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The Cell Cycle and Mitosis
Objectives
what is the purpose of mitosis?
list, describe, and label all parts of the cell cycle.
understand how chromosomes are formed and label a diagram.
what is a checkpoint?
Recall
the nucleus has multiple parts and houses the genetic material of a cell
nuclear envelope (pores)
nucleoplasm (chromatin)
nucleolus (ribosome production)
Recall
chromosomes are hereditary material within the nucleus made of coiled DNA and proteins
formed only before the cell divides
prior to cell division they are chromatin strands within the nucleoplasm
Genetic Material
A cells DNA, it’s genetic material is called it’s “genome”
Eukaryotic genomes usually consist of a number of DNA molecules, packaged into “chromosomes”
Cell Division
functions in reproduction of the cell
functions in growth and repair
Cell Division
Cell division distributes identical sets of chromosomes to daughter cells
increases the number of somatic (body) cells
Vocabulary
Cell division: process by which cells reproduce
Chromosomes: cell parts that determine replication; a chromosome is made up of two identical chromatids
Daughter cells: new cells produced by cell division
Cytokinesis: a division of the cytoplasm of one parent cell into 2 daughter cells.
Nucleosomes: Beadlike structures formed by DNA and histone molecules.
https://www.youtube.com/watch?v=IePMXxQ-KWY
The Nucleus
Chromatin (DNA along with proteins) is actually a collection of separate structures called chromosomes, which are visible as separate units only in a dividing cell
During division, chromatin condenses becoming thick enough to be discerned as separate structures called chromosomes.
nucleosomes - formed from DNA around histone molecules
histones - proteins that are wrapped with DNA
Chromosome DistributionEach eukaryotic species has a certain number of chromosomes
Example: Human
Somatic (body cells): 46 chromosomes in nucleus (diploid; 2n)
Sex cells (sperm/egg): 23 chromosomes (haploid; n)
Chromosomesmade of DNA and protein - highly condensed and tightly wound so its easier to move from one cell to the next
counted by the number of centromere not the number of chromatids
before and after replication
VocabularyCentrioles: small, cylinder shaped structures found near the nucleus, involved in mitosis
only in animal cells
Aster - star like structure made of microtubules that extend from centrioles
Spindle fibers - web like structures made up of microtubule fibers - arranges and moves the chromosomes around
The Cell Cyclehttp://highered.mcgraw-hill.com/sites/0072943696/
student_view0/chapter3/animation__how_the_cell_cycle_works.html
The mitotic phase alternates with interphase in the cell cycle
G1 phase, S phase, G2 phase
Mitosis Phases: prophase, metaphase, anaphase, telophase
Cytokinesis: The mitotic spindle distributes chromosomes to daughter cells
The steps of mitosis ensure that each new cell has the exact number of chromosomes as the original
The Cell Cycle
Interphase
growth phase
technically not part of mitosis, but it is included in the cell cycle
Cell is in a resting phase, performing cell functions
G1 (growth 1), S (DNA Synthesis), G2 (growth 2)
Interphase G1normal cell function and cell growth
DNA is in the chromatin state (kind of like spaghetti)
cells duplicate contents excluding the chromosomes (organelles)
Interphase Schromatin begins to form chromosomes
DNA replicates copies of chromosomes
there are still 46 chromosomes
counted by centromeres
Interphase G2chromosomes are still forming, not yet visible
continues to prepare for division
double checks copies of chromosomes to ensure no errors - makes repairs
centrioles formed
ProphaseChromatin finishes condensing into chromosomes
Become visible
2 chromatids joined by a centromere
Centrioles move to the opposite sides of the nucleus
Nuclear membrane disintegrates
Nucleolus disappears
Spindle forms
Early & Late Prophase
MetaphaseChromosomes line up on the equator of cell
chromosomes meet in the middle; “they meta at the middle”
Chromosomes become attached to spindle fibers by centromeres
AnaphaseSpindle fibres contract dividing centromere
Chromosomes get pulled apart
there are 92 chromosomes in this phase
Chromatids separate and move to the opposite poles of the cell
TelophaseNow there are two nuclei with 46 identical chromosomes in each
Chromosomes unwind back into chromatin
Nuclear membrane reforms
Nucleolus reappears
Spindle disappears
Centrioles duplicate
Cytokinesis
Division of the cytoplasm to form 2 new daughter cells via the cellular membrane.
Process follows telophase
Daughter cells are genetically identical
Animals: cell pinches inward (cleavage furrow)
Plants: a new cell wall between the two new cells (cell plate)
following this stage, the cells individually begin interphase G1
Cytokinesis
Following DNA replication during interphase, each chromosome in the parental nucleus is duplicated and consists of two sister chromatids.
During mitosis, the centromeres divide and the sister chromatids separate, becoming daughter chromosomes that move into the daughter nuclei.
Therefore, daughter cells have the same number and kinds of chromosomes as the parental cells.
Daughter Cells
Regulating Cell CycleCyclins - regulate the timing of the cell cycle in eukaryotic cells
Internal regulators: proteins that respond to events inside the cell
External regulators: proteins that respond to events outside the cell
A molecular control system drives the cell cycle
http://highered.mcgraw-hill.com/sites/0072943696/student_view0/chapter3/
animation__control_of_the_cell_cycle.html
Additional Resources
Mitosis: https://www.youtube.com/watch?v=f-ldPgEfAHI
Chromosomes: https://www.youtube.com/watch?v=gcz1FOWw0Cg