cell and nuclear division Flashcards
what are haploid cells
cells that contain one set of chromosomes
what are diploid cells
cells that contain two complete sets of chromosomes
chromosomes exist as homologous pairs
what are homologous chromosomes
a pair of chromosomes, one of maternal and one of paternal origin
carry the same genes at the same loci but may not carry the same alleles
similar in size, shape, centromere position and staining pattern
what are sister chromatids
(wait actual
2 genetically identical DNA molecules (have a centromere each)
what is a chromosome made up of
2 sister chromatids joined together at the centromere
what occurs in interphase
- G1 phase: cellular synthesis of organelles, RNA, protein, ATP etc
- S phase: DNA is replicated semi-conservatively
- G2 phase: cellular synthesis in preparation for mitosis/meiosis - single microtubule organising center replicates to form 2 centrosomes, centrioles appear
how should the cell look like after interphase
DNA is duplicated
nucleus is bound by nuclear envelope
nucleolus is present
organelles are duplicated
centrosomes with centrioles pairs present
what is mitosis
nuclear divisiom in eukaryotic cells which produces two daughter nuclei containing identical sets of chromosomes as parental cell nucleus
what occurs in prophase
- chromatin condenses, coils and shortens into chromosomes
- centrioles move to opposite poles of the cell
- spindle fibres form and extend from opposite poles of the cell
- nucleolus disappears
- nuclear envelope disintegrates into vesicles
what are the different types of spindle fibres
kinetochore microtubule: spindle fibres that extend towards kinetochore proteins found on centromere of chromosomes
non-kinetochore microtubule: spindle fibres that extend towards metaphase plate
what occurs in metaphase
- chromosomes align at metaphase plate
- each chromosome is attached to 2 kinetochore microtubules at the centromere
- kinetochore microtubules help to position and arrange the chromosomes singly at metaphase plate
what occurs in anaphase
- centromeres divide and sister chromatids divide, now becoming daughter chromosomes
- KCM shorten: pull daughter chromosomes, centromere fitst to opposite poles
- NKCM elongate and slide in opposite directions to elongate the cell
why would the distance between the poles of the cells change in anaphase?
when kinetochore microtubules shorten, the distance between the poles decrease
when non KCM elongate and slide past each other, the distance between the poles increase
what occurs in telophase
- daughter chromosomes decondense to form chromatin
- spindle fibres disintegrate
- nuclear envelope reforms around chromatin at each pole
- nucleolus reappears
- cleavage furrow/cell plate starts to form
what occurs in cytokinesis (animal cells)
- cell membrane invaginates towards region previously occupied by metaphase plate to form cleavage furrow
- the furrow deepens until parent cell is pinched into 2 separate cells
- each cell has its own nucleus, set of organelles and cytosol
what occurs in cytokinesis (plant cells)
- golgi apparatus produces a small number of vesicles and appear in centre of cell
- the fluid filled vesicles fuse to form cell plate
- contents of the vesicles contribute to new cell walls of daughter cells
- membranes of the vesicles contribute to the cell membrane of the daughter cells
- spreading cell plate eventually fuses with parent cell wall = separates daughter cells
what is the importance of mitosis in maintaining genetic stability
- mitosis produces 2 identical nuclei with same number and type of chromosomes as parent cell
- s phase: semi conservative dna replication occurs where each strand acts as a template for synthesis of a complementary strand by complementary base pairing
- during prophase, chromosomes with genetically identical sister chromatids are formed by the 2 newly synthesised identical DNA molecules with same alleles condensing
- during anaphase, after centromere divides and identical sister chromatides separate to opposite poles of the cell = 2 gentically identical daughter cells will result
what is the importance of regulating the miotic cell cycle
cell cycle is regulated at checkpoints = dysregulation at checkpoints causes the cell to escape cell cycle control mechanism = leads to uncontrolled cell division and tumours may form
what is meiosis l about
pairing of homologous chromosomes and subsequent separation of homologous chromosomes into 2 daugther cells, reducing the chromosome number by half
what happens in prophase l
- chromatin coils, condenses and shortens into chromosome
- homologous chromosomes pair up along their length via process of synapsis to form bivalents
- crossing over occurs between non-sister chromatids of homolgous chromosomes to form chiasmata = allow exhcange of corresponding alleles
- centrioles move to opposite poles of the cell and spindle fibres start to form
- nucleolus disappears and nuclear envelope disintegrates
what happens in metaphase l
- homologous chromosomes align in pairs at the metaphase plate independently of other pairs
- at their centromere, each homologue is attached to kinetochore microtubules from the poles it faces
what occurs in anaphase l
- centromeres do not divide = sister chromatids of a homologue move together towards each pole
- homologous chromosomes separate to opposite poles into 2 homologues by shortening of the kinetochore microtubule
- non kinetochore microtubules elongate and slide in opposite directions to elongate the cell
what happens in telophase l
- each pole has a haploid set of chromsomes
- chromosomes decondense to form chromatin
- spindle fibres disintegrate
- nuclear envelope reforms and nucleolus reappears
what happens at the end of cytokinesis l
cell divides (by cleavage furrow/cell plate) to form 2 daughter cells each with a haploid set of chromosomes
what is meiosis ll about
separation of 2 sister chromatids
what happens in prophase ll
- chromatin coils, condenses and shortens into chromosome
- centrioles move to opposite poles of the cell and spindle fibres start to form
- nucleolus disappears and nuclear envelope disintegrates
what happens in metaphase ll
- each chromosome is attached to kinetochore microtubule from both poles
- kinetochore microtubules help
chromosomes align at metaphase plate in 1 row
what happens in anaphase ll
- centromere divides = each non-identical sister chromatid is known now as daughter chromosome
- KCM shorten and pull daughter chromosomes, centromere first to opposite poles
- non KCM elongate and slide in opposite directions to elongate the cell
what happens in telophase ll
- chromosome reach opposite ends of the cell and decondense into chromatin
2, spindle fibres disintegrate - nuclear envelope reforms and nucleolus reappears
what happens at the end of cytokinesis ll
each of the 2 daughter cell divides to give a total of 4 daughter cell
each daughter cell has half the number of chromosomes as the parent cell, and half the DNA amount as the parent cell before S phase/replication
what is the significance of meiotic cell cycle
meiosis is a reduction division that produces 4 haploid gametes from 1 diploid parent cell
meiosis halves the chromosome number so that the diploid chromosome number can be restored when 2 haploid gametes fuse together during fertilisation
chromosome number remains the same throughout generations
what are the events that create genetic variation while achieving haploid number in meiosis
- crossing over of non sister chromatids of homologous chromosomes in prophase l = allows for exchange of genetic material = new combinations of alleles on chromatids
2.independent assortment of homologous chromosomes at metaphase plate and subsequtn separation in metaphase l and anaphase l - random orientation of non identical sister chromatids of each chromosome at each metaphase plate and their subsequent separation during metaphase ll and anaphase ll respectively
2 and 3 result in 2^n possible combinations of maternal and paternal chromosomes, with n being the number of chromosome pairs
how is genetic variation acheieved after meiosis
- haploid number allows for random fusion of gametes during fertilisation = allows for great number of genotypic combinations of a zygote (2^23x2^23 possible types of offspring)
why must the nuclear envelope disintergrate
it must disintergrate so that it would not hinder the movement of the chromosomes
why must chromatin condense into chromosomes in prophase
to prevent tangling of the genetic material stored in the long, thin and thread-like chromatin
what isthe role of mitosis in asexual reproduction
by mitosis, single parent produces offspring genetically identical to itself
offpsring able to receive same set of genes from parent
advantageous to offspring in stable environments
what is the role of mitosis in regeneration and cell replacement
mitosis ensures that damaged ells are replaced by cells that are genetically identical to original cells
what is the role of mitosis in growth
mitosis results in the number of cells within an organism increasing, new cells produced are genetically identical to the cell
