Metabolic Regulation and Nucleic Acids: DNA and RNA Functions

Metabolic Regulation

Enzymes do not always act with the same degree of cellular boost to the economy. Regulation governs many metabolisms at these levels: synthesis and modification of enzyme structure, [S] and [P]. Thus, enzyme inhibition is a control mechanism of cellular metabolism. An important example is allosteric enzymes, whose speed depends not only on the interplay of [S] but also on other substances. Then, in addition to the active sites, they have other allosteric sites that activate them or act as regulatory molecules.

Types of Metabolic Regulation

• Negative Feedback (Feedback Regulation): The product inhibits the pathway.
• Positive Control: The product stimulates the start of the pathway.

Nucleic Acids

Nucleic acids are substances found in the nucleus of eukaryotic cells. They are molecules that are vital for carrying out processes, as they contain instructions for carrying them out and capturing genetic information. Through hydrolysis, they are broken down into units called nucleotides, which have three components: carbohydrates, a nitrogenous base, and phosphoric acid.

Nucleic Acid Structure

Nucleic acids are polynucleotides linked by 5'-3' bonds. The molecular weight of these polymers can be very high.

Differences Between DNA and RNA

1. Composition: DNA contains deoxyribose and the bases A, T, G, and C, while RNA contains ribose and the bases A, U, G, and C.
2. Location: DNA is located in the nucleus, constituting eukaryotic chromosomes, while RNA is found in the nucleus and the cytoplasm.
3. Structure: DNA has long, double-stranded chains, while RNA has shorter, single-stranded chains (although it can have double-stranded regions).
4. Function: DNA carries and stores genetic information, while RNA transmits genetic information from DNA to the ribosomes (transcription) and translates the sequence of ribonucleotides into the amino acid sequence (translation).

DNA

In eukaryotic cells, DNA is associated with proteins, forming nucleoproteins. It is also found in mitochondria and chloroplasts, but not associated with proteins. We distinguish three levels of structure:

• Primary Structure: This is the nucleotide sequence coupled by a 5'-3' phosphodiester bond chain. It has a backbone of phosphodiester bonds and nitrogenous bases.
• Secondary Structure: This is the spatial arrangement of two double chains of polydeoxyribonucleic acid confronted by their A-T and G-C bases and joined by hydrogen bonds.

DNA Denaturation

The double helix is very stable, but when heated, the two strands separate (denature). This is a reversible process and has an important application in hybridization, where two DNA molecules associate based on their degree of complementarity.

DNA Packaging

1. Prokaryotes: Bacterial and mitochondrial DNA have a tertiary structure formed by a fiber twisted on itself, called supercoiled DNA, which reduces the length of the molecule and provides stability.
2. Eukaryotes: Eukaryotic DNA molecules are so long that they require packaging into a volume as small as the cell nucleus. This is achieved by associating with basic proteins that neutralize the charges of DNA. The complex of DNA and proteins is called chromatin. There are different levels of packaging:

• The first level is the nucleosome, formed by an octamer of histones surrounded by a DNA chain.
• A second level originates from the interaction between nucleosomes.
• During cell division, further packaging occurs, ultimately achieving the maximum level of compaction in metaphase chromosomes.

RNA

RNA molecules are polymers of phosphodiester bonds. They have a primary structure, although complementary sequences can pair to form a secondary structure.

• mRNA: Messenger RNA.
• rRNA: Ribosomal RNA is the most abundant type of RNA. It has secondary and tertiary structures and forms ribosomes by binding to different proteins.
• tRNA: Transfer RNA molecules are small in size. They are found in the nucleolus and are responsible for transporting amino acids to the ribosomes during protein synthesis. They have a secondary structure.