Overview of Division Mechanisms

Mitosis and Meiosis are two nuclear division mechanisms

Mitosis Somatic cells- body cells

Growth and repair

Meiosis In germ cells- gonads

Gametes- sperm and egg

Chromosomes

Before a cell starts dividing, the chromosomes are duplicated This process

produces sister chromatids

Centromere

Sister chromatids

Figure 8.4B

When the cell divides, the sister chromatids separate

Two daughter cells are produced

Each has a complete and identical set of chromosomes

Centromere Sister chromatids

Figure 8.4C

Chromosomeduplication

Chromosomedistribution

todaughter

cells

Mitosis and Chromosome Number

Chromosome number: sum total of chromosomes in somatic cells

Chromosomes are in pairs Humans 23 pairs ( one pair from mom,one

from dad)

2n “diploid” ( 46 -human)

1n “haploid” (germ cells, 23 -human)

The Cell Cycle

A diploid cell produces 2 diploid daughter cells

Two phases in cell cycle

InterphaseLongest phase

Increase in mass, doubles components, and duplicates DNA

MitosisNuclear division

Interphase

G1

“Gap” - cell growth before DNA replication

S

“Synthesis” - DNA replication

G2

“Second Gap” - preparation for division

M Mitosis

The Cell Cycle

Mitosis

Four stages

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis Cytoplasmic division

INTERPHASE PROPHASE

Centrosomes(with centriole pairs)

Chromatin

Nucleolus Nuclearenvelope

Plasmamembrane

Early mitoticspindle

Centrosome

CentrosomeChromosome,consisting of twosister chromatids

Fragmentsof nuclearenvelope

Kinetochore

Spindlemicrotubules

Figure 8.6

METAPHASE TELOPHASE AND CYTOKINESIS

Metaphaseplate

Spindle Daughterchromosomes

Cleavagefurrow

Nucleolusforming

Nuclearenvelopeforming

ANAPHASE

Figure 8.6 (continued)

StagesofMitosis

Cell at Interphase

Prophase

Chromosomes are visible

Spindle apparatus formsCentrioles move apart to opposite

poles

Microtubules in two sets

Extend from end and overlap in center

Nuclear envelope breaks up

Prophase

Metaphase

Chromosomes interact with

microtubules on spindle apparatus Attachment at centromeres

•Kinetochore

Microtubules pull on chromosomes

Orientation of sister chromatids to opposite poles

Chromosomes align midway between the poles

Metaphase

Anaphase

Separation of sister chromatids Movement toward opposite poles

Telophase

Chromosomes arrive at spindle poles Chromosomes return to threadlike forms

New nuclear membranes form

Two nuclei form

Cytokinesis Division of cytoplasm

Forms 2 cells

Once two nuclei form, mitosis is finished

Anaphase to Interphase

Division of the Cytoplasm

“Cytokinesis”

Between late Anaphase and end of Telophase

Cell plate forms in plantsVesicles fuse

Cleavage furrow forms in animalsDepression forms at cell’s midsection

Cytoplasmic Division of a Plant Cell

Cytoplasmic Division of an Animal Cell

Cleavage furrow

Levels of Organization in Metaphase Chromosome

Levels of Organization in Metaphase Chromosome

A nucleosome

In Conclusion

A parent cell provides each daughter cell with hereditary instructions

Eukaryotes divide by mitosis or meiosis and Prokaryotes divide by binary fission

Each chromosome is one DNA molecule with proteins attached

Cells with a diploid number (2n) contain two of each kind of chromosome

In Conclusion

Mitosis divides the nucleus into two equivalent nuclei

Mitosis is the basis of growth, tissue repair, and cell replacements among multicelled eukaryotes

Mitosis can be the method of asexual reproduction among single-celled eukaryotes

In ConclusionThe cell cycle starts when a new cell

formsThe cell cycle includes Interphase and

MitosisA duplicated chromosome has two DNA

molecules attached at the centromereThe phases of Mitosis are Prophase,

Metaphase, Anaphase, and TelophaseCytoplasmic divisions differ among

animals and plants