DNA Transcription and Translation | DNA to Protein

Dr. Mikey introduces the central dogma of molecular biology: how DNA turns into RNA, which then turns into protein. DNA, the genetic blueprint, resides in the nucleus of cells (except red blood cells) and dictates the creation of proteins, which perform various functions in the body, such as enzymes, carrier molecules, and neurotransmitters. The video aims to demonstrate how specific DNA strands are converted into proteins and how DNA mutations can impact protein function.

The cell contains a nucleus housing DNA in the form of chromosomes. Humans have 23 pairs of chromosomes: 22 autosomes and 1 pair of sex chromosomes (XX for female, XY for male). The autosomes are crucial for producing a wide range of functionally important proteins. Taking a single chromosome pair as an example, DNA is shown as a double helix, a twisted ladder structure with two strands. DNA is composed of four nucleotides: Adenine (A), Thymine (T), Guanine (G), and Cytosine (C). A always binds with T, and G always binds with C, through hydrogen bonds.

The first step in protein synthesis is transcription, converting DNA into an intermediate molecule called messenger RNA (mRNA). This process is facilitated by RNA polymerase, which unwinds a section of the DNA double helix (about 10-20 nucleotides at a time). The RNA polymerase reads the template strand of DNA and produces a complementary mRNA strand. A key difference in RNA is that Uracil (U) replaces Thymine (T). So, if the DNA template has an 'A', the mRNA will have a 'U'; if it has 'T', it will have 'A'; if 'G', it will have 'C'; and if 'C', it will have 'G'.

Once the mRNA strand is created, the DNA re-closes. Before leaving the nucleus, the mRNA often undergoes processing. This involves the removal of non-coding regions called introns, while the coding regions, called exons, are spliced together. After splicing, the mature mRNA molecule exits the nucleus and moves into the cytosol.

In the cytosol, the mRNA transcript binds to a ribosome. The ribosome reads the mRNA in sets of three nucleotides, called codons. Each codon corresponds to a specific amino acid. There are 64 possible codon combinations but only about 20 amino acids, leading to redundancy (multiple codons can code for the same amino acid). Transfer RNA (tRNA) molecules, with anticodons complementary to the mRNA codons, bring the corresponding amino acids to the ribosome. For example, 'AUG' codes for Methionine.

As the ribosome moves along the mRNA, tRNA molecules deliver amino acids, forming a linear chain. Each amino acid has a unique 'personality' (e.g., hydrophobic, positively charged, negatively charged, hydrophilic). This diverse nature causes the linear amino acid chain to spontaneously fold into a specific three-dimensional structure, known as a protein. The folding is dictated by the interactions between amino acids and their environment; for instance, hydrophobic amino acids will bury themselves inside the protein to avoid water, while hydrophilic ones will be exposed.

Mutations, which are changes in the DNA nucleotide sequence, can alter the amino acid sequence of a protein. For example, if a codon sequence changes from 'CGG' (coding for arginine, which is positively charged) to 'GAG' (coding for glutamine, which has no charge), the resulting protein will have glutamine instead of arginine. This change in amino acid can cause the protein to fold differently, potentially leading to a non-functional protein. Mutations can be caused by UV light, chemicals, or spontaneous errors during DNA replication.