2.1.1 - cell ultrastructure and microscopes

• Magnification of a light microscope is x1500
• light microscopes produce a 2D coloured image
• Light microscopes are used to observe whole cells and tissues
• Resolution is the ability to distinguish between very small separate structures very close together in great detail
• TEMs have a resolution of 0.5nm
• TEMs are used to look at organelle detail
• TEMs produce a 2D black and white image
• Scanning electron microscopes have a magnification of x100000
• Scanning electron microscopes are used to see cell surface detail
• Scanning electron microscopes produce a 3D black and white image
• Laser scanning confocal microscopes produce a 3D coloured image
• To prepare a temporary mount of tissue for a light microscope you:

  obtain a thin section of tissue; place tissue in a drop of water; stain tissue on a slide to make structures visible; add coverslip using mounted needle at 45 degrees.
• TEMs work by passing a high energy beam of electrons through a thin slice of specimen; focus image onto a fluorescent screen; treat with heavy metal solution; more dense structures appear darker as they absorb more electrons.
• An SEM works by focussing a beam of electrons onto a specimens surface using electromagnetic lenses; reflected electrons bounce off at different rates and produce a 3D image.
• Laser scanning confocal microscopes work by focussing a laser beam onto a small area on the samples surface; specimen treated with fluorescent dye; sample emits protons and image is produced pixel by pixel in correct order.
• Microscopic drawings are done with a sharp pencil and solid lines
• Microscopic drawings include a scale bar and annotations of visible structures and how they appear on the microscope.
• Magnification = image size / actual size
• Differential staining is used to differenciate between cell types of different parts.
• To calibrate microscopes place micrometer on stage, line up with the graticule.

  count how many divisions are in 100 eyepiece graticules.
• If 100 eyepiece divisions = 60 micrometers

  Then 1 eyepiece division = 0.6 micrometers
• 1 mm = 1000 micrometers
• 1 micrometer = 1000nm
• Include a title in microscopic drawings and ensure the proportions are correct
• The nucleolus is dense and is made of RNA and proteins. It assembles ribosomes
• Nucleus contains DNA coiled around chromatin which makes chromosomes
• Nucleus controls cellular processes such as gene expression; specialisation; transcription and mitosis
• Nuclear envelope separates nucleus from cell
• Rough endoplasmic reticulum is a system of membranes containing fluid filled cavities - cisternae - that are continuous with the nuclear membrane
• Rough endoplasmic reticulum is studded with ribosomes
• Smooth endoplasmic reticulum is a system of membranes containing fluid filled cavities - cisternae
• Smooth endoplasmic reticulum contains enzymes that catalyse reactions with lipid metabolism
• Golgi apparatus is a stack of membrane bound flattened sacs. Cis face aligns with RER
• Proteins are modified in the Golgi apparatus. molecules are added or its folded into a 3d shape
• Ribosomes are small spherical organelles. There are 70s ribosomes in prokaryotic and 80s in eukaryotic cells.
• Ribosomes, RER and Golgi apparatus are involved production of proteins.
• For protein production:

  the ribosomes that synthesise proteins are attached to the RER.

  the Golgi apparatus aligns with RER
• Mitochondria are surrounded by a double membrane. The inner membrane folds to form cristae. They have a fluid filled space - matrix - that contains mitochondrial DNA, enzymes, lipids and proteins. They can be spherical or rod shaped
• Mitochondria are the site of aerobic respiration to produce ATP.
• Chloroplasts are the site of photosynthesis to convert solar energy to chemical energy