cell cycle Flashcards
the interphase
-it is the stage between cell division
-it occupies 90% of the cell
the chromosomes are not visible since they are long and thin
the G1 phase
-it is the stage in which tRNA and mRNA are formed,
-translation
-transcription
-protein synthesis
-transportation take place
the S phase
it is the stage of semi-conservative replication
the G 2 phase
-organelles divide
-centrioles replicate
-DNA is checked for errors
explain why describing the interphase as a resting phase is wrong ???
during this phase protein synthesis, mRNA formation semi-conservative replication take place
prophase
-the centrosomes replicate before prophase
-during prophase centrosome move to opposite poles of the cell forming poles of spindle
-chromosomes coil up to become thick and condensed
-becomes 2 sister chromatids held by centromere
-nuclear envelope breaks down into vesicles then disappear
-nucleolus disappear
-centrioles start organizing the production of spindle fibers
metaphase
-centrioles acts as MTOC organizing microtubules to form spindle fibers
-the spindle fibers extend themselves and attach centromeres of chromosomes arranging chromosomes at the equator
anaphase
-centromeres divide
-spindle fiber shorten pulling the centromere followed by chromatid to the opposite poles
telophase
-nuclear envelope and nucleolus reforms
-chromosomes uncoil and become chromatin
cytokinesis
-cytoplasm constricts and divide
-cell surface membrane forms cleavage furrow & fuses as it fluid in nature giving 2 genetically identical daughter cell each with the same no of chromosomes
in plant
-there are no centrioles seen in plant cells
-a cell plate is formed between the two daughter cells, as longitudinal microtubules in cytoskeleton direct vesicles containing cell wall material to equator to form a cell plate with plasmodesmata
biological importance of mitosis and its role
-growth= inc no of genetically identical daughter cells
-asexual reproduction= mitosis is the basis of asexual reproduction
-tissue repair
-cell replacement of dead cells
-immune response
explain why cells seen in the figure are smaller than the other cell?
as they are newly formed cells at the end of mitosis that had not enter G1
explain the importance of semi-conservative replication before mitosis
-in semi-conservative replication DNA unwinds due to breakage of H bonds giving 2 strands
-each strand act as template
-during mitosis each DNA forms a chromatid
cancer
-due to random spontaneous genetic mutation, tumor suppressor gene becomes switched off, so uncontrolled cell division by mitosis, forming an irregular mass of undifferentiated cells, known as a tumor with no contact inhibition
metastasis cancer spreads to other parts by blood
