2.1 Eukaryotes and prokaryotes

• Cells are fundamental structural units in all living organisms and determine the function and organisation of biological systems.
• Specialised cells perform specific functions, tissues are made of several cell types, organs are made of several tissue types, and organ systems are composed of several organs.
• The nucleoid is an irregularly-shaped region of cytoplasm where the loop of bacterial DNA is located.
• A plasmid is a 1 or more rings of DNA found in some bacterial cells, containing non-essential genes and can be exchanged between bacterial cells via conjugation.
• Ribosomes in eukaryotic cells are larger than in prokaryotic cells, with the large subunit of eukaryotic ribosomes being 80S and the large subunit of prokaryotic ribosomes being 70S.
• A chloroplast is a vesicular plastid with a double membrane, containing thylakoids, which are flattened discs that stack to form grana and contain photosystems with chlorophyll.
• Intergranal lamellae are tubes that attach thylakoids in adjacent grana.
• A mitochondrion is surrounded by a double membrane and has a folded inner membrane that forms cristae, the site of the electron transport chain.
• The fluid matrix of a mitochondrion contains mitochondrial DNA, respiratory enzymes, lipids, proteins.
• The ER has two types: rough ER with many ribosomes attached for protein synthesis and transport, and smooth ER for lipid synthesis.
• The stroma is the fluid-filled matrix of a chloroplast.
• Ribosomes are formed of protein and rRNA, have a large subunit which joins amino acids and a small subunit with mRNA binding site.
• The endoplasmic reticulum (ER) consists of cisternae, a network of tubules and flattened sacs that extends from the cell membrane and connects to the nuclear envelope.
• The nucleus controls cellular processes such as gene expression, determines specialisation and site of mRNA transcription, mitosis, and semiconservative replication.
• The nucleus is surrounded by a nuclear envelope, a semi-permeable double membrane, and contains DNA coiled around chromatin into chromosomes.
• Stain binds to structures in samples to facilitate absorption of electrons/wavelengths of light to produce an image.
• Resolution is the smallest separation distance at which two separate structures can be distinguished from one another.
• Planar stack of membrane-bound, flattened sacs cis face aligns with rER: molecules are processed in cisternae vesicles bud off trans face via exocytosis.
• A cell vacuole in plants is surrounded by a single phospholipid membrane called the tonoplast, stores cell sap, which contains mineral ions, water, enzymes, and soluble pigments, and controls turgor pressure.
• The Golgi apparatus synthesises glycoproteins.
• A lysosome is a sac surrounded by a single membrane, containing digestive hydrolase enzymes, and protected by a glycoprotein coat.
• The Golgi apparatus modifies and packages proteins for export.
• A plant cell wall is made of cellulose microfibrils for mechanical support, and plasmodesmata form part of an apoplast pathway to allow molecules to pass between cells.
• The middle lamella separates adjacent cell walls.
• Vesicles bud off the trans face of a membrane-bound, flattened sac via exocytosis.
• The cis face of a membrane-bound, flattened sac aligns with the rER, where molecules are processed in cisternae.
• Animal vacuoles, also known as vesicles, are temporary membrane-bound sacs containing water and chemicals, are numerous and much smaller than in plants, and are more commonly referred to as vesicles.
• Magnification is the factor by which the image is larger than the actual specimen.
• Lysosomes digest the contents of a phagosome via exocytosis of digestive enzymes.
• Centrioles are spherical groups of 9 microtubules arranged in triples, located in centrosomes, migrate to opposite poles of a cell during prophase, and spindle fibres form between them.
• Gram positive cell walls have a thick peptidoglycan layer that is insoluble in alcohol and appears purple under a microscope when stained.
• Gram negative cell walls have a thin peptidoglycan layer with an outer lipopolysaccharide membrane that is alcohol-soluble and appears red under a microscope when stained.
• The peptidoglycan (murein) cell wall provides mechanical strength and may be coated by a slime layer to prevent dessication, adhere cells, and provide nutrients.
• Gram positive bacteria respond differently to certain antibiotics, such as penicillin, because these antibiotics inhibit peptidoglycan formation.
• Gram negative bacteria have an outer membrane and a much thinner peptidoglycan layer, so they are not affected by antibiotics that inhibit peptidoglycan formation.
• The process of Gram staining involves staining a culture with crystal violet, removing and rinsing with water, adding iodine solution and removing after 1 min, adding alcohol, counterstaining with red safranin for 1 min, and drying and examining the sample under a microscope.
• A TEM focuses an image onto a fluorescent screen or photographic plate using magnetic lenses.
• A transmission electron microscope (TEM) works by passing a high energy beam of electrons through a thin slice of specimen.
• Reflected electrons hit a collecting device and are amplified to produce an image on a photographic plate.
• Use calibrated values to calculate the actual length of structures.