cell division

• autosomes - any chromosomes not sex chromosomes
• homologous pairs - one from each parent
• diploid - pairs of chromosomes
• haploid - half of the diploid chromosomes
• interphase mitosis

  • G1: protein synthesis, organelles replicate, cytoplasm increases
  • S: semi-conservative DNA replication, DNA is uncoiled and cannot be seen
  • G2: centrioles replicate, increase in ATP required, DNA checked
• prophase mitosis

  • chromosomes become visible as they shorten and thicken
  • centrioles move to poles of the cell
  • microtubules develop from pole to pole, spindle fibres formed
  • nucleolus disappears (forms part of chromosomes)
  • nuclear envelope breaks down
• metaphase mitosis

  • chromosomes line up at the equator
  • centrioles reach poles
  • spindle fibres attach to the centromere and pull the chromosomes to align them along the equator
• anaphase mitosis

  • chromatids pulled apart to opposite ends of the cell
  • centromeres divide
  • spindle fibres contract and shorten, pulling chromatids apart centromere leading, towards opposite ends of the cell
• telophase mitosis

  • a nuclear envelope reforms around chromosomes
  • the chromatids have now reached the poles and can be seen as chromosomes
  • nucleolus reappears
  • chromosomes uncoil to form chromatin
  • no cell plate in animal cells
• chromatid - one half of a chromosome
• cytokinesis - where the cytoplasm divides in two, each cell contains a full set of chromosomes identical to the parent
• cytokinesis in an animal cell

  • cell division involves furrowing and cleavage of the cytoplasm
  • starts at the edge of the cell
• cytokinesis in a plant cell

  • cell division involves formation of a cell plate
  • begins in the middle of the cell
  • areas where there is no cytoplasm = plasmodesmata
• importance of mitosis

  • asexual reproduction - in organisms which reproduce by cloning
  • growth in multicellular organisms
  • repair of tissues
  • replacement of ells
• checkpoints in the cell - monitor whether each stage of the cell cycle has been completed correctly before the cell can proceed

  • prevent uncontrolled division - tumours
  • detect and repair damage to DNA
  • ensure cycle is not reversed
  • DNA only copied once within cell cycle
• checkpoint examples

  • G1: cell size, enough nutrients, any DNA damage
  • G0 phase; cells leave the cell cycle e.g., lymphocytes begin dividing once needed. (resting phase)
  • G2: DNA replication
  • spindle assembly checkpoint: check for chromosome attachment to spindle fibres after metaphase
• mitosis takes place in many cells containing mitosis capability in animal cells
• in plant cells mitosis takes place in

  • meristem cells
  • meristems have thin cell wall
• yeast cells - fungi

  • reproduce by mitosis/budding
  • nucleus divides by mitosis
  • cell swells on one side and forms a bud
  • one nucleus moves into the bud swelling
  • cell wall forms
  • 2 new genetically identical cells
• prokaryote cells - not mitosis

  • reproduce by binary fission
  • cell grows to its limit
  • dna replicates
  • two loops of dna are split, one at each end of the cell
  • cell wall forms
• stem cells - undifferentiated cells that can undergo cell division and differentiation
• totipotent stem cells - can differentiate into any cell type e.g. zygotes
• pluripotent stem cells - can form all tissue types but not whole organisms e.g., embryo cells
• multipotent stem cells - can form a range of cells within a certain type of tissue eg bone marrow
• unipotent stem cells - can only differentiate into one type of cell
• sources of animal stem cells

  • bone marrow
  • embryos
  • umbilical cord
• sources of plant stem cells

  • meristem
• uses of stem cells in research

  • parkinsons disease - caused by death of dopamine producing cells in the brain.
  • azheimers disease - brain cells are destroyed as a result of build up of abnormal proteins
  • developmental biology - the study of changes of multicellular organism growth and development from a single cell
• differentiation - cells can become specialised to perform a particular function
• erythrocytes

  • produced in bone marrow
  • during differentiation cells lose nucleus, mitochondria
  • contain haemoglobin
  • small biconcave disc (large SA)
• neutrophils

  • type of phagocyte found in blood stream
  • produced in bone marrow
  • contain lysosomes
  • engulf microbes = function
• squamous epithelial cells

  • flat, thin cells
  • found within the linings of blood vessels and alveoli
  • provide a short diffusion distance
  • contain a basement membrane made of collagen and glycoproteins
• ciliated epithelial cells

  • column shaped cells which poses cilia which waft mucus/ovum
  • many mitochondria for aerobic respiration
  • found in trachea, bronchi, bronchioles, oviducts
• sperm cells

  • small long and thin
  • undulipodium - contains microtubules for movement
  • nucleus - haploid
  • mitochondria - aerobic respiration
  • acrosome - lysosomes specialised to digest ovum
• palisade cells

  • long thing cells with thin cellulose cell walls
  • light only passes through epidermis and one cell wall
  • contain chloroplasts for photosynthesis
  • chloroplasts can be move by cytoskeleton
• root hair cells

  • hair like projection with thin cells walls
  • found near tips of roots
  • increases surface area
  • aids absorption of water and mineral ions
  • lots of mitochondria
• guard cells

  • only epidermal cells with chloroplasts
  • hoops of cellulose, microfibrils prevent swelling
  • control opening and closing of stomata
• levels of organisation

  • cells - smallest structural unit of an organism
  • tissues - collection of specialised cells working together to perform a particular function
  • organs - collection of tissues working together to perform a particular function
  • organ systems - collection of organs working together to perform a life function
• squamous epithelia - tissue example

  • lining tissue
  • flattened and smooth
  • lining of blood vessels
  • alveoli
  • low friction
  • short diffusion pathway
• ciliated epithelia - example of tissues

  • column shaped cells
  • found in trachea, bronchi, bronchioles and oviduct
  • cilia waft mucus in synchronised movement