Cell division Flashcards
What is the cell cycle?
Results in division of cell and formation of two genetically identical daughter cell.
What occurs during interphase?
DNA replicated
Protein synthesis occurs in cytoplasm
mitochondria/chloroplast grow and divide
Normal metabolic processes of cells occur
Describe G0
When cell leave cycle either temporarily or permanently
Differentiation: cell becomes specialised to carry out specific function.
DNA may be damaged so cell enters permanent cell arrest.
Cell can become senescent —>. reached maximum number of divisions
Describe G1
Transcription/translation/protein synthesis occur
Organelles duplicate
Cell grows in size.
Describe synthesis
DNA replicated
During DNA replication, DNA polymerase makes many random and spontaneous errors resulting in mutations to DNA.
—-> Can be harmful, beneficial or neutral
Describe G2
Second growth phase
Cell continues to increase in size
ATP increases
Duplicated DNA checked for errors
What are the roles of the checkpoints?
Control mechanism of cell cycle.
Monitor and verify whether stages of cell cycle have been accurately completed.
G1 ——> if checked, triggers to begin DNA replication. If not —> enters G0.
G2 ——> Determines if DNA has been replicated without error. If checked then cell initiates mitosis.
Metaphase checkpoint —-> spindle assembly checkpoint where all chromosomes should be attached to spindles.
What is mitosis?
Nuclear division.
Both daughter cells genetically identical.
Each new cell has exact copy of DNA present in parent cell and same number of chromosomes.
Necessary for asexual reproduction.
What is a chromosome?
DNA molecule.
Two identical DNA molecules after synthesis is called a chromatid.
Two chromatids joined together at the region called the centromere.
Why is it necessary to keep the chromatids together during mitosis?
So they can be precisely manoeuvred and segregated equally, one into each daughter cell.
What are the stages of mitosis?
Prophase
Metaphase
Anaphase
Telophase
Outline what happens in Prophase!
Chromatin fibres coil and condense to form chromosomes ——> visible with stain under light microscope.
Nucleolus disappears.
Nuclear membrane starts to break down.
Spindle shaped structures are formed from microtubules.
Two centrioles migrate to opposite poles of the cell.
Spindle fibres attach to specific areas on the centromere and move chromosomes to centre of cell.
Nuclear envelope = disappeared
Outline what happens in metaphase!
Chromosomes moved by spindle fibres to form a plane in centre of the cell ——-> metaphase plate.
Outline what happens in anaphase!!
Centromeres holding the chromatids in each chromosome divide.
Chromatids separated —> pulled to opposite poles of the cell by shortening of spindle fibres.
Outline what occurs in telophase!!!
Chromatids now reached the poles —> now called chromosomes.
Two new sets of chromosomes assemble at each pole
Nuclear envelope reforms around them.
Chromosomes start to uncoil and nucleolus is formed
Cytokinesis begins.
What is cytokinesis?
Actual division of the cell into two separate cells
Begins during telophase.
How is cytokinesis performed in animal cells?
Cleavage furrow formed in middle of cell.
Cell-surface membrane pulled inwards by cytoskeleton until its close enough to fuse around the middle —> formation of 2 cells.
How is cytokinesis performed in plant cells?
Vesicles from Golgi apparatus begin to assemble where the metaphase plate was formed.
Vesicles fuse with each other and cell surface membrane, diving the cell into 2.
New sections of cell wall form along the new sections of the membrane.
What does meiosis mean?
Cell division that halves the original genetic material in cells to make haploid cells/gametes for sexual reproduction.
Sexual reproduction
Nucleus divides twice to produce 4 daughter cells.
What are homologous chromosomes?
What happens in Prophase 1?
Same initial steps of mitosis prophase.
Homologous chromosomes pair up
Crossing over occurs.
~~ Swapping of alleles
Happens at the chiasmata (point of breakage)
What does bivalent mean?
Homologous chromosome pair.
What happens in metaphase 1?
Homologous pairs of chromosomes assemble on the metaphase plate.
Independent assortment occurs —-> orientation of each homologous pair is random and can face either pole.
~~~Leads to genetic variation.
What happens in anaphase 1?
Separates homologous chromosomes
No separation of the centromere.
What happens in telophase 1?
Diplod —> Haploid
same as mitosis
Chromosomes uncoils and nuclear envelope reforms.
What happens in meiosis II?
The second division is similar to mitosis, and the pairs of chromatids present in each daughter cell are separated, forming two more cells.
What happens in prophase II?
Chromosomes condense and become visible.
Nuclear envelope breaks down
Spindle fibres form
What happens in metaphase II?
Independent assortment occurs as due to crossing over the sister chromatids are no longer identical.
What happens in anaphase II?
Separation of sister chromatids
Splitting of the centromere.
What happens in telophase II?
Nuclear envelope reforms
Cytokinesis occurs
1 somatic diploid cell undergoing meiosis = 4 haploid cells in the end (gametes)
