Biology: Chromosomes, Cell Cycle, and Mitosis

Comprehensive vocabulary flashcards covering chromosome structure, DNA packaging, the cell cycle, mitosis stages, stem cells, and the biology of cancer.

Chromosomes

Structures made of one very long, condensed DNA molecule associated with proteins in eukaryotic cells.

Histones

Large positively charged globular proteins whose role is to organize and condense DNA tightly so that it fits into the nucleus.

Chromatin

A loose, uncoiled mix of DNA and proteins found in a cell when it is not dividing; the combination of materials that make up chromatids and chromosomes.

Chromatid

One exact copy of a newly copied chromosome that stays joined during cell division; each is made up of one very long, condensed DNA molecule containing a series of genes.

Centromere

A narrow region that joins two sister chromatids together.

Sister Chromatids

Identical strands of DNA that make up the double structure of a chromosome and contain the same genes.

Telomeres

Protective structures made of non-coding DNA with short repeated base sequences that seal the ends of chromatids.

Nucleosome

A structure consisting of eight histone proteins around which DNA wraps $1.65$ times.

Chromatosome

A complex consisting of a nucleosome plus the $H1$ histone.

Linker DNA

A double-stranded segment of DNA that connects adjacent nucleosome core particles in chromatin, acting like the string in a "beads-on-a-string" model.

Histone Types

A family of small, positively charged proteins termed $H1$, $H2A$, $H2B$, $H3$, and $H4$.

Stem Cell

A cell that can divide by mitosis an unlimited number of times and has the potential to remain a stem cell or develop into a specialized cell.

Telomerase

A type of enzyme found in stem cells that can rebuild telomeres every time they copy, allowing indefinite division.

Potency

The ability of stem cells to differentiate into more specialized cell types.

Totipotent

Stem cells that can turn into any type of cell in the body as well as extra tissue needed for growth, such as a first-day fertilized egg.

Pluripotent

Stem cells that can turn into any type of cell in the body but cannot make extra-embryonic tissues.

Multipotent

Stem cells that can turn into a few related types of cells, such as blood stem cells in bone marrow.

Unipotent

Stem cells that can only turn into one type of cell or more of their own specific type, while still being able to renew themselves.

Cell Cycle

The regulated sequence of events occurring between one cell division and the next, consisting of interphase, nuclear division (mitosis), and cell division (cytokinesis).

Cyclins

Chemical signals that trigger the movement from one phase of the cell cycle to another.

Interphase

The phase where the cell increases in mass and size, synthesizes proteins, and replicates DNA; it consists of $G_{1}$, $S$, and $G_{2}$ phases.

S Phase

The synthesis phase of interphase where DNA replication occurs, resulting in chromosomes consisting of two identical sister chromatids.

G1 Phase

The first gap phase of interphase where cells make the RNA, enzymes, and other proteins required for growth.

G2 Phase

The second gap phase of interphase where the cell continues to grow, checks new DNA for errors, and produces tubulin for mitotic spindles.

Mitosis

The process of nuclear division (M phase) by which two genetically identical daughter nuclei are produced.

Cytokinesis

The stage of cell division following the M phase where the whole cell divides; in animal cells it involves constriction of cytoplasm and in plant cells a new cell wall forms.

Prophase

The first stage of mitosis where chromosomes condense, the nucleolus breaks down, centrosomes move to opposite poles, and spindle fibers emerge.

Metaphase

The mitotic stage where chromosomes line up at the equator of the spindle (metaphase plate) and spindle fibers attach to the centromeres.

Anaphase

The mitotic stage where sister chromatids separate at the centromere and are pulled to opposite poles by shortening spindle fibers.

Telophase

The final stage of mitosis where chromosomes arrive at opposite poles, decondense, nuclear envelopes reform, and the spindle fibers break down.

Meristems

Specific regions in plants, such as the root tip, where growth and mitosis occur.

Mitotic Index

The proportion of cells in a sample undergoing mitosis, calculated as: $\text{mitotic index} = \frac{\text{number of cells with visible chromosomes}}{\text{total number of cells}}$

Mutation

A change in any gene; when occurring in genes controlling cell division, it can lead to cancer.

Oncogene

A mutated gene that causes cancer.

Carcinogen

Any agent that may cause cancer, such as UV light, tar in tobacco smoke, asbestos, and X-rays.

Benign Tumour

A mass of cells that does not spread from its original site, such as a wart.

Malignant Tumour

A cancerous mass that spreads through the body, invading and destroying other tissues.

Metastasis

The process by which malignant tumour cells break off and travel through the blood or lymphatic system to form secondary growths in other parts of the body.