0.5 Glossary  (Page 13/18)

O

• objective lenses on a light microscope, the lenses closest to the specimen, typically located at the ends of turrets
• obligate aerobe organism that requires oxygen for growth
• obligate anaerobe organism that dies in the presence of oxygen
• obligate intracellular pathogen microorganism that cannot synthesize its own ATP and, therefore, must rely on a host cell for energy; behaves like a parasite when inside a host cell, but is metabolically inactive outside of a host cell
• observational study a type of scientific study that involves measurement of study subjects on variables hypothesized to be associated with the outcome of interest, but without any manipulation of the subjects
• ocular lens on a microscope, the lens closest to the eye (also called an eyepiece)
• oil immersion lens a special objective lens on a microscope designed to be used with immersion oil to improve resolution
• Okazaki fragment short fragment of DNA made during lagging strand synthesis
• oligopeptide peptide having up to approximately 20 amino acids
• oligotroph organism capable of living in low-nutrient environments
• opacity the property of absorbing or blocking light
• operator DNA sequence located between the promoter region and the first coding gene to which a repressor protein can bind
• operon a group of genes with related functions often found clustered together within the prokaryotic chromosome and transcribed under the control of a single promoter and operator repression sequence
• ophthalmia neonatorum inflammation of the conjunctiva in newborns caused by Neisseria gonorrhoeae transmitted during childbirth
• opisthotonos characteristic symptom of tetanus that results in uncontrolled muscular spasms and backward arching of the neck and spine
• opportunistic pathogen microorganism that can cause disease in individuals with compromised host defenses
• opsonin any molecule that binds to and coats the outside of a pathogen, identifying it for destruction by phagocytes (examples include antibodies and the complement proteins C3b and C4b)
• opsonization process of coating a pathogen with a chemical substance (an opsonin) that allows phagocytic cells to recognize, engulf, and destroy the pathogen more easily
• optimum growth pH the pH at which an organism grows best
• optimum growth temperature the temperature at which a microorganism’s growth rate is highest
• optimum oxygen concentration the ideal concentration of oxygen for a particular microorganism
• oral herpes an infection caused by herpes simplex virus that results in cold sores, most commonly on and around the lips
• oral thrush Candida infection of the mouth
• orchitis inflammation of one or both of the testes
• organic molecule composed primarily of carbon; typically contains at least one carbon atom bound to one or more hydrogen atoms
• organotroph chemotroph that uses organic molecules as its electron source; also known as chemoheterotroph
• origin of replication specific nucleotide sequence where replication begins
• oropharynx area where air entering mouth enters the pharynx
• osmosis diffusion of water across a semipermeable membrane
• osmotic pressure the force or pressure generated by water diffusing across a semipermeable membrane, driven by differences in solute concentration across the membrane
• osteomyelitis inflammation of bone tissue
• otitis externa an infection of the external ear canal, most commonly caused by Pseudomonas aeruginosa ; often called swimmer’s ear
• otitis inflammation of the ear
• otitis media with effusion accumulation of fluid inside the middle ear with or without infection
• Ouchterlony assay test in which antigen and antisera are added to neighboring wells in an agar gel, allowing visualization of precipitin arcs
• outer membrane a phospholipid bilayer external to the peptidoglycan layer found in gram-negative cell walls
• oxazolidinones class of synthetic protein synthesis inhibitors that interfere with formation of the initiation complex for translation and prevent translocation of the growing protein from the ribosomal A site to the P site
• oxidation reaction chemical reaction that removes electrons (often as part of H atoms) from donor molecules, leaving them oxidized
• oxidative phosphorylation mechanism for making ATP that uses the potential energy stored within an electrochemical gradient to add P _i to ADP
• oxygenic photosynthesis type of photosynthesis found in plants, algae, and cyanobacteria, and in which H ₂ O is used as the electron donor to replace an electron lost by a reaction center pigment, resulting in oxygen as a byproduct