Chromosomes, Mitosis and Meiosis Flashcards
Chromosomes constitution
Genes are informational units made of DNA. In Eukaryotes, DNA associates with protein to form chromatin fibers that make up chromosomes.
How is DNA packed into chromosomes?
In eukaryotic cells DNA is associated with histones to form nucleosomes, each of which consists of a histone bead with DNA wrapped around it. Nucleosomes are organized into large, coiled loops held together by nonhistone scaffolding proteins.
The cell cycle consists of…
Interphase and M phase.
Interphase consists of
The first gap phase (G1), the synthesis phase (S) and the second gap phase (G2).
G1 phase (Int)
During this phase the cell grows and prepares for the S phase.
S phase (Int)
During the S phase DNA and the chromosome proteins are synthesized and chromosome duplication occurs.
G2 phase (Int)
Protein synthesis increases in preparation for cell division.
M phase
It consists of mitosis, the nuclear division that produces two nuclei identical to the parental nucleus, and cytokinesis, the division of the cytoplasm to yield two daughter cells.
The structure of a duplicated chromosome (via mitosis)
It consists of a pair of sister chromatids which contain identical DNA saquences. Each chromatid includes a constricted region called a centromere. Sister chromatids are tightly associated in the region of their centromeres. Attached to each centromere is a kinetochore, a protein structure to which microtubules can bind.
Mitosis significance
It assures that the chromosome number is preserved when one eukaryotic cell divides to form two. Identichal chromosomes are distributed to each pole of the cell.
Prophase (mit1)
The structure of the duplicated chromosomes becomes apparent as the chromatin condenses; each is composed of a pair of identical sister chromatids. The nuclear envelope begins to disassemble, and the mitotic spindle begins to form.
Prometaphase (mit2)
Spindle microtubules attach to kinetochores of chromosomes and they begin to move toward the cell’s midplane.
Metaphase (mit3)
The chromosomes are aligned on the cell’s mid plane or metaphase plate; the mitotic spindle is complete and the kinetochores of the sister chromatids are attached by microtubules to opposite poles of the cell.
Anaphase (mit4)
The sister chromatids separete and move to opposite poles. Each former chromatid is now a chromosome.
Telophase (mit5)
A nuclear envelope re-forms around each set of chromosomes, nucleoli become apparent, the chromosomes uncoil, and the spindle disappears. Cytokinesis generally begins here.