C2: The cell cycle and cell division Flashcards
Define chromosome
A long, thin structure of DNA and protein (Histones), in the nucleus of eukaryotic cells, carrying genes
Define chromatid
One of the two identical copies of a chromosomes, joined at the centromere prior to cell division
Define centromere
Specialised region of a chromosome where two chromatids join and to which the microtubules of the spindle fibres attach during metaphase
Describe the difference between haploid and diploid
Haploid - having one set of chromosomes
Diploid - Having two sets of complete chromosome
Define homologous
Chromosomes that are identical in size shape and they carry the same gene at the same loci, with genes for the same characteristic. One chromosome of each pair comes from each parent.
Define ploidy level and state what is meant by Polyploid
Ploidy level - Is the number of complete sets of chromosomes in an organism
Polyploidy - is when organisms have more than two complete sets of chromosomes
Name all the stages of the cell cycle
3 points
Interphase
Cell division
Cytokinesis
Describe the three stages of interphase
it is a time of high metabolic activity for the cell. interphase has 3 stages:
G1:
there is a replication of organelles
new organelles are made
synthesis of ATP and proteins
Increase in cell size
S
Replication of DNA
G2
Preparation for division
Further Growth occurs
Cell synthesises any other molecules it needs to divide
Define mitosis
A type of cell division that produces two daughter cells that have the same number of chromosomes and are genetically identical with each other and the parent cell.
Name the four stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Describe prophase
Chromosomes condense and become visible.
Centrioles move to opposite sides of cell in animal cells.
Spindle forms from microtubules.
Nuclear envelope disintegrates and nucleolous disappears
Describe Metaphase
Centromeres of chromosomes attach to the spindle fibres and line up on the equator.
Describe anaphase
Spindle fibres shorten
Centromere separates and individual chromatids are pulled to the poles centromere first.
Describe telophase
The spindle breaks down.
Chromosomes uncoil.
Nuclear envelope reforms.
Simply describe cytokenisis
The division of the cytoplasm, to make two new genetically identical cells
Describe how mitosis and cytokenisis is diffierent in plant cells and animal cells
Mitosis:
Centrioles are only present in Animal cells
Spindle degenerates at telophase in animals whereas it remains throughout new cell wall formation in plants
Cytokinesis:
Animals’ cytoplasm and membrane divide by cleavage and it develops from the outside inward
Plant cytoplasms, cell wall and membrane divide by the development of cell plate which develops from the centre outwards
What is the significance of mitosis as a process
It produces cells which are genetically identical to the parent cell, giving genetic stability. Cell division occurs for a number of reasons, including:
Growth
Repairing damaged cells
Replacement of old, worn-out cells
Asexual reproduction.
How is mitosis significant in damage and disease
The length of the cell cycle can be controlled by genes
this allows for the replacement and repair of tissues
but if these genes are damaged or faulty it can lead to unrestricted division leading to cancerous growth
Describe two genes involved in cancerous growth
Tumor suppressor gene - prevents the cell cycle from repeating continuously
Oncogenes - a gene with the potential to cause cancer
Define meiosis
A two-stage cell division in sexually reproducing organisms that produce four genetically identical haploid daughter cells ( With half the chromosomes of the parent cell)
Describe how Prophase I in meiosis differs from prophase in mitosis
Crossing over occurs when the arms of the chromatids cross over at the chiasmata. Here, genetic material can be exchanged between chromatids of homologous chromosomes, therefore increasing the variation in inherited genomes.
Define chiasmata
The site at which chromosomes exchange DNA in genetic crossing over.
Define Bivalent
The association of the two chromosomes of a homologous pair at prophase I of meiosis (pairs of homologous chromosomes).
Describe how Metaphase I in meiosis differs from metaphase in mitosis
Homologous chromosomes arrange themselves in pairs along the equator.
Independent assortment occurs here
Define independant assortment
Describes the random way round (toward different poles) maternal and paternal homologous chromosomes line up at the equator during metaphase in meiosis.
Describe how anaphase I in meiosis differs from anaphase in mitosis
The chromosome bivalents separate as each chromosome is pulled by its centromere towards the opposite pole.
Describe how telophase I in meiosis differs from telophase in mitosis
Nuclear envelopes reform around the chromosomes at the poles.
In meiosis, prophase II occurs after telophase I.
As the chromosome pairs have separated, chromosomes are no longer in pairs and the cells are haploid.
Describe meiosis II
It is essentially the same as the processes in mitosis
Describe where and how genetic variation takes place in meiosis and mitosis
Mitosis:
Does not occur
Meiosis:
Crossing over in Prophase I
Independent assortment in Metaphase I & II
Describe the differences between mitosis and meiosis
8 points
Number of nucleus divisions:
Mitosis - 1 , Meiosis - 2
Number of cells formed
Mitosis - 2 , Meiosis - 4
Ploidy level of parental cells/nuclei
Mitosis: 2(diploid) , Meiosis: 2(diploid)
Ploidy level of daughter cells/nuclei
Mitosis: 2(diploid) , Meiosis: 1(Haploid)
Genetic composition compared to parent cell and each other
Mitosis - Identical , Meiosis - different
Pairing of homologous chromosomes
Mitosis: No , Meiosis: yes to form bivalents
Crossing over
Mitosis: No , Meiosis: yes at chiasmata
Segregation of homologous chromosomes
Mitosis: No , Meiosis: Yes bivalents separate
