silent mutation permanent change in the genetic
material of a cell that has no effect on the
metabolism of the cell. (9.1)
sink a substance or site that absorbs and holds
materials, often for a long period. (15.2)
small nuclear RNA (snRNA) the type of RNA that
is paired with proteins to make a spliceosome.
(8.2)
sodium-potassium pump a transport structure made
up of special carrier proteins. The “pump”
maintains an imbalance of sodium and potassium
in cells, particularly nerve and muscle cells. (2.3)
somatic cell any body cell except germ cells.
(Appendix 4)
somatic cell mutation permanent change in the
genetic material of a body cell, not including
germs cells, during the lifetime of the organism.
(9.1)
somatic gene therapy therapy aimed at correcting
genetic disorders in somatic cells. (9.4)
somatic nervous system relays information to and
from skin and skeletal muscles under conscious
control. (5.1)
somatotropin growth hormone produced by all
mammals. (9.3)
source a supply of specific materials. (15.2)
specialist organism that has very particular climate
or habitat requirements. These organisms
generally have low tolerance of change. (13.1)
speciation the formation of species. (12.2)
specific immune system wide variety of cells,
developed through exposure to disease, that
recognize certain foreign substances and act to
neutralize or destroy them. (4.4)
spermatogenesis the formation of sperm. (6.3)
sphincters two rings of muscle that control the exit
of the bladder. One is voluntarily controlled, and
the other is involuntarily controlled by the brain.
(4.2)
spliceosome molecule made of proteins and snRNA
that removes long stretches of nucleotides before
polypeptides are constructed. The spliceosome
cleaves the pre-mRNA at the ends of each intron
and then splices the remaining exons. (8.2)
spontaneous mutation permanent change in the
genetic material of a cell as a result of the
molecular interactions that take place naturally
within the cell. (9.1)
S-shaped curve the shape of a line describing the
growth of a population as the population reaches
its carrying capacity. (14.2)
stabilizing selection natural selection that favours
intermediate phenotypes and acts against
extreme variants. (11.3)
stereoisomers two molecules that have the same
types of bonds, but different arrangements in
space. Geometrical isomers can have very
different physical properties but the same
chemical properties; optical isomers
(enantiomers) are mirror images of each other
that have the same chemical and physical
properties, but enzymes and proteins on the cell
membrane can distinguish between them. (1.2)
steroid hormones hormones produced from
cholesterol by the endocrine system. (6.1)
sticky ends short sequence of unpaired nucleotides
remaining on a single strand of DNA at each end
of a restriction fragment, after an endonuclease
makes a staggered cut at the restriction site. (9.2)
structural adaptations adaptations that affect the
appearance, shape, or arrangement of particular
physical features, include mimicry and cryptic
coloration. (12.1)
structural isomers two or more compounds with
the same atoms bonded differently. (1.2)
subatomic particles tiny particles, such as protons,
neutrons, and electrons, that make up an atom.
(1.1)
substrate a reactant in an enzymatic reaction. (2.2)
substrate-level phosphorylation the formation of
ATP by transferring a phosphate group to ADP
from a substrate. (3.1)
supercoiled a strand of DNA in prokaryotic cells
coils into a closed loop, then twists in on itself
like a necklace that is coiled into a series of small
loops. Such a structure is said to be supercoiled.
This arrangement helps the prokaryote keep its
entire DNA in the nucleoid region. (7.2)
suppressor T cell lymphocyte that slows and stops
the cellular immune response when the danger
has passed. (4.4)
survivorship the proportion of individuals in a
population that typically live to a given age over
a given period of time. (14.4)
suspensory ligament one of the ligaments that
attach the ciliary muscles to the lens of the eye.
(5.3)
sustainable development the use of renewable
resources in a way that meets the needs of the
present without compromising the ability of
future generations to meet their own needs.
(15.3)
symbiont organism that depends on close
interaction with another organism (a host) for
survival. (14.3)
symbiotic relationship close interaction of two
species in a way that is beneficial to both. (14.3)
sympathetic nervous system the network of nerves
that controls involuntary muscle reactions and
organs in times of stress. (5.1)Glossary • MHR 587