Bio 30: Cell Cycle and Mitosis

Key biological terminology relating to chromosomes, genetic structures, and ploidy levels from the Cell Cycle and Mitosis notes.

Somatic cell

Any cell of a living organism other than the reproductive cells; diploid body cells.

Gamete

Mature sexual reproductive cells (ova or sperm) that are haploid ($1n$) sex cells.

Karyotype

The number and visual appearance of chromosomes in the cell nuclei of an organism.

DNA

Deoxyribonucleic acid; made of sugar and nucleic acid base pairs.

Base pairs

Pairs of nucleotides connecting the complementary strands of a molecule of DNA or RNA.

Histones

Protein bundles of DNA that help to compact chromosomes.

Chromatin

DNA wound up as chromosomes.

Chromosomes

A threadlike structure of nucleic acids and protein, carrying genetic info in the form of genes.

Homologous chromosomes

A pair of chromosomes which carry or contain the same genes but come from different parents.

Centromere

Holds identical chromosomes together when preparing for cell division.

Sister chromatids

The two identical strands formed when a chromosome replicates in preparation for cell division.

Autosomes

Non-sex chromosomes (pairs 1–22 in humans).

Sex chromosomes

Chromosomes that determine the sex of an organism; pair 23 (XX = female, XY = male).

Genes

A segment of DNA that codes for a particular protein.

Locus

The location of a gene on a segment of DNA.

Alleles

Alternate forms of the same gene.

Diploid ($2n$)

To have two copies of each chromosome (1 from each parent).

Haploid ($n$)

To have one of each chromosome; occurs in gametes (sperm and egg).

Polyploidy

To have multiple sets of each chromosome (e.g., $4n$, $5n$, etc.; seen in salmon, ferns, canola).

Interphase

The period of the cell cycle between divisions during which the cell grows, synthesizes new DNA, and prepares for mitosis.

-cell spends most of its time in interphase

-most important feature is replicating DNA

G1 Gap (growth)

-phase after mitosis= rapid growth

S Phase (Synthesis)

-chromosomal DNA is replicated (chromosomes duplication)

G2 Gap (growth)

-after synthesis and before mitosis= growth, preparation for division.

Centrioles

Organelles that produce fibers along which chromosomes travel to opposite poles of the cell during division; generally absent in plant cells.

Cell Cycle

-made up of phases, no pauses in between

-have phases of growth and phases of cellular division

Division Phase

Components of cytoplasm and nucleus of parent cell divides.

-gives rise to TWO identical daughter cells

Mitosis

-duplication of chromosomes (replicating the nuclei), each daughter cell has the same number of chromosomes as parent cell.

Cytokinesis

-divides cytoplasm and organelles equally

Chromatin

-genetic material in nucleus appears as a mass of long intertwined strands.

Mitosis

The phase of cell division in which the replicated nuclear genetic material divides into two identical sets prior to the division of the cytoplasm.

Mitosis Diagram

A visual representation of chromosome replication prior to cell division, showing a single chromosome duplicating into two identical sister chromatids joined at the centromere.

Spindle fibers

Structures produced by centrioles that guide chromosomes toward opposite ends of the cell during division.

Replication

The process of making identical copies of chromosomes prior to division so that each daughter cell receives a complete set of genetic instructions.

Four stages of mitosis

Prophase, metaphase, anaphase, and telophase.

Duration of mitosis

The shortest phase of the cell cycle, lasting from $15\,\text{min}$ to a few hours depending on cell type and temperature.

Typical duration of an animal cell cycle

Approximately $18\,\text{h}$ to $24\,\text{h}$.

Typical duration of a plant cell cycle

Approximately $10\,\text{h}$ to $30\,\text{h}$.

Bacterial cell cycle duration

Can be completed in as few as $20\,\text{min}$.

Prophase

- first true phase of mitosis

-characterized by chromosome condensation

-movement of centrioles to opposite poles to form the spindle apparatus

-the breakdown of the nuclear membrane.

Early prophase

- initial segment of the first mitotic phase where chromosomes begin to condense, becoming shorter, thicker, and visibly distinct.

Late prophase

-complete dissolution of the nuclear membrane.

Metaphase (middle)

-chromosomes composed of sister chromatids align along the cell's equatorial plate (train tracks)

-attached to spindle fibers by their centromeres

-most visible at this phase

-dark, thick structures

Equatorial plate

The central midline plane of a dividing cell along which sister chromatid pairs align during metaphase.

Anaphase

-centromeres split

-sister chromatids are pulled toward opposite poles, each becoming an unduplicated chromosome.

Telophase

- final stage of mitosis in which chromosomes reach opposite poles

-lengthen back into chromatin

-spindle fibers dissolve

-nuclear membranes reform.

Mitotic stage with highest chromosome visibility

Metaphase, during which chromosomes are most condensed and appear as dark, thick, filamentous structures aligned across the center of the cell.

Cytokinesis

-chromosomes already at each pole

-nuclear membrane forming

-cytoplasm begins to divide

→ cell goes back to interphase