cells

• magnification

  = image / object
• resolution

  the minimum distance apart that two objects can be in order for them to appear as separate items.
• before cell fractionation what are the conditions of the solution that they are placed in?

  • cold - to stop enzyme activity
  • the same water potential as the tissue - to stop osmosis
  • buffered - so that the pH does not fluctuate
• process of ultracentrifugation

  • tube of filtrate is placed in a centrifuge and spun at low speed
  • heaviest organelles (nuclei) forced to the bottom, form a pellet
  • fluid at the top (supernatant) is removed
  • supernatant placed into another tube and spun in the centrifuge at a faster speed than before
  • next heaviest organelles (mitochondria) forced to the bottom
  • process is continued, increasing the speed each time, until all of the organelles have seperated
• properties of light microscopes

  low resolution + long wavelengths of light
• limitations of transmission electron microscopes


  must occur in a vacuum so living specimens can not be observed. image not in colour. specimen must be very thin. image may contain artefacts due to the way the specimen is prepared
• what type of image does a TEM produce 


  2D
• limitations of scanning electron microscope


  all the same limitations as a TEM except the specimen does not have to be extremely thin as electrons do not penetrate it.

  SEM has a lower resolution than TEM
• what parts make up the nucleus?

  nuclear envelope - double membrane, controls what enters and exits the nucleus

  nuclear pores - allows things such as RNA out of the nucleus

  nucleoplasm - jelly-like material which makes up the bulk of the nucleus

  chromosomes

  nucleolus - assembles ribosomes and ribosomal RNA
• mitochondria 


  has a double membrane, inner of the two membranes is folded to form cristae - these provide a large surface area. rest of it is made up of the matrix. SITE OF AEROBIC RESPIRATION
• chloroplasts


  carry out photosynthesis. contain grana which are stacks of thylakoids. thylakoids contain chlorophyll. the stroma is a fluid filled matrix - second stage of photosynthesis occurs here
• rough endoplasmic reticulum


  has ribosomes present on its outer surface.

  provides a large surface area for the synthesis of proteins and glycoproteins and provides a pathway for the transport of materials through the cell
• smooth endoplasmic reticulum 


  lacks ribosomes.

  synthesise, store and transport lipids

  synthesise, store and transport carbohydrates
• the golgi apparatus 


  a stack of membranes that make up flattened sacs with vesicles. proteins and lipids produced by the ER pass through. modifies, labels and transports the proteins and lipids. forms lysosomes.
• lysosomes


  contain lysozymes. they hydrolyse material ingested by phagocytic cells, release enzymes to the outside of the cell and completely break down cells once they have died (autolysis)
• ribosomes


  80S - found in eukaryotic cells

  70S - found in prokaryotic cells, mitochondria and chloroplasts and is slightly smaller

  made up of protein and ribosomal RNA

  site of protein synthesis
• cell wall


  cell walls of plants and algae are made up of cellulose - provides mechanical strength to plant

  fungi cell walls made up of chitin
• vacuole


  fluid filled sac

  single membrane is called a tonoplast
• tissue


  a collection of similar cells that perform a specific function
• organ


  combination of tissues that are coordinated to carry out a variety of functions but they usually have one major function
• structure of bacterial cell

  cell wall which is made up of murein

  capsule - secreted to help protect bacteria from other cells and help group bacteria together again for protection

  genetic material in the form of a circular strand of DNA

  70S ribosomes

  plasmids - small circular sections of DNA
• prokaryotic vs eukaryotic cells

  prokaryotic:

  • no nucleus
  • DNA not associated with histones
  • DNA in form of plasmids
  • no membrane-bound organelles
  • no chloroplasts
  • ribosomes smaller - 70S
  • cell wall made of murein
  • capsule

  eukaryotic:

  • nucleus
  • DNA associated with histones
  • DNA linear - no plasmids
  • membrane bound organelles
  • chloroplasts in plant and algae
  • ribosomes larger - 80S
  • cell wall made of cellulose - chitin in fungi
  • no capsule
• structure of virus 


  nucleic acids - such as DNA or RNA as genetic material

  the nucleic acid is contained within a protein coat - capsid

  some surrounded by a further lipid envelope

  attachment proteins

  HIV contains reverse transcriptase
• products of mitosis 


  two daughter cells that have the same number of chromosomes
• products of meiosis


  four daughter cells each with half the number of chromosomes as the parent cell
• structure of a chromosome


  two sister chromatids

  joined by the centromere
• prophase 


  chromosomes become visible

  nucleolus disappears and nuclear envelope breaks down

  chromosomes free in cytoplasm
• metaphase 


  spindle fibres are attached to centromere of chromosomes

  chromosomes are arranged along the equator of the cell
• anaphase 


  centromere divides

  spindle fibres pull individual chromatids to opposite poles

  energy for process provided by mitochondria
• telophase 


  chromosomes become longer and thinner, no longer visible

  nuclear envelope reforms and so does nucleolus
• cytokinesis 


  process of cytoplasm dividing into two
• binary fission 


  cell division of prokaryotic cells

  • circular DNA molecule replicates and both copies attach to the cell membrane
  • plasmids replicate
  • the cell membrane grows between the two DNA molecules and begins to pinch inwards, dividing the cytoplasm
  • a new cell wall also forms between the two DNA molecules.
  • this divides the cell into two daughter cells, each having one copy of the circular DNA and a variable number of plasmids.
• replication of viruses


  non-living so cannot undergo cell division

  they replicate by attaching to a host cell by their attachment proteins

  they inject their nucleic acid into the host cell

  viruses genetic information then provides host cell with instructions to make viral components, which assemble into a virus
• importance of mitosis 


  growth

  repair

  reproduction
• tumour 


  group of abnormal cells
• how do phospholipids arrange themselves in a bilayer 


  the hydrophillic heads point to the outside of the cell-surface membrane attracted by water

  the hydrophobic tails point into the centre of the cell membrane, repelled by water
• functions of phospholipids in the membrane

  allow lipid-soluble substances to enter and leave the cell

  prevent water-soluble substances entering and leaving the cell

  make the membrane flexible (fluid-mosaic model)
• protein channels 


  allow water-soluble ions to diffuse through the membrane
• carrier proteins 


  bind to ions or molecules ( such as glucose) then change to shape to move these molecules across the membrane
• cholesterol molecules are very hydrophobic so prevent the loss of water and dissolved ions from the cell