2 pA 40 msec Figure Q11-4 Patch-clamp measurements of acetylcholine-gated cation channels in young rat muscle (Problem 11-11).
Evolution
The history and science of origin and evolution comprise two events, the beginning of life and expansion of life. Our earth originated about 4.5 billion years ago. The term evolution is derived from two Latin words and means the act of unfolding or unrolling. English philosopher Herbert Spencer first used it. Evolution is defined as the change in heritable traits of biological populations over successive generations. These traits are the manifestations of genes that are passed down from parent to offspring during reproduction.
Cladistics
Cladistics is a technique in the classification of organisms, where they are grouped into different clades. The proof for the relationships that are hypothesized is based on the shared derived characteristics known as synapomorphies. These characteristics do not exist in many of the distant ancestors and groups. The common ancestor along with its descendants is considered to be a part of the clade. The rate of closeness is directly proportional to the cladistic grouping and is useful in analyzing the evolutionary mechanism.
Outgroups
Outgroups are significant in studying cladistics or phylogenetics (that describe the evolutionary relationship between different organisms). Further, it is also important to understand the differences and similarities between different organisms.
Taxonomy
It is the branch of biology that works with the identification of organisms at first, then naming, and classification of them into phenetic or phylogenetic groups (a classification system). In other words, it is the scientific study of biological diversity and a part of systematic biology.
Phylogenetics
Phylogenetics is the scientific study of how various groups of organisms are related at the evolutionary level. It finds the relationship between various organisms based on their evolutionary similarities and differences. It is a part of the taxonomy. Although the taxonomic study is not only concerned about phylogeny but taxonomic studies are also concerned about the classification and nomenclature of the different individuals from different taxon.
Acetylcholine-gated cation channels at the neu-
romuscular junction open in response to acetylcholine
released by the nerve terminal and allow Na+ ions to enter
the muscle cell, which causes membrane depolarization
and ultimately leads to muscle contraction.
A. Patch-clamp measurements show that young rat
muscles have cation channels that respond to acetylcho-
line (Figure Q11–4). How many kinds of channel are there?
How can you tell?
B. For each kind of channel, calculate the number of
ions that enter in one millisecond. (One ampere is a cur-
rent of one coulomb per second; one pA equals 10–12
ampere. An ion with a single charge such as Na+ carries a
charge of 1.6 × 10–19 coulomb.)
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