Growth)

The stage of interphase where the cell recovers from previous division, doubles in size, and synthesizes duplicate organelles such as mitochondria and ribosomes.

$G_0$ Resting Phase

A non-dividing phase entered by specialized, mature cells (such as mature neurons and cardiac muscle) that exit the cell cycle.

S Stage (Synthesis)

The phase of interphase where nuclear DNA replication occurs, doubling the DNA so that each single chromosome forms two identical sister chromatids.

Centromere

The constricted region of a chromosome where two sister chromatids remain joined together until anaphase.

$G_2$ Stage (Second Gap / Preparation)

The final preparation stage between DNA synthesis and mitosis, during which the cell synthesizes division proteins such as tubulin required for mitotic spindle construction.

Nucleosome

The first level of DNA packaging ('beads-on-a-string') consisting of double-helix DNA wrapped around an octamer core of $8$ histone proteins.

$30\text{-nm}$ Chromatin Fiber

The second structural hierarchy level of DNA compaction, created when histone H1 folds nucleosomes into a $30\text{-nm}$ zigzag fiber.

Radial Loop Domains

The third level of DNA packaging consisting of active euchromatin, formed when $30\text{-nm}$ chromatin fibers loop onto a central protein scaffold.

Heterochromatin

The fourth level of DNA packaging that tightly compacts radical loops to form heterochromatin

Metaphase Chromosome

The fifth and highest level of DNA packaging, consisting of highly condensed inactive heterochromatin loops that prevent tangling during chromosome segregation.

Kinetochores

Specialized protein structures that develop on each side of the centromere to bind mitotic spindle fibers.

Centrosome

The microtubule organizing center that duplicates in S phase and separates in early mitosis to organize the dynamic mitotic spindle; contains centrioles in animal cells.

Prophase

The mitotic stage where chromatin condenses into visible chromosomes, the nucleolus disappears, the nuclear envelope fragments, and centrosomes migrate to opposite poles.

Prometaphase

The mitotic stage during which kinetochores develop on centromeres, and kinetochore microtubule fibers attach to sister chromatids and move them back and forth.

Metaphase

The stage of mitosis where chromosomes align single file along the cell's equatorial plane (metaphase plate) and spindle fibers from opposite poles connect to kinetochores.

Anaphase

The stage of mitosis where sister chromatids separate at their centromeres into independent daughter chromosomes and are pulled toward opposite poles by shortening kinetochore microtubules.

Telophase

The mitotic stage in which nuclear envelopes and nucleoli reform around clusters of daughter chromosomes located at opposite poles of the cell.

Cleavage Furrow

The indentation formed in dividing animal cells by an actin filament contractile ring constricting inward around the cell equator to pinch the cytoplasm in two.

Cell Plate

The structure formed during plant cell cytokinesis when Golgi-derived vesicles carrying cell wall materials fuse along the former metaphase plate and expand outward to join the parental cell wall.

$G_1$ Checkpoint

The primary restriction point of the cell cycle that assesses cell size, nutrient availability, growth factors, and DNA integrity, triggering apoptosis if damage cannot be repaired.

$G_2$ Checkpoint

A regulatory control mechanism that verifies DNA replication during S phase was fully and accurately completed before initiating mitosis.

M (Spindle) Checkpoint

A checkpoint occurring during metaphase to confirm that all kinetochores are securely attached to spindle fibers before sister chromatids separate in anaphase.

Apoptosis

A regulated sequence of programmed cell death involving cell shrinkage, chromatin condensation, membrane blebbing, DNA/organelle fragmentation, and engulfment by white blood cells.

Contact Inhibition

A regulatory mechanism where normal cells stop dividing when they touch neighboring cells; its loss in cancer cells leads to cells piling up into tumors.

Angiogenesis

The process where tumor cells secrete chemical signals to induce the growth of new host blood vessels toward the tumor to supply oxygen and nutrients.

Metastasis

The dissemination of cancer cells from a primary tumor through blood or lymphatic vessels to establish secondary tumors in distant organs.

Proto-Oncogenes

Normal genes encoding proteins that promote cell cycle progression and prevent apoptosis; gain-of-function mutations convert them into oncogenes that drive continuous division ('gas pedal stuck down').

Tumor Suppressor Genes

Genes encoding proteins (such as $p53$) that arrest the cell cycle and trigger apoptosis upon DNA damage; loss-of-function mutations disable this brake system ('broken brakes').

Binary Fission

The asexual reproductive process used by prokaryotes (bacteria and archaea) in which a single circular chromosome replicates and partitions to produce two genetically identical daughter cells.

Prokaryotic Organisms for cell division

Bacteria and Archaea use binary fission for cell division because of their simple structure and its function for asexual reproduction

Eukaryotic Organisms for cell division

Prosists and some fungi use Mitosis and cytokinesis for Asexual reproduction. It is also used for growing and repairing the organisms

Plants/Animals/Other Fungi for cell division

These organisms use Mitosis and cytokinesis for cell division for growth and repair because they use sexual reproduction.

Cancer Cells vs Normal Cells: Contact Inhibition

Cancer cells do not have contact inhibition while normal cells do

Cancer vs Normal Cells: Organization

Cancer Cells are disorganized and multilayered while normal cells are organized and one single layer

Cancer vs Normal Cells: Differentiation

Cancer cells are not differentiated (they are the same) while normal cells are differentiated

Cancer vs Normal Cells: Nuclues

Cancer cells have an abnormal nuclei while normal cells have a normal nuclei

Cancer vs Normal Cells: Apoptosis

Cancer cells do not undergo Apoptosis while Normal cells do

Cancer vs Normal Cells: Metastasis

Cancer cells have Metastasis and Angigenenesis while Normal cells do not