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DNA & Genomics (translation) - Coggle Diagram
DNA & Genomics (translation)
synthesis of protein using mRNA as a template
accurate translation of a genetic message requires 2 recognition stages
correct match btw a tRNA & an a.a
amino acid activation
each a.a is joined to the correct tRNA by aminoacyl-tRNA synthetase
active site of aminoacyl-tRNA synthetase recognises & binds to a specific pair of a.a & tRNA
synthetase catalyses the covalent attachment of an a.a to the 3' acceptor stem of the corresponding tRNA
each tRNA has a specific anticodon which binds to codon on mRNA by complementary base-pairing
resulting aminoacyl tRNA (activated a.a) is released from the enzyme & delivers its a.a to a growing polyp. chain on a ribosome
process driven by energy from hydrolysis of ATP
correct match btw a tRNA codon & mRNA codon
complementary base pairing of codon & anticodon
relaxation of the base-pairing rules : wobble effect
synonymous codons for a given a.a can differ in their 3rd base, but usually not in their other bases
STAGE 1 : Initiation
a small ribosomal subunit binds to both 5' end of mRNA & a specific initiator tRNA which carries methionine, with the aid of initiation factors
initiator tRNA with anticodon 3'-UAC-5' carries N-formyl methionine in prokaryotes
initiator tRNA with anticodon 3'-UAC-5' carries methionine in eukaryotes
small subunit scans downstream along the mRNA until it reaches the start codon AUG which signals the start of translation -> start of reading frame for mRNA
hydrogen bonds form btw complementary bases of methionine-tRNA anticodon & start codon on mRNA
a large ribosomal subunit attaches & binds to mRNA , forming the translation initiation complex
at completion of initiation process, initiator tRNA sits in the P site of ribosome -> vacant A site is ready for the next aminoacyl tRNA
polyp. is always synthesised from initial methionine at N-terminus toward final amino acid at C-terminus
STAGE 2 : Elongation
a.a are added 1 by 1 to the preceding a.a via formation of peptide bonds
1) codon recognition
anticodon of incoming aminoacyl tRNA complementary base pairs with mRNA codon in A-site
energy released by hydrolysis of GTP is required
2) peptide bond formation
peptidyl transferase found in a section of tRNA molecule of large subunit catalyses the formation of a peptide bond
peptide bond form btw new a.a in A site & carboxyl end of the growing polyp. in P site
polyp. is transferred to tRNA in A site
3) Translocation
ribosome translocates by advancing a codon along the mRNA
tRNA carrying the polyp. in A site is now found in P site
empty tRNA in P site is now in E site where it is released
ribosome now has an empty A site ready for entry of aminoacyl tRNA corresponding to the next codon
energy released by hydrolysis of GTP is required for translocation
STAGE 3 : Termination
elongation continues until a stop codon in mRNA reaches A site of ribosome
a release factor binds directly to the stop codon in A site
causes addition of a water molecule instead of a.a to polyp. chain
this rxn hydrolyses the completed polyp. from the tRNA in P site, releasing the polyp. through exit tunnel of large subunit
translation assembly comes apart
energy released by hydrolysis of GTP required
polyribosomes
a single mRNA can be used to make many copies of a polyp. simultaneously because several ribosomes can translate the message from 1 mRNA at the same time
once a ribosome moves past the start codon, a 2nd ribosome can attach to the mRNA -> strings of ribosomes are called polyribosomes / polysomes
enable cell to make many copies of a polyp. rapidly
found in both prokaryotes & eukaryotes