Posttranslational Modifications - Essay Example

The process of PTM is governed by enzymes such as transferases, kinases, ligases, and phosphatizes which act upon distinctive amino acid side chains or on the peptide linkages. The mechanism of action of these enzymes involves the addition or removal of distinct functional groups, sugars, lipids, proteins, etc. either from or to the amino acid side chains.PTMs can occur at any stage of protein synthesis to enhance the complexity of proteome:1. During the process of translation (e.g. disulfide bonding).

Disulfide bonds are formed between the two sulfur molecules. Amino acid Cysteine contains sulfur, as a result, a disulfide bond is formed between two residues of cysteine (R-S-S-R). The bond formed is strong and plays an imperative role in accurate folding as well as the stability of protein molecules.2. When folding of a protein molecule is completed its modification occurs during the process of localization (e.g. collagens) (Web. "DNA and protein synthesis: Post-translation").Q2. Explain briefly how a protein is made starting from its DNA coding sequence.

DNA is the basic genetic material that is made up of four nucleotides Adenine (A), Guanine (G), Cytosine (C), and Thiamine (T). Adenine always pairs with Thiamine with a double Hydrogen bond while Guanine pairs with Cytosine with a triple Hydrogen bond. The process of transcription is responsible for the formation of messenger RNA or mRNA. This process takes place inside the nucleus in eukaryotes. The sequence of nucleotides in DNA is responsible for the amino acid sequence of mRNAs which are translated into proteins.

Transcription and translation involve processes such as initiation, elongation, and termination. The process of transcription involves RNA polymerase which is attached to the promoter sequence. When the protein is desired, the gene is “switched on” and when the protein has not required the gene is “switched off”. Elongation is carried out after the assembly of PIC at the promoter site, TFIIH is similar to helicase which unwinds the DNA. Termination of RNA involves the poly-A signal gene which is required to add adenylated residue during RNA processing (Web.

"Transcription Mechanisms in Eukaryotes"). The onset of translation is with the binding of smaller subunits through complementary bases. The bases are read as triplets by the tRNA which is called the transporter. These triplets are called codons while the tRNA carries anti-codon. The AUG is the initiation codon. The initiation process begins when the smaller subunit binds with the specific tRNA called N-formyl methionine or finest. This binds with the initiation codon methionine. The process of elongation involves the formation of peptide bonds, as a result the tRNA in the A site becomes peptidyl RNA and moves to the P site.

Termination of the translation is dependent on the occurrence of three stop signals also called nonsense codons at the A site. These stop codons are UAG, UGA and UAA (Web: "Molecular Biology: Translation"). Q3. Explain the “steps in globin chain synthesis”.Genetic alterations may result in diseases or genetic anomaly. To understand this, genes involved in globin (Hemoglobin) chain synthesis are taken into consideration. The hemoglobin molecule consists of two subunits, α subunit, and β subunit, genes of these subunits are present on two different chromosomes.

Genes of α subunit are present on chromosome 16 while genes of β subunit are present on chromosome 11. The combination of two α chains and two β chains forms a hemoglobin molecule (a tetramer). The synthesis of the globin molecule onsets in the nucleus of the RBC, where the DNA forms the messenger RNA by the process of transcription. The mRNA so formed is the precursor molecule which contains the coding exon sequences and non-coding intron sequences. Splicing removes the introns and all the three exons combine in a linear manner to serve as a template for the formation of the protein molecule.

This mRNA now moves to the cytoplasm where it is translated to the globin protein molecule.