Biochemistry/DNA and RNA
From Wikibooks, the open-content textbooks collection
Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the information storage molecules and working templates for the construction of proteins. Every living cell and virus encodes its genetic information using either DNA or RNA. It is a true marvel of evolution that the vast amount of information needed to produce a human being can fit inside cells.
Friedrich Miescher first isolated DNA and RNA from used surgical bandages in 1869. A series of experiments done by Oswald Avery, Colin MacLeod, and Maclyn McCarty in 1944 along with A.D. Hershey and Martha Chase's work in 1952 showed that DNA is the carrier of genetic information. The structure of DNA was discovered by James Watson and Francis Crick in 1953.
Contents |
[edit] Structure of DNA and RNA
DNA is a polymer of nucleotides. Nucleotides consist of a pentose sugar (2-deoxyribose for DNA and ribose for RNA), a phosphate group (H3PO4), and a nitrogen-containing base. There are five nitrogen bases - adenine, guanine, thymine, cytosine and uracil. Individual nucleotides are connected by phosphodiester bonds to form polynucleotides.
DNA exists as a double helix of two (2) strands of polynucleotides. According to the principle of complementarity nucleotides A (adenine) bases are bound with a hydrogen bridge to the T (thymine) or U (uracil in case of RNA) on the other thread and similarly C (cytosine) bind themselves to G (guanine). This principle allows for DNA and RNA replication and for limited possibilities of repairing the genetic information when one of the threads gets damaged.
[edit] Difference between DNA and RNA
DNA is the permanent genetic information storage medium, found in the nucleus of most cells of most living organisms. RNA is, in the case of eucaryotes, the medium that transfers the genetic information from the nucleus to the cytoplasm where proteins are synthesized.
There are three major types of RNA:
- messenger RNA (mRNA) - temporarily created RNA used for transferring the information from the DNA in the nucleus to the ribosome in the cytoplasm where it is "read," or translated, and a protein is synthesized.Each gene produce a separate mRNA molecule when a certain protein is needed in the cell. In addition, the size of an mRNA depends on the number of nucletides in that particular gene.
- transfer RNA (tRNA) - Is the smallest of the RNA molecules and it is associated with the ribosome and delivers an amino acid to be attached to the growing protein. Only the tRna can translate the genetic information into amino acid for proteins.
Each tRNA contains an "anticodon" which is a series of 3 bases that complements 3 bases on mRNA.
- ribosomal RNA (rRNA) - a major constituent of the ribosome with both structural and catalytic properties.
Additionally, by 2005, other types of RNA, such as siRNA (small, interfering RNA) and miRNA have been characterized.
[edit] Plasmid
Plasmids are small, circular DNA molecules that replicate separately from the much larger bacterial chromosome can be use in laboratory to manipulate genes. Plasmids can carry almost any gene and they can passed it on from one generation of bacteria to the next generation, therefore plasmids are key tools for “gene cloning” which is the production of multiple identical copies of a gene carrying piece of DNA
[edit] DNA Replication ;Semi-conservative replication
In the process of DNA replication, as cells divide, copies of DNA must be produced in order to transfer the genetic information. In DNA replication, the strands in the original DNA separate, and then each of the parent strands make copies by synthesizing complementary strands. Enzyme called helicase will start The process of replication by catalyzing the unwinding of protein of the double helix. This enzyme can break the H bonds between the complementary bases. These single strands now act as templates for the synthesis of new complementary strands. The energy for the reaction can be provided when a nucleoside triphosphate bonds to a sugar (at the end of a growing strand), and 2 phosphate group are cleaved. Then a T in the template forms H bond with an A in ATP, and a G on the template forms H bond with CTP. After the entire double helix of the parent DNA is copied, the new DNA molecule will form . The new DNA molecule is consist of one strand from the parent (original) DNA and one strand from the daughter strand( newly synthesized strand). This process is called "semi-conservative replication".
[edit] Recombination
Recombination refers to ways in which DNA modification leads to distinct gene expressions and functions. Deletions, insertions and substitutions are the most useful changes implemented for the synthesis of new genes. Recombination techniques and recombinant DNA technologies has made possible the modification and creation of new genes for specific proposes. These techniques helps clone, amplified and introduce new DNA into suitable cells for replication. Restriction enzymes and DNA ligase play a vital role in the in the production of recombinant DNA. Vectors are useful for cloning. Plasmids or viral DNA (lambda Phage) used to introduced a DNA sequence into a cell is refer as vector.
