Cell Division Cycle Flashcards

Flashcards covering phases, regulation, and checkpoints in the cell division cycle.

Cell Division in the Cell Cycle

Cell division is a small part of the entire process and is subdivided into many parts.

Why are Cell Division and Reproduction fundamental properties of all living organisms?

Division of a single-celled organism creates two new identical individuals, division of a fertilized egg initiates development of a multicellular organism, division of stem cells in your body permits regeneration, renewal, and growth.

What is the Cell Cycle?

Ordered sequence of events from the appearance of one cell until it divides to produce two cells; cell division is only a small part of the entire cell cycle.

What are the phases of the Cell Cycle?

M Phase (Division of Nucleus and Cytoplasm), Gap 1 (G1 - Growth and Differentiation), S Phase (DNA Synthesis), Gap 2 (G2), G0.

Genome

Total genetic material of an organism.

Examples of Genomes

E. coli: 4.6 million base pairs, single circular DNA molecule; Homo sapiens: 6 billion base pairs, 2 meters long, 46 chromosomes in Somatic Cells

Chromatin

A mixture of protein and DNA.

Mitosis

Division leading to two identical daughter cells - Division of genetic material in the nucleus and Division of the cytoplasm: Cytokinesis

Meiosis

Division leading to four nonidentical daughter cells - Process for generating Gametes (Egg and Sperm Cells).

What are the five stages of Nuclear Division (Karyokinesis)?

Prophase, Prometaphase, Metaphase, Anaphase, Telophase; Cytokinesis overlaps some of the later mitotic phases; M Phase: Mitosis plus Cytokinesis.

Interphase

Growth and Differentiation, DNA replicated (S Phase), Chromosomes not visible, Duplication of the Centrosome (S Phase), Nuclear Envelope intact, Nucleolus present.

Prophase

Condensation of chromatin begins, nucleoli disappear, mitotic Spindle begins to form outside nucleus.

Prometaphase

Nuclear envelope breaks down, chromatin condensation continues, spindle Microtubules invade nucleus, microtubules attach to some chromosomes at Kinetochores.

Metaphase

Chromosomes lined up at 'Metaphase Plate' in the middle.

Anaphase

Sister chromatids separate, kinetochore microtubules shorten, daughter chromosomes move toward opposite poles, cell begins to elongate.

Telophase

Begin to see the appearance of two daughter nuclei, nuclear envelope reforms from fragments, nucleoli reappear, chromosomes begin to decondense, cytokinesis starts.

Cytokinesis: Animal Cells

Begins during telophase; first sign is appearance of Cleavage Furrow; Contractile Ring - Transient bundle of actin filaments - Actin filaments interact with myosin and ATP.

Cytokinesis: Plant Cells

No cleavage furrow - Cell center contains microtubules and Golgi-derived vesicles filled with cell wall material; vesicles fuse to form disc-like early cell plate.

Cell Cycle Regulation

Every cell is regulated separately; defective regulatory mechanisms can lead to cancer.

Control System

Progression through the cycle is regulated by a command and control system, specific molecules trigger and coordinate key events at 3 places, control points are checkpoints.

What are the key events at which specific molecules trigger and coordinate in the Control System?

Entry into Mitosis from G2, Completion of Mitosis, Entry into S from G1.

Checkpoints

Stop Signals set up to halt progress through the cycle if some critical step has not been accomplished; once a cell goes a checkpoint, there is no turning back.

Cytoplasmic Control of the Cycle

MPF (M-Phase Promoting Factor) is present in dividing cell cytoplasm that forces interphase cells to begin dividing. Search was on to characterize and purify MPF.

Cell Cycle Clock

Found 2 types of cycle-regulating proteins: Cyclins (cyclic appearance and disappearance) and Regulatory Protein Kinases (enzymes that transfer phosphate group to proteins).

Cyclin-Dependent Kinases

Protein kinases that regulate progression through the cell cycle are activated by binding cyclin; these are called Cyclin-Dependent Kinases or Cdks.

Mitosis-Promoting Factor (MPF)

Activity of MPF increases in late G2 when [cyclin] is high; Active M Cyclin–Cdk allows cells to move past G2 and into M; At metaphase, mitotic cyclin is degraded, Cdk activity decreases, cells progress through metaphase into G1.