Cell Division - Anatomy and Physiology Lecture Flashcards
Most cells of the human body undergo _____________, the process by which cells reproduce themselves
cell division
The two types of cell division—
- somatic cell division
- reproductive cell division
2 phases of somatic cell division
Mitosis and Cytokinesis
Mitosis
nuclear division
Cytokinesis
cytoplasmic division
produce two genetically identical cells, each with the same number and kind of chromosomes as the original cell
Somatic Cell Division
Reproductive Cell Division produces ______________ the cells needed to form the next generation of sexually reproducing organisms
gametes
produces gametes, the cells needed to form the next generation of sexually reproducing organisms
Reproductive Cell Division
is an orderly sequence of events in which a somatic cell duplicates its contents and divides in two
cell cycle
Human cells contain
23 pairs of chromosomes, for a total of 46
The two chromosomes that make up each pair are called
homologous chromosomes or homologs
The exception to this rule is one pair of chromosomes called the
sex chromosomes
females the homologous pair of sex chromosomes consists of two large
X chromosomes
males the pair consists of an
X and a much smaller Y chromosome
three phases of Interphase
G1, S, G2
cell metabolically active; duplicates organelles and cytosilic components; centrosome replication begins
G1 phase
What happens in G1 phase
cell metabolically active; duplicates organelles and cytosilic components; centrosome replication begins
DNA replicated
S phase
Cell growth continues; enzymes and other proteins are synthesized; centrosome replication completed
G2 phase
What happens in G2 phase
Cell growth continues; enzymes and other proteins are synthesized; centrosome replication completed
exit from cell cycle (non-dividing cell)
G0
The process results in the exact partitioning of genetic information
Mitosis/Mitotic Phase
For convenience, biologists divide the process into four stages:
Prophase, Metaphase, Anaphase, Telophase
prophase chromosome consists of a pair of identical strands called
chromatids
holds the chromatid pair together
centromere
At the outside of each centromere is a protein complex known as the
kinetochore
a football-shaped assembly of microtubules that attach to the kinetochore
mitotic spindle
of the mitotic spindle align the centromeres of the chromatid pairs at the exact center of the mitotic spindle
microtubules
This plane of alignment of the centromeres is called the
metaphase plate (equatorial plane)
The centromeres split, separating the two members of each __________________, which move toward opposite poles of the cell.
chromatid pair
Once separated, the chromatids are termed
chromosomes
- prophase chromosome consists of a pair of identical strands called chromatids.
- centromere holds the chromatid pair together.
- At the outside of each centromere is a protein complex known as the kinetochore
- mitotic spindle, a football-shaped assembly of microtubules that attach to the kinetochore
prophase
- The microtubules of the mitotic spindle align the centromeres of the chromatid pairs at the exact center of the mitotic spindle.
- This plane of alignment of the centromeres is called the metaphase plate (equatorial plane).
metaphase
- The centromeres split, separating the two members of each chromatid pair, which move toward opposite poles of the cell.
- Once separated, the chromatids are termed chromosomes.
anaphase
- The identical sets of chromosomes, now at opposite poles of the cell, uncoil and revert to the threadlike chromatin form.
- A nuclear envelope forms around each chromatin mass, nucleoli reappear in the identical nuclei, and the mitotic spindle breaks up.
telophase
As noted earlier, division of a cell’s cytoplasm and organelles into two identical cells is called
cytokinesis
This process usually begins in late anaphase with the formation of a cleavage furrow, a slight indentation of the plasma membrane, and is completed after telophase.
cytokinesis
This process usually begins in late anaphase with the formation of a __________________, a slight indentation of the plasma membrane, and is completed after telophase.
cleavage furrow
usually appears midway between the centrosomes and extends around the periphery of the cell
cleavage furrow
period between cell divisions; chromosomes not visible under light microscope
interphase
metabolically active cell duplicates most of its organelles and cytosilic components; replication of chromosomes begins
g1 phase
replication of DNA and centrosomes
S phase
cell growth, enzyme and protein synthesis continue; replication of centrosomes complete
g2 phase
parent cell produces identical cells with identical chromosomes; chromosomes visible under light microscope
mitotic phase
nuclear divison; distribution of two sets of chromosomes into separate nuclei
mitosis
- chromatin fibers condensed into paired chromatids
- nucleolus and nuclear envelope disappears
- each centrosome moves to an opposite pole of the cell
prophase
centromeres of chromatid pairs line up at metaphase plate
metaphase
- centromeres cplit
- identical set of chromosomes move to opposite poles of cell
anaphase
- nuclear envolopes and nucleoli reappear
- contractile ring forms cleavage furrow around center of cell, dividing cytoplasm into separate and equal portions
cytokinesis
the reproductive cell division that occurs in the gonads (ovaries and testes), produces gametes in which the number of chromosomes is reduced by half.
Meiosis
As a result, gametes contain a single set of 23 chromosomes and thus are
haploid cells
restores the diploid number of chromosomes
Fertilization
meiosis occurs in two successive stages:
meiosis I and meiosis II
Two sister chromatids of each pair of homologous
chromosomes pair off , an event called ___________
synapsis
The resulting four chromatids form a structure called a
tetrad
Such an exchange between parts of nonsister (genetically
different) chromatids is called
crossing-over
- Two sister chromatids of each pair of homologous chromosomes pair off , an event called synapsis.
- The resulting four chromatids form a structure called a tetrad.
- Parts of the chromatids of two homologous chromosomes may be exchanged with one another.
- Such an exchange between parts of nonsister (genetically different) chromatids is called crossing-over.
Prophase I
- the tetrads formed by the homologous pairs of chromosomes line up along the metaphase plate of the cell, with homologous chromosomes side by side
Metaphase I
- The members of each homologous pair of chromosomes separate as they are pulled to opposite poles of the cell by the microtubules attached to the centromeres.
- The paired chromatids, held by a centromere, remain together.
Anaphase I
Telophase I and cytokinesis of meiosis are
similar to telophase and cytokinesis of mitosis.
Telophase I and Cytokinesis
cell type in mitosis
somatic
cell type in meiosis
gamete
number of divisions in mitosis
1
number of divisions in meiosis
2
does mitosis contain tetrads?
no
does meiosis contain tetrads?
yes
number of cells in mitosis
2
number of cells in meiosis
4
number of chromosomes per cell in mitosis
46, or two sets of 23
number of chromosomes per cell in meiosis
one set of 23