5.3. Molecular Biology: DNA and RNA: DNA Replication

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Molecular biology is a branch of science that focuses on the study of genetic materials and the proteins they produce. This field of study is crucial to understanding how organisms function on a molecular level. In this section, we'll explore DNA and RNA, as well as the process of DNA replication.

DNA and RNA

DNA, or deoxyribonucleic acid, is the molecule that contains the genetic instructions used in the development and functioning of all living organisms. It is a long polymer made of repeating units called nucleotides. Each nucleotide is composed of a sugar (deoxyribose), a phosphate and a nitrogenous base. The nitrogen bases can be adenine (A), thymine (T), cytosine (C) or guanine (G).

RNA, or ribonucleic acid, is similar to DNA, but has some key differences. RNA is usually a single strand whereas DNA is a double helix. Furthermore, RNA contains the sugar ribose instead of deoxyribose and the nitrogenous base uracil (U) instead of thymine.

DNA replication

DNA replication is the process by which one DNA molecule is copied to produce two identical DNA molecules. This is crucial for cell division, as each new cell needs a complete copy of DNA to function properly.

The process of DNA replication begins with the separation of the two strands of DNA. This separation is carried out by an enzyme called helicase, which "unwinds" the DNA double helix. The area where the two strands of DNA separate is called the "replication bubble".

Once the DNA strands are separated, another enzyme called DNA polymerase begins to add new nucleotides to the separated DNA strands. DNA polymerase can only add nucleotides in the 5' to 3' direction. This means that one strand of DNA is replicated continuously, while the other strand is replicated in pieces. These pieces are called Okazaki fragments.

After replication, the two new DNA molecules, each containing an original strand and a newly synthesized strand, rewind into a double helix. This process is called "base pairing", where adenine always pairs with thymine, and cytosine always pairs with guanine.

In summary, DNA replication is a complex process involving many enzymes and proteins. It is a crucial process for cell division and for sustaining life as we know it.

Understanding molecular biology, including DNA, RNA, and DNA replication, is crucial to understanding how organisms function at a molecular level. This knowledge is particularly important for medicine and biotechnology, where the manipulation of DNA and RNA can lead to new treatments and technologies.

Therefore, to effectively prepare for the ENEM exam, it is essential that students fully understand these concepts and be able to apply them in a variety of contexts.

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175.4. Molecular Biology: DNA and RNA: Transcription of DNA to RNA