18. Explain the Central Dogma of Molecular Genetics. What is the genetic code? Describe six (6) types of genetic mutations and explain how they affect the phenotype of the affected organism.
The Central Dogma of Molecular Genetics describes the flow of genetic information within a cell. It consists of three main steps: DNA replication, transcription, and translation.
1. DNA Replication: Before a cell can divide, it must duplicate its DNA. During replication, the DNA double helix unwinds and each strand serves as a template for the synthesis of a new complementary strand. This ensures that each daughter cell receives an exact copy of the genetic material.
2. Transcription: The first step in gene expression is transcription. It involves the synthesis of an RNA molecule, called mRNA, using one strand of the DNA as a template. The enzyme RNA polymerase binds to the DNA at the beginning of a gene, unwinds the helix, and adds the complementary RNA nucleotides to form a single-stranded mRNA molecule.
3. Translation: The mRNA produced in the previous step carries the genetic information from the DNA to the ribosomes, where it is translated into a specific sequence of amino acids to form a protein. Ribosomes read the mRNA codons (groups of three nucleotides) and bring in the appropriate amino acids, linking them together to build the protein.
The genetic code refers to the specific correspondence between the sequence of nucleotides in DNA and RNA and the sequence of amino acids in proteins. It is a triplet code, meaning that every three nucleotides of mRNA, known as a codon, represents a specific amino acid or a stop signal.
Now, let's discuss six types of genetic mutations and how they can affect the phenotype of an organism:
1. Silent Mutation: These mutations do not result in any change in the encoded amino acid sequence. The mutation occurs in a non-essential region of the gene, or the changed codon still codes for the same amino acid. As a result, there is no effect on the phenotype.
2. Missense Mutation: In this type of mutation, a single nucleotide change leads to the substitution of one amino acid for another in the protein sequence. Depending on the significance of the change, it can either have a mild or severe impact on the phenotype.
3. Nonsense Mutation: This mutation creates a premature stop codon in the mRNA sequence, resulting in the premature termination of protein synthesis. This often leads to the production of a nonfunctional or truncated protein, affecting the phenotype.
4. Frameshift Mutation: These mutations involve the insertion or deletion of nucleotides, causing a shift in the reading frame of the mRNA. As a result, every subsequent codon is altered, leading to a completely different amino acid sequence and most likely a nonfunctional protein.
5. Insertion Mutation: This mutation occurs when one or more nucleotides are inserted into the DNA sequence. The addition of extra nucleotides alters the reading frame during translation, causing a significant change in the amino acid sequence and likely resulting in a nonfunctional protein.
6. Deletion Mutation: Similar to insertion mutations, deletion mutations involve the removal of one or more nucleotides from the DNA sequence. This results in a frameshift during translation, leading to an incorrect reading of the codons and a nonfunctional protein.
These mutations can affect the phenotype of an organism by altering the structure, function, or abundance of the protein produced. This, in turn, can impact various biological processes and lead to observable changes in traits or characteristics.