Chap.6 Cell cycle/division Flashcards
When do chromosomes become visible
Chromatin condenses before cell division, coiling up, after each DNA molecule is replicated and has an exact copy of itself
What is the structure of the chromosome after chromatin condensation
2 sister chromatids, joined by a centromere
What is a centromere and it’s function
Specialised region of a chromosome where 2 chromatids join, and where the spindle fibres attach at cell division
Difference between a haploid and a diploid
A haploid consists of 1 complete set of chromosomes while a diploid has 2
Is a normal human cell a haploid or a diploid
Diploid as it receives one complete set of chromosomes from each parent. Chromosome come in pairs so are homologous pairs. 23 pairs of chromosomes, 2 complete sets
What is ploidy level
Refers to the number of complete sets of chromosomes in an organism. Human’s ploidy level is 2 in a body cell
What is mitosis
A type of cell division in which 2 daughter cells carry the identical genetic material as that in their parent cells
What is a cell cycle
A sequence or pattern of process a cell goes through continuously
Regular alternation of DNA synthesis and cell division
What are the 3 big categories of a cell cycle
Interphase, mitosis and cytokinesis
Main features of interphase
Longest phase in the cell cycle when organelles in a cell replicate.
DNA doubles
Histones, enzymes (proteins) synthesised
Chromosomes not visible yet
*Remember that DNA started duplicating in interphase, not prophase
What are the 4 stages in mitosis
Prophase, metaphase, anaphase, telophase
What happens in prophase
Chromosomes condense, coil up, get shorter but thicker, so are visible as pairs of chromatids
Centrioles start to separate and move to opposite poles
Protein microtubules start to form, spindle fibres extend
How is the nucleus changed in later prophase
Nuclear envelope disintegrates and nucleolus disappears
What happens in metaphase
Centrioles approach opposite poles, organise spindle fibres to attach centromeres
Chromosomes line up on equator
What happens in anaphase
Centromeres separate and spindle fibres shorten
Separated chromatids are pulled to the opposite poles
Features of telophase
Final stage of mitosis No longer called chromatids but chromosomes Chromosomes uncoil and lengthen Spindle fibres break down Nuclear envelope reforms Nucleolus reappears
Describe the stage of cytokinesis
Division of cell cytoplasm
Differences between animal and plant cells
Animal: constriction of parent cell around equator, cleavage furrow
Plant: cell plate forms
Differences between mitosis in plant and animal cell
Plants experience no shape changes
Plant cells do not have centrioles
Animal cells form cleavage furrow while plant cells form cell plates
Cleavage furrow from outward to inward
Cell plate from inward to outward
Spindle fibres in animal degenerate at telophase
Remain in plants throughout the whole new cell wall formation
Why is mitosis significant (3 reasons)
Gives genetic stability as cells produced from mitosis are genetically identical to parent cells
Replace worn out tissues, repair
Asexual reproduction in yeasts and bacteria
In what form damage and disease can happen to a cell
Potential cause such as mutations, so genes that control the cell cycle gets damaged.
Disrupting the timing of the cell cycle
Possible factors that damage the genes controlling the cell cycle
Mutations, exposure to radiation, chemicals, viral infections
How can damage to genes lead to cancers
Genes can control timings of a cell cycle, like a brake
Are tumour suppressing genes
Without them cells could divide too rapidly
Prevent rapid replication thus avoid tumour formation
What is an oncogene
A gene with potential cause to cancer. Before altered, are called proto-oncogenes
What is meant by meiosis
Two stage cell division in sexually producing organisms
Produces 4 genetically not identical daughter cells with half the number of chromosomes of parent cell
A haploid
Why does the number of chromosomes change in meiosis
Chromosome number halves
So when 2 haploid gametes fuse in fertilisation, zygote formed, consisted of 2 complete sets of chromosomes, one from each gamete, to restore the diploid condition
To avoid doubling of chromosome number for each generation
What are the sequences of meiosis
Same cell division sequence from prophase to telophase
But repeats twice
Chromosome behaviours are different
Have to specify I and II
What takes place in meiosis I prophase I
Paternal and maternal chromosomes come in homologous pair, called synapsis, chromosome pair is bivalent
Chromosomes coil up, centrioles move to opposite poles forming spindle fibres
Chromatids wrap around each other at chiasmata where DNA is exchanged
Crossing over, gives genetic variation
Mixing genes of 2 parents so have different alleles
Nucleolus disappears, envelope disintegrates
Events at metaphase I meiosis
Arrange on equator
Lie randomly so combination of chromosomes in daughter cells is random as in which parent they come from
Independent assortment
Random mixture of maternal and paternal chromosomes
What happens in anaphase, metaphase, telophase II
Chromosomes in bivalent separate, spindle fibres shorten, pulled to each end of the pole randomly
Nuclear envelope reforms, chromosomes decondense in telophase
Cytoplasm divides in cytokensis
Independent assortment still happens in metaphase II
Comparing mitosis and meiosis stage 2
Very similar. Pretty much like reassembling process of mitosis
What is the importance of meiosis
Keeps chromosome number constant from one generation to another
Generates genetic variations
More able to adapt with the changing environment
Differences between meiosis I and II
No DNA replication or crossing over in II
Not homologous pair but chromosomes in stage II
2 daughter cells in I, 4 in II
Separation and independent assortment of chromatids in II instead of chromosomes in I
