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- Obestatin
- Oceanic zone
- Okazaki fragment
- OKT3
- [More]
- Olfaction, the sense of smell
- Oligonucleotide
- A short polymer of, for example, 20 or so deoxyribonucleotides or ribonucleotides; thus a fragment of DNA or RNA.
- Ommatidia
- Oncogenes
- Oncogenic
- Cancer causing.
- One Gene - One enzyme Theory
- Oogenesis
- Ooplasmic transfer
- Open Reading Frame (ORF)
- DNA sequence beginning with ATG and read in triplets until it ends with a STOP codon. An ORF is potentially able to encode a polypeptide.
- Operator
- The DNA sequence in prokaryotes to which a repressor or activator protein binds, turning on (or off) transcription of the associated structural genes of the operon.
- Operon
- A set of adjacent structural genes and the operator that controls them. [lac operon]
- Opiates
- [and pain relief]
- Opsin
- Opsonin
- Organ
- Group of tissues that performs a specific function for an animal or plant (e.g., stomach, leaf).
- Organelle
- Specialized part of a cell (e.g., mitochondrion) analogous to an organ.
- Organic
- Term describing all compounds whose molecules contain carbon, with a few exceptions such as carbon dioxide and carbonates. [types and functional groups]
- Organism
- Individual living being.
- Organizer (in frog embryology)
- Organ of Corti
- Organophosphates
- Origin of Life
- Origin Recognition Complex (ORC)
- Ornithine
- Orthologous genes
- Homologous genes in different species; thus genes that have descended from a gene in the common ancestor of those species. Compare paralogous genes.
- Osmosis
- Osmotic pressure
- [in guard cells of leaf]
- Ossicles
- Osteichthyes (bony fishes)
- Osteoclasts and osteoblasts
- Osteogenesis imperfecta
- Osteomalacia
- Osteoporosis and calcium
- Otoliths
- Ovary
- Ovulation
- [role of hormones in]
- Ovule
- Oxidation
- Process of removing electrons from a substance. [in mitochondria]
- Oxygen
- transport by blood
- Oxytocin
- Ozone
- Highly active form of oxygen (O3 instead of O2). [ozone hole] [and photochemical smog]