mitosis, meiosis cell cycle Flashcards
mitosis
what are the four stages in mitosis:
-prophase
-metaphsae
-anaphase
-telophase
what is interphase and when does it occur
interphase is the process in which the DNA is replicated and the cell increases its number of organelles. interphase occurs inbetween cell divisions.
before replication, each chromosome exists as a single chromatid however after replication, two sister chromatids are joined together at the centromere forming a chromosome.
definition of homologous pair of chromosomes
matching pair of chromosomes, one donated from each parent. there are two copies of every chromosome in every cell, one from our mother and one from our father.
the overall process of mitosis involves the separation of chromosomes to opposite parts of the cell so that the cells can….
divide,
the overall process of mitosis involves the separation of chromosomes to opposite parts of the cell so that the cells can divide.
what is the first stage of mitosis:
prophase
describe the main features of prophase:
-supercoiling of DNA into chromosomes
-the disintegration of the nuclear envelope
-centrioles forming spindle fibres from two opposite ends of the cell.
prophase each stage explained in detail
firstly in prophase, the DNA supercoils into chromosomes. before prophase the dna is long and tangled threads however during prophase, the dna supercoils into a shortened and more condensed structure.
-then, the nuclear envelope begins to break down and disintegerate allowing the genetic material of the cell to move more freely through the cell
-centrioles, cylindrical hollow protein bundles that divide moving to opposite ends of the cell from where they produce spindle fibres that run across the cell from one pole to the oppsite pole on the other end of the cell. spindle fibres form the centrioles and are long fibres of proteins.
plant cells do not have centrioles, there spindle fibres form from their cytoplasm.
metaphase:
second stage of mitsosis
chromosomes line up at equator of the cell
the chromosomes become attached to the spindle fibres at their centromere. the chromosomes are then pulled along the spindle fibres to the equator of the cell.
this prepares chromatids in each chromosome ready for separation in anaphase.
anaphase:
(centromeres split and chromatids move to separate poles of the cell)
the chromatids on each chromsome are separated and pulled to opposite poles of the cell. chromosomes split while still attached to the spindle fibres, they move to the poles with the help of motor proteins. the process requires ATP so mitochondria gather around the spindle fibres to provide it.
telophase:
(nucleus starts to re appear around each set of chromosomes)
-nucleus starts to reappear around each set of chromosomes.
and the chromosomes become invisible under the microscope because they disperse and become less condensed.
once the separated chromatids begin to reach the poles. the spinlde fibres begin to disintegrate.
the chromosomes lengthen and uncoil so cannot be seen under the microscope.
the nuclear envelope begins to reform around the lengthening chromosomes.
at the end of telophase, the cell ends up with 2 distinct nuclei.
the cell is now ready for the cytoplasm to split in cytokinesis to make two new cells
cytokinesis: after telophase cell is split to create two new daughter cells with identical nuclei
the cell is split to create two new daughter cells with identical nuclei.
in animal cells, the plasma membrane folds inwards until the two dents meet to separate the two daughter cells.
in plant cells, cellulose builds up at the equator this is called the end plate. plasma membrane forms in the middle of the end plate resulting in two fully separated plant cells.
cytokinesis in plants
in plants, cellulose builds up at the equator of the cell, this is known as the end plate. plasma membrane forms in the middle of the end plate resulting in two fully separated plant cells.
cytokinesis in animal cells
in animals, the plasma membrane folds inwards until the two dents meet to separate the two daughter cells.
explain why a cell’s DNA must replicate itself before mitotic cell division.
the DNA must be replicated before mitosis so that each of the 2 identical daughter cells has a complete copy of the genetic material from the parent cell.
diploid cells
2n
two sets of chromosomes
(both mitosis and meiosis start from a diploid cell)
halpoid cell
n
contains one set of chromosomes
one set of chromosomes as in 23 chromosomes
why do gametes need to have half of the number of chromosomes as the rest of the cells in the body
to maintain a constant number of of chromosomes in adults of a species
during fertilisation gametes (haploid) fuse together to form a zygote which is a diploid
where does meosis occur
reproductive organs
ovaries and testes
human cells have a diploid number of
46 chromosomes
human cells have a halpoid number of
23 chromosomes
in a diploid cell where does each of the two sets of chromsomes come from
one set of chromsomes come from the father (paternal chromsomes)
one set of chromosomes comes from the mother ( maternal chromosomes)
homologous pair
a pair of chromosomes ( one maternal and one paternal) that have their genes in the same locations athough they may have different alleles for the same genes.
meosis overview
meiosis is the process of creating halpoid cells ( gametes) from diploid cells through two divisions meiosis 1 and meiosis 2. however before meiosis occurs every chromosome is replicated during the s phase of interphase
what are the four stages of meiosis 1
prophase 1
metaphase 1
anaphsae 1
telophase 1
