Nucleic Acids And Protein Synthesis - Session 4

We have already studied that tRNA is involved in protein synthesis. Let us now understand the structure of tRNA molecule to better understand its functioning. tRNA molecules have a secondary structure that looks like a cloverleaf. This is due to the formation of hydrogen bonds between complementary base-pairs in different regions of the molecule. This structure of tRNA that looks like a cloverleaf has many regions.

The anticodon loop is a crucial part of the tRNA molecule. It contains a three-nucleotide-sequence known as the anticodon. Anticodon is complementary to a specific codon on the mRNA. The anticodon plays a vital role in recognizing and binding to the corresponding codon during the translation process. Do you know amino acid binds at which site in tRNA during translation?.

At the three-end of the tRNA molecule, there is a site where a specific amino acid is attached. This amino acid attachment site is called the acceptor stem. The amino acid that binds to the tRNA is specific to the anticodon sequence. This ensures that the correct amino acid is incorporated into the growing protein chain during translation. tRNA molecules often contain modified nucleotides at specific positions. These modifications contribute to the stability and proper folding of the tRNA molecule.

Genetic mutations are permanent alterations or changes that occur in the DNA sequence of genome of an organism. These mutations can involve a single nucleotide, a segment of DNA, or sometimes entire chromosomes. Genetic mutations can arise spontaneously or be caused by various external factors such as exposure to radiation, chemicals, or particularviruses. They can also be inherited from parents or occur during DNA replication or repair processes.

Genetic mutations can be classified into different types based on their specific effects on the DNA sequence. Point mutation is a type of genetic mutation that involves the alteration of a single nucleotide within the DNA sequence. Point mutations can result in changes in the genetic code and subsequent effects on protein structure and function.

Silent mutation is a type of point mutation that does not alter the amino acid sequence of the protein. Silent mutations occur when the changed nucleotide yet again codes for the same amino acid due to the degeneracy of the genetic code. In other words, silent mutation does not result in a change in the protein sequence. For example, changing the third nucleotide in the codon GAA to GAG would result in a silent mutation. This is because both GAA and GAG are codes for glutamate. As a result, the protein produced remains the same.,

Missense mutation is a type of point mutation that results in the substitution of one amino acid for another in the protein sequence. Substitution means replacement. Missense mutations occur when the changed nucleotide alters the codon. This results in the incorporation of a different amino acid into the protein. For instance, changing of the codon GGC which codes for glycine, to AGC which codes for serine, is a missense mutation. This alteration can affect the structure and function of the protein, resulting in various consequences.

Sickle cell anemia is a genetic disorder caused by missense mutation. Sickle cell anemia is primarily caused by a single nucleotide substitution in the beta globin gene. Beta globin gene is responsible for producing one of the subunits of hemoglobin. The mutation involves a change in the sixth codon of the beta globin gene, where adenine is replaced by thymine. This alteration results in the substitution of the amino acid glutamate with valine in the corresponding position of the hemoglobin protein.

As a result of this missense mutation, the abnormal hemoglobin tends to polymerize. It forms long, rigid chains when deoxygenated. These chains cause red blood cells to become distorted and take on a sickle shape. Sickle shaped red blood cells are less flexible and can block blood vessels.

Nonsense mutation is a type of point mutation that introduces a premature stop codon into the DNA sequence. This results in the production of a non functional protein. Nonsense mutations occur when the changed nucleotide creates a stop codon instead of a codon that codes for an amino acid. This premature stop codon results in the termination of protein synthesis. As a result, shorter and often non functional protein is produced. For example, changing the codon TAC which codes for tyrosine, to TAG which is a stop codon results in the production of non functional protein.

Frameshift mutation is a type of genetic mutation that occurs when nucleotides are inserted or deleted from the DNA sequence. This results in a shift in the reading frame. This shift alters the way the genetic code is interpreted during protein synthesis. A frameshift mutation results in the production of non functional proteins.

An insertion is a type of frameshift mutation that involves the addition of one or more nucleotides to the DNA sequence. Insertions shift the reading frame. The inserted nucleotide causes a displacement in the codons of the insertion site. Insertion changes the reading frame downstream. This results in a completely different amino acid sequence. The resulting protein might be non functional or have severely altered function.

Deletion is a type of frameshift mutation that occurs when one or more nucleotides are removed from the DNA sequence. Deletions also shift the reading frame. This is because the missing nucleotides cause a disruption in the codons downstream of the deletion site. This frameshift mutation disrupts the correct reading frame. As a result non functional protein or protein with altered function is produced.

Frameshift mutations have a great effect on the resulting protein because they alter the entire reading frame of the DNA sequence. The insertion or deletion of nucleotides disrupts the correct grouping of codons. This results in an incorrect protein synthesis. Frameshift mutations often have more severe consequences compared to other types of mutations due to their disruptive nature.

Inversion mutation is a type of genetic mutation that involves the reversal or rearrangement of a segment of a chromosome. An inversion mutation occurs when a segment within a chromosome breaks and reinserts itself in the reverse orientation. For instance, inverting the sequence ABC would result in CBA.