The Size and Scale of Our World

Archaea are a major group of prokaryotes. Similar to bacteria in some ways and similar to eukaryotes in others.

Did you know mites are arachnids??? They're in the same family as scorpions and spiders. For that matter, I didn't even know scorpions are arachnids. Wah. I am submerged in ignorance. By the way, mites feed on dead skin cells.

Rhinoviruses are responsible for about 50% of cases of the common cold. Every time you catch a cold, you soon develop immunity to that virus. You keep getting colds, not because your immunity fails, but because there are so many species of rhinoviruses (well over 100 recognized types, differing in their surface proteins).

Most of the atom is empty space. If the hydrogen atom were magnified to the size of Yale Bowl (a stadium seating about 70,000 people), the nucleus could be represented by a basketball on the 50-yard line, and the electron could be represented by a pea whizzing around the outer rows of bleachers.

Lysozyme was discovered in 1922 by Alexander Fleming, the Scottish bacteriologist who also discovered penicillin. Fleming had a cold, and noticed that when a few drops of his nasal secretions fell on a culture plate containing bacteria, nearby bacteria were dissolved (lysed). Fleming isolated the enzyme responsible and called it lysozyme, from the roots lyso (lysis) and zyme (common name for enzymes in the 1920s). Lysozyme is present in all our secretions -- tears, saliva, mucus, etc. -- and is part of our innate defensive system against bacterial infections.

There is a crustacean called Cyclops, approximately 3mm long, whose name is attributed to its single median eye in the middle of its forehead.

Bacterial ribosomes are 70S while eukaryotic ribosomes are 80S (larger!). 'S' stands for Svedberg units - measure of how fast they are sedimented in a high speed centrifugal field.

Amoeba - the largest unicellular organism. 1 mm in diameter, and visible to the naked eye.

List of Antibiotics

- Penicillins: Ampicillin (interferes in the cross-linking transpeptidation stage of peptidoglycan synthesis. hence causing weak cell wall.)
- Chloramphenicol (produced by Streptomyces venezuelae; prevents peptide bond formation during translation)
- Nalidixic acid (blocks DNA synthesis)
- Rifampin (used to treat TB; Blocks bacteria mRNA polymerase)
- Sulfonamides: Sulfanilamide (blocks nucelotide synthesis)
- Tetracycline (prevents binding of tRNA amino acid complex to the acceptor site in the 70S ribosome)
- Bactrin (am allergic to this!)
- Polymyxin (disrupts cell membrane by interacting with phospholipids; bactericidal on Gram negative bacilli; neurotoxic and nephrotoxic)

Haemorrhoids

a mass of dilated veins in swollen tissue at the margin of the anus or nearby within the rectum —usually used in plural; called also piles

Gram negative and gram positive bacteria

The difference lies in the cell wall of the two types; in contrast to most Gram-positive bacteria, Gram-negative bacteria have only a few layers of peptidoglycan and a secondary cell membrane made primarily of lipopolysaccharide. The space between the layers of peptidoglican and the secondary cell membrane is called periplasmatic space.

The peptidoglycan layer is thicker in Gram-positive bacteria (20 to 80 nm) than in Gram-negative bacteria (7 to 8 nm). It forms around 90% of the dry weight of gram positive bacteria but only 10% of that of gram negative bacteria.

Gram-positive bacteria are those that are stained dark blue or violet by gram staining, in contrast to gram-negative bacteria, which are not affected by the stain. The stain is caused by a high amount of peptidoglycan in the cell wall, which typically, but not always lacks the secondary membrane and lipopolysaccharide layer found in Gram-negative bacteria.