Cell_Cycle_Division Flashcards
What is cell division necessary for in unicellular organisms?
Reproduction, growth, and repair/regeneration
What is cell division necessary for in multicellular organisms?
Reproduction, growth, and repair of tissues
What organism does binary fission?
Prokaryotes
What is binary fission?
It is when a prokaryote divides into new cells that are completely identical
What are the 2 steps of binary fission?
- Replication of DNA
- Seperation of the cytoplasm
What type of cell division does prokaryotic cells do?
Mitosis
What type of cell division do eukaryotic cells do?
Mitosis and meiosis
What is mitosis?
The division of somatic (nonsex) cells
What is mitosis for?
- Tissue repair
- Body growth
- Replace worn out cells
What is meiosis?
Division of germ (sex) cells
What is meiosis for?
- Production of eggs in the ovary or sperm in the testes
- Used for sexual reproduction
What are the 2 main phases in the mitotic cell cycle?
Interphase and mitosis (m phase)
What percentage does interphase cover in the cell cycle?
~90%
What are the sub-phases of interphase?
- G1
- S
- G2
What happens during G1 phase (Gap 1)?
- Cellular growth
- Maintenance
- Chromosomes are single
-unreplicated structures - Restriction point
What happens during the restriction point?
Commitment is made to replicate DNA and then divide the cell
What happens during the S phase (Synthesis)?
- DNA replicates
- One chromosome becomes 2 sister chromatids
What happens during the G2 phase (Gap 2)?
- Cellular growth
- Preparation for mitosis
What is a synonym of the M phase?
Mitosis
What are the sub-phases of the M phase?
Prophase, prometaphase, metaphase, anaphase and telophase
What percentage does mitosis cover in the cell cycle?
~10%
What is cytokinesis?
A cytoplasmic division, and may occur after mitosis
What stimulates the cell cycle?
- Cyclin-Cdk complexes
- Growth factors
- Hormones ( provokes cell division)
What forms chromatin?
DNA and histone proteins
Steps of the S-phase:
- Double-helix unwinds and 2 linear strands separate
- Each strands does complimentary base pairing
- Each chromosomes is composed of 2 identical sister chromatids held together at the centromere
What is a nucleosome?
DNA wrapped around a histone core (4 histone proteins)
When do the centrosomes double?
After DNa replicates
What is a centrosome?
2 centrioles perpendicular to each other
What happens during G2 to M transition?
Centrosomes move to the opposite ends of the nuclear envelope
What happens when the centrosomes go to the opposite ends of the nuclear envelope?
Initiates formation of microtubules which leads to formation of the spindle structure
What happens during prophase?
- chromosomes condense; become visible as paired chromatids
- a kinetochore develops in the centromere region of every chromosome
- centrosomes serve as poles (mitotic centers); microtubules form between the poles to make the spindle
What is a kinetochore?
Ring of proteins
What are the types of microtubules that form the spindle?
Polar microtubules and kinetochore microtubules
What are polar microtubules for?
Form the spindle structure
What are kinetochore microtubules for?
Attach the kinetochores on the chromosomes. Reason why sister chromatids attach to opposite halves of the spindle
What is the use of polar microtubules for chromosomes?
They glide over them (spindle structure) to go to their respective pole
What happens during prometaphase?
- Nuclear envelope and nucleolus disappear
- Chromosomes gradually pushed towards the middle of the cell
What happens during metaphase?
- Chromosomes are now in the middle of the cell (equatorial plate)
- At the end, centromere separate
What happens during telophase?
- Spindle stru ture breaks down
- Chromosomes uncoil and become less condensed
- Nuclear envelope and nucleoli re-form
- Production of 2 nuclei whose chromosomes are identical to each other and to those of the cells who began the cycle
What is cytokinesis?
Division of the cytoplasm
How is cytokinesis accomplished in animal cells?
Through plasma membrane furrowing caused by contraction of the cytoplasmic microfilaments
How is cytokinesis accomplished in plant cells?
By vesicle fusion forming the cell wall
What are the ways asexual reproduction is used?
- Unicellular organism reproduces itself
- Multicellular replicate cells to form new individual
In both cases, the offspring is a clone of the original cell
What is sexual reproduction?
- shuffling of genetic information
- Through meiosis, division that produces gamete (sexual cells)
What are somatic cells?
Every body cells except sexual cells (gametes)
How many sets of chromosomes do somatic cells have?
- 2 sets of chromosomes (2n)
- homologous pairs of chromosomes with matching genes
How is asexuel reproduction used?
- Unicellular reproduce itself
- Multicellular replicate cells to form a new organism
What is the result of asexual reproduction?
Clones, genetically identical to the parent
What is sexual reproduction?
The shuffling of genetic information in a population
What is the difference between asexual and sexual reproduction?
Asexual reproduction: clones, genetically identical
Sexual reproduction: all offsprings are genetically different
What type of cell division does sexual reproduction use?
Meiosis
What are gametes?
Cells specialized for reproduction
What other term can be used to replace S-phase?
Synthesis
How many sets of chromosome do gametes have?
- ## 1 set of chromosomes (haploid: n)
What is fertilization?
2 haploid gametes (female egg and male sperm) fuse to form a diploid (2n) zygote cell
Which cells are haploid?
Gametes
What are the different types of sexual life cycles?
- Haplontic life cycle
- Alternation of generations
- Diplontic life cycle
What is the haplontic life cycle?
Done by fungi and most protists
- zygote the only diploid stage
What is the alternation of generations cycle?
Done by plants and photosynthetic protists
- meiosis gives rise to haploid spores
What is the diplontic life cycle?
Done by animals
- gametes are the only haploid stage
What are the nuclear divisions that are done in meiosis?
Meiosis I and meiosis II
How many cells does meiosis I result in?
2 cells
When is DNA replicated and how many times?
It is replicated before Meiosis I and only once
What is metaphase I?
Each chromosomes has one kinetochore microtubule which associates it to a polar microtubule
What is anaphase I?
When 2 homologous chromosomes seperate
- daughter nuclei contain one set of chromosomes
- each chromosome still has two chromatids
What is telophase I?
The nuclear envelope regenerates
- followed by an interphase called interkinesis
What are the steps of interkinesis?
G1 and G2
What is prophase I?
- homologous chromosomes pair up (synapsis) and chromosomes exchange material by crossing-over (recombination) between non-sister chromatids of two adjacent homologs
What is prometaphase I?
- nuclear envelope and nucleolus disappear
What happens in meiosis II?
The sister chromatids seperate
- results in four cells
What is the advantage of having a lot of chromosome pairs in a diploid cell?
greater diversity of chromosome combinations
What kind of meiotic error could happen and what would it cause?
Nondisjunction: One member of a homologous pair of chromosomes fails to separate from the other or sister chromatids fail to separate and go to their pole
Results in:
- gamete with an extra chromosome (trisomy)
- other gamete lacking that chromosome (monosomy)
What does karyotype mean?
The number, shapes, and sizes of the chromosomes in a cell
