topic 2 - cell division (mitosis) Flashcards
cgp (topic 2A) 34 - 35
what is mitosis
cell division that produces genetically identical cells
what are the two types of cell division in eukaryotes
mitosis and meiosis
what is mitosis needed for
the growth of multicellular organisms and for repairing damaged tissues
what does the cell cycle consist of
a period o called f cell growth and DNA replication called interphase - interphase is subdivided into three separate growth stages - G1, S, G2
what happens in gap phase 1 (G1)
the cell grows and new organelles and proteins are made
what happens in synthesis (S)
the cell replicates its DNA ready to divide by mitosis
what happens in gap phase 2 (G2)
the cell keeps growing and proteins needed for cell division are made
what are the four stages of mitosis
prophase, metaphase, anaphase, telophase
what happens in interphase
the cell carries out normal functions but also prepares to divide - the cell’s DNA is untravelled and replicated to double its genetic content - the organelles are also replicated so it has spare ones and its ATP content is increased
why is the organelles ATP content increased in interphase
because it provides the energy needed for cell division
what happens in prophase
the chromosomes condense, getting shorter and fatter - tiny bundles of protein called centrioles start moving to opposite ends of the cell, forming a network of protein fibres across it called the spindle - the nuclear envelope breaks down and chromosomes lie free in the cytoplasm
what happens in anaphase
the centromeres divide, separating each pair of sister chromatids - the spindle fibres contract putting chromatids to opposite poles of the spindle, centimetre first - this makes the chromatids appear v-shaped
what happens in metaphase
the chromosomes (each with two chromatids) line up along the middle of the cell and become attached to the spindle by their centromere
what happens in telophase
the chromatids reach the opposite poles on the spindle - they uncoil and become long and thin again - they’re now called chromosomes again - a nuclear envelope form around each group of chromosomes, so there are now two nuclei - the cytoplasm divides (cytokinesis) and there are now two daughter cells that are genetically identical to the original cell and to each other - mitosis is finished and each daughter cell starts the interphase part of the cell cycle to get ready for the next round of mitosis
how can you calculate how long each stage of mitosis lasts
what is cancer the result of
uncontrolled cell division
what are mitosis and the cell cycle controlled by
genes
what are mutations
changes in the base sequence of an organism’s DNA
how are tumours formed
normally when cells have divided enough times to make enough new cells they stop but if there’s a mutation in a gene that controls cell division the cells can grow out of control - the cells keep on dividing to make more and more cells which form a tumour
how do cancer treatments that target the cell cycle work
they are designed to control the rate of cell division in tumour cells by disrupting the cell cycle but doesn’t distinguish tumour cells from normal cells so also kill normal body cells that are dividing - however tumour cells divide more frequently than normal cells so the treatments are more likely to kill tumour cells
what are two types of cell cycle targets of cancer treatments
(1) G1 (cell growth and protein production) - chemotherapy
(2) S (DNA replication) - radiation
how does chemotherapy treatments work
it prevents the synthesis of enzymes needed for DNA replication - if these aren’t produced, the cell is unable to enter the synthesis phase, disrupting the cell cycle and forcing the cell to kill itself
how do radiation treatments work
at several points in the cell cycle DNA is checked for damage - if severe damage is detected the cell will kill itself - preventing further tumour growth
