Cell division, Cell diversity and cellular organisation

• The cell cycle

  G1, S, G2, mitosis, cytokinesis
• G0

  A nondividing state occupied by cells that have left the cell cycle, sometimes reversibly.
• G1 phase


  The first growth phase of the cell cycle, consisting of the portion of interphase before DNA synthesis begins.New organelles and proteins are made.
• S phase


  DNA replicates which doubles the amount of chromatin in the cell
• G2 phase

  Second growth phase.

  Prepares for divsion, relevant enzymes are made and organelles are doubled
• mitotic phase


  The phase of the cell cycle that includes mitosis and cytokinesis.
• G1 checkpoint

  checks for cell size, enough energy or nutrients, growth factors and DNA damage. If DNA is damged beyond repair apoptosis occurs (kills itself)
• G2 checkpoint

  Checks that DNA has been completely replicated and checked for error

  Mitosis cant take place until DNa replicates
• M checkpoint

  Checks all proteins are attached to spindle fibres.

  Stops until hromosomes allign
• Chromosomes

  Found in nucleus

  Made of DNA and histone proteins
• Chromatid


  A replicate stand of DNA.

  Each one will end up in a different daughter cell
• Interphase


  Longest stage in cell cycle.During this phase chromosomes are in nucleus but not visible.Production of organelles and proteins, growth of cell.In animals centricles divide In plants and fungi spindle fibres form
• Prophase (Mitosis)


  Chromosomes shorten and thicken

  Can be seen as individual chromosomes

  The point of the process is so the chrooses can move round the cell The nucleous dissolves and nuclear envelope distegrates (this releases the chromosomes).

  In animals the spindals is controlled by centrioles,fibres become attached to centromeres.
• Metaphase (mitosis)

  Spindle fibres drag the chromosomes through the cytoplasm until they line up against section of chromosomes.
• Anaphase (mitosis)


  Centromeres divivde so sister chromatids can separate

  Spindle fibres contract pulling 2 sister chromatids to opposite poles

  once sister chromatids are seperate they can be called

  chromosomes
• Teleophase (mitosis)

  2 identical groups of chromosomes group at opposite poles

  Nuclear envelope form around each group to form 2 identical nuclei

  Each nuclei contains sets of chromosomes identical to parent nuclus

  Chromosomes uncoil
• Cytokenis

  Cytoplasm division ensures cell cytoplasm is divides equally between 2 daughter cells.In animals microfilaments cause constriction along the outside of the cell.This pulls the plasma mebrane splitting it into 2 cells (cleavage furrow)
• What's mitosis used for?

  Increase cell numbers for growth,repair of tissue.

  Significant for prokaroytic reproduction occurs in plants,animals and fungi
• Mitosis in yeast cells

  Produces bud

  Nuclear migration to the bud

  Nuclear divison

  Asemetrical division of cytoplasm and bud pinches off
• How do animal and plant daughter cells differ

  Animals produce cleavage furrow

  Plants produces cell plate
• mitotic index equation

  number of cells in mitosis/ total number of cells x100
• Prohase I (Meiosis)

  Chromosomes condense and appear as double stranded (containing 2 identical sister chromatids)

  Centrioles replicate and move to opposite poles.

  Homologous chromosomes pair up (called bivant)
• Metaphase I (Meiosis)

  Chromosomes line up along the spindle equator.Orientation of biavant is independant to each other - this leads to independant assortment,which is a source of a genetic variation.
• Anaphase I (Meiosis)


  Pairs are pulled apart by shortening microtubles fibres of the spindle attached to centromere(one of each pair is pulled to each pole)
• Telophase I (Meiosis)


  Chromosomes reach opposite poles

  Nuclei form around them

  New nuclei have 1/2 number of chromosomes than parent cells (haploid)
• Cytokenisis


  cytoplasm divides as the cell surface membrane pinches in
• prophase II (meosis)

  Chromosomes condense

  Centrioles replicate and spindle fibres form a right angle at there orginal spindle

  Nuclear envelope disintegrates
• Metaphase II (Meiosis)


  individual chromosomes line along sipindle equator
• Anaphase II (meiosis)


  Centromeres divides.

  Chromatids pulled to the opposite poles by spindle fibres

  Each chromatid is now a chromatid chromosome
• Telophase II (meiosis)

  Chromosomes gather at poles

  Nuclear envelope forms

  Each nucleus contains orginal pair of chromosomes

  Final result = 4 haploid cells - gentically different to each other and parent cell
• Definition of cells

  Basic unit of life
• Definition of tissue

  a group of similar cells that working together to perform a function
• Definition of an organ

  A group of different tissues that work together to perform a certain function.
• Definition of organ system

  group of organs that work together to perform a specific function
• What are the 4 main animal tissues?

  Muscle

  Connective

  Epelial tissue

  Cartilage
• Muscle tissue

  3 types:skeletal muscle,cardiac muscle,smooth muscle

  Skeletal = attached to bones and is required for movement of bones

  Smooth = involuntary muscle,found in places like blood plasma where it helps with blood flow

  Cardiac muscle = found in the heart required to pump blood around the body Muscles are made from proteins actin and myosin
• epithelial tissue

  Lines the interior and exterior body surfaces

  2 types = cilliated tissue and squameuous epitheilial

  Squamous epitheilial :made from squaemouse epitheilial cells, found in aveoli and cappileries.Thin so short diffusion parthway.Sits on basement membrane ,a layer of protein fibres and a polysacchride

  Cilliated tissue :made from cell thst have cillia, found in place tthat need to move something (e.g mucus) they beat in sycronized manner
• Cartilage

  Made from cells called chondroyctes - produces an extracellular maxtrix of collagen (a type of firous protein) and elastin (a fiberous protein)

  Acts to prevent and stengthen,found i places like the ears,nose and joints

  Rings of cartilage found in trachea

  Connective tissue
• What are stem cells?

  unspecialized cells from which can differentiate and become specilised and repliacte themself
• Where are stem cells found in plants?

  Meristems in roots and stems