5. Molecular Biology: DNA and RNA

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One of the most important topics in Biology for the ENEM exam is Molecular Biology, with emphasis on DNA and RNA. This topic is fundamental to understanding not only how life is formed, but also how it is maintained and reproduced.

DNA, or deoxyribonucleic acid, is the molecule that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. DNA is a double helix molecule, which means that it is made up of two strands that wrap around each other. Each chain is made up of a sugar and phosphate backbone, with a nitrogenous base attached to each sugar. The nitrogenous bases are adenine (A), thymine (T), cytosine (C) and guanine (G). Bases A and T are always paired together, as are C and G.

RNA, or ribonucleic acid, is a molecule similar to DNA, but it is single-stranded and contains the nitrogenous base uracil (U) instead of thymine. RNA plays many roles in biology, but perhaps the best known is that of a messenger, carrying instructions from DNA to other parts of the cell to make proteins.

One of the most fundamental processes in molecular biology is DNA replication, where one DNA molecule is copied to create two DNA molecules. This process is vital for cell reproduction, allowing each new cell to have a complete copy of DNA. During DNA replication, the DNA molecule is "uncoiled" and the two strands are separated. Each strand then serves as a template for the formation of a new strand of DNA. The nitrogenous bases are paired (A to T, C to G) and a new sugar and phosphate backbone is formed. The result is two DNA molecules identical to the original.

The process of transcription is where DNA is used to create RNA. During transcription, a section of DNA is "uncoiled" and one of the strands serves as a template for the formation of an RNA molecule. The nitrogenous bases are paired (A to U, C to G) and a new sugar and phosphate backbone is formed. The resulting RNA can then be used to create proteins.

Translation is the process by which messenger RNA is used to create proteins. During translation, messenger RNA is read by a ribosome, a molecular machine that uses messenger RNA as a template for creating a protein. Each set of three bases in messenger RNA (a codon) corresponds to a specific amino acid. The ribosome reads the messenger RNA, one codon at a time, and adds the corresponding amino acid to the growing protein chain.

Understanding molecular biology, and in particular DNA and RNA, is critical to understanding life at its most basic level. This knowledge is vital to many areas of biology, including genetics, evolution, and biotechnology. Therefore, it is an essential component of any ENEM biology course.

In addition, molecular biology has significant practical implications. For example, understanding DNA and RNA is critical to modern medicine, including developing new drugs and therapies, diagnosing disease, and understanding how genes can influence health and disease. Therefore, the study of molecular biology is not only academically important, but also has real and significant implications for everyday life.

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145.1. Molecular Biology: DNA and RNA: Structure of DNA