10 The Cell Cycle - GEN BIO 115

Cell Theory

All living things are made of one or more cells; cells are the basic units of structure and function; all cells come from pre-existing cells.

Cell Division

Process where a cell reproduces; in unicellular organisms = reproduction only, in multicellular = growth, repair, and development.

Main Function of Cell Division

Distribute genetic material into daughter cells.

Genome

The total genetic material of a cell.

Prokaryotic

Genome Usually one circular DNA molecule.

Eukaryotic

Genome Usually more than one linear DNA molecule.

Chromosome (definition 1)

A molecule of DNA.

Chromatin

DNA-protein complex in a dispersed state; DNA form when cell is not dividing.

Chromosome (definition 2)

Highly condensed, “colored body” form of DNA wrapped around proteins; present only during cell division.

Ploid

Refers to how many sets of chromosomes an organism has.

Haploid (n)

One complete set of chromosomes; gametes are haploid.

Diploid (2n)

Two complete sets of chromosomes (homologous pairs); somatic human cells are diploid.

Homologous Chromosomes

Chromosomes with the same length, structure, and genes.

Mitosis

Occurs In Both haploid and diploid cells.

Binary Fission

Cell division in prokaryotes; simpler than mitosis.

Interphase

Time between cell divisions; cell grows, carries out metabolism, and replicates DNA; about 90% of cell cycle.

DNA

During Interphase In the form of chromatin.

G1 Phase (Gap 1)

Cell growth, normal functions, and preparation for DNA synthesis; longest phase of interphase.

S Phase (Synthesis)

DNA replication and chromosomal protein synthesis occur; ploidy does not change.

Sister Chromatids

Identical copies of a chromosome connected at the centromere.

G2 Phase (Gap 2)

Preparation for mitosis; high metabolic activity; DNA still in chromatin form.

M Phase

Mitosis and cytokinesis; shortest part of the cell cycle (<10%).

Mitosis

Nuclear division of somatic cells; continuous process divided into prophase, metaphase, anaphase, and telophase.

Prophase

Chromatin condenses into chromosomes, nuclear envelope breaks down, and mitotic spindle forms.

Mitotic Spindle Fibers

organized pole-to-pole that guide chromosome movement during mitosis.

Metaphase

Chromosomes align along the metaphase plate (middle of the cell).

Anaphase

Sister chromatids separate and move to opposite poles; each chromatid becomes an individual chromosome.

Kinetochores

Proteins at centromeres that pull chromatids along spindle fibers during anaphase.

Telophase

Opposite of prophase; chromosomes de-condense, nuclear envelope reforms, two identical nuclei form.

Cytokinesis

Division of the cytoplasm into two daughter cells; overlaps with telophase.

Cytokinesis in Animal Cells

Cell membrane pinches inward forming a cleavage furrow until cells separate.

Cytokinesis in Plant Cells

Cell plate forms at metaphase plate, becomes new membrane and wall separating daughter cells.