cell division

• mitosis

  • produce two genetically identical daughter cells
  • same number of chromosomes
  • 1 division
  • “give me another just like the other”
• meiosis

  • produce 4 genetically different daughter cells
  • half number of chromosomes
  • 2 division
  • shuffle in the genes
• diploid - chromosomes in the cell are part of a pair

  haploid - chromosomes in the cell are not part of a pair
• uses of mitosis -

  • growth of tissue
  • repair of tissue
  • cloning (asexual reproduction)
  • development of body plans
  • proliferated white blood cells
  • produce gametes from haploid cells
  • make NEW stem cells
• mitotic cycle -

  interphase - G1,S,G2

  mitosis — P,M,A,T

  yeast cells - 4hrs

  prokaryotic cells - 30min

  interphase =longest phase
• interphase

  G1- growth of a cell, protein synthesis, organelle replication

  S- DNA replication

  G2- cell continue to grow, ATP produced
• G0- Resting State

  name of phase when cell leaves the cycle for any reason including;

  • differentiation - no longer able to divide
  • DNA damage
  • majority of cells only divide a limited amount of times and become senescent
  • cytoskeleton may not work affecting chromosome movement
• controls of cell cycle -

  checks for -

  • grown right to size
  • the replicated DNA is error free
  • chromosomes are in correct position

  checkpoints are used to monitor and verify whether the process of cell cycle has been accurately completed to allow it to progress
• checkpoints-

  G1 CHECKPOINT - checks for cell size, nutrients, growth factor or DNA damage

  if GOOD - dna replicates/ if BAD - G0

  S phase CHECKPOINT - checks for dan replication correctly or dna damage

  If GOOD - G2/if BAD - G0

  G2 CHECKPOINT- checks for cell size, dna replicated correctly or dna damage

  if GOOD - mitosis/if BAD - G0

  spindle fibre assembly CHECKPOINT

  checks for chromosome attachment to spindle fibres

  if GOOD - mitosis/ if BAD- no mitosis
• if genetic info wasn’t checked may lead to -

  • mutations - error in copying
  • daughter cells do not receive genetically identical info
  • protein/new cell isn’t made or doesn’t function correctly
• homologous chromosomes-

  • one paternal and one maternal
  • both carry same gene at same position
  • same length/shape
  • pair up in meiosis to form a bivalent
  • once interphase is done chromosomes consist of two chromatids held together by a centromere at same position
• observing mitosis -

  • must be in the growing part (MERISTEMATIC TISSUE)
  • shoot/root tip is where meristematic tissue is and where cell division occurs
  • no chloroplast
  • squash slide so it’s a very thin layer of cells
  • must be stained (methylene blue)
• prophase-

  • chromosomes supercool becoming visible and consists of two chromatids held together by centromere
  • centrioles divide and move to opposite poles
  • spindle fibres come out of the centrioles and attach to the centromere
  • nucleolus disappears and nuclear envelope disintegrates
• metaphase -

  • chromosomes allign at the equator helped by spindle fibres
  • chromosomes are still attached to centromere
• anaphase -

  • spindle fibres shorten pulling chromatids apart
  • centromere divides
  • chromosomes move to opposite poles
  • chromosome number doubles
• telophase -

  • nuclear envelope form around the groups of chromosomes
  • chromosome uncoils into chromatin
  • nucleolus is formed
• cytokenesis -

  • when cell cytoplasm divides
  • occurs between telophase and interphase
  • happens once nucleus has divuded but before DNA is replicated again
• cytokinesis in animals -

  1. two protein filaments - myosin and actin form a constricting belt
  2. as the filament slides past each other the belts diameter decreases
  3. this pinches the cell creating a cleavage furrow
  4. the cell surface membrane is pulled inwards
  5. the furrow deepens and eventually splits cell in two
• cytokinesis in plants -

  1. golgi body form vesicles that assemble at middle of cell (at metaphase place)
  2. vesicles fuse together to form a tubular structure which forms two plasma membranes
  3. cellulose is deposited between the plasma membrane forming new sections of cell wall along the cell membrane
• cell division in yeast cells (BUDDING)

  1. swelling/bulge is found on surface of cell
  2. DNA is replicated
  3. mitosis occurs (nucleus divides)
  4. nucleur division is complete
  5. nucleus, cytoplasm and organelles move into the bulge/swelling
  6. the swelling/bulge pinches off to form 2 genetically identical cells
• also reproduce asexually, using mitosis to divide their nucleus

  • strawberry plants use both sexual and asexual
  • special runners develop roots and shoots by mitosis (genetically identica)
  • potatoes are tuber that can sprout shoots and roots by mitosis to make a new clone plant
• bacteria - have no nucleus, chromosomes or centrioles so reproduce through binary fission
• stem cells - unspecialised/undifferentiated cells that are capable of dividing by mitosis. they can then differentiate into other cell types

  once specialised they lose the ability to divide, entering the G0 phase of cell cycle
• totipotent- capable of differentiating into any type of cell

  e.g embryonic stem cells
• pluripotent - can form all tissue types but not whole organisms

  • they are present after the 16 stell stages
  • origin of the different tissue within an organism
• multipotent - only form a range of cells within a certain type of tissue

  e.g umbilical cord
• umbilical cord stem cells - multipotent

  • inside the cord are blood stem cells which can help people with blood disease
  • high availability
  • easy to harvest
  • present at early stage of development
  • stored for future use
  • no donor pain
• adult stem cells -

  present throughout life from birth

  • found in specific areas such as bone marrow (neutrophil and erythrocyte)
  • they’re multipotent
  • but can be triggered to become pluripotent
  • found in brain, gut, liver, ovarian epithelium, testes, fat , skin and teeth
• embryonic stem cells - totipotent

  present at a very early stage of development

  • totipotent until a mass of cells form called a blastocyst and it becomes pluripotent until birth
• usea of stem cells -

  • type 1 diabetes
  • alzheimers
  • parkinsons
  • macular degeneration
  • heart disease

  spinal cord - scientists restored movement to hind limbs in rats with damaged spinal cord

  treat burns - stem cells grown on biodegradable meshes produce skin quicker then a graft

  drug trials - test drugs on stem cells before animals and humans

  development of biology - study changes that occur to multicellular organisms as they grow and develop from a single cell
• stem cell ethics -

  • embryos can’t give consent
  • lack of consensus on who has rights/owns the genetic material
  • moral obligation- many people believe life starts at conception
  • religious objections
  • removal of stem cells cause destruction of embryo
  • improved quality of life for patients
  • find treatments for incurable diseases
  • techniques developed allowing stem cells to be removed without harming the embryo
  • embryos left over from fertility treatments are normally discarded away
• plant stem cells

  • meristematic tissue found in growing parts of plants like the apex of shoots and roots
  • cambium is meristematic tissue that can differentiate into xylem and phloem
  • cambium is found in vascular bundles between the xylem and the phloem
• differentiation-when a stem cell becomes specialised to perform a particular function
• erythrocyte - (red blood cell)

  • flat biconcave disc shape
  • large SA:V ratio for rapid oxygen exchange
  • small (7.5um) and flexible so can squeeze through capillaries
  • no nucleus so more room for haemoglobin
  • haemoglobin binds to oxygen
• neutrophil - (white blood cell)

  • defend body against pathogens
  • large multilobed nucleus
  • flexible shape due to well developed cytoskeleton
  • ribosomes that make enzymes
  • golgi body produce lysosomes
  • lysosomes contain lytic enzyme that hydrolyses pathogens
  • mitochondria produces ATP for protein synthesis and cytoskeleton
• sperm cell-

  • acrosome enzyme that breaks down protective layer off egg
  • flagellum allows sperm to swim to the egg
  • mitochondria provide ATP for flagellum
• epithelium cells -

  • cells linked with a basement membrane made of collagen
  • cilliated - (columnar) contain goblet cells that produce mucus to trap pathogens and bacteria and then cillia waft this mucus down the throat to be digested
  • microvilli - provide large SA:V ratio found in small intestine
  • squamous - flat, one cell thick, short diffusion pathway and act as a surface found on walls of blood vessels and alveoli
• palisade mesophyll-

  specialised to its function of maximising photosynthesis

  • long and thin forming a continuous layer on leaf surface
  • thin to provide short diffusion distance for CO2
  • moveable chloroplast to maximise light absorption
  • large permanent vacuole that moves the chloroplast to the edge of the cell
• root hair cells - specialised for its function of taking in water and minerals

  • cells have an extension called root hair cells
  • increased SA to absorb water by osmosis and minerals by active transport
  • mitochondria provides ATP for active transport of minerals
  • thin walls so short diffusion pathway
• guard cells -

  photosynthesis produces ATP (has a lot of mitochondria for ATP) which allows active transport of K+ ions into guard cell from epithelium cell.

  this produces a water potential so water moves down concentration gradient into the guard cell by osmosis. this causes the thicker inner wall and thinner outer wall to bend causing stomata to open.

  this is why it is open during the day and closed at night as ATP is required and that is from photosynthesis which requires sunlight. K+ ions