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 is a fundamental concept in biology that describes the flow of genetic information within a cell. It consists of three main processes: DNA replication, transcription, and translation.
1. DNA replication: Before a cell divides, its DNA needs to be replicated to ensure each daughter cell receives a complete set of genetic information. DNA replication occurs in the cell nucleus and involves the separation of the DNA double helix and the synthesis of two new complementary strands.
2. Transcription: The process of transcription converts the information encoded in DNA into an RNA molecule. It takes place in the nucleus, where an enzyme called RNA polymerase binds to the DNA template and synthesizes a complementary RNA strand. This RNA molecule is known as messenger RNA (mRNA).
3. Translation: Translation is the process by which the genetic information carried by mRNA is used to synthesize proteins. It occurs in the ribosomes, cellular structures found in the cytoplasm. Transfer RNA (tRNA) molecules, carrying specific amino acids, bind to the mRNA codons (triplets of nucleotides) through complementary base pairing. As the ribosome moves along the mRNA, it links the amino acids together to form a protein.
The genetic code is the set of rules that determines how the sequence of nucleotides in DNA is translated into the sequence of amino acids in a protein. It is based on the codons, which are groups of three nucleotides in mRNA.
Now, let's move on to the six types of genetic mutations and how they affect the phenotype of organisms:
1. Silent mutation: This type of mutation does not produce any change in the resulting protein. It occurs when a nucleotide substitution in the DNA sequence does not alter the corresponding amino acid in the protein. As a result, the phenotype remains unaffected.
2. Missense mutation: In this type of mutation, a nucleotide substitution leads to a change in the corresponding amino acid. As a result, the protein's structure and function may be altered, thus affecting the phenotype of the organism.
3. Nonsense mutation: This mutation results in the premature termination of protein synthesis. It occurs when a nucleotide substitution creates a stop codon in the mRNA sequence, causing the protein to be shorter than normal. The truncated protein often lacks essential functional domains and can have a severe impact on the phenotype.
4. Insertion mutation: An insertion mutation occurs when one or more nucleotides are added to the DNA sequence. This causes a shift in the reading frame, altering the codon sequence and leading to significant changes in the resulting protein. The phenotype can be affected depending on the size and location of the inserted segment.
5. Deletion mutation: Similar to an insertion mutation, a deletion mutation involves the loss of one or more nucleotides from the DNA sequence. As a result, the reading frame is shifted, causing a change in the codon sequence. This alteration in the protein's amino acid sequence can disrupt its structure and function, leading to phenotypic changes.
6. Frameshift mutation: Frameshift mutations occur due to insertions or deletions of nucleotides that are not multiples of three. Since codons are read in groups of three, this disrupts the reading frame, leading to a completely different sequence of amino acids. Frameshift mutations can have severe consequences on the phenotype, as the resulting protein may be non-functional or entirely different from the original.
In summary, these six types of genetic mutations can affect the phenotype of an organism by altering the structure and function of the proteins they encode. The severity of the phenotypic effects depends on the specific mutation and its location within the DNA sequence.