Extension of Nucleic Acids

• The schematic view of tRNA consists of DHU loop, anti codon loop, T-PSI-C loop, and an amino acid-attachment site
• The 3 sequence of nucleotides are called codons
• The anticodon of tRNA is complementary to the codon of the mRNA
• The RNA is read as 5'-3'
• The schematic view of tRNA is a cloverleaf structure
• The four helical regions are arranged to form two apparent continuous segments of double helix
• Most of the bases in the nonhelical regions participate in H-bond interactions
• The CCA terminus containing the amino acid attachment site extends from one end of the L
• The anticodon loop is at the other end of the L, making accessible the three bases of tRNA that make up the anticodon
• The four helices of the secondary structure of t-RNA stack to form an L-shaped structure
• One stack contains has an CCA terminus which has amino acids while the other contains an anticodon loop
• The tRNA recognizes the molecule in the mRNA and the other is where peptide bond formation happens
• Activation of tRNA refers to the esterification of amino acid on the 3' end of tRNA with the enzyme aminoacyl-tRNA synthetases
• Anticodon allows the tRNA to recognize the correct mRNA codon and properly align its amino acid for protein synthesis
• The tRNA loops help facilitate interactions with the correct aminoacyl-tRNA synthetases
• rRNA is found in ribosomes, where it is the site of protein synthesis
• Only a few types of rRNA exist in cells
• Ribosomes has rRNA and proteins
• ribosomes are bigger in prokaryotes than in eukaryotes
• Particles are characterized by sedimentation coefficients, expressed in Svedberg units or S
• The prokaryotic ribosome has a sedimentation coefficient of 70 S, with big and small units of 50S and 30S respectively
• The eukaryotic ribosome has a sedimentation coefficient of 80 S, with big and small units of 60S and 40S respectively
• Sedimentation coefficients refers to the rate at which the ribosome precipitate
• The sedimentation factor is non additive, as it reflects both on the shape and its weight
• There are 3 ribosomal subunits in the prokaryotic ribosomal rRNA; 1 small ribosomal subunit and 2 large ribosomal subunit
• There is 1 small subunit, and 3 large subunit in the eukaryotic ribosomal RNA
• Small nuclear RNA is found in the nucleus of eukaryotes
• Micro RNA (miRNA) are only 22 nucleotides long which bind to a section of mRNA and prevent their translation
• Small interfering RNA (siRNA) are strong stretches of RNA found to have control over gene transcription
• siRNA have protecting role
• RNA component of telomerase is an enzyme that keeps the telomeres of chromosomes during replication
• small RNA molecule is an important component of the signal recognition particle in the cytoplasm that target newly synthesized proteins
• snRNA participate in the splicing of the eukaryotic mRNA
• Small interfering RNA removes undesirable genes
• Supercoiled DNA molecules are more compact than relaxed molecules with the same number of nucleotides
• Prokaryotic DNA tends to join together or circular
• Supercoiling occurs in prokaryotic DNA by twisting before joined together
• The enzyme that uncoils the DNA is topoisomerase
• The two types of supercoiling in prokaryotic DNA include negatively supercoiled and positvely supercoiled
• Topoisomerase hydrolyzes a phosphodiester bond, which relaxes the supercoiling by rotating in one strand, then reseal the break in prokaryotic DNA