TOPIC 2 - CELLS

• Cell membrane structure

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• Cell membrane function

  • Selectively permeable barrier
  • controls passage of substances in and out the cell
  • barrier between internal and external cell environments
• Nucleus Structure


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• Nucleus Function

  • Site of transcription & pre- mRNA splicing - mRNA production
  • site of DNA replication 
  • nucleolus makes ribosomes 
  • nuclear pore allows movement of substances to/from cytoplasm
• Mitochondria Structure


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• Mitochondria Function

  • Site of aerobic respiration
  •  produces ATP
• Chloroplast structure


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• chloroplast function


  • Chlorophyll absorbs light for photosynthesis to produce organic molecules (glucose)
• Organisms containing chloroplasts

  • plants
  • algae
• Golgi apparatus stucture


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• Golgi apparatus function

  • Modifies proteins received from RER
  • packages them into vesicles to transport to cell membrane for exocytosis
  • makes lysosomes
• Lysosome structure


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• Lysosome function

  • Contains digestive enzymes 
  • e.g lysozymes to hydrolyse pathogens/cell waste products
• Rough endoplasmic reticulum function

  • Site of protein synthesis
  • folds polypeptides to secondary & tertiary structures
  • packaging into vesicles to transport to Golgi
• Smooth endoplasmic reticulum function

  • Synthesises and processes lipids
• Cell wall function

  • Provides structural strength, rigidity and support to cell
  • helps resist osmotic pressures
• Ribosome structure


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• Ribosome function

  • Site of translation in protein synthesis
• Rough endoplasmic reticulum structure


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• Smooth endoplasmic reticulum structure


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• Cell wall structure


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• Cell vacuole structure


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• Contrast prokaryotic &eukaryotic cells

  • Prokaryotic cells are smaller 
  • prokaryotes have no membrane bound organelles
  • prokaryotes have smaller 70s ribosomes
  • prokaryotes have no nucleus
  • circular DNA not associated with histones
  • prokaryotic cell wall made of murrain instead of cellulose
• Occasional features of prokaryotes

  • Plasmids - loops of DNA
  • capsule surrounding cell wall - helps agglutination + adds protection
  • flagella for movement
• Cell vacuole function

  • Makes cells turgid - structural support
  • temporary store of sugars, amino acids
  • coloured pigments attract pollinators
• Protein carriers


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• Protein channels


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• Features of viruses

  • Non living and acellular
  • contain genetic material, capsid and attachment proteins
  • some (HIV) contain a lipid envelope + enzymes (reverse transcriptase)
• 3 types of microscopes

  • Optical (light) microscopes 
  • Scanning electron microscopes(SEM)
  • Transmission electron microscopes (TEM)
• Magnification


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• Resolution

  • The minimum distance between two objects in which they can still be viewed as separate 
  • determined by wavelength of light (for optical microscopes) or electrons (for electron microcopes)
• Optical microscopes

  • Beam of light used to create image
  • glass lens used for focusing 
  • 2D coloured image produced
• Evaluate optical microscopes

  • Poorer resolution as long wavelength of light - small organelles not visible 
  • lower magnification
  • can view living samples 
  • simple staining method vaccum not required
• Transmission electron microscopes

  • Beam of electrons passes through the sample used to create an imagefocused using electromagnets
  • 2D, black & white image produced
  • can see internal ultrastructure of cell
  • structures absorb electrons and appear dark
• Evaluation TEMs

  • Highest resolving power
  • high magnification 
  • extremely thin specimens required
  • complex staining method
  • specimen must be dead
  • vaccum required
• Scanning electron microscopes

  • Beam of electrons pass across sample used to create image
  • focused using electromagnets
  • 3D, black and white image produced
  • electrons scattered across specimen producing image
• Evaluation SEMs

  • High resolving power
  • high magnification
  • thick specimens usable 
  • complex staining method
  • specimen must be dead
  • vaccum required
• Why calibrate eyepiece graticule?

  • Calibration of the eyepiece is required each time the objective lens is changed
  • calibrate to work out the distance between each division at that magnification
• Purpose of cell fractionation

  • Break open cells & remove cell debris
  • so organelles can be studied
• Homogenisation

  • Process by which cells are broken open so organelles are free to be separated
  • done using homogeniser (blender)