PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Biological Evolution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 541 records · Page 30Linked to original sources
PubMed1990

Biogenesis of mitochondrial c-type cytochromes.

Cytochromes c and c1 are essential components of the mitochondrial respiratory chain. In both cytochromes the heme group is covalently linked to the polypeptide chain via thioether bridges. The location of the two cytochromes is in the intermembrane space; cytochrome c is loosely attached to the surface of the inner mitochondrial membrane, whereas cytochrome c1 is firmly anchored to the inner membrane. Both cytochrome c and c1 are encoded by nuclear genes, translated on cytoplasmic ribosomes, and are transported into the mitochondria where they become covalently modified and assembled. Despite the many similarities, the import pathways of cytochrome c and c1 are drastically different. Cytochrome c1 is made as a precursor with a complex bipartite presequence. In a first step the precursor is directed across outer and inner membranes to the matrix compartment of the mitochondria where cleavage of the first part of the presequence takes place. In a following step the intermediate-size form is redirected across the inner membrane; heme addition then occurs on the surface of the inner membrane followed by the second processing reaction. The import pathway of cytochrome c is exceptional in practically all aspects, in comparison with the general import pathway into mitochondria. Cytochrome c is synthesized as apocytochrome c without any additional sequence. It is translocated selectively across the outer membrane. Addition of the heme group, catalyzed by cytochrome c heme lyase, is a requirement for transport. In summary, cytochrome c1 import appears to follow a "conservative pathway" reflecting features of cytochrome c1 sorting in prokaryotic cells. In contrast, cytochrome c has "invented" a rather unique pathway which is essentially "non-conservative."

Animals↗
PubMed1990

Current views on chloroplast protein import and hypotheses on the origin of the transport mechanism.

Most chloroplastic proteins are synthesized as precursors in the cytosol prior to their transport into chloroplasts. These precursors are generally synthesized in a form that is larger than the mature form found inside chloroplasts. The extra amino acids, called transit peptides, are present at the amino terminus. The transit peptide is necessary and sufficient to recognize the chloroplast and induce movement of the attached protein across the envelope membranes. In this review, we discuss the primary and secondary structure of transit peptides, describe what is known about the import process, and present some hypotheses on the evolutionary origin of the import mechanism.

Amino Acid Sequence↗
PubMed1968

Life in space.

Explore the source record for details and available documents.

Animals↗
PubMed1981

Primordial transport of sugars and amino acids via Schiff bases.

Experimental support is given for a model concerning the origin of a primordial transport system. The model is based on the facilitated diffusion of amino acids stimulated by aliphatic aldehyde carriers and sugars stimulated by aliphatic amine carriers. The lipid-soluble diffusing species is the Schiff base. The possible role of this simple transport system in the origin of an early protocell is discussed.

Amino Acids↗
PubMed1982

Between history and physics.

Biology has traditionally occupied a middle ground between the determinism of classical physics and the uncertainties of history. These issues are analyzed with respect to statistical laws which are applied to the prebiotic domain and strategy laws which characterize evolutionary biology. The differences in approach between biology and physics are discussed in detail. The origin of life is discussed in the context of physical chemical laws. A scenario for biogenesis is presented in terms of known molecular hardware. Evolutionary biology is then examined with respect to the kinds of laws that are possible in a domain where thermal fluctuations (mutations) have macroscopic effects. Game theory is employed to demonstrate the kinds of theory appropriate to this historical domain. The transition point between physics and history is the origin and development of the code. This is discussed and it is concluded that we are not yet able to assign the code to either the deterministic domain or to the arena of history.

Animals↗
PubMed1990

Did membrane electrochemistry precede translation?

The discovery of RNA-based enzymes, such as ribonuclease-P, has stimulated new interest in the idea that catalytic functions of RNA preceded the use of coded enzymes during an era loosely termed 'the RNA world'. This paper examines various lines of evidence which support the idea that electrochemical processes associated with the membrane may have preceded the development of coded protein enzymes and may have provided a basis for the phosphorylation energy of the RNA world.

Biological Evolution↗
PubMed1976

Similarities between sodium channels in excitable membranes and in epithelia.

The inhibitory effects of the pyrazine derivative, amiloride, on sodium transport in an amphibian epithelium has been studied as a function of pH. It is concluded that the charged (guanidinium) group interacts with a negatively charged acid grouping in the membrane. Similarities between sodium channels in excitable membranes and epithelia are highlighted.

Amiloride↗
PubMed1983

Thinking about mind and matter from biology.

In biology, man is an object of research; therefore the question might be asked whether inspirations can go from biological data to the reflections on the mind-matter relation in man. The social aspect of man, as treated by sociobiology, is left out of consideration. The knowledge that man is mind, or has a mind, is no result of biological research. It is a datum from philosophy. The biologist, however, is living in a culture which knows about the mental character of man, and this is incorporated in his investigations. He knows that mental activities are connected with processes in the central nervous system and that, especially in the brain, localizations of mental activities are found. As a result of the split-brain experiments with patients and animals, some have arrived at the conclusion that there is a double consciousness. An approach from biology can lead to statements of a philosophical character, as, for example, statements about the unity, or even identity, of mind and matter. The theories of identity meet with great interest in scientific circles, and the truth value of identity statements is investigated. The system theory is taken into consideration. On a philosophical level a revaluation of the concept of matter can lead to a different sort of identity theory.

Biological Evolution↗
PubMed1984

Temperature as a determinative factor in the evolution of genetic systems.

Heat induces a number of premutational lesions (for example, the deamination of cytosine to uracil) in DNA and RNA. These kinds of errors occur in resting as well as replicating polynucleotides. However, an increase in temperature also raises the probability of copying error occurring in nucleic acids because of increased thermal noise in the replicative machinery. In most modern genetic systems, the majority of heat-induced lesions are efficiently repaired. It follows that the importance of heat-induced error increases as the effectiveness of repair declines. We show in this paper that the error rate of enzymatic polynucleotide copying is expected to increase monotonically with temperature. We also explore the effects of temperature variations on the early evolution of biological information transmission mechanisms.

Biological Evolution↗
PubMed1996

Fertility technologies and trans-kin altruism.

If a couple wishes to have children, is able to have them through the usual biological process, and there are no known genetic problems facing such children, then that couple would be best advised to have biological offspring. In fact, most people would consider this to be simply the natural "default setting" for such decisions. But if they are not able to have such offspring, or if there is a significant probability that such offspring would have some catastrophic genetic problem, then it might be better for the couple to adopt a child not related to them biologically. This would, in the first place, avoid problematic uses of fertility technologies, such as the use of ova from aborted fetuses. But it would also provide an opportunity for the exercise of trans-kin altruism, something which is not always easy to practice but which is an essential feature of our humanity as it has developed through the evolutionary process. That is to say, there are both negative and positive reasons for adoption. Negatively, it may enable us to avoid ethically questionable uses of technology. Positively, it responds to and reinforces a feature of our evolutionary history which is crucial to what it means for us to be human.

Aborted Fetus↗