TOPIC F: CELL & NUCLEAR DIVISION Flashcards
What is the chromatin structure?
Chromatin is the complex of DNA and proteins. It is the less condensed form of a chromosome. Dispersed as a mass of long thin fibres during interphase.
What is the structure of a duplicated chromosome?
Four-arm structure visible under light microscope, consisting of two DNA molecules. Consists of two identical sister chromatids joined at the centromere. Identical sister chromatids joined at the centromere formed due to semi-conservative DNA replication during synthesis phase of interphase.
Centromere is a constricted region of satellite DNA. Bound to kinetochore proteins which allow for attachment of spindle fibres.
The centromere holds 2 sister chromatids together and are involved in chromosome movement during cell division.
What are homologous chromosomes?
We inherit one chromosome of each pair from each parent. A maternal set and a paternal set.
They
1. Have the same length.
2. Same position of centrosome.
3. Same gene at the same loci.
4. May have different alleles from each other.
5. They pair to form bivalents during prophase 1 of meiosis.
6. Each homolog consists of double structure containing two identical sister chromatids during prophase 1 of meiosis.
What happens during mitosis prophase?
Chromatin fibre becomes more tightly coiled, condensing into chromosomes. Each duplicated chromosome appears as 2 identical sister chromatids joined at the centromere.
Centrosome organise microtubules into spindle fibres and the radial array of short microtubules extending from each centrosome are called asters.
Centromeres migrate to opposite poles of the cell by microtubule lengthening. Nucleolus disperses and seems to disappear, nuclear envelope fragments.
What happens during mitosis metaphase?
Microtubules from centrosome are attached to kinetochore at the centromere of each chromatid of chromosome, becoming kinetochore microtubules. Centromeres of chromosomes are aligned along metaphase plate.
What is anaphase mitosis?
Centromere separates and two sister chromatids separates, thus becoming 2 daughter chromosomes. Daughter chromosomes migrate towardds opposite poles of the cell, with the centromere leading the way as kinetochore microtubules shorten. Non-kinetochore microtubules lengthen, leading to cell elongation.
What is mitosis telophase?
Nuclear envelopes reform from the fragments of the endomembrane system to form 2 nuclei. Nucleolus reappears. Chromosome becomes less condensed to form chromatin, microtubules disperse by depolymerising.
What is cytokinesis?
(ANIMAL CELL)
Usually occurs by late telophase, dividing the cytoplasm evenly between the two daughter cells that appear shortly after end of mitosis.
CSM invaginates towards the metaphase plate. A ring of actin microfilaments contracts by interacting w myosin molecules. Cleavage furrow deepens until parent call is pinched into 2, producing two daughter cells.
What is cytokinesis (PLANT CELL)
Golgi Vesicles that contain cell wall material move along microtubules towards metaphase plate and fuses together to produce a cell plate.
Cell plate enlarges as more vesicles fuse with it, until the surrounding membrane fuses with CSM along the cell perimeter.
What is the significance of mitosis?
Mitosis confers genetic stability between cell generations. Each parent cell produces two genetically identical daughter cells with same number and types of chromosomes as parent nucleus. The daughter cells have identical genetic information as a parent cell due to semi-conservative replication of parental DNA during synthesis phase of interphase.
Organism Growth. Cells are able to differentiate to different cell types due to differential gene expression.
Tissue Repair. Cells that are lost damaged or worn out are replaced by genetically identical cells.
Asexual reproduction. Involves one single parent producing offsprings that are genetically identical to parents (clones) Vegetative propagation.
What happens during meiosis 1 prophase?
Chromatin fibre becomes more tightly coiled, condensing into chromosomes.
Each duplicated chromosome appears as two identical sister chromatids joined at their centromeres.
Homologous chromosomes pair to form bivalents in a state called synapsis.
Crossing over occurs between non-sister chromatids of homologous chromosomes results in chiasmata formation.
The exchange of corresponding DNA segments between non-sister chromatids.
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 microtubules lengthening. Nucleolus disperses and seems to disappear, nuclear envelopes fragment.
Last 3 lines is prophase 2 as well.
What happens during meiosis 1 metaphase?
The bivalents align themselves at the metaphase plate, with one chromosome in each pair facing each pole.
The arrangement of chromosome of each bivalent is independent of the arrangement of the other bivalents. INDEPENDENT ASSORTMENT.
Both chromatids of one homolog are attached to kinetochore microtubules from one pole, the other homolog are attached to microtubules from the opposite pole.
What is meiosis anaphase 1?
Each homolog of a bivalent separates.
Homologous 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.
What is meiosis telophase 1?
Nuclear envelopes reform from the endomembrane system, forming two nuclei.
Each nucleus has a haploid set of chromosomes.
Nucleolus reappears, chromosomes become less condensed to form chromatin. Microtubules disperse by depolymerising.
What is meiosis metaphase 2?
Microtubules from centrosome attaches to kinetochore at the centromere of each chromatid of chromosome, becoming kinetochore microtubules.
Centromeres of chromosome are aligned along the metaphase plate perpendicular to the metaphase plate 1 by microtubules.
