DNA, RNA, and Genetic Code: Understanding the Basics
Nucleic Acids: DNA and RNA
Nucleic acids store and transmit genetic information. They are macromolecules formed by the junction of nucleotides (DNA and RNA).
Nucleotides
Nucleotides are composed of phosphoric acid, pentose, and a nitrogenous base (G, C, A, T, U).
DNA
- Molecule carrying genetic information
- Double helix, antiparallel and complementary
- Contains deoxyribose and thymine
- Can replicate (create identical copies of itself)
RNA
- Involved in the expression of information contained in DNA through protein synthesis
- Contains ribose and uracil
- Types: mRNA, rRNA, tRNA
mRNA
mRNA copies information from nuclear DNA and transports it to the ribosome.
rRNA
rRNA, associated with proteins, forms the ribosomes, where proteins are synthesized.
tRNA
tRNA binds to amino acids and transports them to the ribosome to form proteins.
Gene
A gene is a fragment of DNA that carries the information for a protein, necessary for expressing a particular trait in an individual. A gene fragment contains the genetic information for a certain character (trait).
Genome
The genome is the complete set of genes of an organism. The Human Genome Project (HGP) aimed to identify and determine the function of all human genes and locate their place on the chromosomes.
Mutations
Mutations are random changes occurring in the DNA of an organism. They are a source of genetic variability and an engine for the evolution of species.
Mutations can be harmful, beneficial, or neutral. They can also be somatic (causing serious injury or illness, and are not hereditary) or germline (affecting the gametes and are inherited). There are different types of mutations:
- Gene mutations (causing changes in the nucleotide sequence of a gene)
- Genomic mutations (varying the total number of chromosomes)
- Chromosomal mutations (causing changes that affect the internal structure of chromosomes)
Proteins and the Genetic Code
Proteins
Proteins are large molecules that result from the combination of amino acids.
Triplet
A triplet is a combination of three nucleotides. DNA information is organized in triplets.
Decoding: Transcription and Translation
- Transcription: Copying genetic information from DNA into an mRNA molecule. Thymine is replaced by uracil.
- Translation: Translating the message contained in mRNA into the language of proteins. This occurs in the cytoplasm, where ribosomes read the information in the form of triplets (codons) and translate it into the language of proteins.
Genetic Code
The genetic code is the correlation between mRNA codons and the amino acids that form proteins.
Biotechnology and Genetic Engineering
Biotechnology
Biotechnology is the use of living organisms, or parts thereof, in order to obtain products of interest to people.
Genetic Engineering
Genetic engineering involves manipulating the DNA of an organism to achieve a practical purpose. This uses restriction enzymes, DNA ligases, and transfer vectors.
Applications of Genetic Engineering
- Obtaining drugs
- Improving agricultural and animal production
- Gene therapy (treating diseases caused by a genetic disorder, such as diabetes or Parkinson’s disease)
Genetically Modified (GM) Food
GM foods are foods to which a gene, called a transgene, has been introduced from another organism.
Cloning
Cloning is the creation of one or more identical copies of an original organism.
Therapeutic Cloning
Therapeutic cloning is used to treat diseases and regenerate tissues (e.g., nervous tissue). Stem cells (undifferentiated cells that can divide indefinitely and give rise to cells and tissues) are needed.
Reproductive Cloning
Reproductive cloning serves to get individuals that are identical to each other and to the original. The process involves:
- Removal of mammary cells and the production of ova.
- Mammary cell culture and extraction of the nucleus.
- Cell fusion and development of the embryo.
- Implantation of the embryo in a third individual.
- Birth of the fourth individual.