Guide To Learn
Most of the proteins that are translated from mRNA undergo chemical modifications before becoming functional in different body cells. The modifications collectively are known as post-translational modifications (Figure 5.16). The protein post-translational modifications (PTMs) play a crucial role in generating the heterogeneity in proteins and also help in utilizing identical proteins for different cellular functions […]
Eukaryotic mRNAs are characterized by two post-transcriptional modifications: the 5′-7-methyl-GTP cap and the poly(A) tail. The 7-methyl-GTP cap is essential for ribosomal binding of mRNAs in eukaryotes and also enhances the stability of these mRNAs by preventing their degradation by 5′-exonucleases (Figure 5.14). The poly(A) tail enhances both the stability and translational efficiency of eukaryotic […]
Protein biosynthesis in all cells is characterized by three distinct phases: initiation, elongation and termination. At each stage, the energy required for the process is provided by GTP hydrolysis. Specific soluble protein factors participate in the events. Activation of the Amino Acids Amino acid activation takes place in the cytosol and not on the ribosomes. […]
Ribosomes are compact ribonucleoprotein particles found in the cytosol of all cells, as well as in the matrix of mitochondria and the stroma of chloroplasts. Ribosomes are mechano-chemical systems that move along mRNA templates, co-ordinates the interactions between successive codons and the corresponding anticodons of the aminoacyl-tRNAs. Ribosomes also catalyse the formation of peptide bonds […]
Codon-anticodon Interactions The genetic code is read in the 5′ → 3′ direction along the mRNA by sequential binding of the codons to the complementary anticodons of specific tRNA molecules. Each codon of the mRNA can be hydrogen bonded to a tRNA anticodon (present in the tRNA anticodon loop) consisting of complementary base sequence. The […]
The genetic dictionary of the mRNA codons reveals the following important features of triplet codons: The Mitochondrial Genetic Code Human mitochondrial DNA encodes only 22 tRNA that are used for the translation of mitochondrial mRNAs. The U of the anticodon in tRNA can pair with any of the four bases in the third codon position […]
Nirenberg and Khorana Experiment Marshall W. Nirenberg and Heinrich J. Matthaei (1962) made their own simple and artificial mRNA and identified the polypeptide product that was encoded by it. They used the enzyme polynucleotide phosphorylase, which randomly polymerizes any RNA nucleotides that it finds. They began with the simplest codes possible. Polynucleotide phosphorylase was added […]
Codons DNA specifies protein through an mRNA. Hidden within the mRNA lies the ‘triplet code’, a series of three nucleotides, called codons that code for a single amino acid. There are only 20 amino acids that occur in naturally derived proteins. The mRNA contains four different nucleotides namely: adenine (A), uracil (U), guanine (G) and […]
Proteins are the end products of most information pathways. A cell requires about thousands of different proteins. Translation is the process of the synthesis of proteins in the cell. Translation is a complex biosynthetic process that involves several proteins, enzymes and RNA molecules. The genetic information stored in the DNA is transcribed into a messenger […]