Cell nuclear divison Flashcards
1
Q
Cell cycle
A
- When G1, G2 and metaphase checkpoints are passed, cell cycle continues to the next stage :)
- Dysregulation of checkpoints of cell division can result in uncontrolled cell division and cancer is required :(
2
Q
G1 phase (fIrst growth phase)
A
- Synthesis of organelles
- Nucleolus actively synthesizes rRNA for formation of ribosomes
- Synthesis of proteins
- Increase in cytoplasmic volume, resulting in increase in cell size
Ensures that cell size is adequate and there are sufficient nutrients available and growth factors present for cell to undergo mitosis
3
Q
S phase (synthesis)
A
- DNA semi-conservative replication occurs, resulting in doubling of DNA content
- Histone proteins are synthesized
- Newly synthesized DNA molecules wound tightly around the histone proteins
- Each chromatin fibre is composed of 2 DNA molecules
4
Q
G2 phase (second growth phase)
A
- Intensive synthesis of organelles
- 2 centrosomes have formed by duplication of centrosomes. Each centrosome is made up of a pair of centrioles
- Synthesis of proteins
- Synthesis of ATP for energy
- Ensures that cell size is adequate and semi-conservative DNA replication has been completed successfully
5
Q
Cytokinesis in animal cells
A
- Cell membrane invaginates towards the metaphase plate
- A ring of actin microfilaments contracts by interacting with myosin molecules
- The cleavage furrow deepens until the parent cell is pinched into 2, producing 2 daughter cells
6
Q
Cytokineses in plant cells
A
- Golgi vesicles that containing cell wall material (cellulose) move along microtubules towards the metaphase plate and fuse together to produce a cell plate
- Cell plate enlarges as more vesicles fuse with it, until the surrounding membrane fuses with cell surface membrane along the perimeter of the cell
- A new cell wall is formed between the 2 daughter cells
7
Q
Defn. Mitosis
A
Nucleus of parent cell divides once to produce 2 genetically identical daughter nuclei with same number and types of chromosomes as parent nucleus
8
Q
Mitosis: Prophase
A
- Chromatin fibre becomes more tightly coiled, condensing into chromosomes
- Each duplicated chromosome appears as two identical sister chromatids joined together at their centromeres
- Centrosome organise microtubules into spindle fibres and the radial array of short microtubules extending from each centrosome are called asters
- Centrosomes migrate to opposite poles of the cell by
lengthening of microtubules - Nucleolus disperses and seems to disappear
- Nuclear envelope fragments
9
Q
Mitosis: Metaphase
A
*longest phase
- Microtubules from centrosome are attached to kinetochore at the centromere of each chromatid of chromosome, becoming kinetochore microtubules
- Centromeres of chromosomes are aligned along the metaphase plate by microtubules
- Non-kinetochore microtubules interact with those from the opposite pole of the spindle
Metaphase checkpoint:
Ensures that all chromosomes are attached to spindle fibers/ microtubules at the metaphase plate before proceeding to anaphase
10
Q
Mitosis: Anaphase
A
*shortest phase
- Centromere separates and 2 sister chromatids separate, thus becoming 2 daughter chromosomes
- Daughter chromosomes migrate towards opposite poles of the cell, with the centromere leading the way as kinetochore microtubules shorten
- Non-kinetochore microtubules lengthen, leading to cell elongation (non-kinetochore microtubules push against each other)
- By the end of anaphase, the two poles of the cell have equivalent and complete set of chromosomes
11
Q
Mitosis: Telophase
A
- Nuclear envelope reform from the fragments of the endomembrane system to form nuclei
- Nucleolus reappears
- Chromosomes become less condensed to form chromatin
- Microtubules disperse by depolymerising
12
Q
Significance of mitosis
A
- Mitosis confers genetic stability between generations of cells
- Each parent cell produces 2 genetically identical daughter cells with the same number and types of chromosomes as parent nucleus (no variation in genetic information
- The daughter cells have identical genetic information as the parent cell, due to semi-conservative replication of parental DNA during the synthesis phase of interphase
- This enables growth, repair and asexual reproduction
- To grow from one cell to a multicellular organism, all daughter cells must be genetically identical to the parent cell.
But, genetically identical cells are able to differentiate to different cell types due to differential gene expression
- Cells that are lost, damaged or worn-out are replaced by genetically identical cells
- Involves one single parent, producing offsprings that are genetically identical to parent known as clones
This is common in plants - vegetative propagation
13
Q
Defn. Meiosis
A
- Nucleus of parent cell divides twice to produce 4 genetically non-identical haploid daughter nuclei
- Each daughter nuclei contains half the number of chromosomes in the parent nucleus by reducing two sets of chromosomes to 1 set of chromosome
- It is vital for sexual reproduction and takes place in the reproductive organs of plants and animals
14
Q
…
A
15
Q
Significance of meiosis
A
- The production of haploid gametes by meiosis is important prior to fertilisation in sexual reproduction, where fusion of gametes from different parents occur to form a zygote
- Meiosis ensures maintenance of chromosomal number in offspring and prevent doubling of chromosomal numbers during fertilisation
- Meiosis generates genetic variation in offspring by producing recombinant gametes through
- Crossing over between non-sister chromatids of homologous chromosomes
- Independent assortment of homologous chromosomes
