nucleic acid hybridization construction of a probe
made of RNA or single-stranded DNA that is
possible when at least part of the nucleic acid
sequence of a gene is known. The probe consists
of a nucleic acid sequence complementary to the
known gene sequence, along with a radioactive
or fluorescent tag. (9.3)
nucleoid specific region in the nuclear zone of the
cell with an arrangement of DNA that prokaryotic
cells use to pack their genetic material tightly.
(7.2)
nucleosome the bead-like structural unit of
chromosomes, composed of a short segment of
DNA (about 200 base pairs) wrapped twice
around a cluster of eight histone molecules. (7.2)
nucleotides the monomers of nucleic acids. Each
nucleotide is composed of a five-carbon sugar, a
phosphate group, and one of four nitrogen-
containing bases. The bases found in DNA
nucleotides are adenine (A), guanine (G),
cytosine (C), and thymine (T). In RNA, uracil (U)
is found instead of thymine. (7.1)
nucleus the small, dense core composed of protons
and neutrons that is found at the centre of an
atom. (1.1)occipital lobe the part of the brain that receives
optical information. (5.1)
Okazaki fragments short nucleotide fragments used
during DNA replication of the lagging strand.
They are made by DNA polymerase working in
the direction opposite to the direction of
movement of the replication fork, after which
they are spliced together. (7.3)
open system system in which substances and/or
energy can be exchanged with the surroundings.
(2.1)
operator DNA sequence located between the
promoter sequences and gene sequences that
governs whether RNA polymerase can bind to the
promotor sequences to begin transcription of the
genes. (8.4)
operon stretch of DNA, common in prokaryotes,
that contains one or more genes involved in a
metabolic pathway along with a regulatory
sequence called an operator. (8.4)
opportunistic life history r-selected reproduction
in which individuals quickly produce many
offspring when environmental conditions are
favourable, but may quickly die off if
environmental conditions become unfavourable.
(14.4)
organic term generally used to describe substances
made up of carbon-based molecules, such as
carbohydrates and proteins. (1.2)organic acids carbon-based molecules that are
acidic, such as acetic acid and amino acids. (1.3)
organic bases carbon-based molecules that are
basic, such as purines and pyrimidines. (1.3)
ovaries two glands that are suspended in the
abdominal cavity and produce eggs (ova). (6.3)
overlapping generations populations in which
parents do not die when they reproduce, so that
two or more generations may be alive and
reproducing in a population at the same time.
(14.2)
ovulation the releasing of an egg from an ovary.
(6.3)
oxidation the loss of electrons in a reaction. (1.3)
oxidative decarboxylation the process of removing
a carbon dioxide from pyruvate to form an acetyl
group that then combines with coenzyme A. (3.1)
oxidative enzyme enzymes that catalyze redox
reactions. (2.2)
oxidative phosphorylation the formation of ATP
using energy obtained from redox reactions in the
electron transport chain. (3.2)
oxytocin hormone that triggers muscle contractions
during childbirth and the release of milk from the
breasts. (6.1)
ozone depletion reduction of the ozone layer. (15.3)paleontology the study of fossils. (10.2)
pancreas a small gland near the small intestine,
which is made of two types of tissues that
independently function as exocrine and
endocrine glands. As an exocrine organ, the
pancreas secretes digestive enzymes into the
duodenum. As an endocrine organ, the pancreas
produces insulin and glucagons. (6.1)
parasitism type of symbiotic relationship in which
a symbiont lives off and harms the host. (14.3)
parasympathetic nervous system counteracts the
sympathetic nervous system to slow heart and
breathing rates and relax muscles. (5.1)
parathyroid hormone (PTH) a hormone produced
in the parathyroid glands, which regulates the
calcium levels in the blood. Works in
conjunction with the hormone calcitonin. (6.1)
parietal lobe the part of the brain that receives
sensory information from the tastebuds, skin,
and skeletal muscles. (5.1)
pathogen disease-causing agent (e.g., a bacterium
or virus). (4.4)
pelvis (renal) part of the kidney where urine
accumulates before moving through the ureters.
(4.2)
PEP phosphenolpyruvate. (3.1)P
O
582 MHR • Glossary