Summarizing Cell Division

Summary

Prokaryotes have a single circular chromosome composed of double-stranded DNA, whereas eukaryotes have multiple, linear chromosomes composed of chromatin surrounded by a nuclear membrane. The 46 chromosomes of human somatic cells are composed of 22 pairs of autosomes (matched pairs) and a pair of sex chromosomes, which may or may not be matched. This is the 2n or diploid state.

Human gametes have 23 chromosomes or one complete set of chromosomes; a set of chromosomes is complete with either one of the sex chromosomes. This is the n or haploid state. Genes are segments of DNAthat code for a specific protein. An organism’s traits are determined by the genes inherited from each parent. Duplicated chromosomes are composed of two sister chromatids.

Chromosomes are compacted using a variety of mechanisms during certain stages of the cell cycle. Several classes of protein are involved in the organization and packing of the chromosomal DNA into a highly condensed structure. The condensing complex compacts chromosomes, and the resulting condensed structure is necessary for chromosomal segregation during mitosis.

Glossary

cell cycle

ordered sequence of events that a cell passes through between one cell division and the next

centromere

region at which sister chromatids are bound together; a constricted area in condensed chromosomes

chromatid

single DNA molecule of two strands of duplicated DNA and associated proteins held together at the centromere

diploid

cell, nucleus, or organism containing two sets of chromosomes (2n)

gamete

haploid reproductive cell or sex cell (sperm, pollen grain, or egg)

gene

physical and functional unit of heredity, a sequence of DNA that codes for a protein.

genome

total genetic information of a cell or organism

haploid

cell, nucleus, or organism containing one set of chromosomes (n)

histone

one of several similar, highly conserved, low molecular weight, basic proteins found in the chromatin of all eukaryotic cells; associates with DNA to form nucleosomes

homologous chromosomes

chromosomes of the same morphology with genes in the same location; diploid organisms have pairs of homologous chromosomes (homologs), with each homolog derived from a different parent

locus

position of a gene on a chromosome

nucleosome

subunit of chromatin composed of a short length of DNA wrapped around a core of histone proteins