Cell Structure 2.1

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Microscopes

Magnification - The ratio between the size of the image and the size of the object.

Resolution - The ability of a lens to distinguish between two objects next to eachother 

Magnification of a light microscope - 1500 x

Resolution of a light microscope - 200nm 

Magnification of a TEM - 100,000x

Magnification of a SEM- 500,000 X

Resolution of a EM - 0.2 nm

Transmission electron microscopes create a 2D image, scanning electron microscope create a 3D image. Both in black and white. Dead, dehydrated specimen.

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Slides

Dry mount - Specimens whole or cut thinly. Cover slip.

Wet mount - Specimens suspended in liquid. 

Squash slides - Wet mount, then press down with lens tissue

Smear slides - Edge of slide used to smear to give thin even coating.

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Staining

Cell components are transparent. 

Low contrast so it is difficult to distinguish between them. 

Positively charged dyes (methelyne blue and crystal violet) are attracted to negatively charged components in the cytoplasm. 

Negatively charged dyes (congo red and nigrosin) are repelled and cell stands out against stain.

Differential staining - Distinguishing between two organisms. 

Gram stain technique - Bacteria seperated into gram positive and gram negative.

Acid fast technique - Differentiate species of bacteria. Mycobacterium are not affected by alcohol and retain their stain. 

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Eukaryotic Cells Organelles

Nucleus

Double membrane bound, outer membrane attaches to RER with nuclear pores. Contains RNA. Controls all cellular functions and divides before the cell divides. 

Smooth ER

Squashed sacs of membrane with fluid filled cavities called cisternae. Contains enzymes to catalyse reactions and synthesise lipids.

Rough ER

Squashed sacs of membrane with fluid filled cavities called cisternae. Contains ribosomes to assemble amino acids into proteins. 

Golgi apparatus 

Membrane bound squashed sacs of cells. Recieves proteins from RER and modifies, packages into vesicles for transport. 

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Eukaryotic Cells Organelles (pt2)

Mitochondria

Produce ATP through aerobic respiration. Self replicating. Spherical or sausage shaped; with a double membrane that is seperated by liquid. Inner membrane is highly folded into cristae. Fluid filled matrix.

Ribosomes 

Small spherical, two subunits. Involved in protein synthesis using mRNA to assemble amino acids. 

Chloroplasts (plant only) 

Double membrane, inner membrane is continuous with thylakoids containing chlorophyll. Stack of thylakoids is a granum. Fluid filled membrane is called the stroma. Also contain loops of DNA and starch grains. Photosynthesis occurs in the grana. 

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Eukaryotic Cells Organelles (pt3)

Lysosomes 

Small sacs containing digestive enzymes to digest old organelles and foreign material. 

Centrioles

Pair of microtubules found next to the cell to aid with cell division.

Cillia and flagellum

Protrusions from the cell. 9+2 structure, cillia sweep mucus and flagellum aid movement. 

Cytoskeleton 

Microfilaments give mechanical structure, Microtubules move substances around the cell on a track. Form a spindle before cell division. Intermediate filaments anchor the nucleus within the cytoplasm. Extend between cells in some tissues.

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Protein synthesis

1)mRNA passes out through the pores in the nuclear envelope to the ribosomes

2) Protein molecules are assembled which are passed into the cisternae of RER

3) Transported via microtubules to the golgi where they are modified for use. 

4) Packaged into a vesicle and transported to the plasma membrane

5) Fuse to the plasma membrane, release to outside of cell (exocytosis) 

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Prokaryotic Cells

Similarities to eukaryotic cells

  • Plasma membrane
  • Cytoplasm 
  • Ribosomes
  • DNA & RNA

Differences from eukaryotic cells

  • Much smaller
  • More basic cytoskeleton 
  • No nucleus
  • No membrane bound organelles
  • Peptidoglycan wall not cellulose. 
  • Smaller ribosomes
  • Naked DNA that is a loop 
  • Flagella
  • Pili ( small hair like projections that allow the bacteria to cling to cells) 
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