2.1 - Cell Structure - P&M tutor

• To prepare a temporary mount of tissue for a light microscope, obtain a thin section of tissue using an ultratome or by maceration, place the tissue in a drop of water, stain the tissue on a slide to make structures visible, add a coverslip using a mounted needle at 45° to avoid trapping air bubbles, and focus rays of light and magnify the view of a thin slice of specimen.
• Light microscopes work by focusing rays of light and magnifying the view of a thin slice of specimen.
• Different structures absorb different amounts and wavelengths of light, and reflected light is transmitted to the observer via the objective lens and eyepiece.
• A transmission electron microscope (TEM) works by passing a high energy beam of electrons through a thin slice of specimen, with more dense structures appearing darker since they absorb more electrons, and focusing the image onto a fluorescent screen or photographic plate using magnetic lenses.
• Prokaryotic cells have small ribosomes (70S), while Eukaryotic cells have larger ribosomes (80S).
• Prokaryotic cells have circular DNA that is not associated with proteins, while Eukaryotic cells have linear chromosomes associated with histones.
• Prokaryotic cells reproduce through binary fission, which is always asexual, while Eukaryotic cells undergo mitosis and meiosis, which can be sexual or asexual.
• The cell wall of Prokaryotic cells is made of murein, also known as peptidoglycan, which is absent in animal cells, while the cell wall of Eukaryotic cells is made of cellulose, which is also absent in animal cells.
• Prokaryotic cells are always unicellular and smaller in size compared to Eukaryotic cells, which are often multicellular and have organelles and a nucleus.
• Prokaryotic cells have a capsule, sometimes plasmids and a cytoskeleton, while Eukaryotic cells have no capsule, no plasmids, and always have a cytoskeleton.
• A scanning electron microscope (SEM) works by focusing a beam of electrons onto a specimen’s surface using electromagnetic lenses, and reflecting electrons hit a collecting device and are amplified to produce an image on a photographic plate.
• Cholesterol is a steroid molecule that connects phospholipids and reduces fluidity.
• Centrioles are spherical groups of 9 microtubules arranged in triples and are located in centrosomes.
• Eukaryotic and prokaryotic cells both have a cell membrane, cytoplasm and ribosomes.
• Bacterial and fungal cell walls are made of peptidoglycan (murein) for bacteria and chitin for fungi.
• Flagella are hollow helical tubes made of the protein flagellin that rotate to propel a usually unicellular organism.
• Glycolipids are involved in cell signalling and cell recognition.
• Cilia are hairlike protrusions on eukaryotic cells that move back and forth rhythmically to sweep foreign substances such as dust or pathogens away or to enable the cell to move.
• The cell-surface plasma membrane is a 'Fluid mosaic' phospholipid bilayer with extrinsic and intrinsic proteins embedded.
• The cytoskeleton provides mechanical strength, aids transport within cells and enables cell movement.
• Glycoproteins are involved in cell signalling, cell recognition (antigens) and binding cells together.
• A laser scanning confocal microscope works by focusing a laser beam onto a small area on a sample’s surface using objective lenses, with fluorophores in the sample emitting photons, and a photomultiplier tube amplifying the signal onto a detector, producing an image pixel by pixel in the correct order.
• The field of view in microscopy should be recorded by drawing a diagram with a sharp pencil, including a scale bar, annotating visible structures, and stating an equation to calculate the actual size of a structure from microscopy.
• Magnification is the factor by which the image is larger than the actual specimen.
• Vesicles bud off trans face via exocytosis.
• Mitochondria are surrounded by a double membrane and have a folded inner membrane that forms cristae, the site of electron transport chain.
• Lysosomes are sacs surrounded by a single membrane and contain a H+ pump that maintains acidic conditions and digestive hydrolase enzymes.
• Intergranal lamellae are tubes that attach thylakoids in adjacent grana.
• The stroma of chloroplasts is a fluid-filled matrix.
• Chloroplasts are vesicular plastids with a double membrane.
• Thylakoids are flattened discs that stack to form grana and contain photosystems with chlorophyll.
• Synthesises glycoproteins.
• Planar stack of membrane-bound, flattened sacs, cis face aligns with rER.
• The Golgi apparatus, which modifies proteins for secretion, aligns with the rER.
• Ribosomes are formed of protein & rRNA.
• The glycoprotein coat of lysosomes protects the cell interior by digesting the contents of phagosomes and exocytosis of digestive enzymes.
• The structure of a plant cell wall is made of cellulose microfibrils for mechanical support, plasmodesmata form part of the apoplast pathway to allow molecules to pass between cells, and a middle lamella separates adjacent cell walls.
• The ribosomes that synthesise proteins are attached to the rER.
• The fluid matrix of mitochondria contains mitochondrial DNA, respiratory enzymes, lipids, proteins.
• The magnification and resolution of a compound light microscope are x 2000 and 200 nm respectively.