Cell Division, Cell Diversity and Cell Organisation Flashcards
What happens in the G1 phase of the cell cycle?
-Organelle replication
-Cell increases in volume
-Protein synthesis
What happens at the G1 checkpoint of the cell cycle?
-Checks for DNA damage
-Checks cell is large enough
-Checks cell has duplicated organelles
What happens in the S phase of the cell cycle?
-Ensures there is twice the original DNA content (each daughter cell will receive half)
What happens in the G2 phase of the cell cycle?
-Cell increases in volume
-Energy stores increase
-Key proteins synthesised for cell division
What happens at the G2/S checkpoint of the cell cycle?
-Checking for correct DNA replication
What happens at the M (metaphase) checkpoint of the cell cycle?
-Checks spindle fibres are correctly attached to chromosomes
What does it mean if a cell is in resting phase?
-Cells are not actively dividing
What is the order of stages in mitosis?
- Prophase
- Metaphase
(metaphase checkpoint) - Anaphase
- Telophase
What happens during prophase in mitosis?
-Chromatin condenses- chromosomes become visible (form X shape)
-Nuclear envelope breaks down
-Nucleolus disappears
-Centrioles migrate to opposite poles of the cell
-Spindle fibres start to form
What happens during metaphase in mitosis?
-Spindle fibres attach to centromeres of each pair of sister chromatids
-Chromosomes line up along the equator of the cell
What happens during anaphase in mitosis?
-Spindle fibres shorted and pull sister chromatids apart and separate them to opposite poles of the cell
-Centromere has divided
What happens during telophase in mitosis?
-There is now a full set of chromosomes at each pole of the cell
-Nuclear membrane forms around each set of chromosomes
-Nucleolus reappears
-Chromosomes uncoil and reforms chromatin
What are the stages of cytokinesis in animal cells
-Cleavage furrow forms down the centre of the cell
-Actin microfilaments contract (requires ATP)
-Cell separates by pinching the plasma membranes together
-Forms two genetically identical daughter cells
What are the stages of cytokinesis in plant cells?
-Vesicles containing cellulose are deposited at cell plate
-Cellulose molecules hydrogen bond together
-Forms two genetically identical daughter cells
(plants do not contain centrioles)
What is a stem cell?
An unspecialised, self renewing cell that has potential to turn into most cells, including another stem cell
What are the different types of stem cell?
-Totipotent stem cell (embryonic)
-Pluripotent stem cells (embryonic)
-Multipotent stem cells (somatic / adult)
-Induced pluripotent stem cells
What are totipotent stem cells?
-They are extracted from the first 1-32 cells of an embryo
-They can differentiate into ALL cell types
-This has the ability to form whole living organisms
What are pluripotent stem cells?
-Extracted from the first 64-256 cells of an embryo
-Can differentiate into all cell types, EXCEPT placenta and umbilical chord cells
What are multipotent stem cells?
-Found in bone marrow
-Can differentiate into many cell types, including lymphocytes, ect.
What are Pluripotent stem cells?
-They reprogram differentiated cells to become embryonic/ pluripotent stem cells
-These have potential in areas like regenerative medicine
What are the stages of Meiosis 1?
-Prophase 1
-Crossing over
-Metaphase 1
-Independent assortment
-Anaphase 1
-Telophase 1
What happens in prophase 1 in meiosis 1?
-Chromatin condenses and chromosomes become visible
-Nuclear envelope breaks down and nucleolus disappears
-Spindle fibres start to form
What happens in the crossing over stage 1 in meiosis 1?
-Non sister chromatids within the same homologous pair exchange short sections of DNA
-This forms a new collection of alleles
What happens in metaphase 1 in meiosis 1?
-Each homologous pair lines up along the equator
-Spindle fibres attach to centromeres
What is the independent assortment phase in meiosis 1?
-The orientation of each homologous pair along the equator is random (increases variation)
What happens in anaphase 1 in meiosis 1?
-Spindle fibres shorten and separate each member of a homologous pair to opposite poles
-The centromere remains intact
What happens in telophase 1 in meiosis 1?
-Nuclear envelope reforms and nucleolus reappears
What happens prior to meiosis 2?
There is a short cell cycle without DNA replication
What happens in Prophase 2 of meiosis 2?
-Chromatin condenses and chromosomes become visible
-Nuclear envelope breaks down
-Nucleolus disappears
-Spindle fibres start to form
What happens in metaphase 2 of meiosis 2?
-Chromosomes line up along the equator
-Spindle fibres attach to centromeres
What is independent assortment in meiosis 2?
-Variation in metaphase 2 - there is a random orientation of chromosomes along the equator which determines which daughter cell each sister chromatid is separated to
What happens in anaphase 2 of meiosis 2?
-Spindle fibres shorten
-Centromere divides
-Sister chromatids pulled to opposite poles
What happens in telophase 2 of meiosis 2?
-Nuclear membrane forms around each set of chromatids at each pole
-Nucleolus reappears
-Chromatids relax to reform chromatin
