2.1 cell structure

• eukaryotic cells = cells that contain a nucleus and other membrane - bound organelles
• nucleus structure

  • large organelle containing DNA
  • the outer of the 2 membranes is continuous with the endoplasmic reticulum
  • nuclear envelope controls entry + exist of materials
  • nuclear pores which allow larger molecules (mRNA) out of the nucleus
• nucleus function:

  • holds the genetic material in the form of DNA
  • the nucleolus manufactures rRNA and assembles ribosomes
• mitochondria structure

  • inner membrane is folded to form cristae
• mitochondria function

  • site of aerobic respiration, so responsible for production of ATP
• golgi apparatus structure:

  • a series of flattened sacs of plate-like membranes known as cisternae
  • proteins and lipids pass through cavities of cisternae
• golgi apparatus function

  • modifies proteins
  • produces secretary enzymes
  • transports, modifies, and stores lipids
  • forms lysosomes
• golgi vesicles structure

  • single membrane formed off the membranes of the golgi apparatus
• golgi vesicles function

  • transports protein / glycoproteins from golgi apparatus to the cell surface membrane to be released from the cell
• lysosomes structure

  • a vesicle produced by the golgi apparatus that contains digestive enzymes
• lysosome function

  • transport + release enzymes outside the cell by exocytosis
  • to hydrolyse material ingested by phagocytic cells
  • to break down old redundant organelles so that useful chemicals can be recyled
• ribosome structure:

  made of ribosomal RNA and protein, consists of two subunits (one large, one small)
• ribosome function:

  site of protein synthesis
• rough endoplasmic reticulum structure

  system of flattened cavities with ribosomes attached
• rough endoplasmic reticulum function

  protein synthesis
• smooth endoplasmic reticulum structure

  system of flattened cavities with no ribosomes attached
• smooth endoplasmic reticulum function

  where lipids and steroids are made
• chloroplast structure

  an envelope consisting of two plasma membranes. a series of grana (stacks of thylakoids)
• chloroplast function

  absorbs light for photosynthesis, produces carbohydrates in photosynthesis
• cell wall structure

  made of a matrix of microfibrils composed of cellulose
• cell wall function

  provides mechanical strength to prevent cell bursting

  provides mechanical strength for the whole plant

  assists with the movement of water throughout a plant by allowing water to pass along it
• vacuole structure

  a fluid-filled space surrounded by a single membrane,

  contains a solution of sugars, salts, amino acids, and waste products
• vacuole function

  helps make the cell turgid

  sugars + amino acids may act as a temporary food supply

  pigments may colour the petals to attract pollinating insects
• prokaryote (differences to eukaryotes)

  • always unicellular organisms
  • cytoplasm lacks membrane-bound organelles
  • no nucleus
  • cell wall contains murein
  • smaller in size
  • DNA not associated with any proteins
• features of a prokaryotic cell

  • plasmids (loops of DNA)
  • capsule surrounding the cell
  • flagella
• features of viruses

  • acellular and non-living
  • smaller than bacteria
  • have no plasma membrane, cytoplasm, or ribosomes
  • have attachment proteins on surface
  • capsid, containing genetic material (either RNA or DNA)
  • reverse transcriptase (enzyme) in the capsid
• largest cell organelle

  • nucleus
  • mitochondria
  • lysosomes
  • ribosomes

  smallest cell organelle
• cell fractionation basic process

  1. homogenise sample
  2. fractionate homogenate with a centrifuge
  3. repeat fractionation with supernatant until all required organelle pellets are formed
• homogenisation process

  1. add buffer solution to sample of tissue
  2. place homgeniser on ice
  3. homogenise sample --> break up the tissue and break open the cells, using either a blender or a homogeniser (a plunger in a glass tube)
  4. this produces a cell homogenate
• importance of using a buffer solution in homogenisation

  • keeps pH constant --> if pH changes, enzymes in the cell's organelles could denature
  • water potential of the buffer is the same as the inside of the cell to prevent water moving into cells via osmosis and causing them to burst
• importance of placing homogeniser on ice

  • cools the sample, meaning that destructive enzymes work more slowly
• process of fractionating a homogenate with a centrifuge

  1. place tubes containing homogenate into the sample holder
  2. centrifuge spins at a low speed
  3. large organelle (nucleus) experience a greater centrifugal force ad move to the bottom of the tube faster than smaller organelle, so will form a pellet at the bottom fo the tube, leaving a supernatant
  4. transfer supernatant into a new tube and respin at a higher speed
  5. repeat until all required cell organelle have formed pellets
• magnification: how many times bigger an image is than the actual object
• magnification = size of image / size of object
• resolution: the minimum distance apart two objects can be and still be distinguishable as separate
• unit conversions

  cm -- x 10 --> mm

  mm -- x 1000 --> micrometers

  micrometers -- x 1000 --> nm
• transmission electron microscope principles

  electron beam passes through specimen
• transmission electron microscope pros

  high resolution power
• transmission electron microscope cons

  • can't observe living specimens
  • image not in colour
  • image is 2D
  • specimen must be extremely thin
• scanning electron microscope principle

  beam of electrons pass over surface of speciment