DNA and RNA
Deoxyribonucleic Acid and Ribonucleic Acid
• DNA is deoxyribonucleic acid. It is located in the nuclei of cells, which make up the body. Consequently, DNA can be considered as one of the building blocks of the body.
Where is DNA found?
DNA, or deoxyribonucleic acid, is the hereditary material that lies within the nucleus of all cells in humans and other living organisms. Most of the DNA is placed within the nucleus and is called nuclear DNA. However, a small portion of DNA can also be found in the mitochondria and is called mitochondrial DNA or mtDNA.
What is DNA made of?
DNA contains four chemical bases:
• Adenine (A)
• Guanine (G)
• Cytosine (C)
• Thymine (T).
• RNA stands for ribonucleic acid. It is an important molecule with long chains of nucleotides. A nucleotide contains a nitrogenous base, a ribose sugar, and a phosphate. Just like DNA, RNA is vital for living beings.
Functions of RNA
The main job of RNA is to transfer the genetic code need for the creation of proteins from the nucleus to the ribosome. This process prevents the DNA from having to leave the nucleus. This keeps the DNA and genetic code protected from damage. Without RNA, proteins could never be made.
RNAs as enzymes
Some RNAs are enzymes. It was widely believed for many years that only proteins could be enzymes. RNAs are now known to adopt complex tertiary structures and act as biological catalysts. Such RNA enzymes are known as ribozymes, and they exhibit many of the features of a classical enzyme, such as an active site, a binding site for a substrate and a binding site for a cofactor, such as a metal ion. One of the ﬁrst ribozymes to be discovered was RNase P, a ribonuclease that is involved in generating tRNA molecules from larger, precursor RNAs. RNase P is composed of both RNA and protein; however, the RNA moiety alone is the catalyst.
DNA compared to RNA
DNA is defined as a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms. RNA molecules are involved in protein synthesis and sometimes in the transmission of genetic information. However unlike DNA, RNA comes in a variety of shapes and types. While DNA looks like a double helix and a twisted ladder, RNA may be of more than one type. RNA is usually single-stranded, while DNA is usually double-stranded. In addition, RNA contains ribose while DNA contains deoxyribose. Deoxyribose lacks one oxygen atom. RNA has the bases Adenine (A), Uracil (U) (instead of thymine in DNA), Cytosine (C) and Guanine (G). Deoxyribose sugar in DNA is less reactive because of C-H bonds. DNA is stable in alkaline conditions. DNA has smaller grooves where the damaging enzyme can attach which makes it harder for the enzyme to attack DNA. Ribose sugar however is more reactive because of C-OH (hydroxyl) bonds. RNA is not stable in alkaline conditions. RNA has larger grooves, which makes it easier to be attacked by enzymes. The helix geometry of DNA is of B Form. DNA can be damaged by exposure to Ultraviolet rays. The helix geometry of RNA is of A-Form. RNA strands are continually made, broken down and reused. RNA, however, is more resistant to damage by Ultra-violet rays.
DNA to RNA Transcription
The DNA contains the master plan for the creation of the proteins and other molecules and systems of the cell, but the carrying out of the plan involves transfer of the relevant information to RNA in a process called transcription. The RNA to which the information is transcribed is messenger RNA (mRNA). The process associated with RNA polymerase is to unwind the DNA and build a strand of mRNA by placing on the growing mRNA molecule the base complementary to that on the template strand of the DNA. In the mRNA, Uracil is substituted for thymine as the base complementary to adenine. Since the other strand of the DNA has bases complementary to the template strand, the mRNA has the same sequence of bases at the upper strand of DNA shown above (with U substituted for T) , which is called the coding strand. According to Karp, the RNA polymerase is capable of adding 20 to 50 nucleotides per second to the growing mRNA chain. Electron microscope images suggest that there can be over a hundred RNA polymerases operating simultaneously. A coding region of the DNA for a specific protein (a gene) contains the pattern for the creation of the protein. The coding region is preceded by a promotion region, and a transcription factor binds to that promotion region of the DNA. It recruits the necessary RNA polymerase to activate the copying of the pattern of the coding region over to RNA. The segment of DNA transcribed to the RNA contains some material that is not translated on both the beginning (5') and end (3') of the segment. It also typically has segments called introns that are not translated as well as segments called exons that are actually part of the pattern for the protein.
Eunice T. Loyola
Theories on the Origin of Life
Marine Theory - Life originated from the sea
Philosophical theory is a theory that explains or accounts for a general philosophy or specific branch of philosophy. Some examples of philosophical theories include:
• Metatheory; theories about the formation and content of theories, such as Kurt Gödel's incompleteness theorem. • Political theory; theories that underlie a political philosophy, such as John Rawls' theory of justice. • Ethical theory and meta-ethics; theories about the nature and purpose of ethical statements, such as the ethical theory of Immanuel Kant. • Critical theory; in its narrow sense, a Western European body of Frankfurt School Marxist thought that aims at criticizing and transforming, rather than merely explaining, social structures.In a broader sense, "critical theory" relates to a wide variety of political, literary, and philosophical positions that take at least some of their inspiration from the Frankfurt School and its dialectic, and that typically contest the possibility of objectivity or aloofness from political positions and privileges. Electric Spark: Inspired by the Miller-Urey experiment of 1953, this theory suggests that lightning interacting with methane gas in the earth's atmosphere created amino acids.
Community Clay: This is the idea that mineral crystals in clay helped organize the first living cells.
Deep-Sea Vents: Some people believe life began in the hydrogen-rich environment of submarine, hydrothermal vents.
Chilly Start: Instead of super-hot, hydrothermal vents, some believe life began inside hundreds of feet of ice that supposedly covered the early oceans.
RNA World: Before DNA, some speculate that life began with RNA. Of course, they don't have a conclusive theory on the origin of RNA either.
Simple Beginnings: Instead of developing from complex molecules such as RNA, life might have begun with smaller molecules interacting with each other in cycles of reactions.
Panspermia: This is the idea that life did not begin on earth at all but was brought here from space via comets or meteors. Some extremists who hold this view believe life was intentionally planted here by intelligent aliens but Live Science didn't mention them in their description of panspermia.[pic]