restriction fragment small segment of DNA cut from
the DNA molecule by a restriction endonuclease
enzyme. (9.2)
restriction site specific location on a strand of DNA
where a restriction endonuclease will cut the
strand of DNA. (9.2)
retina the innermost layer of the eye. (5.3)
reverse mutation change in a the genetic material of
a cell; the change restores the effect of a previous
change in the genetic material of the cell. (9.1)
reverse transcriptase enzyme that creates a DNA
strand complementary to the RNA strand. (9.3)
rhodopsin purple pigment in the optical receptors
of the eye; it enables the rod and cone cells to
function. (5.3)
ribonucleic acid (RNA) nucleic acid consisting of
long chains of individual nucleotides, each of
which is composed of the five-carbon sugar
ribose, a phosphate group, and the nitrogenous
base adenine, guanine, cytosine, or uracil. It
assists DNA in controlling protein synthesis in
cells. Originally called “ribose nucleic acid” by
its discoverer, Phoebus Levene. (7.1)
ribose nucleic acid Phoebus Levene’s name for
ribonucleic acid (RNA). (7.1)
ribosomal RNA (rRNA) most common class of RNA
molecules. During polypeptide synthesis, these
RNA molecules supply the site on the ribosome
where the polypeptide is assembled. (8.3)
ribosome the cell structure that brings together the
mRNA strand, the aa-tRNAs, and the enzymes
involved in building polypeptides in order to
enable protein synthesis to occur within the
cytoplasm. (8.3)
RNA seeribonucleic acid. (7.1)
RNA polymerase main enzyme that catalyzes the
formation of RNA from a DNA template. (8.2)
rods photoreceptors in the eye; more sensitive to
light than cones, but unable to distinguish colour.
(5.3)
r-selection natural selection that produces
opportunistic life histories. (14.4)
RuBP ribulose bisphosphate. (3.3)
RuBP carboxylase enzyme in green plants that
catalyzes the fixation of carbon into organic
molecules. (3.3)sample small portion of an entire population that is
counted or estimated. (14.1)
Schwann cells insulating cells around the axon of a
nerve cell. (5.2)
sclera the thick white outer layer that gives the eye
its shape. (5.3)secondary consumer carnivore or omnivore that
eats mainly herbivores and occupies the third
trophic level. (13.2)
secondary structure in protein, the shape resulting
from hydrogen bonding between the N–H and
C=O groups of the primary structure.
(Appendix 5)
secondary succession the redevelopment of a
previously existing community after a
disturbance. (13.1)
selective pressure environmental condition or
conditions that select for certain characteristics of
individuals, and select against others. (10.1)
semen fluid consisting of sperm and fluid from the
prostate and Cowper’s glands. The fluid is
ejaculated from the male penis into the female
vagina during sexual intercourse. (6.3)
semi-conservative theory the theory that in the
replication of DNA, the daughter DNA molecules
are each made up of one parental strand and one
new strand. This was the model suggested by
James Watson and Francis Crick, who proposed
the double helix for the molecular structure of
DNA. (7.3)
seminal vesicles glands that produce a mucus-like
fluid containing fructose as energy for sperm.
(6.3)
seminiferous tubules tubes inside the testes. (6.3)
sense strand strand of nucleotides containing the
instructions that direct protein synthesis. It is
located within a stretch of DNA that includes a
gene. (8.2)
sensory nerves nerves that carry impulses from the
body’s sense organs to the CNS. (5.1)
sensory receptors scattered throughout the body,
cells or groups of cells that work continually to
receive information about the body’s internal
conditions, such as temperature, pH, glucose
levels, and blood pressure. (4.1)
seratonin organic compound formed from
tryptophan and found in tissue, especially
the brain, blood serum, and gastric mucous
membranes. The compound is active in
vasoconstriction, muscle stimulation,
transmission of impulses between nerve cells,
and regulation of cyclic processes. (5.2)
Sertoli cells cells in the seminiferous tubules that
support, regulate, and nourish developing sperm.
(6.3)
sexual dimorphism the difference between
phenotypes of males and females of the same
species. (11.3)
sexual selection selection for mating based, in
general, on competition between males and
choices made by females. (11.3)S
586 MHR • Glossary