Guide To Learn
Membrane and soluble secretory proteins that are synthesized on the rough ER undergo four principal modifications before they reach their final destination. Protein Glycosylation One or more carbohydrate chains are added to vast majority of proteins that are synthesized on the rough ER; indeed glycosylation is the principal chemical modification to most of these proteins. […]
The same secretory pathway is used by all eukaryotic cells for synthesizing and sorting secreted proteins and soluble luminal proteins in the ER, Golgi apparatus and lysosomes. These proteins are collectively referred to as ‘secretory proteins’. Although all cells secrete a variety of proteins (e.g., extracellular matrix proteins), certain types of cells are specialized for […]
Signal sequences are the sequences that help in targeting proteins to their proper cellular destinations. These sequences are present in the synthesized protein itself. They are about 20–50 amino acids in length. These signal sequences or uptake-targeting sequences are bound by receptor proteins. These govern the specificity of targeting. After binding with the receptor, the […]
There are 10,000 different kinds of proteins in a mammalian cell. Most of these proteins are synthesized by cytosolic ribosomes and they remain within the cytosol. However, many of the proteins produced in a cell are delivered either to a particular cell membrane or to the cell surface for secretion. For example, many hormone receptor […]
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 […]