Lectrure 11: Cell Division Flashcards
Why is cell division necessary?
it is necessary for reproduction (for unicellular and multicellular) and growth and repair/regeneration (for multicellular only)
What is binary fission?
The result of 2 new cells in prokaryotes that are exact copies of one another
How many chromosomes do most prokaryotes have? What is the usual shape?
One. Circular
What are the 2 cellular division methods found in eukaryotes?
Mitosis and Meiosis
What is Mitosis?
Division of somatic (non sex) cells,
Ex: tissue repair, body growth, replace worn out cells
What is Meiosis?
Division of germ (sex) cells
Ex: eggs in ovary or sperm in testes.
What are the 2 main phases of the Mitotic cell cycle?
Interphase and Mitosis phase (M-phase)
What are the 3 sub-phases of Interphases?
G1, S, and G2
What happens in the G1 phase?
-Most cellular growth
-Chromosomes are single
-Unreplicated structure
-Restriction point: a commitment is made to replicate DNA and then divide the cell, creating a SA:V imbalance
What happens in the S phase?
-1 chromosome becomes 2 chromatids
-the centrosome replicates
What happens in the G2 phase?
-some cellular growth & preparation for mitosis
What are the subphases does the M phase have?
1) Prophase
2) Prometaphase
3) Metaphase
4) Anaphase
5) Telophase
How much of the cell cycle does Mitosis take up?
10%
What is cytokinesis?
A cytoplasmic division. May occur right after mitosis.
What stimulates a cell cycle?
-Cyclin-Cdk complexes
-growth factors
-hormones
How do DNA molecules fit in the nucleus?
They are extensively “packed”
How is packing achieved for DNA? What is it called?
By winding DNA molecules around histone proteins forming nucleosomes. This is called Chromatin.
What are Eukaryotic chromosomes?
Strands of chromatin
How does the chromosome make a copy of itself in S phase6
It’s double helix unwinds and each strand does complementary base pairing. Now there are 2 identical sister chromatids held together at centromere.
What do the chromosomes do in prophase?
They condense even more forming a characteristic shape of mitotic chromosomes.
What happens after DNA replicates?
The centrosome doubles.
What does the centrosome consist of?
Two centrioles at right angles to each other.
What happens to the centrosome during the G2 to M transition?
-The centrosomes move to the opposite ends of the nuclear envelope.
-They then initiate formation of microtubules, which lead to formation of the spindle structure
What are the sub-phases of Mitosis?
1) Prophase
2) Prometaphase
3) Metaphase
4) Anaphase
5) Telophase
What happens during prophase?
-chromosomes condense and become visible pairs (chromatids)
-a kinetochore develops in the centromere region of every chromosome
-mictrotubules form between poles (chromosomes) to make the spindle
What are the two types of microtubules?
1) Polar microtubules
2) Kinetochore microtubules
How do Polar microtubules form?
From the spindle structure
How do Kinetochore microtubules form?
They attach to kinetochores on chromosomes and then sister chromatids attach to the opposite halves of the spindle
What happens DURING prometaphase?
-nuclear envelope & nucleolus disappear
-chromosomes gradually push towards middle of cell
What happens DURING metaphase?
Chromosomes now are at middle of cell; the equatorial plate
What happens at the END of metaphase?
Centromeres separate
What happens DURING anaphase?
Each member of pair of chromatids migrate to its pole along the microtubules track
What happens DURING telophase?
-spindle structure breaks down
-chromosomes uncoil and become less condensed
-nuclear envelopes & nucleoli reform
-production of 2 nucleoli whose chromosomes are identical to each other and to those of the cell that began that cycle
What is cytokinesis?
The division of the cytoplasm. Usually follows nuclear division
How does cytokinesis work in animal cells?
It divides by plasma membrane furrowing (cleavage) caused by contraction of cytoplasmic microfilaments
How does cytokinesis work in plant cells?
Vesicle fusion forms the cell plate which begins to form the new cell wall.
What is asexual reproduction based on?
Mitosis of the nucleus.
How does asexual reproduction work for unicellular organisms?
They reproduce themselves,
How does asexual reproduction work for multicellular organisms?
They break off from themselves to form a new individual.
What are the off spring of asexual reproduction called?
Clones
What is meiosis?
The nuclear division that produces gametes that differ genetically from the parents and each other.
What do somatic cells contain?
They contain 2 sets of chromosomes. (diploid=2n)
Which cells in the body are somatic cells?
All the ones NOT specialized for reproduction.
What does each somatic cell contain?
Homologous pairs of chromosomes with corresponding genes. Each parent has one homolog.
What is sexual reproduction?
It is the result of shuffling of genetic information in a population, and the offsprings are NOT identical to their parents.
What are gametes?
Sexual cells that contain only 1 sect of chromosomes (haploid=n) and are specialized just for reproduction
What is fertilization?
2 haploid gametes that fuse together to form a diploid zygote cell. (n+n=2n)
What is the Haplontic life cycle?
Life cycle of fungi and most protists. Zygote is only ever in diploid stage
What is the Alternation of generations life cycle?
Life cycle of plants and photosynthetic protists. They have haploid spores.
What is the Diplontic life cycle?
Life cycle of animals where gametes are only at haploid stage.
What are the two stages of Meiosis?
Meiosis l and Meiosis ll.
How many times is DNA replicated in meiosis?
Once.
True or False. Gametes (n) undergo meiosis giving rise to germ cells (2n).
False, it’s the germ cells (2n) undergo meiosis giving rise to gametes (n).
True or False. Products of meiosis are different from the parents cells and to each other.
True.
What happens during prophase l?
Homologous chromosomes pair up and material is exchanged by crossing over between non-sister chromatids of two adjacent homologous.
What happens during prometraphase l?
Nuclear envelope & nucleolus disappear.
What happens in metaphase l?
-Paired homologs are now at the equatorial plate.
-Each chromosome has one kinetochore and associates with polar microtubules for one pole.
What happens in anaphase l?
-homologous chromosomes separate
-daughter nuclei contains only one set of chromosomes
-each still consists of two chromatids
What happens in telophase l?
-the nuclear envelope reaggregates
-it’s followed by an interphase called interkinesis.
Does DNA. replicate before meiosis ll?
No
What happens to the sister chromatids in meiosis ll?
They seperate.
What is the result of meiosis?
4 haploid cells.
What does the crossing over during prophase l and the random selection of homolog pairs migrating to poles in anaphase l ensure?
That each haploid gamete is different from that of the other gametes.
True or False. The more chromosome pairs there are in a diploid cell, the lesser of a diversity of chromosome combinations there is generated by meiosis.
False. The more chromosome pairs there are in a diploid cell, the greater the diversity of chromosome combinations generated by meiosis.
What is nondisjunction?
1) The one member of a homologous pair of chromosomes that fails to separate from the other, resulting in both of them going to the same pole in anaphase l.
OR
2) Sister chromatids that refuse to separate in anaphase ll.
Both lead to an extra chromosome in one gamete and one less chromosome in the other.
What’s the result of a nondisjunction and a normal haploid gametes fertilizing?
Aneuploidy and harmful or lethal genetic abnormalities.
What is Karyotype?
Number, shape, and size of the chromosomes in a cell.
