Structure of Chromosomes, Cell Cycle and Cell Division

Comprehensive vocabulary flashcards covering the structure of DNA and chromosomes, the phases of the cell cycle, and the mechanisms and differences between mitosis and meiosis as described in the lecture notes.

Chromatin

A network of thread-like structures in the nucleus made of DNA (about $40\%$) and histones (about $60\%$) that condense into chromosomes during cell division.

Histone

Proteins that help in the coiling and packaging of DNA into structural units.

Nucleosome

A complex formed when a DNA strand is wound around a histone octamer (a core of eight histone molecules).

Gene

A specific sequence of nucleotides on a chromosome that constitutes a unit of heredity and regulates body features.

Nucleotide

The repeating structural unit of a DNA strand, composed of a phosphate group, a pentose sugar, and a nitrogenous base (adenine, guanine, cytosine, or thymine).

Cell Cycle

A series of organized, predictable events in a cell leading to the duplication of its DNA and the subsequent division into two daughter cells.

Interphase

The non-dividing phase of the cell cycle where the cell grows and prepares for division; formerly called the 'resting phase'.

First Growth Phase ($G_1$)

The phase of interphase where RNA and proteins are synthesized, the volume of cytoplasm increases, and organelles like mitochondria or chloroplasts divide.

Synthesis Phase ($S$)

The phase of interphase where DNA is synthesized and chromosomes are duplicated; DNA content is doubled but the chromosome number remains the same.

Second Growth Phase ($G_2$)

A shorter phase in interphase during which RNA and proteins necessary for cell division continue to be synthesized.

Mitosis

The type of cell division occurring in body cells where one parent cell divides into two identical daughter cells, maintaining the same chromosome number.

Meiosis

A reduction division occurring in reproductive organs to produce sex cells (gametes) with half the number of chromosomes ($n$) compared to the parent cell ($2n$).

Karyokinesis

The division of the nucleus during cell division, occurring in four main phases: prophase, metaphase, anaphase, and telophase.

Cytokinesis

The division of the cytoplasm that follows karyokinesis to produce two separate daughter cells.

Prophase

The first phase of mitosis where chromosomes become short and thick, the nuclear membrane and nucleolus disappear, and spindle fibres appear.

Centromere

The small region where two sister chromatids of a duplicated chromosome remain attached to each other.

Aster

A star-like structure formed by a centriole surrounded by radiating rays found in animal cells during division.

Metaphase

The stage of mitosis where duplicated chromosomes arrange themselves on the equatorial plane and attach to spindle fibres.

Anaphase

The stage of mitosis where the centromere divides and sister chromatids separate to move toward opposite poles of the cell.

Telophase

The final stage of mitosis where daughter chromosomes reach the poles, thin out into chromatin, and the nuclear membrane and nucleoli reappear.

Cell Plate

A structure that forms at the center of a plant cell during cytokinesis and grows toward the periphery to separate the daughter cells.

Diploid ($2n$)

Having the full set of chromosomes in pairs, which in humans is 46 chromosomes (23 pairs).

Haploid ($n$)

Having half the number of chromosomes (one member from each pair), characteristic of gametes like sperms and eggs.

Crossing Over

The process of exchange of genetic material between two non-sister chromatids of a pair of homologous chromosomes during meiosis.

Chiasma

The X-shaped structure or point of attachment formed between non-sister chromatids during the process of crossing over.

Meristems

The growing points in plants where cells divide very rapidly to produce new leaves, buds, and flowers.