How does DNA control the synthesis of carbohydrates and lipids in a cell?

Answer 1

First of all, note that almost everything in the body is regulated by enzymes, or protein complexes that lower the activation energy of a reaction and there increasing the rate at which it occurs.

DNA is composed of four nitrogenous bases: adenine, thymine, cytosine, and guanine. These four bases connect in specific sequences called genes, which the cell uses as "instructions" for every intra- and extracellular activity. When the cell or some extracellular unit requires information for the construction of a macromolecule, it sends a signal protein to a receptor on the plasma membrane or in the cytoplasm. When the signal is received, a signal transduction pathway begins that eventually tells the nucleus to activate a certain gene on one of its chromosomes. When the gene is activated, RNA is sent through a nuclear pore and DNA is unwound with DNA-Helicase (this protein breaks the weak hydrogen bonds between the nitrogenous bases). When the RNA transcribes (copies) the complementary bases, it returns to the cytoplasm as messenger RNA. Complementary bases here means whatever purine is found with its matching pyrimidine. For example, adenine always pairs with thymine and cytosine with guanine. In RNA, thymine is replaced with uracil. This means a gene with the combination TGCAAT would be complemented by ACGUUA on the mRNA sequence. When the mRNA reaches the cytoplasm, it uses its new information in structures called ribosomes which are the protein builders of the cell. As the ribosome reads the sequence, it creates a polypeptide chain from amino acids that are synthesized according the the demands mRNA strand sequence. Once the polypeptide, or protein chain, is complete, the structure changes from primary to secondary and from secondary to tertiary. When enough protein chains are synthesized, they combine to form the final quaternary structure of the enzyme. All this is occurring due to hydrogen and ionic bonds twisting and pulling the protein chains upon themselves to form the unique three-dimensional structure of the enzyme. Once the enzyme is complete, it is used to synthesize whatever it is the cell initially required for the process of life.

When there is enough enzyme created, another signal transduction pathway begins that halts the synthesis of the enzyme. This is called negative feedback inhibition in which the cell recognizes the growing quantity of the substance it is creating and stops synthesis for the sake of conserving cell resources. If the concentration of the substance drops below the required amount, positive feedback begins and the substance is once again synthesized by the same process.